PARP1 and cholangiocarcinoma: Considering these findings, we explored the amount of USP7 that was bound to HIF-1a in PARP1-knockdown or PARGi-transfected CCA cells and found that the level of PARylated HIF-1a or USP7-bound HIF-1a was significantly decreased in PARP1-knockdown HuCCT1 cells, while the level in PARGi-transfected HuCCT1 cells showed the opposite results (Fig. 6D, Supplementary 5F).