PARP1 promotes the progression of hepatocellular carcinoma by regulating expression of POU2F2

Background and purpose: Hepatocellular carcinoma (HCC) is a major disease seriously threatening human health. Poly (ADP-ribose) polymerase-1 (PARP1) is an enzyme that catalyzes poly ADP-ribosylation. Given the role of PARP1 in DNA damage repair, it is generally considered as an oncogene. However, the expression of PARP1 and its mechanism in HCC are not yet clear. This study aimed to investigate the role of PARP1 in the occurrence and development of HCC and its potential mechanisms. Methods: First, we analyzed the expression pattern of PARP1 in The Cancer Genome Atlas (TCGA) and Clinical Proteomic Tumor Analysis Consortium (CPTAC) HCC database, and identified the expression trend of PARP1 in our HCC cohort using real-time fluorescence quantitative polymerase chain reaction (RTFQ-PCR) and Western blot. Then, the enzyme activity of PARP1 was inhibited by PJ34, an inhibitor of PARP1 and the expression of PARP1 in HCC cell lines was downregulated with small RNA interference technology. Based on these models, the following experiments were conducted: First, the effect of PARP1 on cell viability was assessed by cell counting kit-8 (CCK-8) assay and flow cytometry; Second, the expression levels of stemness-related genes in HCC cells were identified using RTFQ-PCR; Third, the effect of inhibition of PARP1 on migration and invasion of HCC cells was detected by migration and invasion assay (transwell assay). Finally, bioinformatic analysis was performed to identify new target genes and the pathways regulated by PARP1 in HCC progression. Rescue experiments were performed to determine whether PARP1 target genes were involved in the malignant phenotypes of HCC cells. Results: The expression of PARP1 was significantly up-regulated in HCC tissues in both TCGA and CPTAC database. RTFQ-PCR and Western blot assays showed that PARP1 was obviously up-regulated in HCC tissues compared to paracancerous tissues. Survival analysis showed that PARP1 expression was significantly negatively correlated with the prognosis of patients. The results of CCK-8, flow cytometry, RTFQ-PCR and transwell assay indicated that inhibition of PARP1 attenuated proliferation and activity of HCC cells, as well as weakened their stemness, migration and invasion. Bioinformatics analysis suggested that PARP1-regulated genes were enriched in the nuclear factor-κB (NF-κB) and necroptosis pathways, with POU class homeobox 2 (POU2F2) potentially being a target gene of PARP1. Correlation analysis, along with RTFQ-PCR and Western blot detection, confirmed that the expression of POU2F2 was regulated by PARP1, while not affected by PJ34, indicating the effect of nonenzymatic function of PARP1 on POU2F2. CCK-8, flow cytometry and RTFQ-PCR results showed that the reintroduction of POU2F2 enhanced proliferative capacity, increased activity, and promoted stemness of HCC cell lines with PARP1 knockdown. Conclusion: By positively regulating the expression of POU2F2, PARP1 promotes malignant phenotypes of HCC cells, providing new insights for clinical treatment and drug development for HCC.