Hepatocyte-specific Wtap deficiency promotes hepatocellular carcinoma by activating GRB2–ERK depending on downregulation of proteasome-related genes

Wilm's tumor 1-associating protein (WTAP), a regulatory protein of the m6A methyltransferase complex, has been found to play a role in regulating various physiological and patholog-ical processes. However, the in vivo role of WTAP in the path-ogenesis of hepatocellular carcinoma (HCC) is unknown. In this study, we have elucidated the crucial role of WTAP in HCC progression and shown that hepatic deletion of Wtap promotes HCC pathogenesis through activation of multiple signaling pathways. A single dose of diethylnitrosamine injection causes more and larger HCCs in hepatocyte-specific Wtap knockout (Wtap-HKO) mice than Wtapflox/flox mice fed with either normal chow diet or a high-fat diet. Elevated CD36, IGFBP1 (insulin-like growth factor-binding protein 1), and chemokine (C-C motif) ligand 2 (CCL2) expression leads to steatosis and inflammation in the Wtap-HKO livers. The hepatocyte proliferation is dramatically increased in Wtap-HKO mice, which is due to higher activation of extracellular signal-regulated kinase (ERK) and signal transducer and activator of transcription-3 signaling pathways. Hepatic deletion of Wtap activates the ERK signaling pathway by increasing the protein stability of GRB2 and ERK1/2, which is due to the decreased expression of proteasome-related genes. Restoring PSMB4 or PSMB6 (two key components of the proteasome) leads to the downregulation of GRB2 and ERK1/2 in Wtap-HKO hepatocytes. Mechanistically, WTAP interacts with RNA polymerase II and H3K9ac to maintain expression of proteasome-related genes. These results demonstrate that he-patic deletion of Wtap promotes HCC progression through activating GRB2-ERK1/2-mediated signaling pathway depend-ing on the downregulation of proteasome-related genes espe-cially Psmb4 and Psmb6.