A PAK1-PIX-PKL complex is activated by the T-cell receptor independent of Nck, Slp-76 and LAT.
Given the importance of the Rho GTPase family member Rac1 and the Rac1/Cdc42 effector PAK1 in T-cell activation, we investigated the requirements for their activation by the T-cell receptor (TCR). Rac1 and PAK1 activation required the tyrosine kinases ZAP-70 and Syk, but not the cytoplasmic adaptor Slp-76. Surprisingly, PAK1 was activated in the absence of the transmembrane adaptor LAT while Rac1 was not. However, efficient PAK1 activation required its binding sites for Rho GTPases and for PIX, a guanine nucleotide exchange factor for Rho GTPases. The overexpression of ssPIX that either cannot bind PAK1 or lacks GEF function blocked PAK1 activation. These data suggest that a PAK1-PIX complex is recruited to appropriate sites for activation and that PIX is required for Rho family GTPase activation upstream of PAK1. Furthermore, we detected a stable trimolecular complex of PAK1, PIX and the paxillin kinase linker p95PKL. Taken together, these data show that PAK1 contained in this trimolecular complex is activated by a novel LAT- and Slp-76-independent pathway following TCR stimulation.
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Howard Hughes Medical Institute, Department of Medicine, Biomedical Sciences Graduate Program, University of California, San Francisco, CA 94143-0414, USA.
Yablonski
D
D
Manser
E
E
Lim
L
L
Weiss
A
A
D048868:Adaptor Proteins, Signal Transducing; D000595:Amino Acid Sequence; D002352:Carrier Proteins / Q000378:metabolism*; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D020690:GTPase-Activating Proteins; D020662:Guanine Nucleotide Exchange Factors / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D019169:Jurkat Cells; D008213:Lymphocyte Activation; D008565:Membrane Proteins; D008954:Models, Biological; D008969:Molecular Sequence Data; D015513:Oncogene Proteins / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011948:Receptors, Antigen, T-Cell / Q000378:metabolism*; D064067:Rho Guanine Nucleotide Exchange Factors; D015398:Signal Transduction; D013601:T-Lymphocytes / Q000276:immunology / Q000378:metabolism; D014162:Transfection; D051746:ZAP-70 Protein-Tyrosine Kinase; D054462:p21-Activated Kinases; D020830:rac1 GTP-Binding Protein / Q000378:metabolism
D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; C430213:GIT2 protein, human; D020690:GTPase-Activating Proteins; D020662:Guanine Nucleotide Exchange Factors; C110810:LAT protein, human; D008565:Membrane Proteins; C078332:Nck protein; D015513:Oncogene Proteins; D010750:Phosphoproteins; D011948:Receptors, Antigen, T-Cell; D064067:Rho Guanine Nucleotide Exchange Factors; C092947:SLP-76 signal Transducing adaptor proteins; D011505:Protein-Tyrosine Kinases; D051746:ZAP-70 Protein-Tyrosine Kinase; C497261:ZAP70 protein, human; C515903:PAK1 protein, human; D017346:Protein Serine-Threonine Kinases; D054462:p21-Activated Kinases; D020830:rac1 GTP-Binding Protein