GEF‐H1 over‐expression in hepatocellular carcinoma promotes cell motility via activation of RhoA signalling

Abstract

The interstitial chromosome (chr.) 1q21-q22 region is frequently amplified in human cancers, where it has been reported to carry prognostic significance for patients. We attempted to delineate chr. 1q21-q22 for affected gene(s) in hepatocellular carcinoma (HCC) by array-CGH and detected copy number gains of ρ-guanine nucleotide exchange factor-H1 (GEF-H1) as most significant event. Gene expression evaluation in the HCC cohort indicated common up-regulations of GEF-H1 in 64% tumours compared to adjacent non-tumoural liver (64/100; paired t-test p < 0.0001). Moreover, GEF-H1 over-expressions correlated with microvascular invasion and advanced-stage tumours (p < 0.05). High GEF-H1 levels also predict shorter disease-free and overall survival of HCC patients (p < 0.03). Functional knock-down of GEF-H1 by RNAi indicated marked reduction in cell invasion through matrigel and an inhibition of cell migration (p < 0.035), but an effect on cell viability was not apparent. More interestingly, a mesenchymal-epithelial transition (MET) was readily observed in GEF-H1 knock-down cells, where a concomitant re-expression of epithelial markers (E-cadherin and cytokeratin 18) and cell adhesion proteins (α-catenin and γ-catenin) was found but down-regulation of mesenchymal features (N-cadherin, vimentin and fibronectin). This phenotype was accompanied by reduced filamentous actin polymerizations and diminution of the stress fibre formation. In addition, reduced active form of GTP-RhoA, together with its downstream effectors, including cleaved ROCK1 and phosphorylated MLC2, were also detected in GEF-H1-depleted cells. Taken together, our findings underscore a potent oncogenic role for GEF-H1 in promoting the metastatic potentials of HCC, possibly through activation of RhoA signalling and the EMT phenomenon.

Vimentin intermediate filaments control actin stress fiber assembly through GEF-H1 and RhoA

“…Because extensive stress fibers enhance adhesion and inhibit cell motility, we speculate that upregulation of vimentin stimulates cell migration at least partially through inhibiting stress fiber assembly and contractility. In this context, it is important to note that altered GEF-H1 activity and expression levels have been linked to cancer progression (Cheng et al, 2012; Cullis et al, 2014; Biondini et al, 2015). Thus, in the future it will be interesting to examine how the vimentin–GEF-H1–RhoA pathway identified in our study contributes to the role of vimentin in cell migration and invasion in vivo .…”

Signaling pathway cooperation in TGF-β-induced epithelial–mesenchymal transition

“…TGF-β induces the expression of the Rho-associated GEF-H1, which enhances RhoA activity and contributes to α-SMA expression [23]. Depletion of GEF-H1, thus decreasing RhoA activity, was shown to attenuate mesenchymal marker and increase E-cadherin expression in liver carcinomas [24]. Integrin stimulation of the focal adhesion kinase, FAK, can control Rho GEFs and GAPs, and, consequently, actin dynamics and cell membrane protrusions [25].…”

The microtubule end-binding protein EB2 is a central regulator of microtubule reorganisation in apico-basal epithelial differentiation

“…Microtubule depolymerisation by Nocodazole, for example, activates RhoA/ROCK and destabilises microtubules due to release of the Rho effector GEF-H1 from microtubules. RhoA/ ROCK inhibition, on the other hand, induces microtubule stability and bundle formation as well as reducing stress fibres (Chang et al, 2008;Cheng et al, 2012;Gao et al, 2004;Kadir et al, 2011;Krendel et al, 2002;Scaife et al, 2003;Takesono et al, 2010).…”