PBRM1 Inactivation Promotes Upregulation of Human Endogenous Retroviruses in a HIF-Dependent Manner

Clear cell renal cell carcinoma (ccRCC) is considered an immunotherapy-responsive disease; however, the reasons for this remain unclear. Studies have variably implicated PBRM1 mutations as a predictive biomarker of immune checkpoint blockade (ICB) response, and separate studies demonstrate that expression of human endogenous retroviruses (hERV) might be an important class of tumor-associated antigens. We sought to understand whether specific mutations were associated with hERV expression. Two large, annotated genomic datasets, TCGA KIRC and IMmotion150, were used to correlate mutations and hERV expression. PBRM1 mutations were consistently associated with increased hERV expression in primary tumors. In vitro silencing of PBRM1, HIF1A, and HIF2A followed by RNA sequencing was performed in UMRC2 cells, confirming that PBRM1 regulates hERVs in a HIF1 alpha- and HIF2 alpha-dependent manner and that hERVs of the HERVERI superfamily are enriched in PBRM1-regulated hERVs. Our results uncover a role for PBRM1 in the negative regulation of hERVs in ccRCC. Moreover, the HIF-dependent nature of hERV expression explains the previously reported ccRCC-specific clinical associations of PBRM1-mutant ccRCC with both a good prognosis as well as improved clinical outcomes to ICB.