Dissection of PD-L1 promoter reveals differential transcriptional regulation of PD-L1 in VHL mutant clear cell renal cell carcinoma

Abstract

Through analysis of the PD-L1 promoter, the authors describe two clear cell renal cell carcinoma (ccRCC) models that exhibit differential PD-L1 expression levels upon IFN gamma and hypoxia stimulation. Mutant-VHL ccRCC cells display higher PD-L1 expression than wild-type-VHL ccRCC cells due to high basal HIF2 alpha expression and a stronger response to IFN gamma stimulation. Thus, mutant-VHL ccRCC cells are expected to respond well to immune checkpoint inhibitors. Programmed death-ligand 1 (PD-L1) is constitutively expressed by hypoxia-inducible factor 2 alpha (HIF2 alpha). It can be induced by interferon gamma (IFN gamma) signaling in clear cell renal cell carcinoma (ccRCC). Clinical trials of metastatic ccRCCs have suggested that a canonical IFN gamma signature is a better biomarker for therapeutic response to immune checkpoint inhibitors (ICIs) than PD-L1 expression levels in tumor cells. To understand the therapeutic response to ICIs according to PD-L1 expression levels, we analyzed transcriptional regulation of the PD-L1 promoter by HIF2 alpha and IFN gamma-inducible interferon regulatory factor-1 (IRF-1) in ccRCC cells. Here, we present two ccRCC cell models showing differential PD-L1 expression levels in response to IFN gamma and hypoxia. Analysis of The Cancer Genome Atlas RNA-sequencing data revealed that PD-L1 expression correlated with JAK2 and STAT1 expression of the canonical IFN gamma signature in ccRCC tissues. Upon IFN gamma stimulation, PD-L1 was induced by sequential activation of JAK2/STAT1/IRF-1 signaling in both WT- and Mut- VHL ccRCC cells. IFN gamma activated the IRF-1 alpha site of the PD-L1 promoter. The IFN gamma-mediated increase of PD-L1 expression in Mut-VHL cells was 4.8-fold greater than that in WT-VHL cells. Under normoxia condition, PD-L1 expression in Mut-VHL cells was significantly higher than that in WT-VHL cells due to high basal HIF2 alpha expression. Under hypoxia condition, PD-L1 expression in WT-VHL cells was induced up to 1.8-fold through activation of hypoxia-response elements 2 and 3. In contrast, although PD-L1 in Mut-VHL cells was already highly expressed in the basal state through activation of hypoxia-response elements 2, 3, and 4, it was no longer induced by hypoxia. In conclusion, Mut-VHL ccRCC cells displayed higher PD-L1 expression due to high basal HIF2 alpha expression and a stronger response to IFN gamma stimulation than WT-VHL cells. The fact that HIF2 alpha antagonists can potentially reduce PD-L1 expression levels should be considered in ICI combination therapy.