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

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.