DNA Methylation of CNRIP1 Promotes Pathogenesis of Intrahepatic Cholangiocarcinoma Through Suppressing Parkin-Dependent PKM2 Ubiquitination.

Methylation landscape is important for maintaining the silence of cannabinoid receptor-interacting protein 1 (CNRIP1) in some tumors. However, the role of CNRIP1 in intrahepatic cholangiocarcinoma (ICC) remains poorly defined. In our study, we showed that CNRIP1 was down-regulated in ICC tissues and low expression of CNRIP1 was significantly associated with poor prognosis of ICC patients in 3-year overall survival (OS) and tumor-free survival (TFS). Investigating the genomic DNA methylation profile, we disclosed a novel CpG island site named CNRIP1 MS-2 (CNRIP1 methylation site-2) contributing to the down-regulation of CNRIP1. In addition, the methylation level of CNRIP1 MS-2 was correlated to the pathological grade, metastasis, and tumor-node-metastasis (TNM) classification in ICC. Notably, we observed that CNRIP1 suppressed tumor cell migration, invasion, and proliferation by inhibiting the activity of pyruvate kinase M2 (PKM2). The sustained overexpression of CNRIP1 suppressed the in vivo tumor growth in a mouse xenograft model. It was also found that CNRIP1 overexpression activated Parkin (a novel E3 ubiquitin [Ub] ligase), which resulted in the protein degradation of PKM2 in ICC cells. Conclusion: We identified that CNRIP1 acted as a putative tumor suppressor in ICC, which suggested that CNRIP1 could be a candidate biomarker for predicting tumor recurrence in ICC patients. Furthermore, these findings highlight a potential therapeutic approach in targeting the CNRIP1/Parkin/PKM2 pathway for the treatment of ICC.