PARP1 and hepatocellular carcinoma: In this study, we unexpectedly found that PARP1 inhibition by TLR9 (Figure 3B-C) led to a decrease in the PARylation and an increase in the Tyr705 phosphorylation of STAT3 to increase PD-L1 expression (Figure 3D, Figure 3I), which indicated that TLR9 regulated the crosstalk of STAT3 PARylation and phosphorylation by affecting PARP1 expression in HCC cells.