MYC inhibition increases PD-L1 expression induced by IFN-γ in hepatocellular carcinoma cells.

The effectiveness of immunotherapy targeting the immune checkpoint PD-L1/PD-1 pathway highlights importance of elucidating the regulatory mechanisms of PD-L1 expression in cancer cells. Previous studies demonstrate that oncogene MYC up-regulates PD-L1 expression in lymphomas. In the present study, we investigated the regulatory role of MYC in the PD-L1 expression induced by IFN-γ in HCC cells. Unexpectedly, knockdown of MYC expression using siRNA assay increased the inducible expression of PD-L1 both at mRNA and protein levels. Mechanistically, the inhibition of MYC elevated expression of STAT1, a critical component of IFN-γ signaling pathway, leading to the elevation of PD-L1 expression in HCC cells exposed to IFN-γ. These results suggest that MYC may down-regulate PD-L1 expression in the context of HCC. This study implicates that a combination therapy targeting MYC function and PD-L1/PD-1 pathway might be effective for treatment of HCC.