A tyrosine-phosphorylated protein that binds to an important regulatory region on the cool family of p21-activated kinase-binding proteins.
The p21-activated kinases (Pak) are major targets of the small GTPases Cdc42 and Rac. We, and others, recently identified a family of proteins termed Cool/Pix, which interact with Pak3. In cells, p50(Cool-1) suppresses Pak activation by upstream activators; p85(Cool-1) has a permissive effect on Pak activation, and we now show that the closely related Cool-2 stimulates Pak kinase activity. To understand the differential regulation of Pak by Cool proteins, we screened for Cool-interacting proteins by affinity purification and microsequencing. This has led to the identification of two closely related proteins called Cat (Cool-associated, tyrosine phosphorylated), which contain a zinc finger followed by three ankyrin repeats. Cat-1 is identical to the recently identified binding partner for the beta-adrenergic receptor kinase (betaARK or GRK-2), which was shown to have Arf-GAP activity. Cat-1 and Cat-2 both bind to the COOH-terminal region of p85(Cool-1) and p85(Cool-2) but do not bind to p50(Cool-1). Cat-1 is tyrosine-phosphorylated in growing NIH 3T3 fibroblasts, and its tyrosine phosphorylation is increased following cell spreading on fibronectin, decreased in cells arrested in mitosis, and increased in the ensuing G(1) phase. Cat proteins are tyrosine-phosphorylated when co-expressed in cells with the focal adhesion kinase Fak and Src. These findings suggest that in addition to playing a role in Cool/Pak interactions, Cat proteins may serve as points of convergence between G protein-coupled receptors, integrins, Arf GTPases, cell cycle regulators, and Cdc42/Rac/Pak signaling pathways.
Bagrodia
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S
Department of Molecular Medicine, Molecular and Cell Biology, Cornell University, Ithaca, New York 14853-6401, USA.
Bailey
D
D
Lenard
Z
Z
Hart
M
M
Guan
J L
JL
Premont
R T
RT
Taylor
S J
SJ
Cerione
R A
RA
D048868:Adaptor Proteins, Signal Transducing; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002448:Cell Adhesion / Q000502:physiology*; D002453:Cell Cycle / Q000502:physiology*; D018797:Cell Cycle Proteins / Q000378:metabolism*; D003001:Cloning, Molecular; D004789:Enzyme Activation; D020690:GTPase-Activating Proteins; D020662:Guanine Nucleotide Exchange Factors; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins; D051379:Mice; D008969:Molecular Sequence Data; D005810:Multigene Family; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D011485:Protein Binding; D011494:Protein Kinases / Q000302:isolation & purification / Q000378:metabolism*; D064067:Rho Guanine Nucleotide Exchange Factors; D017422:Sequence Analysis, DNA; D015398:Signal Transduction
C576603:ARHGEF6 protein, human; C576606:ARHGEF7 protein, human; D048868:Adaptor Proteins, Signal Transducing; D018797:Cell Cycle Proteins; C485647:GIT1 protein, human; D020690:GTPase-Activating Proteins; C120766:Git1 protein, mouse; C120767:Git2 protein, mouse; D020662:Guanine Nucleotide Exchange Factors; D036341:Intercellular Signaling Peptides and Proteins; D010750:Phosphoproteins; D064067:Rho Guanine Nucleotide Exchange Factors; D011494:Protein Kinases