Abstract

Caveolin-1 (CAV1) is a well-established nitric oxide synthase inhibitor, whose function as a tumor suppressor is favored by, but not entirely dependent on, the presence of E-cadherin. Tumors are frequently hypoxic and the activation of the hypoxia-inducible factor-1 alpha (HIF1 alpha) promotes tumor growth. HIF1 alpha is regulated by several post-translational modifications, including S-nitrosylation. Here, we evaluate the mechanisms underlying tumor suppression by CAV1 in cancer cells lacking E-cadherin in hypoxia. Our main findings are that CAV1 reduced HIF activity and Vascular Endothelial Growth Factor expression in vitro and in vivo. This effect was neither due to reduced HIF1 alpha protein stability or reduced nuclear translocation. Instead, HIF1 alpha S-nitrosylation observed in hypoxia was diminished by the presence of CAV1, and nitric oxide synthase (NOS) inhibition by N omega-Nitro-L-arginine methyl ester hydrochloride (L-NAME) reduced HIF1 alpha transcriptional activity in cells to the same extent as observed upon CAV1 expression. Additionally, arginase inhibition by (S)-(2-Boronoethyl)-L-cysteine (BEC) partially rescued cells from the CAV1-mediated suppression of HIF1 alpha transcriptional activity. In vivo, CAV1-mediated tumor suppression was dependent on NOS activity. In summary, CAV1-dependent tumor suppression in the absence of E-cadherin is linked to reduced HIF1 alpha transcriptional activity via diminished NOS-mediated HIF1 alpha S-nitrosylation.