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© The Rockefeller University Press, 0021-9525/1998//1001 $5.00
The Journal of Cell Biology, Volume 142, Number 4, , 1998 1001-1012

Articles

Mechanism of Cdc42-induced Actin Polymerization in Neutrophil Extracts



Sally H. Zigmond*, Michael Joyce*, Changsong Yang*, Kevin Brown*, Minzhou Huang*, and Martin Pring{ddagger}

* Department of Biology, University of Pennsylvania; and {ddagger} Department of Physiology, University of Pennsylvania Medical School, Philadelphia, Pennsylvania 19104-6018

Cdc42, activated with GTP{gamma}S, induces actin polymerization in supernatants of lysed neutrophils. This polymerization, like that induced by agonists, requires elongation at filament barbed ends. To determine if creation of free barbed ends was sufficient to induce actin polymerization, free barbed ends in the form of spectrin-actin seeds or sheared F-actin filaments were added to cell supernatants. Neither induced polymerization. Furthermore, the presence of spectrin-actin seeds did not increase the rate of Cdc42-induced polymerization, suggesting that the presence of Cdc42 did not facilitate polymerization from spectrin-actin seeds such as might have been the case if Cdc42 inhibited capping or released G-actin from a sequestered pool.

Electron microscopy revealed that Cdc42-induced filaments elongated rapidly, achieving a mean length greater than 1 µm in 15 s. The mean length of filaments formed from spectrin-actin seeds was <0.4 µm. Had spectrin-actin seeds elongated at comparable rates before they were capped, they would have induced longer filaments. There was little change in mean length of Cdc42-induced filaments between 15 s and 5 min, suggesting that the increase in F-actin over this time was due to an increase in filament number. These data suggest that Cdc42 induction of actin polymerization requires both creation of free barbed ends and facilitated elongation at these ends.

Key Words: actin polymerization • Cdc42 • leukocytes • actin filament barbed ends • G proteins

Address all correspondence to Sally H. Zigmond, Biology Department, University of Pennsylvania, Philadelphia, PA 19104-6018. Tel.: (215) 898-4559. Fax: (215) 898-8780. E-mail: szigmond{at}sas.upenn.edu

1. Abbreviation used in this paper: GST, glutathione-S-transferase.


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