Dexamethasone-induced cellular tension requires SGK1-stimulated Sec5/GEF-H1 interaction

Abstract

Dexamethasone, a synthetic glucocorticoid, is often used to induce osteoblast commitment of mesenchymal stem cells (MSCs), and this process requires RhoA-dependent cellular tension. The underlying mechanism is unclear. In this study, we show that dexamethasone stimulates expression of fibronectin and integrin α5 (ITGA5), accompanied by an increase in the interaction of GEF-H1 (also known as ARHGEF2) with Sec5 (also known as EXOC2), a microtubule (MT)-regulated RhoA activator and a component of the exocyst, respectively. Disruption of this interaction abolishes dexamethasone-induced cellular tension and GEF-H1 targeting to focal adhesion sites at the cell periphery without affecting dexamethasone-induced levels of ITGA5 and fibronectin, and the extracellular deposition of fibronectin at adhesion sites is specifically inhibited. We demonstrate that dexamethasone stimulates the expression of serum-glucocorticoid-induced protein kinase 1 (SGK1), which is necessary and sufficient for the induction of the Sec5-GEF-H1 interaction. Given the function of SGK1 in suppressing MT growth, our data suggest that the induction of SGK1 through treatment with dexamethasone alters MT dynamics to increase Sec5-GEF-H1 interactions, which promote GEF-H1 targeting to adhesion sites. This mechanism is essential for the formation of fibronectin fibrils and their attachment to integrins at adhesion sites in order to generate cellular tension.

Adaptable Hydrogels Mediate Cofactor‐Assisted Activation of Biomarker‐Responsive Drug Delivery via Positive Feedback for Enhanced Tissue Regeneration

“…We also observed that cells in the HA‐Pam‐Mg·Dex group mainly maintained a spherical morphology, whereas cells in the former two groups exhibited more isotropic spreading, as evidenced by the larger cell area and smaller sphericity (Figure c,d). It has been reported that Dex can stimulate expression of fibronectin and integrin at cell adhesion sites, which are essential to cell spreading and generation of cellular tension . Thus, sustained supply of Dex in the HA‐Pam‐Mg&Dex and HA‐Pam‐Mg‐DexP group may promote the cellular adhesion and interaction with the hydrogel network, thereby facilitating the spreading of encapsulated cells.…”

A Rho signaling network links microtubules to PKD controlled carrier transport to focal adhesions

“…For example, the junctional adaptor cingulin recruits GEF-H1 to tight junctions thereby inactivating its GEF activity and inhibiting Rho signaling ( Aijaz et al, 2005 ). By contrast, the interaction of GEF-H1 with Sec5 promotes RhoA activation at the exocyst complex ( Pathak et al, 2012 ) and is important for GEF-H1 localization to FAs ( Wang et al, 2015 ). Recently, plasma membrane associated active RhoA was demonstrated to recruit GEF-H1 thereby promoting a self-amplification loop.…”

Rab5 GTPases are required for optimal TORC2 function

“…It has been reported that SGK1, the mammalian homologue of Ypk1 (Casamayor et al, 1999), facilitates PM recycling of KCNQ1 channels in a Rab5-dependent manner, but whether that behavior was dependent on SGK1-mediated phosphorylation of any Rab5 GEF was not explored (Seebohm et al, 2008). Likewise, it has been reported that SGK1 function promotes association of a Rho- and Rac-specific GEF (ARHGEF2/GEF-H1) with a component (Sec5/EXOC2) of the mammalian exocyst complex, but again whether that behavior was dependent on SGK1-mediated phosphorylation of the GEF was not determined (Wang et al, 2015).…”