Role of p57 in cGAS-STING-mediated innate sensing and immunotherapy response in hepatocellular carcinoma.

2585 Background: Hyperactivation of cell cycle programs in cancer cells suppresses the antitumor immune response. The endogenous cyclin-dependent kinase inhibitor p57 is an important tumor suppressor and a potential therapeutic target for hepatocellular carcinoma (HCC). However, the role of p57 in modulating antitumor immunity to HCC remains unclear. Methods: We examined p57 expression in HCC patient samples prior to treatment with immune checkpoint inhibitors (ICIs) through immunohistochemistry (IHC). Multiple mice tumor models were constructed to explore the role of p57 on the recruitment of CD8 + T cells in the tumor immune microenvironment. Through performing transcriptome sequencing, we analyzed the differential genes and activation pathways induced by p57 overexpression; through Real-Time Quantitative Polymerase Chain Reaction (RT-qPCR), western blot (WB）, Enzyme-Linked Immunosorbent Assay (ELISA), IHC, immunofluorescence（IF）, Flow Cytometry (FCM) and other molecular experimental methods, we verified the molecular mechanism of increasing CD8 + T infiltration and elevating PD-L1 caused by p57 overexpression; Through constructing mice model and giving different treatments, we explored the anti-tumor efficacy of p57 overexpression combining with ICIs. Results: We found that patients with p57 expression had a higher disease control rate, correlating with the number of tumor infiltration CD8 + T cells. Using mouse models, we discovered that p57 promoted CD8 + T cells infiltration and that CD8 + T cells were required for p57 to function as a tumor growth suppressor. Furthermore, through RNA-sequencing analysis and the multiplex assay in vitro and in vivo , we found that p57 induced chromosomal instability and subsequently stimulates cGAS-STING-type I IFN signaling, leading to upregulation of the chemokines CCL5 and CXCL10, which promoted CD8 + T cell infiltration into the tumor microenvironment. Meanwhile, p57 also elevated the expression of PD-L1 on the surface of HCC cells. Moreover, combining p57 overexpression with anti-PD-1 treatment synergistically inhibited tumor growth in vivo . Conclusions: Our studies demonstrated that p57 may serve as a new biomarker for ICIs efficacy and that increasing p57 expression is a potential therapeutic strategy for improving the efficacy of immunotherapy in HCC patients.