Lfc subcellular localization and activity is controlled by αv-class integrin

GEF-H1 drives breast cancer cells to tumor progression

Rho GTPases are involved in several biological processes, including cytoskeletal remodeling, gene transcription, cell proliferation and differentiation. Dysregulation of Rho GTPases activity can lead to enhanced tumor cell proliferation and metastasis. Rho guanine nucleotide exchange factor-H1 (GEFH1) is a RhoA activator that is associated with microtubules (MT) and its localization and activity are regulated, in part, by MT and fibronectin-binding integrins. Our findings showed that GEF-H1 expression is significantly higher in human breast cancer biopsies than in normal tissues. Moreover, patients with increased GEF-H1 expression had a lower survival rate and a higher incidence of metastasis. We generated a GEF-H1 knockout (KO) breast cancer cell line and observed a significant reduction in the number of focal adhesions, formation of stress fibers, and activation of downstream signaling pathways. Concordantly, cell proliferation, migration, adhesion, and invasion were reduced. Furthermore, when GEF-H1 knockout (KO) cells were orthotopically implanted into the mammary fat pads of BALB/c mice, a significant decrease was observed in both tumor formation and lung metastasis compared to control breast cancer cells. These results suggest that GEF-H1/RhoA activation mediates cytoskeletal remodeling and signaling pathways critical for breast cancer cell proliferation, migration, and invasion. In vivo assays and human biopsy studies further support GEF-H1 as a potential biomarker of breast tumor progression.

Mechanosignaling via Integrins: Pivotal Players in Liver Fibrosis Progression and Therapy

Liver fibrosis, a consequence of chronic liver injury, represents a major global health burden and is the leading cause of liver failure, morbidity, and mortality. The pathological hallmark of this condition is excessive extracellular matrix deposition, driven primarily by integrin-mediated mechanotransduction. Integrins, transmembrane heterodimeric proteins that serve as primary ECM receptors, orchestrate complex mechanosignaling networks that regulate the activation, differentiation, and proliferation of hepatic stellate cells and other ECM-secreting myofibroblasts. These mechanical signals create self-reinforcing feedback loops that perpetuate the fibrotic response. Recent advances have provided insight into the roles of specific integrin subtypes in liver fibrosis and revealed their regulation of key downstream effectors-including transforming growth factor beta, focal adhesion kinase, RhoA/Rho-associated, coiled-coil containing protein kinase, and the mechanosensitive Hippo pathway. Understanding these mechanotransduction networks has opened new therapeutic possibilities through pharmacological manipulation of integrin-dependent signaling.

Cyclosporine A improves the binding of mouse embryos to fibronectin

AIM

The binding of integrin αvβ3 with endometrial fibronectin (FN) promotes the migration of preimplantation embryos in mice. We have previously shown that cyclosporine A (CsA) improves the adhesion and invasion of mouse preimplantation embryos. In this study, we evaluated the roles of calcium ions and downstream signaling factors in the binding of integrin αvβ3 to FN.

METHODS

Female Institute of Cancer Research (ICR) mice were superovulated and mated, and two-cell embryos were harvested from the oviducts and cultured to the blastocyst stage The adhesion and stretching growth of hatched embryos in laminin-coated dishes were evaluated, and integrinβ3 expression was determined using qPCR. Blastocytes were cultured with 0 or 1  μM cyclosporine A (CsA) and the attachment of embryonic integrin αvβ3 to FN120 was observed using a fluorescent bead. To further determine the mechanism, the cells were also incubated with calcium ions and protein kinase C and calmodulin antagonists. The binding of integrin αvβ3 to FN120 was examined via confocal laser scanning microscopy.

RESULTS

The adhesion and stretching growth of peri-implantation embryos were greater and integrinβ3 expression was higher in the 1 μM CsA group than in the 0 μM CsA group (p < 0.05). When incubated with calcium ions and protein kinase C and calmodulin antagonists, the ability of peri-implantation embryos to bind to FN decreased; CsA treatment promoted this binding.

CONCLUSION

This study revealed that CsA up - regulates integrinβ3 expression in peri - implantation embryos and promotes binding to FN via calcium ions, and protein kinase C, and calmodulin. These findings provide evidence supporting the beneficial effect of CsA on the peri - implantation embryo adhesion.

Bone resorption by osteoclasts involves fine tuning of RHOA activity by its microtubule-associated exchange factor GEF-H1

Bone health is controlled by the balance between bone formation by osteoblasts and degradation by osteoclasts. A disequilibrium in favor of bone resorption leads to osteolytic diseases characterized by decreased bone density. Osteoclastic resorption is dependent on the assembly of an adhesion structure: the actin ring, also called podosome belt or sealing zone, which is composed of a unique patterning of podosomes stabilized by microtubules. A better understanding of the molecular mechanisms regulating the crosstalk between actin cytoskeleton and microtubules network is key to find new treatments to inhibit bone resorption. Evidence points to the importance of the fine tuning of the activity of the small GTPase RHOA for the formation and maintenance of the actin ring, but the underlying mechanism is not known. We report here that actin ring disorganization upon microtubule depolymerization is mediated by the activation of the RHOA-ROCK signaling pathway. We next show the involvement of GEF-H1, one of RHOA guanine exchange factor highly expressed in osteoclasts, which has the particularity of being negatively regulated by sequestration on microtubules. Using a CRISPR/Cas9-mediated GEF-H1 knock-down osteoclast model, we demonstrate that RHOA activation upon microtubule depolymerization is mediated by GEF-H1 release. Interestingly, although lower levels of GEF-H1 did not impact sealing zone formation in the presence of an intact microtubule network, sealing zone was smaller leading to impaired resorption. Altogether, these results suggest that a fine tuning of GEF-H1 through its association with microtubules, and consequently of RHOA activity, is essential for osteoclast sealing zone stability and resorption function.