Krit1 modulates β1-integrin-mediated endothelial cell proliferation

OBJECTIVE: Using ribonucleic acid interference on cultured cell lines, we examined the role of Krev interaction trapped 1 (krit1) and integrin cytoplasmic domain-associated protein-1 alpha (icap1 alpha) in beta 1-integrin-mediated cell proliferation. METHODS: Upon depletion of either krit1 or icap1 alpha in the HeLa cells, umbilical vein endothelial cells, and microvascular endothelial cells, we examined the cell number and proliferation changes in the cells, followed by the evaluation of beta 1-integrin-mediated mitogen-activated protein kinase signal pathway and microscopic study. RESULTS: Depletion of krit1 reduces cell number and decreases endothelial cell proliferation. Examination of beta 1-integrin signaling downstream of focal adhesion kinase reveals decreased phosphorylation along the extracellular signal-regulated kinase/mitogen-activated protein kinase pathway. Depletion of icap1 alpha, a protein known to interact with krit1, has similar effects, suggesting synergistic function. We also show that krit1 colocalizes with icap1 alpha in both the nucleus and the cytoplasm; however, most of icap1 alpha is found in the nucleus and most of krit1 is found in the cytoplasm at steady state. On depletion of krit1, icap1 alpha decreases in the cytoplasm and is no longer detected in the nucleus. CONCLUSION: Both krit1 and icap1 alpha act concordantly to play a critical role in Pi integrin-mediated cell proliferation. Our data further suggest that krit1 both stabilizes and shuttles icap1 alpha and thus modulates its regulation of beta 1-integrin-mediated signal transduction.