Background—The G-protein–coupled receptor kinase interacting protein-1 (GIT1) is a multidomain scaffold protein that participates in many cellular functions including receptor internalization, focal adhesion remodeling, and signaling by both G-protein–coupled receptors and tyrosine kinase receptors. However, there have been no in vivo studies of GIT1 function to date.

Methods and Results—To determine essential functions of GIT1 in vivo, we generated a traditional GIT1 knockout mouse. GIT1 knockout mice exhibited 60% perinatal mortality. Pathological examination showed that the major abnormality in GIT1 knockout mice was impaired lung development characterized by markedly reduced numbers of pulmonary blood vessels and increased alveolar spaces. Given that vascular endothelial growth factor (VEGF) is essential for pulmonary vascular development, we investigated the role of GIT1 in VEGF signaling in the lung and cultured endothelial cells. Because activation of phospholipase-C (PLC) and extracellular signal-regulated kinases 1/2 (ERK1/2) by angiotensin II requires GIT1, we hypothesized that GIT1 mediates VEGF-dependent pulmonary angiogenesis by modulating PLC and ERK1/2 activity in endothelial cells. In cultured endothelial cells, knockdown of GIT1 decreased VEGF-mediated phosphorylation of PLC and ERK1/2. PLC and ERK1/2 activity in lungs from GIT1 knockout mice was reduced postnatally.

Conclusions—Our data support a critical role for GIT1 in pulmonary vascular development by regulating VEGF-induced PLC and ERK1/2 activation.