Interplay between HIF-1alpha and HIF-2alpha modulates TNBC phenotypes

Hypoxia-driven adaptation is a central feature of triple-negative breast cancer (TNBC) and contributes to its aggressive behavior. TNBC lacks ER, PR, and HER2 expression, which limits targeted treatment options. Hypoxia-inducible factors (HIFs), particularly the HIF-1alpha and HIF-2alpha isoforms, orchestrate the transcriptional response to low oxygen to maintain survival and metabolic programs, making them attractive therapeutic targets. HIF-1alpha is the main hypoxic responder in TNBC, but efforts to target it have failed in the clinic. The FDA approval of the HIF-2alpha inhibitor belzutifan for kidney cancer makes it urgent to determine whether inhibition may be effective in other solid tumors. Although HIF-1alpha and HIF-2alpha share some targets, their functions vary by cancer type, and the significance of HIF-2alpha in TNBC remains unclear. To address this, we investigated the individual and combined contributions of HIF-1alpha and HIF-2alpha in TNBC. Here, we show that HIF-2alpha is an important regulator in TNBC, in part due to previously unrecognized redundant or compensatory interactions between the two isoforms. Dual knockout of HIF-1alpha and HIF-2alpha did not further inhibit tumor growth compared to single knockouts, indicating functional overlap. Notably, HIF-2alpha acted antagonistically to HIF-1alpha and limited pro-metastatic effects, as HIF-2alpha knockout tumors showed increased metastatic burden in a syngeneic mouse model. This phenotype was supported by scRNA-seq analysis, which revealed elevated EMT hallmark signatures in HIF-2alpha-deficient xenograft tumors, and by in vitro observations where HIF-2alpha-deficient cells displayed a more invasive morphology. Some HIF-2alpha functions are context-specific and further shaped by the tumor microenvironment. Together, our findings reveal that HIF-1alpha and HIF-2alpha engage in redundant, compensatory, or antagonistic interactions dependent on the specific pathway. Thus, both factors contribute to stress responses, but HIF-2alpha also exhibits cancer-intrinsic functions that may potentially counteract the pro-metastatic effects of HIF-1alpha. Overall, these findings reveal the nuanced roles of HIF isoforms in tumor progression and highlight the need for careful consideration of HIF-2alpha targeting in TNBC therapy.