Contraction reaction: mechanical regulation of Rho GTPase.

Epithelial cell differentiation is influenced by the physical environment. Local external changes in rigidity of the extracellular matrix are 'sensed' as increased or decreased tension and communicated intracellularly. The communications network that signals the state of the extracellular physical environment acts through the actin cytoskeleton to modulate Rho GTPase activity. A recent paper reports the surprising finding that breast epithelial cells respond to flexible surroundings by downregulating Rho activity through the actions of the Rho-regulated ROCK kinases.