Endosomal spatio-temporal modulation of the cortical RhoA zone conditions epithelial cell organization

At the basis of cell shape and behavior, actomyosin organization and force-generating property are widely studied, however very little is known about the regulation of the contractile network in space and time. Here we study the role of the epithelial-specific protein EpCAM, a contractility modulator, in cell shape and motility, and we show that it is required for the maturation of stress fibers and frontrear polarity acquisition at the single cell level. There, EpCAM ensures the remodeling of a transient active RhoA zone in the cortex of spreading epithelial cells. GTP-RhoA follows the endosomal pathway mediated by Rab35 and EHD1, where it co-evolves together with EpCAM. In fact, EpCAM balances GTP-RhoA turnover in order to tune actomyosin remodeling for cell shape, polarity and mechanical property acquisition. Impairment of GTP-RhoA endosomal trafficking either by EpCAM silencing or Rab35 / EHD1 mutant expression prevents correct myosin-II activity, stress fiber formation, and ultimately cell polarization. Collectively, this work shows that the coupling of EpCAM/RhoA co-trafficking to actomyosin rearrangement is critical for spreading, and advances our understanding of how biochemical and mechanical properties can be coupled for cell plasticity.