241 human active and 13 inactive phosphatases in total;
194 phosphatases have substrate data;
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336 protein substrates;
83 non-protein substrates;
1215 dephosphorylation interactions;
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299 KEGG pathways;
876 Reactome pathways;
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last scientific update: 11 Mar, 2019
last maintenance update: 01 Sep, 2023
Isoform 1: Cell membrane; Single-pass type Imembrane protein Cytoplasm, perinuclear region NucleusNote=Translocation to the nucleus requires endocytosis, probablyendosomal sorting and is mediated by importin beta-1/KPNB1 Isoform 2: Cytoplasm Nucleus Isoform 3: Cytoplasm Nucleus
Function (UniProt annotation)
Protein tyrosine kinase that is part of several cellsurface receptor complexes, but that apparently needs a coreceptorfor ligand binding Essential component of a neuregulin-receptorcomplex, although neuregulins do not interact with it alone GP30is a potential ligand for this receptor Regulates outgrowth andstabilization of peripheral microtubules (MTs) Upon ERBB2activation, the MEMO1-RHOA-DIAPH1 signaling pathway elicits thephosphorylation and thus the inhibition of GSK3B at cell membraneThis prevents the phosphorylation of APC and CLASP2, allowing itsassociation with the cell membrane In turn, membrane-bound APCallows the localization of MACF1 to the cell membrane, which isrequired for microtubule capture and stabilization In the nucleus is involved in transcriptionalregulation Associates with the 5'-TCAAATTC-3' sequence in thePTGS2/COX-2 promoter and activates its transcription Implicatedin transcriptional activation of CDKN1A; the function involvesSTAT3 and SRC Involved in the transcription of rRNA genes by RNAPol I and enhances protein synthesis and cell growth
Catalytic Activity (UniProt annotation)
ATP + a [protein]-L-tyrosine = ADP + a[protein]-L-tyrosine phosphate
EGFR is a tyrosine kinase that participates in the regulation of cellular homeostasis. EGFR also serves as a stimulus for cancer growth. EGFR gene mutations and protein overexpression, both of which activate down- stream pathways, are associated with cancers, especially lung cancer. Several tyrosine kinase inhibitor (TKI) therapies against EGFR are currently administered and are initially effective in cancer patients who have EGFR mutations or aberrant activation of EGFR. However, the development of TKI resistance is common and results in the recurrence of tumors. Studies over the last decade have identified mechanisms that drive resistance to EGFR TKI treatment. Most outstanding mechanisms are: the secondary EGFR mutation (T790M), activation of alternative pathways (c-Met, HGF, AXL), aberrance of the downstream pathways (K-RAS mutations, loss of PTEN), impairment of the EGFR-TKIs-mediated apoptosis pathway (BCL2-like 11/BIM deletion polymorphism), histologic transformation, etc.
Endocrine therapy is a key treatment strategy to control or eradicate hormone-responsive breast cancer. The most commonly used endocrine therapy agents are selective estrogen receptor modulators (SERMs, e.g. tamoxifen), estrogen synthesis inhibitors (e.g. aromatase inhibitors (AIs) such as anastrozole, letrozole, and exemestane), and selective estrogen receptor down-regulators (SERDs, e.g. fulvestrant). However, resistance to these agents has become a major clinical obstacle. Mechanisms of endocrine resistance include loss of ER-alpha expression, altered expression of coactivators or coregulators that play a critical role in ER-mediated gene transcription, ligand-independent growth factor signaling cascades that activate kinases and ER-phosphorylation, altered availability of active tamoxifen metabolites regulated by drug-metabolizing enzymes, such as CYP2D6, and deregulation of the cell cycle and apoptotic machinery.
Platinum-based drugs cisplatin, carboplatin and oxaliplatin are widely used in the therapy of solid malignancies, including testicular, ovarian, head and neck, colorectal, bladder and lung cancers. The mechanism of action of Platinum-based drugs involves covalent binding to purine DNA bases, which primarily leads to cellular apoptosis. Their clinical success is, however, limited due to severe side effects and intrinsic or acquired resistance to the treatment. Platinum resistance could arise from decreased drug influx, increased drug efflux, intracellular detoxification by glutathione, etc., decreased binding (e.g., due to high intracellular pH), increased DNA repair, decreased mismatch repair, defective apoptosis, and altered oncogene expression.
The mitogen-activated protein kinase (MAPK) cascade is a highly conserved module that is involved in various cellular functions, including cell proliferation, differentiation and migration. Mammals express at least four distinctly regulated groups of MAPKs, extracellular signal-related kinases (ERK)-1/2, Jun amino-terminal kinases (JNK1/2/3), p38 proteins (p38alpha/beta/gamma/delta) and ERK5, that are activated by specific MAPKKs: MEK1/2 for ERK1/2, MKK3/6 for the p38, MKK4/7 (JNKK1/2) for the JNKs, and MEK5 for ERK5. Each MAPKK, however, can be activated by more than one MAPKKK, increasing the complexity and diversity of MAPK signalling. Presumably each MAPKKK confers responsiveness to distinct stimuli. For example, activation of ERK1/2 by growth factors depends on the MAPKKK c-Raf, but other MAPKKKs may activate ERK1/2 in response to pro-inflammatory stimuli.
The ErbB family of receptor tyrosine kinases (RTKs) couples binding of extracellular growth factor ligands to intracellular signaling pathways regulating diverse biologic responses, including proliferation, differentiation, cell motility, and survival. Ligand binding to the four closely related members of this RTK family -epidermal growth factor receptor (EGFR, also known as ErbB-1 or HER1), ErbB-2 (HER2), ErbB-3 (HER3), and ErbB-4 (HER4)-induces the formation of receptor homo- and heterodimers and the activation of the intrinsic kinase domain, resulting in phosphorylation on specific tyrosine residues (pY) within the cytoplasmic tail. Signaling effectors containing binding pockets for pY-containing peptides are recruited to activated receptors and induce the various signaling pathways. The Shc- and/or Grb2-activated mitogen-activated protein kinase (MAPK) pathway is a common target downstream of all ErbB receptors. Similarly, the phosphatidylinositol-3-kinase (PI-3K) pathway is directly or indirectly activated by most ErbBs. Several cytoplasmic docking proteins appear to be recruited by specific ErbB receptors and less exploited by others. These include the adaptors Crk, Nck, the phospholipase C gamma (PLCgamma), the intracellular tyrosine kinase Src, or the Cbl E3 ubiquitin protein ligase.
Ca2+ that enters the cell from the outside is a principal source of signal Ca2+. Entry of Ca2+ is driven by the presence of a large electrochemical gradient across the plasma membrane. Cells use this external source of signal Ca2+ by activating various entry channels with widely different properties. The voltage-operated channels (VOCs) are found in excitable cells and generate the rapid Ca2+ fluxes that control fast cellular processes. There are many other Ca2+-entry channels, such as the receptor-operated channels (ROCs), for example the NMDA (N-methyl-D-aspartate) receptors (NMDARs) that respond to glutamate. There also are second-messenger-operated channels (SMOCs) and store-operated channels (SOCs).The other principal source of Ca2+ for signalling is the internal stores that are located primarily in the endoplasmic/sarcoplasmic reticulum (ER/SR), in which inositol-1,4,5-trisphosphate receptors (IP3Rs) or ryanodine receptors (RYRs) regulate the release of Ca2+. The principal activator of these channels is Ca2+ itself and this process of Ca2+-induced Ca2+ release is central to the mechanism of Ca2+ signalling. Various second messengers or modulators also control the release of Ca2+. IP3, which is generated by pathways using different isoforms of phospholipase C (PLCbeta, delta, epsilon, gamma and zeta), regulates the IP3Rs. Cyclic ADP-ribose (cADPR) releases Ca2+ via RYRs. Nicotinic acid adenine dinucleotide phosphate (NAADP) may activate a distinct Ca2+ release mechanism on separate acidic Ca2+ stores. Ca2+ release via the NAADP-sensitive mechanism may also feedback onto either RYRs or IP3Rs. cADPR and NAADP are generated by CD38. This enzyme might be sensitive to the cellular metabolism, as ATP and NADH inhibit it.The influx of Ca2+ from the environment or release from internal stores causes a very rapid and dramatic increase in cytoplasmic calcium concentration, which has been widely exploited for signal transduction. Some proteins, such as troponin C (TnC) involved in muscle contraction, directly bind to and sense Ca2+. However, in other cases Ca2+ is sensed through intermediate calcium sensors such as calmodulin (CALM).
Hypoxia-inducible factor 1 (HIF-1) is a transcription factor that functions as a master regulator of oxygen homeostasis. It consists of two subunits: an inducibly-expressed HIF-1alpha subunit and a constitutively-expressed HIF-1beta subunit. Under normoxia, HIF-1 alpha undergoes hydroxylation at specific prolyl residues which leads to an immediate ubiquitination and subsequent proteasomal degradation of the subunit. In contrast, under hypoxia, HIF-1 alpha subunit becomes stable and interacts with coactivators such as p300/CBP to modulate its transcriptional activity. Eventually, HIF-1 acts as a master regulator of numerous hypoxia-inducible genes under hypoxic conditions. The target genes of HIF-1 encode proteins that increase O2 delivery and mediate adaptive responses to O2 deprivation. Despite its name, HIF-1 is induced not only in response to reduced oxygen availability but also by other stimulants, such as nitric oxide, or various growth factors.
The phosphatidylinositol 3' -kinase(PI3K)-Akt signaling pathway is activated by many types of cellular stimuli or toxic insults and regulates fundamental cellular functions such as transcription, translation, proliferation, growth, and survival. The binding of growth factors to their receptor tyrosine kinase (RTK) or G protein-coupled receptors (GPCR) stimulates class Ia and Ib PI3K isoforms, respectively. PI3K catalyzes the production of phosphatidylinositol-3,4,5-triphosphate (PIP3) at the cell membrane. PIP3 in turn serves as a second messenger that helps to activate Akt. Once active, Akt can control key cellular processes by phosphorylating substrates involved in apoptosis, protein synthesis, metabolism, and cell cycle.
Cell-matrix adhesions play essential roles in important biological processes including cell motility, cell proliferation, cell differentiation, regulation of gene expression and cell survival. At the cell-extracellular matrix contact points, specialized structures are formed and termed focal adhesions, where bundles of actin filaments are anchored to transmembrane receptors of the integrin family through a multi-molecular complex of junctional plaque proteins. Some of the constituents of focal adhesions participate in the structural link between membrane receptors and the actin cytoskeleton, while others are signalling molecules, including different protein kinases and phosphatases, their substrates, and various adapter proteins. Integrin signaling is dependent upon the non-receptor tyrosine kinase activities of the FAK and src proteins as well as the adaptor protein functions of FAK, src and Shc to initiate downstream signaling events. These signalling events culminate in reorganization of the actin cytoskeleton; a prerequisite for changes in cell shape and motility, and gene expression. Similar morphological alterations and modulation of gene expression are initiated by the binding of growth factors to their respective receptors, emphasizing the considerable crosstalk between adhesion- and growth factor-mediated signalling.
Cell-cell adherens junctions (AJs), the most common type of intercellular adhesions, are important for maintaining tissue architecture and cell polarity and can limit cell movement and proliferation. At AJs, E-cadherin serves as an essential cell adhesion molecules (CAMs). The cytoplasmic tail binds beta-catenin, which in turn binds alpha-catenin. Alpha-catenin is associated with F-actin bundles directly and indirectly. The integrity of the cadherin-catenin complex is negatively regulated by phosphorylation of beta-catenin by receptor tyrosine kinases (RTKs) and cytoplasmic tyrosine kinases (Fer, Fyn, Yes, and Src), which leads to dissociation of the cadherin-catenin complex. Integrity of this complex is positively regulated by beta -catenin phosphorylation by casein kinase II, and dephosphorylation by protein tyrosine phosphatases. Changes in the phosphorylation state of beta-catenin affect cell-cell adhesion, cell migration and the level of signaling beta-catenin. Wnt signaling acts as a positive regulator of beta-catenin by inhibiting beta-catenin degradation, which stabilizes beta-catenin, and causes its accumulation. Cadherin may acts as a negative regulator of signaling beta-catenin as it binds beta-catenin at the cell surface and thereby sequesters it from the nucleus. Nectins also function as CAMs at AJs, but are more highly concentrated at AJs than E-cadherin. Nectins transduce signals through Cdc42 and Rac, which reorganize the actin cytoskeleton, regulate the formation of AJs, and strengthen cell-cell adhesion.
Tight junctions (TJs) are essential for establishing a selectively permeable barrier to diffusion through the paracellular space between neighboring cells. TJs are composed of at least three types of transmembrane protein -occludin, claudin and junctional adhesion molecules (JAMs)- and a cytoplasmic 'plaque' consisting of many different proteins that form large complexes. These are proposed to be involved in junction assembly, barrier regulation, cell polarity, gene transcription, and other pathways.
Many proteoglycans (PGs) in the tumor microenvironment have been shown to be key macromolecules that contribute to biology of various types of cancer including proliferation, adhesion, angiogenesis and metastasis, affecting tumor progress. The four main types of proteoglycans include hyaluronan (HA), which does not occur as a PG but in free form, heparan sulfate proteoglycans (HSPGs), chondroitin sulfate proteoglycans (CSPGs), dematan sulfate proteoglycans (DSPG) and keratan sulfate proteoglycans (KSPGs) [BR:00535]. Among these proteoglycans such as HA, acting with CD44, promotes tumor cell growth and migration, whereas other proteoglycans such as syndecans (-1~-4), glypican (-1, -3) and perlecan may interact with growth factors, cytokines, morphogens and enzymes through HS chains [BR: 00536], also leading to tumor growth and invasion. In contrast, some of the small leucine-rich proteolgycans, such as decorin and lumican, can function as tumor repressors, and modulate the signaling pathways by the interaction of their core proteins and multiple receptors.
MicroRNA (miRNA) is a cluster of small non-encoding RNA molecules of 21 - 23 nucleotides in length, which controls gene expression post-transcriptionally either via the degradation of target mRNAs or the inhibition of protein translation. Using high-throughput profiling, dysregulation of miRNAs has been widely observed in different stages of cancer. The upregulation (overexpression) of specific miRNAs could lead to the repression of tumor suppressor gene expression, and conversely the downregulation of specific miRNAs could result in an increase of oncogene expression; both these situations induce subsequent malignant effects on cell proliferation, differentiation, and apoptosis that lead to tumor growth and progress. The miRNA signatures of cancer observed in various studies differ significantly. These inconsistencies occur due to the differences in the study populations and methodologies used. This pathway map shows the summarized results from various studies in 9 cancers, each of which is presented in a review article.
Infiltrating ductal adenocarcinoma is the most common malignancy of the pancreas. When most investigators use the term 'pancreatic cancer' they are referring to pancreatic ductal adenocarcinoma (PDA). Normal duct epithelium progresses to infiltrating cancer through a series of histologically defined precursors (PanINs). The overexpression of HER-2/neu and activating point mutations in the K-ras gene occur early, inactivation of the p16 gene at an intermediate stage, and the inactivation of p53, SMAD4, and BRCA2 occur relatively late. Activated K-ras engages multiple effector pathways. Although EGF receptors are conventionally regarded as upstream activators of RAS proteins, they can also act as RAS signal transducers via RAS-induced autocrine activation of the EGFR family ligands. Moreover, PDA shows extensive genomic instability and aneuploidy. Telomere attrition and mutations in p53 and BRCA2 are likely to contribute to these phenotypes. Inactivation of the SMAD4 tumour suppressor gene leads to loss of the inhibitory influence of the transforming growth factor-beta signalling pathway.
Endometrial cancer (EC) is the most common gynaecological malignancy and the fourth most common malignancy in women in the developed world after breast, colorectal and lung cancer. Two types of endometrial carcinoma are distinguished with respect to biology and clinical course. Type-I carcinoma is related to hyperestrogenism by association with endometrial hyperplasia, frequent expression of estrogen and progesterone receptors and younger age, whereas type-II carcinoma is unrelated to estrogen, associated with atrophic endometrium, frequent lack of estrogen and progesterone receptors and older age. The morphologic differences in these cancers are mirrored in their molecular genetic profile with type I showing defects in DNA-mismatch repair and mutations in PTEN, K-ras, and beta-catenin, and type II showing aneuploidy, p53 mutations, and her2/neu amplification.
Prostate cancer constitutes a major health problem in Western countries. It is the most frequently diagnosed cancer among men and the second leading cause of male cancer deaths. The identification of key molecular alterations in prostate-cancer cells implicates carcinogen defenses (GSTP1), growth-factor-signaling pathways (NKX3.1, PTEN, and p27), and androgens (AR) as critical determinants of the phenotype of prostate-cancer cells. Glutathione S-transferases (GSTP1) are detoxifying enzymes. Cells of prostatic intraepithelial neoplasia, devoid of GSTP1, undergo genomic damage mediated by carcinogens. NKX3.1, PTEN, and p27 regulate the growth and survival of prostate cells in the normal prostate. Inadequate levels of PTEN and NKX3.1 lead to a reduction in p27 levels and to increased proliferation and decreased apoptosis. Androgen receptor (AR) is a transcription factor that is normally activated by its androgen ligand. During androgen withdrawal therapy, the AR signal transduction pathway also could be activated by amplification of the AR gene, by AR gene mutations, or by altered activity of AR coactivators. Through these mechanisms, tumor cells lead to the emergence of androgen-independent prostate cancer.
The urothelium covers the luminal surface of almost the entire urinary tract, extending from the renal pelvis, through the ureter and bladder, to the proximal urethra. The majority of urothelial carcinoma are bladder carcinomas, and urothelial carcinomas of the renal pelvis and ureter account for only approximately 7% of the total. Urothelial tumours arise and evolve through divergent phenotypic pathways. Some tumours progress from urothelial hyperplasia to low-grade non-invasive superficial papillary tumours. More aggressive variants arise either from flat, high-grade carcinoma in situ (CIS) and progress to invasive tumours, or they arise de novo as invasive tumours. Low-grade papillary tumors frequently show a constitutive activation of the receptor tyrosine kinase-Ras pathway, exhibiting activating mutations in the HRAS and fibroblast growth factor receptor 3 (FGFR3) genes. In contrast, CIS and invasive tumors frequently show alterations in the TP53 and RB genes and pathways. Invasion and metastases are promoted by several factors that alter the tumour microenvironment, including the aberrant expression of E-cadherins (E-cad), matrix metalloproteinases (MMPs), angiogenic factors such as vascular endothelial growth factor (VEGF).
Lung cancer is a leading cause of cancer death among men and women in industrialized countries. Non-small-cell lung cancer (NSCLC) accounts for approximately 85% of lung cancer and represents a heterogeneous group of cancers, consisting mainly of squamous cell (SCC), adeno (AC) and large-cell carcinoma. Molecular mechanisms altered in NSCLC include activation of oncogenes, such as K-RAS, EGFR and EML4-ALK, and inactivation of tumorsuppressor genes, such as p53, p16INK4a, RAR-beta, and RASSF1. Point mutations within the K-RAS gene inactivate GTPase activity and the p21-RAS protein continuously transmits growth signals to the nucleus. Mutations or overexpression of EGFR leads to a proliferative advantage. EML4-ALK fusion leads to constitutive ALK activation, which causes cell proliferation, invasion, and inhibition of apoptosis. Inactivating mutation of p53 can lead to more rapid proliferation and reduced apoptosis. The protein encoded by the p16INK4a inhibits formation of CDK-cyclin-D complexes by competitive binding of CDK4 and CDK6. Loss of p16INK4a expression is a common feature of NSCLC. RAR-beta is a nuclear receptor that bears vitamin-A-dependent transcriptional activity. RASSF1A is able to form heterodimers with Nore-1, an RAS effector.Therefore loss of RASSF1A might shift the balance of RAS activity towards a growth-promoting effect.
Breast cancer is the leading cause of cancer death among women worldwide. The vast majority of breast cancers are carcinomas that originate from cells lining the milk-forming ducts of the mammary gland. The molecular subtypes of breast cancer, which are based on the presence or absence of hormone receptors (estrogen and progesterone subtypes) and human epidermal growth factor receptor-2 (HER2), include: hormone receptor positive and HER2 negative (luminal A subtype), hormone receptor positive and HER2 positive (luminal B subtype), hormone receptor negative and HER2 positive (HER2 positive), and hormone receptor negative and HER2 negative (basal-like or triple-negative breast cancers (TNBCs)). Hormone receptor positive breast cancers are largely driven by the estrogen/ER pathway. In HER2 positive breast tumours, HER2 activates the PI3K/AKT and the RAS/RAF/MAPK pathways, and stimulate cell growth, survival and differentiation. In patients suffering from TNBC, the deregulation of various signalling pathways (Notch and Wnt/beta-catenin), EGFR protein have been confirmed. In the case of breast cancer only 8% of all cancers are hereditary, a phenomenon linked to genetic changes in BRCA1 or BRCA2. Somatic mutations in only three genes (TP53, PIK3CA and GATA3) occurred at >10% incidence across all breast cancers.
Gastric cancer (GC) is one of the world's most common cancers. According to Lauren's histological classification gastric cancer is divided into two distinct histological groups - the intestinal and diffuse types. Several genetic changes have been identified in intestinal-type GC. The intestinal metaplasia is characterized by mutations in p53 gene, reduced expression of retinoic acid receptor beta (RAR-beta) and hTERT expression. Gastric adenomas furthermore display mutations in the APC gene, reduced p27 expression and cyclin E amplification. In addition, amplification and overexpression of c-ErbB2, reduced TGF-beta receptor type I (TGFBRI) expression and complete loss of p27 expression are commonly observed in more advanced GC. The main molecular changes observed in diffuse-type GCs include loss of E-cadherin function by mutations in CDH1 and amplification of MET and FGFR2F.
Malignant transformation of cells requires specific adaptations of cellular metabolism to support growth and survival. In the early twentieth century, Otto Warburg established that there are fundamental differences in the central metabolic pathways operating in malignant tissue. He showed that cancer cells consume a large amount of glucose, maintain high rate of glycolysis and convert a majority of glucose into lactic acid even under normal oxygen concentrations (Warburg's Effects). More recently, it has been recognized that the 'Warburg effect' encompasses a similarly increased utilization of glutamine. From the intermediate molecules provided by enhanced glycolysis and glutaminolysis, cancer cells synthesize most of the macromolecules required for the duplication of their biomass and genome. These cancer-specific alterations represent a major consequence of genetic mutations and the ensuing changes of signalling pathways in cancer cells. Three transcription factors, c-MYC, HIF-1 and p53, are key regulators and coordinate regulation of cancer metabolism in different ways, and many other oncogenes and tumor suppressor genes cluster along the signaling pathways that regulate c-MYC, HIF-1 and p53.
ERBB2, also known as HER2 or NEU, is a receptor tyrosine kinase (RTK) belonging to the EGFR family. ERBB2 possesses an extracellular domain that does not bind any known ligand, contrary to other EGFR family members, a single transmembrane domain, and an intracellular domain consisting of an active kinase and a C-tail with multiple tyrosine phosphorylation sites. Inactive ERBB2 is associated with a chaperone heat shock protein 90 (HSP90) and its co-chaperone CDC37 (Xu et al. 2001, Citri et al. 2004, Xu et al. 2005). In addition, ERBB2 is associated with ERBB2IP (also known as ERBIN or LAP2), a protein responsible for proper localization of ERBB2. In epithelial cells, ERBB2IP restricts expression of ERBB2 to basolateral plasma membrane regions (Borg et al. 2000).\nERBB2 becomes activated by forming a heterodimer with another ligand-activated EGFR family member, either EGFR, ERBB3 or ERBB4, which is accompanied by dissociation of chaperoning proteins HSP90 and CDC37 (Citri et al. 2004), as well as ERBB2IP (Borg et al. 2000) from ERBB2. ERBB2 heterodimers function to promote cell proliferation, cell survival and differentiation, depending on the cellular context. ERBB2 can also be activated by homodimerization when it is overexpressed, in cancer for example. \nIn cells expressing both ERBB2 and EGFR, EGF stimulation of EGFR leads to formation of both ERBB2:EGFR heterodimers (Wada et al. 1990, Karunagaran et al. 1996) and EGFR homodimers. Heterodimers of ERBB2 and EGFR trans-autophosphorylate on twelve tyrosine residues, six in the C-tail of EGFR and six in the C-tail of ERBB2 - Y1023, Y1139, Y1196, Y1221, Y1222 and Y1248 (Margolis et al. 1989, Hazan et al. 1990,Walton et al. 1990, Helin et al. 1991, Ricci et al. 1995, Pinkas-Kramarski 1996). Phosphorylated tyrosine residues in the C-tail of EGFR and ERBB2 serve as docking sites for downstream signaling molecules. Three key signaling pathways activated by ERBB2:EGFR heterodimers are RAF/MAP kinase cascade, PI3K-induced AKT signaling, and signaling by phospholipase C gamma (PLCG1). Downregulation of EGFR signaling is mediated by ubiquitin ligase CBL, and is shown under Signaling by EGFR.\nIn cells expressing ERBB2 and ERBB3, ERBB3 activated by neuregulin NRG1 or NRG2 binding (Tzahar et al. 1994) forms a heterodimer with ERBB2 (Pinkas-Kramarski et al. 1996, Citri et al. 2004). ERBB3 is the only EGFR family member with no kinase activity, and can only function in heterodimers, with ERBB2 being its preferred heterodimerization partner. After heterodimerization, ERBB2 phosphorylates ten tyrosine residues in the C-tail of ERBB3, Y1054, Y1197, Y1199, Y1222, Y1224, Y1260, Y1262, Y1276, Y1289 and Y1328 (Prigent et al. 1994, Pinkas-Kramarski et al. 1996, Vijapurkar et al. 2003, Li et al. 2007) that subsequently serve as docking sites for downstream signaling molecules, resulting in activation of PI3K-induced AKT signaling and RAF/MAP kinase cascade. Signaling by ERBB3 is downregulated by the action of RNF41 ubiquitin ligase, also known as NRDP1. \nIn cells expressing ERBB2 and ERBB4, ligand stimulated ERBB4 can either homodimerize or form heterodimers with ERBB2 (Li et al. 2007), resulting in trans-autophosphorylation of ERBB2 and ERBB4 on C-tail tyrosine residues that will subsequently serve as docking sites for downstream signaling molecules, leading to activation of RAF/MAP kinase cascade and, in the case of ERBB4 CYT1 isoforms, PI3K-induced AKT signaling (Hazan et al. 1990, Cohen et al. 1996, Li et al. 2007, Kaushansky et al. 2008). Signaling by ERBB4 is downregulated by the action of WWP1 and ITCH ubiquitin ligases, and is shown under Signaling by ERBB4
All ERBB2 heterodimers, ERBB2:EGFR, ERBB2:ERBB3 and ERBB2:ERBB4, are able to activate RAF/MAP kinase cascade by recruiting SHC1 (Pinkas-Kramarski et al. 1996, Sepp-Lorenzino et al. 1996) to phosphorylated C-tail tyrosine residues in either EGFR (Y1148 and Y1173), ERBB2 (Y1196, Y1221, Y1222 and Y1248), ERBB3 (Y1328) or ERBB4 (Y1188 and Y1242 in JM-A CYT1 isoform, Y1178 and Y1232 in JM-B CYT1 isoform, Y1172 and Y1226 in JM-A CYT2 isoform). SHC1 recruitment is followed by phosphorylation (Segatto et al. 1993, Soler et al. 1994), and the phosphorylated SHC1 recruits GRB2:SOS1 complex (Xie et al. 1995), which leads to SOS1-mediated guanyl-nucleotide exchange on RAS (Xie et al. 1995) and downstream activation of RAF and MAP kinases
Activation of PLCG1 signaling is observed only in the presence of ERBB2:EGFR heterodimers, with PLCG1 binding to phosphorylated tyrosine Y992 and Y1173 in the C-tail of EGFR (Chattopadhyay et al. 1999), and potentially Y1023 in the C-tail of ERBB2 (Fazioli et al. 1991, Cohen et al. 1996)
Signaling by AKT is one of the key outcomes of receptor tyrosine kinase (RTK) activation. AKT is activated by the cellular second messenger PIP3, a phospholipid that is generated by PI3K. In ustimulated cells, PI3K class IA enzymes reside in the cytosol as inactive heterodimers composed of p85 regulatory subunit and p110 catalytic subunit. In this complex, p85 stabilizes p110 while inhibiting its catalytic activity. Upon binding of extracellular ligands to RTKs, receptors dimerize and undergo autophosphorylation. The regulatory subunit of PI3K, p85, is recruited to phosphorylated cytosolic RTK domains either directly or indirectly, through adaptor proteins, leading to a conformational change in the PI3K IA heterodimer that relieves inhibition of the p110 catalytic subunit. Activated PI3K IA phosphorylates PIP2, converting it to PIP3; this reaction is negatively regulated by PTEN phosphatase. PIP3 recruits AKT to the plasma membrane, allowing TORC2 to phosphorylate a conserved serine residue of AKT. Phosphorylation of this serine induces a conformation change in AKT, exposing a conserved threonine residue that is then phosphorylated by PDPK1 (PDK1). Phosphorylation of both the threonine and the serine residue is required to fully activate AKT. The active AKT then dissociates from PIP3 and phosphorylates a number of cytosolic and nuclear proteins that play important roles in cell survival and metabolism. For a recent review of AKT signaling, please refer to Manning and Cantley, 2007
Heterodimers of ERBB2 and ERBB3 are able to bind GRB7 (Fiddes et al. 1998) through phosphorylated tyrosine residues in the C-tail of ERBB3 (Y1199 and Y1262) (Fiddes et al. 1998), but the exact downstream signaling of this complex has not been elucidated. GRB7 can recruit SHC1 to the active ERBB2 complex, and contributes to ERBB2 signaling-induced RAS activation, which promotes cellular proliferation, but the exact mechanism has not been elucidated (Pradip et al. 2013). In addition, GRB7 can be phosphorylated by the integrin-activated PTK2 (FAK), leading to VAV2-dependent activation of RAC1 and promotion of cell migration. The exact mechanistic details of GRB7-induced RAC1 activation are not known (Pradip et al. 2013)
Level of plasma membrane ERBB3 is regulated by E3 ubiquitin ligase RNF41 (also known as NRDP1), which binds and ubiquitinates both inactive and activated ERBB3, targeting it for degradation (Cao et al. 2007). RNF41 is subject to self-ubiquitination which keeps its levels low when ERBB3 is not stimulated, and preserves ERBB3 expression on the cell surface (Qiu et al. 2002). Self-ubiquitination of RNF41 is reversible, through the action of ubiquitin protease USP8, an enzyme stabilized by AKT-mediated phosphorylation. Therefore, activation of AKT by ERBB2:ERBB3 signaling leads to phosphorylation of USP8 (Cao et al. 2007), which increases level of RNF41 through deubiquitination, and results in degradation of activated ERBB3 (Cao et al. 2007) - a negative feedback loop of ERBB3 signaling. Downregulation of EGFR and ERBB4 signaling is explained in pathways Signaling by EGFR and Signaling by ERBB4
ERBB2:EGFR and ERBB2:ERBB4 can directly recruit GRB2:SOS1 complex through phosphorylated C-tail tyrosines of EGFR (Y1068 and Y1086) and ERBB2 (Y1139) that serve as docking sites for GRB2 (Xie et al. 1995, Sepp-Lorenzino et al. 1996), which, again, results in SOS1-mediated guanyl-nucleotide exchange on RAS and activation of RAF and MAP kinases (Janes et al. 1994, Sepp-Lorenzino et al. 1996)
ERBB2:ERBB3 and ERBB2:ERBB4cyt1 heterodimers activate PI3K signaling by direct binding of PI3K regulatory subunit p85 (Yang et al. 2007, Cohen et al. 1996, Kaushansky et al. 2008) to phosphorylated tyrosine residues in the C-tail of ERBB3 (Y1054, Y1197, Y1222, Y1224, Y1276 and Y1289) and ERBB4 CYT1 isoforms (Y1056 in JM-A CYT1 isoform and Y1046 in JM-B CYT1 isoform). Regulatory subunit p85 subsequently recruits catalytic subunit p110 of PI3K, resulting in the formation of active PI3K, conversion of PIP2 to PIP3, and PIP3-mediated activation of AKT signaling (Junttila et al. 2009, Kainulainen et al. 2000). Heterodimers of ERBB2 and EGFR recruit PI3K indirectly, through GRB2:GAB1 complex (Jackson et al. 2004), which again leads to PIP3-mediated activation of AKT signaling
Signaling by PI3K/AKT is frequently constitutively activated in cancer via gain-of-function mutations in one of the two PI3K subunits - PI3KCA (encoding the catalytic subunit p110alpha) or PIK3R1 (encoding the regulatory subunit p85alpha). Gain-of-function mutations activate PI3K signaling by diverse mechanisms. Mutations affecting the helical domain of PIK3CA and mutations affecting nSH2 and iSH2 domains of PIK3R1 impair inhibitory interactions between these two subunits while preserving their association. Mutations in the catalytic domain of PIK3CA enable the kinase to achieve an active conformation. PI3K complexes with gain-of-function mutations therefore produce PIP3 and activate downstream AKT in the absence of growth factors (Huang et al. 2007, Zhao et al. 2005, Miled et al. 2007, Horn et al. 2008, Sun et al. 2010, Jaiswal et al. 2009, Zhao and Vogt 2010, Urick et al. 2011)
Sema4D-mediated attraction of endothelial cells requires Rho, but not R-Ras, signaling. Sema4D-mediated plexinB1 activation activates Rho and its downstream effector ROCK. ROCK then phosphorylates MLC to induce actomyosin stress fiber contraction and to direct the assembly of focal adhesion complexes and integrin-mediated adhesion
The RAS-RAF-MEK-ERK pathway regulates processes such as proliferation, differentiation, survival, senescence and cell motility in response to growth factors, hormones and cytokines, among others. Binding of these stimuli to receptors in the plasma membrane promotes the GEF-mediated activation of RAS at the plasma membrane and initiates the three-tiered kinase cascade of the conventional MAPK cascades. GTP-bound RAS recruits RAF (the MAPK kinase kinase), and promotes its dimerization and activation (reviewed in Cseh et al, 2014; Roskoski, 2010; McKay and Morrison, 2007; Wellbrock et al, 2004). Activated RAF phosphorylates the MAPK kinase proteins MEK1 and MEK2 (also known as MAP2K1 and MAP2K2), which in turn phophorylate the proline-directed kinases ERK1 and 2 (also known as MAPK3 and MAPK1) (reviewed in Roskoski, 2012a, b; Kryiakis and Avruch, 2012). Activated ERK proteins may undergo dimerization and have identified targets in both the nucleus and the cytosol; consistent with this, a proportion of activated ERK protein relocalizes to the nucleus in response to stimuli (reviewed in Roskoski 2012b; Turjanski et al, 2007; Plotnikov et al, 2010; Cargnello et al, 2011). Although initially seen as a linear cascade originating at the plasma membrane and culminating in the nucleus, the RAS/RAF MAPK cascade is now also known to be activated from various intracellular location. Temporal and spatial specificity of the cascade is achieved in part through the interaction of pathway components with numerous scaffolding proteins (reviewed in McKay and Morrison, 2007; Brown and Sacks, 2009). The importance of the RAS/RAF MAPK cascade is highlighted by the fact that components of this pathway are mutated with high frequency in a large number of human cancers. Activating mutations in RAS are found in approximately one third of human cancers, while ~8% of tumors express an activated form of BRAF (Roberts and Der, 2007; Davies et al, 2002; Cantwell-Dorris et al, 2011)
Activated ERBB2 heterodimers regulate cell motility through association with MEMO1. MEMO1 retains activated RHOA GTPase and its associated protein DIAPH1 at the plasma membrane, thus linking ERBB2 activation with the microtubule and actin dynamics downstream of the RHOA:GTP:DIAPH1 complex (Marone et al. 2004, Qiu et al. 2008, Zaoui et al. 2008, Zaoui et al. 2010)
Phosphatidylinositol-5-phosphate (PI5P) may modulate PI3K/AKT signaling in several ways. PI5P is used as a substrate for production of phosphatidylinositol-4,5-bisphosphate, PI(4,5)P2 (Rameh et al. 1997, Clarke et al. 2008, Clarke et al. 2010, Clarke and Irvine 2013, Clarke et al. 2015), which serves as a substrate for activated PI3K, resulting in the production of PIP3 (Mandelker et al. 2009, Burke et al. 2011). The majority of PI(4,5)P2 in the cell, however, is produced from the phosphatidylinositol-4-phosphate (PI4P) substrate (Zhang et al. 1997, Di Paolo et al. 2002, Oude Weernink et al. 2004, Halstead et al. 2006, Oude Weernink et al. 2007). PIP3 is necessary for the activating phosphorylation of AKT. AKT1 can be deactivated by the protein phosphatase 2A (PP2A) complex that contains a regulatory subunit B56-beta (PPP2R5B) or B56-gamma (PPP2R5C). PI5P inhibits AKT1 dephosphorylation by PP2A through an unknown mechanism (Ramel et al. 2009). Increased PI5P levels correlate with inhibitory phosphorylation(s) of the PP2A complex. MAPK1 (ERK2) and MAPK3 (ERK1) are involved in inhibitory phosphorylation of PP2A, in a process that involves IER3 (IEX-1) (Letourneux et al. 2006, Rocher et al. 2007). It is uncertain, however, whether PI5P is in any way involved in ERK-mediated phosphorylation of PP2A or if it regulates another PP2A kinase
PTK6 (BRK) is activated downstream of ERBB2 (HER) (Xiang et al. 2008, Peng et al. 2015) and other receptor tyrosine kinases, such as EGFR (Kamalati et al. 1996) and MET (Castro and Lange 2010). However, it is not clear if MET and EGFR activate PTK6 directly or act through ERBB2, since it is known that ERBB2 forms heterodimers with EGFR (Spivak-Kroizman et al. 1992), and MET can heterodimerize with both EGFR and ERBB2 (Tanizaki et al. 2011)
Signaling by ERBB2 can be downregulated by ubiquitination and subsequent proteasome-dependent degradation of ERBB2 or activated ERBB2 heterodimers. In addition, protein tyrosine phosphatases that dephosphorylate tyrosine residues in the C-terminus of ERBB2 prevent the recruitment of adapter proteins involved in signal transduction, thus attenuating ERBB2 signaling.STUB1 (CHIP) and CUL5 are E3 ubiquitin ligases that can target non-activated ERBB2 for proteasome-dependent degradation (Xu et al. 2002, Ehrlich et al. 2009). RNF41 (NRDP1) is an E3 ubiquitin ligase that targets ERBB3 and activated heterodimers of ERBB2 and ERBB3 for proteasome-dependent degradation by ubiquitinating ERBB3 (Cao et al. 2007).Two protein tyrosine phosphatases of the PEST family, PTPN12 and PTPN18, dephosphorylate tyrosine residues in the C-terminus of ERBB2, thus preventing signal transduction to RAS and PI3K effectors (Sun et al. 2011, Wang et al. 2014)
TFAP2A and TFAP2C directly stimulate transcription of the estrogen receptor ESR1 gene (McPherson and Weigel 1999). TFAP2A expression correlates with ESR1 expression in breast cancer, and TFAP2C is frequently overexpressed in estrogen-positive breast cancer and endometrial cancer (deConinck et al. 1995, Turner et al. 1998). TFAP2A, TFAP2C, as well as TFAP2B can directly stimulate the expression of ERBB2, another important breast cancer gene (Bosher et al. 1996). Association of TFAP2A with the YY1 transcription factor significantly increases the ERBB2 transcription rate (Begon et al. 2005). In addition to ERBB2, the expression of another receptor tyrosine kinase, KIT, is also stimulated by TFAP2A and TFAP2B (Huang et al. 1998), while the expression of the VEGF receptor tyrosine kinase ligand VEGFA is repressed by TFAP2A (Ruiz et al. 2004, Li et al. 2012). TFAP2A stimulates transcription of the transforming growth factor alpha (TGFA) gene (Wang et al. 1997). TFAP2C regulates EGFR expression in luminal breast cancer (De Andrade et al. 2016). In placenta, TFAP2A and TFAP2C directly stimulate transcription of both subunits of the human chorionic gonadotropin, CGA and CGB (Johnson et al. 1997, LiCalsi et al. 2000)
Affinity Capture-MS, Affinity Capture-Western, Co-localization, anti bait coimmunoprecipitation, beta galactosidase complementation, protein cross-linking with a bifunctional reagent, protein kinase assay, proximity ligation assay, pull down, tandem affinity purification
Affinity Capture-Western, anti tag coimmunoprecipitation, beta galactosidase complementation, blue native page, confocal microscopy, fluorescent resonance energy transfer, protein kinase assay, proximity ligation assay
colocalization, direct interaction, physical, physical association
Affinity Capture-Western, Co-localization, anti bait coimmunoprecipitation, beta galactosidase complementation, cosedimentation in solution, cross-linking study, protein cross-linking with a bifunctional reagent, proximity ligation assay, pull down
association, direct interaction, physical, physical association
Affinity Capture-MS, Affinity Capture-Western, Co-localization, anti bait coimmunoprecipitation, beta galactosidase complementation, protein cross-linking with a bifunctional reagent, protein kinase assay, proximity ligation assay, pull down, tandem affinity purification
Affinity Capture-Western, anti tag coimmunoprecipitation, beta galactosidase complementation, blue native page, confocal microscopy, fluorescent resonance energy transfer, protein kinase assay, proximity ligation assay
colocalization, direct interaction, physical, physical association
Affinity Capture-Western, Co-localization, anti bait coimmunoprecipitation, beta galactosidase complementation, cosedimentation in solution, cross-linking study, protein cross-linking with a bifunctional reagent, proximity ligation assay, pull down
association, direct interaction, physical, physical association
Affinity Capture-MS, Affinity Capture-Western, Co-localization, anti bait coimmunoprecipitation, beta galactosidase complementation, protein cross-linking with a bifunctional reagent, protein kinase assay, proximity ligation assay, pull down, tandem affinity purification
Affinity Capture-Western, anti tag coimmunoprecipitation, beta galactosidase complementation, blue native page, confocal microscopy, fluorescent resonance energy transfer, protein kinase assay, proximity ligation assay
colocalization, direct interaction, physical, physical association
Affinity Capture-MS, Affinity Capture-Western, Co-localization, anti bait coimmunoprecipitation, beta galactosidase complementation, protein cross-linking with a bifunctional reagent, protein kinase assay, proximity ligation assay, pull down, tandem affinity purification
Affinity Capture-Western, anti tag coimmunoprecipitation, beta galactosidase complementation, blue native page, confocal microscopy, fluorescent resonance energy transfer, protein kinase assay, proximity ligation assay
colocalization, direct interaction, physical, physical association
Affinity Capture-Western, Co-localization, anti bait coimmunoprecipitation, beta galactosidase complementation, cosedimentation in solution, cross-linking study, protein cross-linking with a bifunctional reagent, proximity ligation assay, pull down
association, direct interaction, physical, physical association