Activation of PD-1 by p53 is critical for its tumor suppression in an immunity-independent manner.

Cancer cells frequently reprogram one-carbon metabolic pathways to fulfill their vigorous demands of biosynthesis and antioxidant defense for survival and proliferation. Dysfunction of oncogenes or tumor suppressor genes is critically involved in this process, but the precise mechanisms by which cancer cells actively trigger one-carbon metabolic alterations remain incompletely elucidated. Here, by using untargeted metabolomic analysis, we identify the oncoprotein SE translocation (SET) as a key regulator of one-carbon metabolism in cancer cells. SET physically interacts with mitochondrial SHMT2 and facilitates SHMT2 enzymatic activity. Loss of SET profoundly suppresses serine-derived one-carbon metabolic flux, whereas reexpression of ectopic SET leads to the opposite effect. Notably, although the presence of SHMT2 is critical for SET-mediated one-carbon metabolic alterations, the depletion of SHMT2 alone is insufficient to antagonize SET-induced tumor growth, probably due to functional compensation by its cytosolic isozyme SHMT1 upon SHMT2 knockdown. Instead, pharmacological targeting of cellular SHMT (including both SHMT1 and SHMT2) activity results in dramatic suppression of SET-induced tumor growth. Moreover, by using a Kras/Lkb1 mutation-driven lung tumor mouse model, we demonstrate that the loss of SET compromises both tumor formation and intratumoral SHMT2 enzymatic activity. Clinically, the overexpression of SET and SHMT2 is observed in lung tumors, both of which correlate with poor prognosis. Our study reveals a SET–SHMT2 axis in regulating serine-derived one-carbon metabolism and uncovers one-carbon metabolic reprogramming as a mechanism for SET-driven tumorigenesis.

Although p53 plays a central role in tumor suppression, how it is regulated in T cells to exert antitumor effects remains unclear. In this study, we show that activation of T cell–intrinsic p53 via carboxyl-terminal domain (CTD) acetylation during immunotherapy activates the IFN-γ pathway, promotes CD8+ T-cell infiltration, and elicits CD8+ T cell–dependent antitumor immunity. Using T cell–specific knockin mouse models, we demonstrate that loss of CTD acetylation in T cells abrogates CD8+ T cell–dependent antitumor immunity whereas expression of CTD acetylation–mimicking p53 in T cells enhances this immune response. Moreover, we identify IFNG as a direct target of T cell–intrinsic p53 and uncover a positive feedback loop between p53 and the IFN-γ pathway for enhancing T cell–dependent antitumor immunity. Our study reveals that CTD acetylation–mediated activation of T cell–intrinsic p53 promotes antitumor immunity in response to immunotherapy, highlighting a non–tumor cell–autonomous mechanism of p53 action by regulating adoptive immune responses. Significance: This study identifies T cell–intrinsic p53 as a key determinant of immunotherapy efficacy. CTD acetylation, rather than stabilization, activates a p53–IFN-γ feedback loop and promotes CD8+ T cell–mediated antitumor immunity independently of tumor p53 status. These findings reveal a non–tumor cell–autonomous action of p53 to boost PD-1–based immunotherapy.

This file contains the raw data of this study.

Supplementary Figure 1 Host p53 regulates cancer immunotherapy in melanoma model. Supplementary Figure 2 Analysis of tumor-infiltrating cells in response to PI immunotherapy. Supplementary Figure 3 Cd8+ T cells are essential for tumor suppression in response to PI immunotherapy. Supplementary Figure 4 Establishment of PDX-based immunotherapeutic model with humanized mouse. Supplementary Figure 5 Further analysis of T cell-intrinsic p53 CTD acetylation in response to immunotherapy. Supplementary Figure 6 Generation of the p53fl7KR/fl7KR cKI mouse model. Supplementary Figure 7 CTD acetylation of T cell-intrinsic p53 contributes to PI immunotherapy in melanoma model. Supplementary Figure 8 Generation and characterization of p53fl7KQ/fl7KQ cKI mouse model. Supplementary Figure 9 Functional analysis of tumor-infiltrating T cells in p53+/-, Lck-Cre and p53fl7KQ/-, Lck-Cre mice. Supplementary Figure 10 CTD acetylation-mimicking p53 in T cells regulates antitumor immunity in melanoma model. Supplementary Figure 11 The effect of PI immunotherapy in p53fl7KQ/-, Lck-Cre recipient mice. Supplementary Figure 12 Activation of T cell-intrinsic p53 slightly enhances T cell-mediated cytotoxicity. Supplementary Figure 13 scRNA-seq analysis of tumor-infiltrating lymphocytes. Supplementary Figure 14 Functional analysis of Ccl5 in T cell-intrinsic p53-mediated antitumor immunity. Supplementary Figure 15 Activation of the IFN-γ pathway promotes Ccl5 transcriptional expression in Cd8+ T cells. Supplementary Figure 16 Further analysis of the crosstalk between p53 CTD acetylation and IFN-γ. Supplementary Figure 17 Mechanistic details of VPRBP-mediated repression of p53-dependent Ifng transcription. Supplementary Figure 18 Further analysis of IFN-γ/JAK-STAT pathways regulated by p53 CTD acetylation in Cd8+ T cells.

Although p53 plays a central role in tumor suppression, how it is regulated in T cells to exert antitumor effects remains unclear. In this study, we show that activation of T cell–intrinsic p53 via carboxyl-terminal domain (CTD) acetylation during immunotherapy activates the IFN-γ pathway, promotes CD8+ T-cell infiltration, and elicits CD8+ T cell–dependent antitumor immunity. Using T cell–specific knockin mouse models, we demonstrate that loss of CTD acetylation in T cells abrogates CD8+ T cell–dependent antitumor immunity whereas expression of CTD acetylation–mimicking p53 in T cells enhances this immune response. Moreover, we identify IFNG as a direct target of T cell–intrinsic p53 and uncover a positive feedback loop between p53 and the IFN-γ pathway for enhancing T cell–dependent antitumor immunity. Our study reveals that CTD acetylation–mediated activation of T cell–intrinsic p53 promotes antitumor immunity in response to immunotherapy, highlighting a non–tumor cell–autonomous mechanism of p53 action by regulating adoptive immune responses.Significance:This study identifies T cell–intrinsic p53 as a key determinant of immunotherapy efficacy. CTD acetylation, rather than stabilization, activates a p53–IFN-γ feedback loop and promotes CD8+ T cell–mediated antitumor immunity independently of tumor p53 status. These findings reveal a non–tumor cell–autonomous action of p53 to boost PD-1–based immunotherapy.