ARHGAP18-ezrin functions as an autoregulatory module for RhoA in the assembly of distinct actin-based structures

Abstract

The assembly of a three-dimensional actin cytoskeleton is largely mediated by local Rho GTPases. Restriction of microvilli to the epithelial apical surface requires local regulation of actin structure. On epithelial cells, the presence of microvilli depends on RhoA activation of its effector kinases LOK and SLK that phosphorylate ezrin to function as a membrane-actin linker. Further, previous work has revealed that active ezrin negatively regulates RhoA, but the mechanism was unknown. Here, we show this regulation is mediated by recruitment and activation of ARHGAP18 by active ezrin, which stimulates its GTPase activity towards RhoA. Loss of ARHGAP18 enhances ezrin phosphorylation and results in abundant stubby microvilli that turn over rapidly. This phenotype can be rescued by re-expression of ARHAGP18, and by a construct that targets just the GTPase domain to active ezrin, but not a GAP-dead version. Loss of ARHGAP18 also results in enhanced phosphorylation of myosin light chain, the classic response to elevated RhoA levels. This leads to inappropriate assembly of non-muscle myosin-II into microvilli and the disruption of the normal apical actomyosin organization. Thus, the localization and activation of ARGHAP18 by active ezrin constitutes a local auto-regulatory module to fine tune RhoA to ensure appropriate microvilli organization.

Intestinal tuft cells assemble a cytoskeletal superstructure composed of co-aligned actin bundles and microtubules

“…For example, stereocilia core bundles contain espin-1, fimbrin/plastin-1, and fascin-2 [44][45][46] whereas enterocyte microvilli contain espin, villin, fimbrin, and mitotic spindle positioning protein (MISP) [47][48][49][50]. Recent research also indicated that these bundlers occupy distinct 'neighborhoods' relative to the ends of the bundle [50,51]. In tuft cells, previous studies identified specific expression of actin-binding proteins including fimbrin, advillin, and girdin (Y1798) [2,21,23,24].…”

Synthetic dysmobility screening reveals a phosphorylation-independent facet of the SLK-Ezrin-F-actin signaling cascade

“…Additionally, the interaction between ezrin and ARHGAP18, a RhoA GTPaseactivating protein, modulates RhoA activity in microvilli (20). This modulation is vital for maintaining the proper architecture and functionality of microvilli by regulating ezrin phosphorylation and preventing inappropriate myosin assembly.…”

Astrocytic LRRK2 Controls Synaptic Connectivity through ERM Phosphorylation

“…Astrocytes control synapse formation and function both through cell adhesion and secreted proteins that signal to neurons 31,160 . The canonical function of ERM proteins is linking the actin cytoskeleton with the plasma membrane, thus allowing cellular process outgrowth and morphogenesis [161][162][163] . Less is known about the roles of ERM in the secretion process.…”