Rho and Rab Family Small GTPases in the Regulation of Membrane Polarity in Epithelial Cells

Abstract

Membrane polarity, defined as the asymmetric distribution of lipids and proteins in the plasma membrane, is a critical prerequisite for the development of multicellular tissues, such as epithelia and endothelia. Membrane polarity is regulated by polarized trafficking of membrane components to specific membrane domains and requires the presence of intramembrane diffusion barriers that prevent the intermixing of asymmetrically distributed membrane components. This intramembrane diffusion barrier is localized at the tight junctions (TJs) in these cells. Both the formation of cell-cell junctions and the polarized traffic of membrane proteins and lipids are regulated by Rho and Rab family small GTPases. In this review article, we will summarize the recent developments in the regulation of apico-basal membrane polarity by polarized membrane traffic and the formation of the intramembrane diffusion barrier in epithelial cells with a particular focus on the role of Rho and Rab family small GTPases.

RhoGDI1 regulates cell-cell junctions in polarized epithelial cells

“…In addition, Cdc42 at the apical membrane activates MRCK thereby stimulating apical myosin II activation and inhibiting lateral/junctional RhoA activity, which triggers an actomyosin contractility-based mechanism of PAR protein segregation ( Zihni et al, 2017 ). Consistent with a role of Rho GTPases in epithelial polarization, several RhoGEFs and RhoGAPs have been identified at AJs and TJs ( Citi et al, 2014 ; Mack and Georgiou, 2014 ; Braga, 2018 ; Ebnet and Gerke, 2022 ). The principal mechanism underlying the spatial regulation of the activities of Rho GTPases is their global delivery to membranes by GDP dissociation inhibitors (GDIs) and the regulation of their activities by locally resident RhoGEFs and RhoGAPs ( Cherfils and Zeghouf, 2013 ).…”

“…Based on the important function of Rho family small GTPases in junction formation and maturation in polarized epithelial cells ( Braga, 2018 ; Ebnet and Gerke, 2022 ), we analyzed the role of RhoGDI1 in Eph4 cells, a murine mammary gland-derived cell line that develops apical-basal polarity with well-developed tight junctions (TJs) ( Umeda et al, 2006 ). We stably expressed RhoGDI1-specific shRNAs in Eph4 cells ( Supplementary Figure S1 ) and analyzed the localization of several integral membrane and peripheral membrane proteins localized at AJ and TJ, including E-cadherin, JAM-A, ZO-1 and ZO-2.…”

Tuning apicobasal polarity and junctional recycling in the hemogenic endothelium orchestrates the morphodynamic complexity of emerging pre-hematopoietic stem cells

“…Owing to the significance of apicobasal polarity control on EHT features, as suggested by our work, we investigated which proteins may be essential for actin/actomyosin regulation and focused on regulators of Rho GTPases, in particular Rho GEFs that catalyse exchange of GDP for GTP to positively regulate their activity ( Rossman et al, 2005 ). As for Pard3 proteins, several of these Rho GEFs contain one or several PDZ domain(s) that target most proteins to complexes acting at the apical side therefore interlinking actin/actomyosin regulation with cell polarity ( Mack and Georgiou, 2014 ; Ebnet and Gerke, 2022 ). We focused on ine PDZ-domain containing Rho GEFs, all encoded by different genes in the zebrafish ( Figure 7—figure supplement 1 ): ArhGEF11/PDZ-RhoGEF (thereafter shortened as ArhGEF11), ArhGEF12a, ArhGEF12b, PRex1, PRex2, Tiam1a, Tiam1b, Tima2a, Tiam2b.…”

Tuning apicobasal polarity and junctional recycling in the hemogenic endothelium orchestrates the morphodynamic complexity of emerging pre-hematopoietic stem cells

“…Owing to the significance of apicobasal polarity control on EHT features, as suggested by our work, we investigated which proteins may be essential for actin/actomyosin regulation and focused on regulators of Rho GTPases, in particular Rho GEFs that catalyse exchange of GDP for GTP to positively regulate their activity (Rossman, Der, and Sondek 2005). As for Pard3 proteins, several of these Rho GEFs contain one or several PDZ domain(s) that target most proteins to complexes acting at the apical side therefore interlinking actin/actomyosin regulation with cell polarity (Mack and Georgiou 2014; Ebnet and Gerke 2022). We focused on 9 PDZ-domain containing Rho GEFs, all encoded by different genes in the zebrafish ( Figure 7- figure supplement 1 ): ArhGEF11/PDZ-RhoGEF (thereafter shortened as ArhGEF11), ArhGEF12a, ArhGEF12b, PRex1, PRex2, Tiam1a, Tiam1b, Tima2a, Tiam2b.…”