Immune checkpoint protein PD-L1 promotes transcription of angiogenic and oncogenic proteins IL-8, Bcl3, and STAT1 in ovarian cancer cells

Immunotherapies blocking cell surface signaling of the immune checkpoint PD-L1 have shown great promise in several cancers, but the results have been disappointing in ovarian cancer (OC). One of the main underlying mechanisms likely consists of the cell-intrinsic intracellular functions of PD-L1, which are incompletely understood. The expression of PD-L1 in OC cells is induced by interferon-γ (IFNγ), a pleiotropic cytokine produced in response to chemotherapy or immune checkpoint blockade. We have recently shown that IFNγ induces expression of the proto-oncogene Bcl3, the proangiogenic chemokine interleukin-8 (IL-8)-CXCL8, and the transcription factor STAT1, resulting in increased OC cell proliferation and migration. Here, we report that IFNγ-induced expression of PD-L1 results in PD-L1 recruitment to IL-8, Bcl3, and STAT1 promoters. The occupancy of PD-L1 at IL-8, Bcl3, and STAT1 promoters is associated with increased histone acetylation and RNA polymerase II recruitment to these promoters. Suppression of IFNγ-induced PD-L1 decreases the expression of IL-8, Bcl3, and PD-L1 and increases apoptosis in OC cells. Together, these findings demonstrate that PD-L1 promotes transcription of IL-8, Bcl3, and STAT1, thus providing a novel function of PD-L1 in cancer cells, and suggesting that the increased IL-8, Bcl3, and STAT1 expression mediated by PD-L1 might contribute to the limited effectiveness of cancer immunotherapies targeting the surface expression of PD-L1 in OC.