Defining functional interactions during biogenesis of epithelial junctions

In spite of extensive recent progress, a comprehensive understanding of how actin cytoskeleton remodelling supports stable junctions remains to be established. Here we design a platform that integrates actin functions with optimized phenotypic clustering and identify new cytoskeletal proteins, their functional hierarchy and pathways that modulate E-cadherin adhesion. Depletion of EEF1A, an actin bundling protein, increases E-cadherin levels at junctions without a corresponding reinforcement of cell-cell contacts. This unexpected result reflects a more dynamic and mobile junctional actin in EEF1A-depleted cells. A partner for EEF1A in cadherin contact maintenance is the formin DIAPH2, which interacts with EEF1A. In contrast, depletion of either the endocytic regulator TRIP10 or the Rho GTPase activator VAV2 reduces E-cadherin levels at junctions. TRIP10 binds to and requires VAV2 function for its junctional localization. Overall, we present new conceptual insights on junction stabilization, which integrate known and novel pathways with impact for epithelial morphogenesis, homeostasis and diseases

Mtss1 promotes cell-cell junction assembly and stability through the small GTPase Rac1

Cell-cell junctions are an integral part of epithelia and are often disrupted in cancer cells during epithelial-to-mesenchymal transition (EMT), which is a main driver of metastatic spread. We show here that Metastasis suppressor-1 (Mtss1; Missing in Metastasis, MIM), a member of the IMD-family of proteins, inhibits cell-cell junction disassembly in wound healing or HGF-induced scatter assays by enhancing cell-cell junction strength. Mtss1 not only makes cells more resistant to cell-cell junction disassembly, but also accelerates the kinetics of adherens junction assembly. Mtss1 drives enhanced junction formation specifically by elevating Rac-GTP. Lastly, we show that Mtss1 depletion reduces recruitment of F-actin at cell-cell junctions. We thus propose that Mtss1 promotes Rac1 activation and actin recruitment driving junction maintenance. We suggest that the observed loss of Mtss1 in cancers may compromise junction stability and thus promote EMT and metastasis

FRET-ting about RhoA signalling in heart and vasculature: a new tool in our cardiovascular toolbox

Commentary on ‘A RhoA-FRET Biosensor Mouse for Intravital Imaging in Normal Tissue Homeostasis and Disease Contexts’ by Nobis M, Herrmann D et al., Cell Rep, 2017

Mtss1 promotes cell-cell junction assembly and stability through the small GTPase Rac1

Cell-cell junctions are an integral part of epithelia and are often disrupted in cancer cells during epithelial-to-mesenchymal transition (EMT), which is a main driver of metastatic spread. We show here that Metastasis suppressor-1 (Mtss1; Missing in Metastasis, MIM), a member of the IMD-family of proteins, inhibits cell-cell junction disassembly in wound healing or HGF-induced scatter assays by enhancing cell-cell junction strength. Mtss1 not only makes cells more resistant to cell-cell junction disassembly, but also accelerates the kinetics of adherens junction assembly. Mtss1 drives enhanced junction formation specifically by elevating Rac-GTP. Lastly, we show that Mtss1 depletion reduces recruitment of F-actin at cell-cell junctions. We thus propose that Mtss1 promotes Rac1 activation and actin recruitment driving junction maintenance. We suggest that the observed loss of Mtss1 in cancers may compromise junction stability and thus promote EMT and metastasis

Thymosin β4 mediates vascular protection via regulation of low density lipoprotein receptor related protein 1 (LRP1)

Background and Aims: Thymosin β4 (Tβ4), is a small peptide implicated in mural VSMC differentiation in developing embryo. A proportion of Tβ4KO embryos die with vascular haemorrhage and surviving adults display aortic VSMC and elastin defects. We found an interaction between LRP1 and Tβ4. LRP1 an endocytic co regulator of PDGF-BB signalling was associated by GWAS with risk of abdominal aortic aneurysm (AAA) and shown, in animal studies, to protect against AAA and atherosclerosis. Hypothesis: Tβ4 controls vasculoprotective signalling by regulating endocytosis of LRP1. Methods: Predisposition to vascular disease was confirmed in global, endothelial- and VSMC- specific Tβ4KO mouse models of AAA and atherosclerosis. Inflammation, ECM composition and elastin were analysed, alongside VSMC phenotype and signalling. We used surface biotinylation assays to track LRP1 distribution in Tβ4 knockdown aortic VSMCs. Finally, we evaluated the potential of exogenous Tβ4 to protect against vascular disease. Results: Tβ4KO mice displayed increased susceptibility to AAA, ranging from aortic dilation to medial dissection in Conclusions: We identify Tβ4 as a key regulator of LRP1-PDGFRb endocytic signalling, for maintaining VSMC differentiation and vascular health. Tβ4 may emerge as a promising candidate for treatment of vascular disease.</p