Force-induced cell polarisation is linked to RhoA-driven microtubule-independent focal-adhesion sliding

Department of New Materials and Biosystems, Max Planck Institute for Metals Research, 70569 Stuttgart, Germany.
Journal of Cell Science (Impact Factor: 5.43). 10/2009; 122(Pt 20):3644-51. DOI: 10.1242/jcs.054866
Source: PubMed


Mechanical forces play a crucial role in controlling the integrity and functionality of cells and tissues. External forces are sensed by cells and translated into signals that induce various responses. To increase the detailed understanding of these processes, we investigated cell migration and dynamic cellular reorganisation of focal adhesions and cytoskeleton upon application of cyclic stretching forces. Of particular interest was the role of microtubules and GTPase activation in the course of mechanotransduction. We showed that focal adhesions and the actin cytoskeleton undergo dramatic reorganisation perpendicular to the direction of stretching forces even without microtubules. Rather, we found that microtubule orientation is controlled by the actin cytoskeleton. Using biochemical assays and fluorescence resonance energy transfer (FRET) measurements, we revealed that Rac1 and Cdc42 activities did not change upon stretching, whereas overall RhoA activity increased dramatically, but independently of intact microtubules. In conclusion, we demonstrated that key players in force-induced cellular reorganisation are focal-adhesion sliding, RhoA activation and the actomyosin machinery. In contrast to the importance of microtubules in migration, the force-induced cellular reorganisation, including focal-adhesion sliding, is independent of a dynamic microtubule network. Consequently, the elementary molecular mechanism of cellular reorganisation during migration is different to the one in force-induced cell reorganisation.

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    • "It has been hypothesized that directional ruffling is a prerequisite for stress fiber reorientation to cyclic stretch. Huang et al. (2010) demonstrated that edge ruffling was concentrated perpendicular to the direction of cyclic uniaxial stretch axis, consistent with the eventual stress fiber alignment direction as reported previously (Goldyn et al., 2009). Inhibition of actinrelated protein-2/3 (Arp 2/3), which suppressed lamellipodia to result in a non-elongated morphology did, not block stress fiber reorientation perpendicular to the stretch direction (Huang et al., 2010), suggesting that directional edge ruffling is not a primary mechanism guiding cytoskeletal alignment in response to stretch. "
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    • "RhoA activates the cofilin kinase LIM kinase through ROCK [34]. In addition, it has been reported that both uniaxial mechanical stretch [35] and the Nox4-positive regulator Poldip2 increase RhoA activity [21]. Therefore, we sought to evaluate if the RhoA/LIM kinase pathway contributes to the Nox4-mediated cofilin activation after biaxial strain that we reported. "
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    • "This underlies the continuing lack of knowledge on what governs the turnover rate of focal adhesions . In some cells, moreover, sliding of these structures with respect to the matrix-coated substrate has been reported (Goldyn et al. 2009; Smilenov et al. 1999) but, once again, it is not known how this property relates to the molecular constitution of adhesions. Whether PKC isoforms have roles to play in the stability or half-life of adhesions is unknown. "
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