Nuclear compartmentalization of PD-L1 suppresses tumorigenesis and overcomes immunocheckpoint therapy resistance via histone macroH2A1 phosphorylation
Canonically PD-L1 functions as the inhibitory immune checkpoint on cell surface. Recent studies observed PD-L1 expression in the nucleus of cancer cells. But the biological function of nuclear PD-L1 (nPD-L1) in tumor growth and antitumor immunity is unclear. Here we enforced nPD-L1 expression and established stable cells. nPD-L1 suppressed tumorigenesis and aggressiveness in vitro and in vivo.  Compared with PD-L1 deletion, nPD-L1 expression repressed tumor growth and improved survival more significantly in immunocompetent mice. p-AMPKa facilitated nuclear PD-L1 compartmentalization and then cooperated with it to directly phosphorylate S146 of histone variant macroH2A1 (mH2A1) to epigenetically activate expression of genes of cellular senescence, JAK-STAT, and Hippo signaling pathways. Lipoic acid (LA) that induced nuclear PD-L1 translocation suppressed tumorigenesis and boosted antitumor immunity. Importantly, LA treatment synergized with PD-1 antibody and overcame immune checkpoint blockade (ICB) resistance, which may result from nPD-L1-increased MHC-I expression and sensitivity of tumor cells to IFN-?. These findings offer a conceptual advance for PD-L1 function and suggest LA as a promising therapeutic option for overcoming ICB resistance. Overall design: To explore the mechanisms by which nPD-L1 inhibits tumor growth and enhances antitumor immunity, we performed RNA-sequencing analysis to compare gene expression profiles between nPD-L1-overexpressed and vector groups in Hep3B cells with endogenous PD-L1 deletion.