Regulation of microtubule dynamics in 3T3 fibroblasts by Rho family GTPases

Abstract

To get insight into the action of Rho GTPases on the microtubule system we investigated the effects of Cdc42, Rac1, and RhoA on the dynamics of microtubules in Swiss 3T3 fibroblasts. In control cells microtubule ends were dynamic: plus ends frequently switched between growth, shortening and pauses; the growth phase predominated over shortening. Free minus ends of microtubules depolymerized rapidly and never grew. Free microtubules were short-lived, and the microtubule network was organized into a radial array. In serum-starved cells microtubule ends became more stable: although plus ends still transited between growth and shortening, polymerization and depolymerization excursions became shorter and balanced each other. Microtubule minus ends were also stabilized. Consequently lifespan of free microtubules increased and microtubule array changed its radial pattern into a random one. Activation of Cdc42 and Rac1 in serum-starved cells promoted dynamic behavior of microtubule plus and minus ends, while inhibition of these GTPases in serum-grown cells suppressed microtubule dynamics and mimicked all effects of serum starvation. Activation of RhoA in serum-grown cells had effects similar to Cdc42 /Rac1 inactivation: it suppressed the dynamics of plus and minus ends, reduced the length of growth and shrinking episodes, and disrupted the radial organization of microtubules. However, in contrast to Cdc42 and Rac1 inactivation, active RhoA had no effect on the balance between microtubule growth and shortening. We conclude that Cdc42 and Rac1 have similar stimulating effects on microtubule dynamics while RhoA acts in an opposite way. Cell Motil.

The contributions of microtubule stability and dynamic instability to adenovirus nuclear localization efficiency

“…We have previously demonstrated that, upon infection, Ad induces the formation of ''pioneer-like'' MTs at the periphery; these MTs undergo catastrophe less often, leading to more persistent MT growth and a positive drift velocity [Warren et al, 2006]. Inhibition of Rac1 by treatment of cells with 100 lM NSC23766 abrogated the Ad-induced formation of ''pioneer-like'' MTs [Warren et al, 2006], consistent with previous reports that Rac1 activation stimulates assembly of ''pioneer'' MTs [Wittman et al, 2003;Grigoriev et al, 2006]. To investigate the role of Rac1 on Ad NLE, we treated A549 cells with 100 lM NSC23766 and examined the NLE of Ad following synchronous infection.…”

Integrins Regulate Microtubule Nucleating Activity of Centrosome through Mitogen-activated Protein Kinase/Extracellular Signal-regulated Kinase Kinase/Extracellular Signal-regulated Kinase (MEK/ERK) Signaling

“…Although the activity of these GTPases has not yet been assayed in our system, we know that the mutant integrin inhibits cell spreading, which is a Rac1-dependent process (26,32), and Rac1 has been shown to promote microtubule growth (54,55). Another potential integrin target is GSK-3␤, which inhibits the activity of multiple microtubule-binding proteins that promote microtubule anchorage and growth (54,(57)(58)(59)(60).…”

Reactive oxygen species in vascular endothelial cell motility. Roles of NAD(P)H oxidase and Rac1

“…In addition, the same molecules also control polymerization dynamics of the microtubule cytoskeleton [77][78][79]. In particular Rac1 is an extremely versatile molecule that interacts specifically with numerous upstream regulators and downstream effectors [42] (Fig.…”