Hypoxia-Induced Caveolin-1 Expression Promotes Migration and Invasion of Tumor Cells

Background: Exacerbated proliferation of cancer cells in nascent tumors leads to the genesis of a hypoxic microenvironment, which is associated with poor patient prognosis, because these stress conditions enhance migratory, invasive and metastatic capacities of tumor cells. These changes are associated with the induction of the hypoxia-inducible factors (HIFs, mainly HIF1 alpha) and increased expression of target genes, including Caveolin-1 (CAV1). Results from our group have shown that CAV1 expression in metastatic cancer cells promotes cell migration/invasion in vitro and metastasis in vivo in a manner dependent on tyrosine-14 phosphorylation by src family kinases. Here, we evaluated whether hypoxia-induced expression of CAV1 was required for hypoxia-dependent migration and invasion in cancer cells. Methods: B16-F10 murine melanoma and HT29(US) colon adenocarcinoma cells were exposed to hypoxia (1% O-2). CAV1 expression was evaluated by western blotting. Endogenous CAV1 and HIF1 alpha were knocked-down using different shRNA constructs. Cell migration and invasion were evaluated in Boyden Chamber and Matrigel assays, respectively. Results: We observed that hypoxia increased CAV1 protein levels in a HIF1 alpha dependent manner, in B16-F10 and HT29(US) cells. Importantly, hypoxia-dependent migration of both tumor cell lines was blocked upon CAV1 knock-down. Likewise, pharmacological inhibition of HIF prevented hypoxia-induced migration and invasion in B16-F10 cells. Finally, hypoxia-induced migration was also blocked by the src-family kinase inhibitor 4-amino-5-(4-chloro-phenyl)-7-(t-butyl) pyrazolo3,4-dpyrimidine (PP2), an inhibitor of CAV1 phosphorylation. Conclusion: Hypoxia induced migration and invasion of metastatic cancer cells require HIF1 alpha-dependent induction of CAV1 expression and src family kinase activation.