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First published online April 28, 2005

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PAK4: a cytoskeleton key

Crosstalk between microtubules and actin is essential for changes in cell morphology. Rho-family GTPases, such as Rho, Rac and Cdc42, regulate both systems and are therefore ideally positioned to relay this. On p. 1861, Tod Smeal and co-workers describe one way they do so, showing that the kinase PAK4 is critical. PAKs are important Rho-family effectors but few of their targets are known. Smeal and co-workers now reveal that PAK4 (a Cdc42 effector) phosphorylates the guanine-nucleotide-exchange factor GEF-H1 (a Rho/Rac activator) and that the two form a complex on microtubules in vivo. The authors show that phosphorylation of Ser180 causes release of GEF-H1 from microtubules. Furthermore it blocks GEF-H1-dependent formation of actin stress fibres, promoting lamellipodial protrusion instead – reminiscent of Rac. When Ser180 is mutated, GEF-H1 by contrast induces stress fibres – reminiscent of Rho. The authors note that the mutant GEF-H1 retains GEF activity. They therefore conclude that PAK4 phosphorylation regulates the targeting rather than exchange activity of GEF-H1. Their findings are consistent with a model in which PAK4 acts both upstream and downstream of Rho-family GTPases and functions as a switch that links microtubules with different actin rearrangements.

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PAK4 mediates morphological changes through the regulation of GEF-H1

Marinella G. Callow, Sergey Zozulya, Mikhail L. Gishizky, Bahija Jallal, and Tod Smeal
JCS 2005 118: 1861-1872. [Abstract] [Full Text]  

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Related articles in JCS Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Search for Related Content Social Bookmarking                         What's this?