γ-Tubulin serves as a template in the γ-TuRC machinery to nucleate microtubules. Curiously, γ-tubulin also interacts with Arp2/3, a complex that nucleates actin filaments, and with the Arp2/3 activator WASH. We previously reported that γ-tubulin and Arp2/3 colocalize at the centrosome, where WASH localizes. Here, we report that γ-tubulin localizes at actin-based membrane protrusions, where Arp2/3 operates. This was confirmed by the presence of tagged γ-tubulin at membrane protrusions in stimulated cells and by downregulation of γ-tubulin expression. Surprisingly, expression of tagged γ-tubulin dramatically inhibited the formation of stress-fibers, while having no effect on microtubules. This phenotype is similar to the disruption of stress-fibers by the overexpression of the WCA domain of WASH and other Wiskott-Aldrich syndrome (WAS) family members. We hypothesize that γ-tubulin regulates Arp2/3 and actin nucleation promoting factors such as WASH, explaining the similar effect of γ-tubulin expression and WCA domain expression on stress-fibers. The data presented here indicate that γ-tubulin has a profound relationship with actin filament dynamics.
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