Caveolin-1 null mice axe viable but show evidence of hyperproliferative and vascular abnormalities

Caveolin-1 is the principal structural protein of caveolae membranes in fib roblasts and endothelia. Recently, we have shown that the human CAV-1 gene is localized to a suspected tumor suppressor locus, and mutations in Cav-1 have been implicated in human cancer. Here, we created a eaveolin-1 null (C AV-1 -/-) mouse model, using standard homologous recombination techniques, to assess the role of caveolin-1 in caveolae biogenesis, endocytosis, cell proliferation, and endothelial nitric-oxide synthase (eNOS) signaling. Surp risingly, Cav-1 null mice are viable. We show that these mice lack caveolin -1 protein expression and plasmalemmal caveolae. In addition, analysis of c ultured fibroblasts from Cav-1 null embryos reveals the following: W a loss of caveolin-2 protein expression; (ii) defects in the endocytosis of a kno wn caveolar ligand, i.e. fluorescein isothiocyanate-albumin; and (iii) a hy perproliferative phenotype. Importantly, these phenotypic changes are rever sed by recombinant expression of the caveolin-1 cDNA. Furthermore, examinat ion of the lung parenchyma (an endothelial-rich tissue) shows hypercellular ity with thickened alveolar septa and an increase in the number of vascular endothelial growth factor receptor (Flk-1)-positive endothelial cells. As predicted, endothelial cells from Cav-1 null mice lack caveolae membranes. Finally, we examined eNOS signaling by measuring the physiological response of aortic rings to various stimuli. Our results indicate that eNOS activit y is up-regulated in Cav-1 null animals, and this activity can be blunted b y using a specific NOS inhibitor, nitro-L-arginine methyl ester. These find ings are in accordance with previous in vitro studies showing that caveolin -1 is an endogenous inhibitor of eNOS. Thus, caveolin-1 expression is requi red to stabilize the caveolin-2 protein product, to mediate the caveolar en docytosis of specific ligands, to negatively regulate the proliferation of certain cell types, and to provide tonic inhibition of eNOS activity in end othelial cells.