Vacuolar Protein Sorting 35 Controls Hepatocellular Proliferation Through SRC Signaling and Promotes Diethyl...

Hepatocellular carcinoma is the third leading cause of cancer-related mortality worldwide. Therapeutic options for hepatocellular carcinoma remain limited, and the mechanisms underlying hepatocellular carcinoma are not fully understood. Therefore, gaining a comprehensive understanding of the pathways that drive hepatocellular carcinoma is essential for improving treatments. Recent studies have identified vacuolar protein sorting 35, a component of the endosomal cargo sorting machinery called retromer, as a novel oncogene in various types of cancer, including hepatocellular carcinoma. However, its role in the initiation and progression of hepatocellular carcinoma is still unclear.

To study the role of vacuolar protein sorting 35 in hepatocellular proliferation and the development of hepatocellular carcinoma, we generated a liver-specific Vps35 knockout mouse model using the Cre-LoxP system (Vps35^HepKO). Hepatocellular proliferation was studied in young and middle-aged mice, as well as during liver regeneration after two-thirds partial hepatectomy. Diethyl nitrosamine was used to induce hepatocellular carcinoma. Livers were analyzed at histological, transcriptional, and proteomic levels.

Hepatic loss of vacuolar protein sorting 35 enhanced hepatocellular proliferation in post-natal livers via SRC and its downstream target signal transducer and activator of transcription 3. Pharmacologic inhibition of SRC with saracatinib normalized hepatocellular proliferation in Vps35^HepKO mice. In contrast, hepatic vacuolar protein sorting 35 deficiency did not alter hepatocellular proliferation after partial hepatectomy in adult mice. Although vacuolar protein sorting 35-deficient postnatal livers exhibited an increased proliferative phenotype, hepatic loss of vacuolar protein sorting 35 reduced the number of diethyl nitrosamine-induced liver lesions without affecting tumor size.

Our in vivo data identify murine vacuolar protein sorting 35 as a critical regulator of hepatocellular proliferation in postnatal livers, but not after partial hepatectomy. Although vacuolar protein sorting 35 deficiency mitigates diethyl nitrosamine-induced liver lesion formation, it does not affect tumor progression, arguing against a role for vacuolar protein sorting 35 as a canonical oncogene.