Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:2.7.11.1 (protein kinase)
81,284 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The p21-activated kinase (PAK) family of protein kinases has recently attracted considerable attention as an effector of Rho family of small G proteins and as an upstream regulator of MAPK signalling pathways during cellular events such as re-arrangement of the cytoskeleton and apoptosis. We have cloned a novel human PAK family kinase that has been designated as PAK5. PAK5 contains a CDC42/Rac1 interactive binding (CRIB) motif at the N-terminus and a Ste20-like kinase domain at the C-terminus. PAK5 is structurally most related to PAK4 and PAK6 to make up the PAK-II subfamily. We have shown that PAK5 preferentially binds to CDC42 in the presence of GTP and that CRIB motif is essential for this interaction. PAK5 is a functional protein kinase but unlike PAK-I family kinases (PAK1, 2, and 3), the kinase activity of PAK5 does not seem to require the binding of CDC42. Overexpression of PAK5 activates the JNK kinase pathway but not p38 or ERK pathways. PAK5 transcript is predominantly expressed in brain as revealed by Northern blot and in situ hybridization. The expression pattern of PAK5 is distinct from that of PAK4 and PAK6, suggesting a functional division among PAK-II subfamily kinases based on differential tissue distribution.
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PMID:Cloning and characterization of PAK5, a novel member of mammalian p21-activated kinase-II subfamily that is predominantly expressed in brain. 1203 33

Exposure of cells to mitogens or growth factors stimulates Raf-1 activity through a complex mechanism that involves binding to active Ras, phosphorylation on multiple residues, and protein-protein interactions. Recently it was shown that the amino terminus of Raf-1 contains an autoregulatory domain that can inhibit its activity in Xenopus oocytes. In the present work we show that expression of the Raf-1 autoinhibitory domain blocks extracellular signal-regulated kinase 2 activation by the Raf-1 catalytic domain in mammalian cells. We also show that phosphorylation of Raf-1 on serine 338 by PAK1 and tyrosines 340 and 341 by Src relieves autoinhibition and that this occurs through a specific decrease in the binding of the Raf-1 regulatory domain to its catalytic domain. In addition, we demonstrate that phosphorylation of threonine 491 and serine 494, two phosphorylation sites in the catalytic domain that are required for Raf-1 activation, is unlikely to regulate autoinhibition. These results demonstrate that the autoinhibitory domain of Raf-1 is functional in mammalian cells and that its interaction with the Raf-1 catalytic domain is regulated by phosphorylation of serine 338 and tyrosines 340 and 341.
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PMID:Phosphorylation of Raf-1 by p21-activated kinase 1 and Src regulates Raf-1 autoinhibition. 1255 23

Members of the Snf1/AMP-activated protein kinase family are activated under conditions of nutrient stress by a distinct upstream kinase. Here we present evidence that the yeast Pak1 kinase functions as a Snf1-activating kinase. Pak1 associates with the Snf1 kinase in vivo, and the association is greatly enhanced under glucose-limiting conditions when Snf1 is active. Snf1 kinase complexes isolated from pak1Delta mutant strains show reduced specific activity in vitro, and affinity-purified Pak1 kinase is able to activate the Snf1-dependent phosphorylation of Mig1 in vitro. Purified Pak1 kinase promotes the phosphorylation of the Snf1 polypeptide on threonine 210 within the activation loop in vitro, and an increased dosage of the PAK1 gene causes increased Snf1 threonine 210 phosphorylation in vivo. Deletion of the PAK1 gene does not produce a Snf phenotype, suggesting that one or more additional protein kinases is able to activate Snf1 in vivo. However, deletion of the PAK1 gene suppresses many of the phenotypes associated with the deletion of the REG1 gene, providing genetic evidence that Pak1 activates Snf1 in vivo. The closest mammalian homologue of yeast Pak1 kinase, calcium-calmodulin-dependent protein kinase kinase beta, may play a similar role in mammalian nutrient stress signaling.
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PMID:Yeast Pak1 kinase associates with and activates Snf1. 1274 92

Synapsins are neuronal proteins that bind and cluster synaptic vesicles in the presynaptic space, presumably by anchoring to actin filaments, but specific regulatory functions of the synapsins are unknown. We found that a sub-population of brain synapsin Ia, a splice variant of one of three synapsin isoforms, inhibits the GTPase-activating protein (GAP) activity of several RGS proteins. Inhibition is highly selective for Galphaz, a member of the Gi family that is found in neurons, platelets, adrenal chromaffin cells, and a few other neurosecretory cells. Gz has been indirectly implicated in the regulation of secretion. Synapsin Ia constitutes a major fraction of the total GAP-inhibitory activity in brain, and its inhibitory activity is absent from the brains of synapsin I(-/-)/II(-/-) mice. Inhibition depends on the cationic D/E domain of synapsin. Phosphorylation of synapsin Ia at serine 9 by either cyclic AMP-dependent protein kinase or p21-activated protein kinase (PAK1) attenuates its potency as a GAP inhibitor more than 7-fold. Synapsin can thus act as a phosphorylation-modulated mediator of feedback regulation of Gz signaling by the synaptic machinery.
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PMID:Phosphorylation-regulated inhibition of the Gz GTPase-activating protein activity of RGS proteins by synapsin I. 1455 63

In examining the protein kinase components of mitogen-activated protein (MAP) kinase (MAPK) cascades that regulate the c-Jun N-terminal kinase (JNK) in Drosophila S2 cells, we previously found that distinct upstream kinases were involved in responses to sorbitol and lipopolysaccharide. Here we have extended that analysis to the possible MAPK kinase kinase kinases (MAP4Ks) in the JNK pathway. Fray, a putative Drosophila MAP4K, provided a major contribution to JNK activation by sorbitol. To explore the possible link to JNK in mammalian cells, we isolated and characterized OSR1 (oxidative stress-responsive 1), one of two human Fray homologs. OSR1 is a 58-kDa protein of 527 amino acids that is widely expressed in mammalian tissues and cell lines. Of potential regulators surveyed, endogenous OSR1 is activated only by osmotic stresses, notably sorbitol and to a lesser extent NaCl. However, OSR1 did not increase the activity of coexpressed JNK, nor did it activate three other MAPKs, p38, ERK2, and ERK5. A two-hybrid screen implicated another Ste20p family member, the p21-activated protein kinase PAK1, as an OSR1 target. OSR1 phosphorylated threonine 84 in the N-terminal regulatory domain of PAK1. Replacement of threonine 84 with glutamate reduced the activation of PAK1 by an active form of the small G protein Cdc42, suggesting that phosphorylation by OSR1 modulates the G protein sensitivity of PAK isoforms.
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PMID:Characterization of OSR1, a member of the mammalian Ste20p/germinal center kinase subfamily. 1470 32

Cyclic-GMP-dependent protein kinase (PKG) is widely appreciated as having diverse roles in a variety of cell types. Many reports have indicated that PKG might regulate cell function by activating members of the mitogen-activated protein kinase (MAPK) family of signaling proteins. In this study, stimulation of HEK-293 cells with nitric oxide (NO) was found to induce a rapid accumulation of phosphorylated p38 MAPK. The involvement of PKG in this process was confirmed by cotransfection of a dominant negative PKG construct (G1alphaR-GFP), which was able to block cGMP-induced p38 MAPK activation. Transfection of cells to express dominant negative Rac1(T17N) was also able to dose-dependently block cGMP-stimulated activation of p38 MAPK, thus indicating the importance of this pathway downstream of PKG. GST-PDB affinity-precipitation experiments revealed that stimulation of HEK293 cells with either nitric oxide or 8-Br-cGMP resulted in a rapid and transient activation of Rac1 with similar kinetics to p38 MAPK phosphorylation. Moreover, using in vitro kinase assays it was found that cGMP also stimulated the activity of the Rac1 effector Pak1. The activation of both Rac1 and Pak1 by 8-Br-cGMP was completely abolished by transfection of the cells with G1alphaR-GFP. Expression of the Rac1(T17N) mutant inhibited PKG-dependent activation of PAK1 indicating that Rac1 functions upstream of PAK1 in this pathway. Immunofluorescence experiments demonstrated clear colocalization of PKG and Rac1 in membrane ruffles and dynamic membrane regions supporting a functional interaction. However, in vitro kinase assays demonstrated that Rac1 is not a substrate for PKG suggesting an indirect activation mechanism. Taken together these data demonstrate a novel PKG-dependent pathway by which the Rac1/Pak1 pathway is activated. Furthermore, we demonstrate that this pathway is central to the activation of p38 MAPK by PKG in these cells.
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PMID:Activation of the small GTPase Rac1 by cGMP-dependent protein kinase. 1521 66

Rho family small G-protein activity is controlled by guanine nucleotide exchange factors that stimulate the release of GDP, thus allowing GTP binding. Once activated, Rho proteins control cell signaling through interactions with downstream effector proteins, leading to changes in cytoskeletal organization and gene expression. The ability of Rho family members to modulate the activity of other Rho proteins is also intrinsic to these processes. In this work we show that the Rac/Cdc42hs-regulated protein kinase PAK1 down-regulates the activity of the RhoA-specific guanine nucleotide exchange factor NET1. Specifically, PAK1 phosphorylates NET1 on three sites in vitro: serines 152, 153, and 538. Replacement of serines 152 and 153 with glutamate residues down-regulates the activity of NET1 as an exchange factor in vitro and its ability to stimulate actin stress fiber formation in cells. Using a phospho-specific antibody that recognizes NET1 phosphorylated on serine 152, we show that PAK1 phosphorylates NET1 on this site in cells and that Rac1 stimulates serine 152 phosphorylation in a PAK1-dependent manner. Furthermore, coexpression of constitutively active PAK1 inhibits the ability of NET1 to stimulate actin polymerization only when serines 152 and 153 are present. These data provide a novel mechanism for the control of RhoA activity by Rac1 through the PAK-dependent phosphorylation of NET1 to reduce its activity as a guanine nucleotide exchange factor.
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PMID:PAK1 negatively regulates the activity of the Rho exchange factor NET1. 1568 29

B-Raf is a key regulator of the ERK pathway and is mutationally activated in two-thirds of human melanomas. In this work, we have investigated the activation mechanism of B-Raf and characterized the roles of Ras and of B-Raf phosphorylation in this regulation. Raf-1 is regulated by an N-terminal autoinhibitory domain whose actions are blocked by interaction with Ras and subsequent phosphorylation of Ser(338). We observed that B-Raf also contains an N-terminal autoinhibitory domain and that the interaction of this domain with the catalytic domain was inhibited by binding to active H-Ras. However, unlike Raf-1, the phosphorylation of B-Raf at Ser(445) was constitutive and was only moderately increased by expression of constitutively active H-Ras or constitutively active PAK1. Ser(445) phosphorylation is important to the B-Raf activation mechanism, however, because mutation of this site to alanine increased the affinity of the regulatory domain for the catalytic domain and increased autoinhibition. Similarly, expression of constitutively active PAK1 also decreased auto-inhibition. B-Raf autoinhibition was negatively regulated by acidic substitutions at phosphorylation sites within the activation loop of B-Raf and by the oncogenic substitution V599E. However, these substitutions did not affect the ability of the regulatory domain to co-immunoprecipitate with the catalytic domain. These data demonstrate that B-Raf activity is autoregulated, that constitutive phosphorylation of Ser(445) primes B-Raf for activation, and that a key feature of phosphorylation within the activation loop or of oncogenic mutations within this region is to block autoinhibition.
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PMID:B-Raf and Raf-1 are regulated by distinct autoregulatory mechanisms. 1571 Jun 5

The protein kinase, PAK1, is overexpressed in human breast cancer and may contribute to malignancy through induction of proliferation and invasiveness. In this study, we examined the role of PAK1 in the survival of detached MCF10A breast epithelial cells to test whether it may also regulate the early stages of neoplasia. MCF10A cells undergo anoikis, as measured by the cleavage of caspase 3 and poly(ADP-ribose) polymerase (PARP), after more than 8 hours of detachment. Endogenous Akt, PAK1, and BAD are phosphorylated in attached MCF10A cells, but these phosphorylation events are all lost during the first 8 hours of detachment. Expression of constitutively active PAK1 or Akt suppresses the cleavage of caspase 3 and PARP in detached MCF10A cells. Co-overexpression of active PAK1 with dominant-negative Akt, or of active Akt with dominant-negative PAK1, still suppresses anoikis. Thus, Akt and PAK1 enhance survival through pathways that are at least partially independent. PAK1-dependent regulation of anoikis is likely to occur early in the apoptotic cascade as expression of dominant-negative PAK1 increased the cleavage of the upstream caspase 9, while constitutively active PAK1 inhibited caspase 9 activation. These results support a role for activated PAK1 in the suppression of anoikis in MCF10A epithelial cells.
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PMID:Active p21-activated kinase 1 rescues MCF10A breast epithelial cells from undergoing anoikis. 1602 43

PKN is a serine/threonine protein kinase, which has a catalytic domain highly homologous to that of protein kinase C (PKC) in the carboxyl-terminal region and three repeats of the antiparallel coiled coil (ACC) domain in the amino-terminal region. Mammalian PKN has three isoforms each derived from different genes, PKN1 (PKNalpha/PRK1/PAK1), PKN2 (PRK2/PAK2/PKNgamma), and PKN3 (PKNbeta). PKN isoforms show different enzymatic properties and tissue distributions and have been implicated in various distinct cellular processes (reviewed in Mukai [2003]). This chapter discusses methods to prepare purified enzymes and to assay substrate phosphorylation activities.
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PMID:Purification and kinase assay of PKN. 1647 61


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