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 HIF1α) 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% O2). CAV1 expression was evaluated by western blotting.
Endogenous CAV1 and HIF1α were knocked-down using different shRNA constructs.
Cell migration and invasion were evaluated in Boyden Chamber and Matrigel assays,
Results: We observed that hypoxia increased CAV1 protein levels in a HIF1 α-
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
HIF1α-dependent induction of CAV1 expression and src family kinase activation.