Parkin modulates the hepatocellular carcinoma microenvironment by regulating PD-1/PD-L1 signalling.

Introduction: Parkin-mediated mitophagy is essential for the clearance of damaged mitochondria, and it inhibits tumour development. The role of mitophagy in modulating tumour immunity is becoming clearer, but the underlying mechanism is still poorly understood.

Objective: This study was designed to examine the role for Parkin in the immune microenvironment of liver tumors induced by carbon tetrachloride (CCl).

Methods: Single-cell RNA sequencing analysis, Western blot, immunofluorescence and co-immunoprecipitation were used to verify the mechanism of Parkin affecting the tumor microenvironment by altering the expression of PD-1.

Results: Our data revealed that Park2 mice showed severe liver damage and increased malignancy. Single-cell RNA sequencing analysis of T lymphocytes in liver tumor showed that the number of cytotoxic CD8 T cells (Gzmb/Ifng/Fasl) was significantly decreased and the number of exhausted CD8 T cells (Pdcd1/Lag3/Tigit/Havcr2/Ctla4) was significantly increased in Park2 mice, indicating the immune suppressive microenvironment. Single-cell RNA sequencing analysis of myeloid-derived cells also displayed the increase of M2-like macrophages in Park2 mice. Through quantitative proteomic analysis, it was found that the differential proteins expression between two groups mainly localized in plasma membrane and extracellular, including PD-1, MHC-Ⅰ molecules etc., and was mainly associated with PD-1 and antigen presentation pathways. It could impair anti-tumor immune response with Parkin deficiency. Parkin deficiency leads to the decrease of hepatic mitophagy level and the formation of immune suppressive microenvironment, which promotes the tumorigenesis of liver cancer.

Conclusion: As an E3 ubiquitin ligase, Parkin induces the ubiquitination and degradation of PD-1 in liver cancer and could influence the anti-tumor immunity through the PD-1/PD-L1 signalling pathway. Thus, remodeling the tumor microenvironment through reintroduction of Parkin or enhancement of mitophagy could activate anti-tumor immune response and improve the immunotherapy efficacy, which may be a promising strategy for the treatment of HCC.