Id1 induces tubulogenesis by regulating endothelial cell adhesion and cytoskeletal organization through β1-integrin and Rho-kinase signalling.

The inhibitor of differentiation 1 (Id1) protein is required for tubulogenesis, but the molecular signalling pathways remain unclear. Overexpression (Id1-t) or down-regulation (si-Id1) of Id-1 in cell lines, were used to study the function of Id1. The expression of Id1 and β1-integrin was assessed by Western blotting. Up-regulation of Id1 in human umbilical vascular endothelial cells (HUVECs) activated the expression of β1-integrin and promoted cell adhesion and spreading. Conversely, down-regulation of Id1 suppressed β1-integrin expression and inhibited tubulogenesis. By using a β1-integrin antibody to inhibit β1-integrin function, we demonstrated that Id1-induced cell adhesion and tubulogenesis were mediated by β1-integrin. In addition, HUVECs overexpressing Id1 were able to promote capillary tube formation through cytoskeleton reorganization and cell contraction. Finally, the Rho-kinase inhibitor Y27632 inhibited tubulo-genesis induced by Id1. Our findings provide evidence that Id1 regulates tubulogenesis in vitro through β1-integrin and Rho-kinase signalling.