Lemos, Robert

The hypoxia‐inducible factor (HIF), HIF‐1, is a central regulator of the response to low oxygen or inflammatory stress and plays an essential role in survival and function of immune cells. However, the mechanisms regulating nonhypoxic induction of HIF‐1 remain unclear. Here, we assess the impact of germline heterozygosity of a novel, oxygen‐independent ubiquitin ligase for HIF‐1α: hypoxia‐associated factor (HAF; encoded by SART1). SART1−/− mice were embryonic lethal, whereas male SART1+/− mice spontaneously recapitulated key features of nonalcoholic steatohepatitis (NASH)‐driven hepatocellular carcinoma (HCC), including steatosis, fibrosis, and inflammatory cytokine production. Male, but not female, SART1+/− mice showed significant up‐regulation of HIF‐1α in circulating and liver‐infiltrating immune cells, but not in hepatocytes, before development of malignancy. Additionally, Kupffer cells derived from male, but not female, SART1+/− mice produced increased levels of the HIF‐1‐dependent chemokine, regulated on activation, normal T‐cell expressed and secreted (RANTES), compared to wild type. This was associated with increased liver‐neutrophilic infiltration, whereas infiltration of lymphocytes and macrophages were not significantly different. Neutralization of circulating RANTES decreased liver neutrophilic infiltration and attenuated HCC tumor initiation/growth in SART1+/− mice. Conclusion: This work establishes a new tumor‐suppressor role for HAF in immune cell function by preventing inappropriate HIF‐1 activation in male mice and identifies RANTES as a novel therapeutic target for NASH and NASH‐driven HCC. (Hepatology 2016;63:1576‐1591)

Abstract Clear-cell renal cell cancer (CRCC) is initiated typically by loss of the tumor-suppressor VHL, driving constitutive activation of hypoxia-inducible factor-1 (HIF1) and HIF2. However, whereas HIF1 has a tumor-suppressor role, HIF2 plays a distinct role in driving CRCC. In this study, we show that the HIF1α E3 ligase hypoxia-associated factor (HAF) complexes with HIF2α at DNA to promote HIF2-dependent transcription through a mechanism relying upon HAF SUMOylation. HAF SUMOylation was induced by hypoxia, whereas HAF-mediated HIF1α degradation was SUMOylation independent. HAF overexpression in mice increased CRCC growth and metastasis. Clinically, HAF overexpression was associated with poor prognosis. Taken together, our results show that HAF is a specific mediator of HIF2 activation that is critical for CRCC development and morbidity. Cancer Res; 75(2); 316–29. ©2014 AACR.