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
Serine/threonine-protein kinase PAK 2:Cytoplasm Note=MYO18A mediates the cellular distribution of thePAK2-ARHGEF7-GIT1 complex to the inner surface of the cellmembrane PAK-2p34: Nucleus Cytoplasm, perinuclearregion Membrane; Lipid-anchor Note=Interaction with ARHGAP10probably changes PAK-2p34 location to cytoplasmic perinuclearregion Myristoylation changes PAK-2p34 location to the membrane
Function (UniProt annotation)
Serine/threonine protein kinase that plays a role in avariety of different signaling pathways including cytoskeletonregulation, cell motility, cell cycle progression, apoptosis orproliferation Acts as downstream effector of the small GTPasesCDC42 and RAC1 Activation by the binding of active CDC42 and RAC1results in a conformational change and a subsequentautophosphorylation on several serine and/or threonine residuesFull-length PAK2 stimulates cell survival and cell growthPhosphorylates MAPK4 and MAPK6 and activates the downstream targetMAPKAPK5, a regulator of F-actin polymerization and cellmigration Phosphorylates JUN and plays an important role in EGF-induced cell proliferation Phosphorylates many other substratesincluding histone H4 to promote assembly of H33 and H4 intonucleosomes, BAD, ribosomal protein S6, or MBP Additionally,associates with ARHGEF7 and GIT1 to perform kinase-independentfunctions such as spindle orientation control during mitosis Onthe other hand, apoptotic stimuli such as DNA damage lead tocaspase-mediated cleavage of PAK2, generating PAK-2p34, an activep34 fragment that translocates to the nucleus and promotescellular apoptosis involving the JNK signaling pathway Caspase-activated PAK2 phosphorylates MKNK1 and reduces cellulartranslation
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.
The Ras proteins are GTPases that function as molecular switches for signaling pathways regulating cell proliferation, survival, growth, migration, differentiation or cytoskeletal dynamism. Ras proteins transduce signals from extracellular growth factors by cycling between inactive GDP-bound and active GTP-bound states. The exchange of GTP for GDP on RAS is regulated by guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs). Activated RAS (RAS-GTP) regulates multiple cellular functions through effectors including Raf, phosphatidylinositol 3-kinase (PI3K) and Ral guanine nucleotide-dissociation stimulator (RALGDS).
Axon guidance represents a key stage in the formation of neuronal network. Axons are guided by a variety of guidance factors, such as netrins, ephrins, Slits, and semaphorins. These guidance cues are read by growth cone receptors, and signal transduction pathways downstream of these receptors converge onto the Rho GTPases to elicit changes in cytoskeletal organization that determine which way the growth cone will turn.
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.
Activation of T lymphocytes is a key event for an efficient response of the immune system. It requires the involvement of the T-cell receptor (TCR) as well as costimulatory molecules such as CD28. Engagement of these receptors through the interaction with a foreign antigen associated with major histocompatibility complex molecules and CD28 counter-receptors B7.1/B7.2, respectively, results in a series of signaling cascades. These cascades comprise an array of protein-tyrosine kinases, phosphatases, GTP-binding proteins and adaptor proteins that regulate generic and specialised functions, leading to T-cell proliferation, cytokine production and differentiation into effector cells.
Human immunodeficiency virus type 1 (HIV-1) , the causative agent of AIDS (acquired immunodeficiency syndrome), is a lentivirus belonging to the Retroviridae family. The primary cell surface receptor for HIV-1, the CD4 protein, and the co-receptor for HIV-1, either CCR5 or CXCR4, are found on macrophages and T lymphocytes. At the earliest step, sequential binding of virus envelope (Env) glycoprotein gp120 to CD4 and the co-receptor CCR5 or CXCR4 facilitates HIV-1 entry and has the potential to trigger critical signaling that may favor viral replication. At advanced stages of the disease, HIV-1 infection results in dramatic induction of T-cell (CD4+ T and CD8+ T cell) apoptosis both in infected and uninfected bystander T cells, a hallmark of HIV-1 pathogenesis. On the contrary, macrophages are resistant to the cytopathic effect of HIV-1 and produce virus for longer periods of time.
Renal cell cancer (RCC) accounts for ~3% of human malignancies and its incidence appears to be rising. Although most cases of RCC seem to occur sporadically, an inherited predisposition to renal cancer accounts for 1-4% of cases. RCC is not a single disease, it has several morphological subtypes. Conventional RCC (clear cell RCC) accounts for ~80% of cases, followed by papillary RCC (10-15%), chromophobe RCC (5%), and collecting duct RCC (<1%). Genes potentially involved in sporadic neoplasms of each particular type are VHL, MET, BHD, and FH respectively. In the absence of VHL, hypoxia-inducible factor alpha (HIF-alpha) accumulates, leading to production of several growth factors, including vascular endothelial growth factor and platelet-derived growth factor. Activated MET mediates a number of biological effects including motility, invasion of extracellular matrix, cellular transformation, prevention of apoptosis and metastasis formation. Loss of functional FH leads to accumulation of fumarate in the cell, triggering inhibition of HPH and preventing targeted pVHL-mediated degradation of HIF-alpha. BHD mutations cause the Birt-Hogg-Dube syndrome and its associated chromophobe, hybrid oncocytic, and conventional (clear cell) RCC.
Nef interferes with cellular signal transduction pathways in a number of ways. Nef is associated with lipid rafts through its amino-terminal myristoylation and a proline-rich SH3-binding domain. These cholesterol-rich membrane microdomains appear to concentrate potent signaling mediators. Nef was found to complex with and activate serine/threonine protein kinase PAK-2, which may contribute to activation of infected cells. In vitro, HIV-infected T cells produce enhanced levels of interleukin-2 during activation. When expressed in macrophages, Nef intersects the CD40L signaling pathway inducing secretion of chemokines and other factors that attract resting T cells and promote their infection by HIV
In addition to serving as a scaffold via auto-phosphorylation, ZAP-70 also phosphorylates a restricted set of substrates following TCR stimulation - including LAT and SLP-76. These substrates have been recognized to play pivotal role in TCR signaling by releasing second messengers. When phosphorylated, LAT and SLP-76 act as adaptor proteins which serve as nucleation points for the construction of a higher order signalosome: GADS, PLC-gamma1 and GRB2 bind to the LAT on the phosphorylated tyrosine residues (steps 8 and 13). SLP-76 and SOS are then moved to the signalosome by interacting with the SH3 domains of GRB2 and GADS via their proline rich sequences (step 9). Three SLP-76 acidic domain N-term tyrosine residues are phosphorylated by ZAP-70, once SLP-76 binds to GADS (step 10). These phospho-tyrosine residues act as binding sites to the SH2 domains of PLC-gamma1, Vav and Itk (steps 11 and 12).
PLC-gamma1 is activated by dual phosphorylation on the tyrosine residues at positions 771, 783 and 1254 by Itk and ZAP-70 (step 14). Phosphorylated PLC-gamma1 subsequently detaches from LAT and SLP-76 and translocates to the plasma membrane by binding to phosphatidylinositol-4,5-bisphosphate (PIP2) via its PH domain (step 15). PLC-gamma1 goes on to hydrolyse PIP2 to second messengers DAG and IP3. These second messengers are involved in PKC and NF-kB activation and calcium mobilization (step 16)
PS-GAP (RGH10) interacts specifically with caspase-activated PAK-2p34 reducing the ability of PAK-2p34 to induce cell death. This interaction inhibits the kinase activity of PAK-2p34 and changes the localization of PAK-2p34 from the nucleus to the perinuclear region (Koeppel et al., 2004)
Stimulation of cell death by PAK-2 requires the generation and stabilization of the caspase-activated form, PAK-2p34 (Walter et al., 1998;Jakobi et al., 2003). Levels of proteolytically activated PAK-2p34 protein are controlled by ubiquitin-mediated proteolysis. PAK-2p34 but not full-length PAK-2 is degraded by the 26 S proteasome (Jakobi et al., 2003). It is not known whether ubiquitination and degradation of PAK-2p34 occurs in the cytoplasm or in the nucleus
In response to stress signals, the p21-activated protein kinase PAK-2 stimulates a cell death response characterized by increased cell rounding and apoptotic chromatin condensation (see Jakobi et al., 2003). PAK-2 is proteolytically cleaved by caspase-3 producing a constitutively active fragment, PAK-2p34. Following cleavage, PAK-2p34 is autophosphorylated at Thr 402 and transported to the nucleus where it accumulates due to the loss of its nuclear export signal motif (Jakobi et al., 2003). The activity of PAK-2p34 appears to be regulated both by proteosomal degradation (Jakobi et al., 2003) and by association with the GTPase-activating protein PS-GAP/\nRHG-10. This interaction inhibits the kinase activity of PAK-2p34 and changes the localization of PAK-2p34 from the nucleus to the perinuclear region (Koeppel et al., 2004). PAK-2p34 may function in the down-regulation of translation initiation in apoptosis through phosphorylation of Mnk1 (Orton et al.,2004)
Formation of the LAT signaling complex leads to activation of MAPK and production of cytokines. The sequence of events that leads from LAT to cytokine production has not been as clearly defined as the sequence that leads to degranulation. However, the pathways that lead to cytokine production require the guanine-nucleotide-exchange factors SOS and VAV that regulate GDP-GTP exchange of RAS. After its activation, RAS positively regulates the RAF-dependent pathway that leads to phosphorylation and, in part, activation of the mitogen-activated protein kinases (MAPKs) extracellular-signal-regulated kinase 1 (ERK1) and ERK2 (Gilfillan & Tkaczyk 2006)
CD28 binds to several intracellular proteins including PI3 kinase, Grb-2, Gads and ITK. Grb-2 specifically co-operates with Vav-1 in the up-regulation of NFAT/AP-1 transcription. CD28 costimulation resulted in a prolonged and sustained phosphorylation and membrane localization of Vav1 in comparison to T-cell receptor activation alone. Tyrosine-phosphorylated Vav1 is an early point of integration between the signaling routes triggered by the T-cell receptor and CD28.Vav1 transduces TCR and co-stimulatory signals to multiple biochemical pathways and several cytoskeleton-dependent processes. The products of Vav1 activation, Rac1 and Cdc42, in turn activate the mitogen-activated protein kinases JNK and p38. Vav1 is also required for TCR-induced calcium flux, activation of the ERK MAP kinase pathway, activation of the NF-kB transcription factor, inside-out activation of the integrin LFA-1, TCR clustering, and polarisation of the T cell
The interaction between ephrin (EFN) ligands and EPH receptors results not only in forward signaling through the EPH receptor, but also in 'reverse' signaling through the EFN ligand itself. Reverse signaling through EFNB is required for correct spine morphogenesis and proper path-finding of corpus callosum and dorsal retinal axons. The molecular mechanism by which EFNBs transduce a reverse signal involves phosphorylation of multiple, conserved tyrosines on the intracellular domain of B-type ephrins, facilitating binding of the SH2/SH3 domain adaptor protein GRB4 and subsequent cytoskeletal remodeling (Bruckner et al. 1997, Cowan & Henkemeyer 2001, Lu et al. 2001). The other mechanism of reverse signaling involves the C-terminus PSD-95/Dlg/ZO-1 (PDZ)-binding motif of EFNBs which recruits various PDZ domain containing proteins. Phosphorylation and PDZ-dependent reverse signaling by ephrin-B1 have each been proposed to play important roles in multiple contexts in development and disease (Bush & Soriano 2009)
A low level of RAC1 activity is essential to maintain axon outgrowth. ROBO activation recruits SOS, a dual specificity GEF, to the plasma membrane via Dock homolog NCK (NCK1 or NCK2) to activate RAC1 during midline repulsion
Angiogenesis is the formation of new blood vessels from preexisting vasculature. One of the most important proangiogenic factors is vascular endothelial growth factor (VEGF). VEGF exerts its biologic effect through interaction with transmembrane tyrosine kinase receptors VEGFR, selectively expressed on vascular endothelial cells. VEGFA signaling through VEGFR2 is the major pathway that activates angiogenesis by inducing the proliferation, survival, sprouting and migration of endothelial cells (ECs), and also by increasing endothelial permeability (Lohela et al. 2009, Shibuya & Claesson-Welsh 2006, Claesson-Welsh & Welsh, 2013). The critical role of VEGFR2 in vascular development is highlighted by the fact that VEGFR2-/- mice die at E8.5-9.5 due to defective development of blood islands, endothelial cells and haematopoietic cells (Shalaby et al. 1995)
Layers of smooth muscle cells can be found in the walls of numerous organs and tissues within the body. Smooth muscle tissue lacks the striated banding pattern characteristic of skeletal and cardiac muscle. Smooth muscle is triggered to contract by the autonomic nervous system, hormones, autocrine/paracrine agents, local chemical signals, and changes in load or length.\nActin:myosin cross bridging is used to develop force with the influx of calcium ions (Ca2+) initiating contraction. Two separate protein pathways, both triggered by calcium influx contribute to contraction, a calmodulin driven kinase pathway, and a caldesmon driven pathway.\nRecent evidence suggests that actin, myosin, and intermediate filaments may be far more volatile then previously suspected, and that changes in these cytoskeletal elements along with alterations of the focal adhesions that anchor these proteins may contribute to the contractile cycle.\nContraction in smooth muscle generally uses a variant of the same sliding filament model found in striated muscle, except in smooth muscle the actin and myosin filaments are anchored to focal adhesions, and dense bodies, spread over the surface of the smooth muscle cell. When actin and myosin move across one another focal adhesions are drawn towards dense bodies, effectively squeezing the cell into a smaller conformation. The sliding is triggered by calcium:caldesmon binding, caldesmon acting in an analogous fashion to troponin in striated muscle. Phosphorylation of myosin light chains also is involved in the initiation of an effective contraction
The free radical nitric oxide (NO), produced by endothelial NO synthase (eNOS), is an important vasoactive substance in normal vascular biology and pathophysiology. It plays an important role in vascular functions such as vascular dilation and angiogenesis (Murohara et al. 1998, Ziche at al. 1997). NO has been reported to be a downstream mediator in the angiogenic response mediated by VEGF, but the mechanism by which NO promotes neovessel formation is not clear (Babaei & Stewart 2002). Persistent vasodilation and increase in vascular permeability in the existing vasculature is observed during the early steps of angiogenesis, suggesting that these hemodynamic changes are indispensable during an angiogenic processes. NO production by VEGF can occur either through the activation of PI3K or through a PLC-gamma dependent manner. Once activated both pathways converge on AKT phosphorylation of eNOS, releasing NO (Lin & Sessa 2006). VEGF also regulates vascular permeability by promoting VE-cadherin endocytosis at the cell surface through a VEGFR-2-Src-Vav2-Rac-PAK signalling axis
CD209 (also called as DC-SIGN (DC-specific intracellular adhesion molecule-3-grabbing non-integrin)) is a type II transmembrane C-type lectin receptor preferentially expressed on dendritic cells (DCs). CD209 functions as a pattern recognition receptor (PRR) that recognises several microorganisms and pathogens, contributing to generation of pathogen-tailored immune responses (Gringhuis & Geijtenbeek 2010, den Dunnen et al. 2009, Svajger et al. 2010). CD209 interacts with different mannose-expressing pathogens such as Mycobacterium tuberculosis and HIV-1 (Gringhuis et al. 2007, Geijtenbeek et al. 2000a). It also acts as an adhesion receptor that interacts with ICAM2 (intracellular adhesion molecule-2) on endothelial cells and ICAM3 on T cells (Geijtenbeek et al. 2000b,c). \nCD209 functions not only as an independent PRR, but is also implicated in the modulation of Toll-like receptor (TLR) signaling at the level of the transcription factor NF-kB (Gringhuis et al. 2009). CLEC7A (Dectin-1) and CD209 (DC-SIGN) signalling modulates Toll-like receptor (TLR) signalling through the kinase RAF1 that is independent of the SYK pathway but integrated with it at the level of NF-kB activation. The activation of RAF1 by CLEC7A or CD209 does not lead to activation of extracellular signal-regulated kinase 1 (ERK1)/2 or Mitogen-activated protein kinase kinase 1 (MEK1)/2 but leads to the phosphorylation and subsequent acetylation of RELA (p65). RELA phosphorylated on S276 not only positively regulates the activity of p65 through acetylation of p65, but also represses RELB activity by sequestering active RELB into inactive p65-RELB dimers that do not bind DNA (Gringhuis et al. 2007, Svajger et al. 2010, Jacque et al. 2005). RAF1-dependent signaling pathway is crucial in dectin-1 mediated immunity as it modulates both the canonical (promoting p65 phosphorylation and acetylation) and non-canonical (forming inactive p65-RELB dimers) NK-kB activation
The PAKs (p21-activated kinases) are a family of serine/threonine kinases mainly implicated in cytoskeletal rearrangements. All PAKs share a conserved catalytic domain located at the carboxyl terminus and a highly conserved motif in the amino terminus known as p21-binding domain (PBD) or Cdc42/Rac interactive binding (CRIB) domain. There are six mammalian PAKs that can be divided into two classes: class I (or conventional) PAKs (PAK1-3) and class II PAKs (PAK4-6). Conventional PAKs are important regulators of cytoskeletal dynamics and cell motility and are additionally implicated in transcription through MAPK (mitogen-activated protein kinase) cascades, death and survival signaling and cell cycle progression (Chan and Manser 2012).
PAK1, PAK2 and PAK3 are direct effectors of RAC1 and CDC42 GTPases. RAC1 and CDC42 bind to the CRIB domain. This binding induces a conformational change that disrupts inactive PAK homodimers and relieves autoinhibition of the catalytic carboxyl terminal domain (Manser et al. 1994, Manser et al. 1995, Zhang et al. 1998, Lei et al. 2000, Parrini et al. 2002; reviewed by Daniels and Bokoch 1999, Szczepanowska 2009). Autophosphorylation of a conserved threonine residue in the catalytic domain of PAKs (T423 in PAK1, T402 in PAK2 and T436 in PAK3) is necessary for the kinase activity of PAK1, PAK2 and PAK3. Autophosphorylation of PAK1 serine residue S144, PAK2 serine residue S141, and PAK3 serine residue S154 disrupts association of PAKs with RAC1 or CDC42 and enhances kinase activity (Lei et al. 2000, Chong et al. 2001, Parrini et al. 2002, Jung and Traugh 2005, Wang et al. 2011). LIMK1 is one of the downstream targets of PAK1 and is activated through PAK1-mediated phosphorylation of the threonine residue T508 within its activation loop (Edwards et al. 1999). Further targets are the myosin regulatory light chain (MRLC), myosin light chain kinase (MLCK), filamin, cortactin, p41Arc (a subunit of the Arp2/3 complex), caldesmon, paxillin and RhoGDI, to mention a few (Szczepanowska 2009).
Class II PAKs also have a CRIB domain, but lack a defined autoinhibitory domain and proline-rich regions. They do not require GTPases for their kinase activity, but their interaction with RAC or CDC42 affects their subcellular localization. Only conventional PAKs will be annotated here
MAPK6 and MAPK4 (also known as ERK3 and ERK4) are vertebrate-specific atypical MAP kinases. Atypical MAPK are less well characterized than their conventional counterparts, and are generally classified as such based on their lack of activation by MAPKK family members. Unlike the conventional MAPK proteins, which contain a Thr-X-Tyr motif in the activation loop, MAPK6 and 4 have a single Ser-Glu-Gly phospho-acceptor motif (reviewed in Coulombe and Meloche, 2007; Cargnello et al, 2011). MAPK6 is also distinct in being an unstable kinase, whose turnover is mediated by ubiquitin-dependent degradation (Coulombe et al, 2003; Coulombe et al, 2004). The biological functions and pathways governing MAPK6 and 4 are not well established. MAPK6 and 4 are phosphorylated downstream of class I p21 activated kinases (PAKs) in a RAC- or CDC42-dependent manner (Deleris et al, 2008; Perander et al, 2008; Deleris et al, 2011; De La Mota-Peynado et al, 2011). One of the only well established substrates of MAPK6 and 4 is MAPKAPK5, which contributes to cell motility by promoting the HSBP1-dependent rearrangement of F-actin (Gerits et al, 2007; Kostenko et al, 2009a; reviewed in Kostenko et al, 2011b). The atypical MAPKs also contribute to cell motility and invasiveness through the NCOA3:ETV4-dependent regulation of MMP gene expression (Long et al, 2012; Yan et al, 2008; Qin et al, 2008)
Protein-peptide, Reconstituted Complex, Two-hybrid, anti bait coimmunoprecipitation, two hybrid, two hybrid array, two hybrid pooling approach, two hybrid prey pooling approach, validated two hybrid
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