Hypoxia upregulates integrin gene expression in microvascular endothelial cells and promotes their migration and capillary-like tube formation

Tissue hypoxia affects gene expression through the hypoxia-inducible transcription factors, HIF-1 and HIF-2, in both physiological and pathological angiogenesis. Angiogenesis is a complex response of endothelial cells integrating cell proliferation, migration, tube formation, and their interaction with the extracellular matrix through integrin receptors. In this report, we studied the effect of hypoxia on the angiogenic functions of human microvascular endothelial cells (HMEC-1) as well as on expression of the angiogenic integrins alpha(v)beta(3),alpha(v)beta(5), and alpha(5)beta(1). Exposure of HMEC-1 to hypoxia (1% O-2) or to DMOG, a prolyl-4-hydroxylase inhibitor, caused significant reduction to their proliferation rate, whereas their migration ability toward laminin-1 or collagen IV and capillary-like tube formation were significantly enhanced. In addition, alpha(v), beta(1), beta(3), and beta(5) integrins expression was increased under hypoxia in HMEC-1, while alpha(5) integrin was not affected. Both HIF-1 and HIF-2 protein expression and transcriptional activity were induced under hypoxia in HMEC-1. The knockdown of either HIF-1 alpha or HIF-2 alpha inhibited integrin beta(3) hypoxic stimulation, suggesting a HIF-dependent induction of b3 integrin in HMEC-1. Taken together, our results indicate that hypoxia transcriptionally up-regulates angiogenic integrins in microvascular endothelial cells along with promoting migration and tube formation of HMEC-1.