Cellular senescence is a stress response that activates innate immune cells, but little is known about its interplay with the adaptive immune system. Here, we show that senescent cells combine several features that render them highly efficient in activating dendritic cells (DCs) and antigen-specific CD8 T cells. This includes the release of alarmins, activation of interferon signaling, enhanced MHC class I machinery, and presentation of senescence-specific self-peptides that can activate CD8 T cells. In the context of cancer, immunization with senescent cancer cells elicits strong anti-tumor protection mediated by DCs and CD8 T cells. Interestingly, this protection is superior to immunization with cancer cells undergoing immunogenic cell death. Finally, the induction of senescence in human primary cancer cells also augments their ability to activate autologous antigen-specific tumor-infiltrating CD8 lymphocytes. Our study indicates that senescent cancer cells can be exploited to develop efficient and protective CD8-dependent anti-tumor immune responses.

The human transcriptome contains thousands of small open reading frames (sORFs) that encode microproteins whose functions remain largely unexplored. Here, we show that TINCR lncRNA encodes pTINCR, an evolutionary conserved ubiquitin-like protein (UBL) expressed in many epithelia and upregulated upon differentiation and under cellular stress. By gain- and loss-of-function studies, we demonstrate that pTINCR is a key inducer of epithelial differentiation in vitro and in vivo. Interestingly, low expression of TINCR associates with worse prognosis in several epithelial cancers, and pTINCR overexpression reduces malignancy in patient-derived xenografts. At the molecular level, pTINCR binds to SUMO through its SUMO interacting motif (SIM) and to CDC42, a Rho-GTPase critical for actin cytoskeleton remodeling and epithelial differentiation. Moreover, pTINCR increases CDC42 SUMOylation and promotes its activation, triggering a pro-differentiation cascade. Our findings suggest that the microproteome is a source of new regulators of cell identity relevant for cancer.

Mitochondrial diseases due to mutations in the mitochondrial (mt) DNA are heterogeneous in clinical manifestations but usually include OXPHOS dysfunction. Mechanisms by which OXPHOS dysfunction contributes to the disease phenotype invoke, apart from cell energy deficit, maladaptive responses to mitochondria-to-nucleus retrograde signaling. Here we used five different cybrid models of mtDNA diseases to demonstrate that the expression of the nuclear-encoded mt-tRNA modification enzymes TRMU, GTPBP3 and MTO1 varies in response to specific pathological mtDNA mutations, thus altering the modification status of mt-tRNAs. Importantly, we demonstrated that the expression of TRMU, GTPBP3 and MTO1 is regulated by different miRNAs, which are induced by retrograde signals like ROS and Ca2+ via different pathways. Our data suggest that the up- or down-regulation of the mt-tRNA modification enzymes is part of a cellular response to cope with a stoichiometric imbalance between mtDNA- and nuclear-encoded OXPHOS subunits. However, this miRNA-mediated response fails to provide full protection from the OXPHOS dysfunction; rather, it appears to aggravate the phenotype since transfection of the mutant cybrids with miRNA antagonists improves the energetic state of the cells, which opens up options for new therapeutic approaches.

Cellular senescence is a stress response that activates innate immunity. However, the interplay between senescent cells and the adaptive immune system remains largely unexplored. Here, we show that senescent cells display enhanced MHC class I (MHC-I) antigen processing and presentation. Immunization of mice with senescent syngeneic fibroblasts generates CD8 T cells reactive against both normal and senescent fibroblasts, some of them targeting senescence-associated MHC-I-peptides. In the context of cancer, we demonstrate that senescent cancer cells trigger strong anti-tumor protection mediated by antigen-presenting cells and CD8 T cells. This response is superior to the protection elicited by cells undergoing immunogenic cell death. Finally, induction of senescence in patient-derived cancer cells exacerbates the activation of autologous tumor-reactive CD8 tumor-infiltrating lymphocytes (TILs) with no effect on non-reactive TILs. Our study indicates that immunization with senescent cancer cells strongly activates anti-tumor immunity, and this can be exploited for cancer therapy.