Abstract
One key to malignant progression is the acquired ability of tumor cells to escape immune-mediated lysis. Whereas tumor hypoxia is known to play a causal role in cancer metastasis and resistance to therapy, the link between hypoxia and immune escape in cancer remains poorly understood. Here, we show that hypoxia induces tumor cell resistance to lysis mediated by immune effectors and that this resistance to lysis occurs via a hypoxia-inducible factor-1 (HIF-1)-dependent pathway linked to increased expression of the metalloproteinase ADAM10. This enzyme is required for the hypoxia-induced shedding of MHC class I chain-related molecule A (MICA), a ligand that triggers the cytolytic action of immune effectors, from the surface of tumor cells. Indeed, our findings show a mechanistic link between hypoxia-induced accumulation of the α-subunit of HIF-1 (HIF-1α), increased expression of ADAM10, and decreased surface MICA levels leading to tumor cell resistance to lysis mediated by innate immune effectors. Nitric oxide mimetic agents interfered with the hypoxia-induced accumulation of HIF-1α and with the hypoxia-induced upregulation of ADAM10 expression required for decreased surface MICA expression and resistance to lysis. Furthermore, treatment of tumor-bearing mice with nitroglycerin, a nitric oxide mimetic, attenuated tumor growth by a mechanism that relied upon innate immune effector cells. Together, these findings reveal a novel mechanism by which the hypoxic tumor microenvironment contributes to immune escape in cancer, lending support to potential immunotherapeutic strategies involving the use of nitric oxide mimetics.
Highlights
Studies conducted in the last 15 years have provided convincing evidence that the immune system plays a critical role in the prevention and control of cancer [1]
To determine whether the hypoxia-mediated inhibition of surface MICA expression is dependent on hypoxiainducible factor-1 (HIF-1) transcriptional activity, we knocked down hypoxia-inducible factor-1a (HIF-1a) using validated siRNA
Western blot analysis revealed that transient transfection of HIF-1a siRNA in DU145 prostate cancer cells effectively inhibited the hypoxic accumulation of HIF-1a protein (Supplementary Fig. S2)
Summary
Studies conducted in the last 15 years have provided convincing evidence that the immune system plays a critical role in the prevention and control of cancer [1]. An important aspect of malignant progression is the acquired ability of tumor cells to escape detection and destruction by the innate and adaptive arms of the immune system [1]. While many studies have shown the important contribution of tumor hypoxia to the acquisition of malignant properties in cancer cells, such as resistance to chemotherapeutic agents [2,3,4] and increased metastatic potential [5,6,7], the effect of hypoxia on tumor immune escape remains poorly understood. I.B. Barsoum and T.K. Hamilton contributed to this study
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