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A correction to this article has been published: J. Cell Biol. 145 (7) 1523
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© The Rockefeller University Press, 0021-9525/1999//851 $5.00
The Journal of Cell Biology, Volume 145, Number 4, , 1999 851-863


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Paxillin LD4 Motif Binds PAK and PIX through a Novel 95-kD Ankyrin Repeat, ARF–GAP Protein: A Role in Cytoskeletal Remodeling



Christopher E. Turner*, Michael C. Brown*, Joseph A. Perrotta*, M.C. Riedy*, Sotiris N. Nikolopoulos*, A. Rosa McDonald*, Shubha Bagrodia{ddagger}, Sheila Thomas§, and Phillip S. Leventhal*

* Department of Anatomy and Cell Biology, State University of New York, Health Science Center, Syracuse, New York 13210; {ddagger} Department of Molecular Medicine, Cornell University, Ithaca, New York 14853; and § Department of Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts 02215

Paxillin is a focal adhesion adaptor protein involved in the integration of growth factor- and adhesion-mediated signal transduction pathways. Repeats of a leucine-rich sequence named paxillin LD motifs (Brown M.C., M.S. Curtis, and C.E. Turner. 1998. Nature Struct. Biol. 5:677–678) have been implicated in paxillin binding to focal adhesion kinase (FAK) and vinculin. Here we demonstrate that the individual paxillin LD motifs function as discrete and selective protein binding interfaces. A novel scaffolding function is described for paxillin LD4 in the binding of a complex of proteins containing active p21 GTPase–activated kinase (PAK), Nck, and the guanine nucleotide exchange factor, PIX. The association of this complex with paxillin is mediated by a new 95-kD protein, p95PKL (paxillin-kinase linker), which binds directly to paxillin LD4 and PIX. This protein complex also binds to Hic-5, suggesting a conservation of LD function across the paxillin superfamily. Cloning of p95PKL revealed a multidomain protein containing an NH2-terminal ARF–GAP domain, three ankyrin-like repeats, a potential calcium-binding EF hand, calmodulin-binding IQ motifs, a myosin homology domain, and two paxillin-binding subdomains (PBS). Green fluorescent protein- (GFP-) tagged p95PKL localized to focal adhesions/complexes in CHO.K1 cells. Overexpression in neuroblastoma cells of a paxillin LD4 deletion mutant inhibited lamellipodia formation in response to insulin-like growth fac- tor-1. Microinjection of GST–LD4 into NIH3T3 cells significantly decreased cell migration into a wound. These data implicate paxillin as a mediator of p21 GTPase–regulated actin cytoskeletal reorganization through the recruitment to nascent focal adhesion structures of an active PAK/PIX complex potentially via interactions with p95PKL.

Key Words: migration • signal transduction • integrins • trafficking • vesicular transport



Abbreviations used in this paper: aa, amino acid; FAK, focal adhesion kinase; FRNK, FAK-related nonkinase; GFP, green fluorescent protein; GIT, G protein-coupled receptor kinase-interacting protein; MLCK, myosin light chain kinase; PAK, p21 GTPase–activated kinase; PBS, paxillin binding subdomain; PIX, PAK-interacting exchange factor; PKL, paxillin-kinase linker.



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