Parkin Modulates the Hepatocellular Carcinoma Microenvironment by Regulating PD-1/PD-L1 Signalling

Introduction: Parkin-mediated mitophagy is essential for clearing 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 of Parkin in the immune microenvironment of liver tumours 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 tumour 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 tumours 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 protein expression between the two groups mainly localized in the 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 the antitumour immune response with Parkin deficiency. Parkin deficiency leads to the decrease of hepatic mitophagy levels and the formation of an immune suppressive microenvironment, which promotes the tumourigenesis of liver cancer.

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