Data from Hypoxia-Inducible Factor 1α Mediates Anoikis Resistance via Suppression of α5 Integrin

The transcription factor hypoxia-inducible factor 1 (HIF-1) α is abundantly expressed in the majority of human carcinomas and their metastases. HIF-1α controls central metastasis-associated pathways such as glycolysis, angiogenesis, and invasion. Functional inhibition of HIF-1α leads to impaired metastasis formation in murine tumor models. However, the precise molecular mechanisms underlying the metastasis-promoting role of HIF-1α have not been fully characterized. The ability of transformed epithelial cells to initiate the metastatic cascade relies on their ability to escape anoikis, a default program of apoptosis induction following loss of integrin anchoring to the extracellular matrix. Therefore, we addressed the function of HIF-1α in anoikis resistance and anchorage-independent growth. Inhibition of HIF-1α via RNA interference resulted in up-regulation of α5 integrin on the cell surface of human gastric cancer cells, whereas other integrins remained unaffected. Integrin α5 induction occurred at the level of transcription and was dependent on elevated intracellular superoxide in HIF-1α-knockdown cells. HIF-1α–deficient cells displayed significantly increased anoikis susceptibility due to up-regulated α5 integrin. Finally, colony formation in soft agar was shown to be dependent on HIF-1α as HIF-1α–deficient cells displayed a 70% reduction in anchorage-independent proliferation. Results obtained by RNA interference could be entirely confirmed by application of the pharmacologic HIF-1α-inhibitor 2-methoxyestradiol. Hence, our data argue for a pivotal role for HIF-1α in anoikis control via suppression of α5 integrin. HIF-1α–inhibiting drugs might therefore offer an innovative strategy for antimetastatic cancer therapy. [Cancer Res 2008;68(24):10113–20]