SMAD7 drives natural killer cell antitumor activity through canonical TGF-β blockade and non-canonical transcriptional activation of STAT5A

BACKGROUND: Natural killer (NK) cells are key effectors in antitumor immunity, yet their function is markedly suppressed by transforming growth factor-β (TGF-β) in the tumor microenvironment. SMAD7 is an established intracellular antagonist of TGF-β signaling, but its specific role within NK cells remains poorly defined. METHODS: knockout mice in syngeneic tumor models and gain-of-function experiments using a SMAD7-overexpressing human NK-92MI cell line. NK cell antitumor function was assessed through cytotoxicity assays and by measuring the expression of selected effector and exhaustion markers. SMAD7-mediated transcriptional targets were identified by integrating RNA sequencing, chromatin immunoprecipitation followed by quantitative PCR, and luciferase reporter assays. The potential role of SMAD7 in NK cell-based therapy was evaluated in adoptive transfer tumor models. RESULTS: High SMAD7 expression in tumor-infiltrating NK cells was associated with a favorable patient prognosis across multiple cancer types. Conditional deletion of SMAD7 in NK cells markedly impaired their antitumor cytotoxicity, leading to accelerated tumor progression in mouse models of both pancreatic and liver cancers. In contrast, SMAD7 overexpression enhanced NK cell cytotoxicity and alleviated functional exhaustion, partly by counteracting TGF-β-mediated suppression. Notably, we uncovered a previously unrecognized nuclear function of SMAD7 in NK cells. SMAD7 directly binds to the STAT5A promoter and promotes its transcription, thereby strengthening STAT5A signaling in NK cells. Disruption of STAT5A largely abolished the enhanced cytotoxicity conferred by wild-type SMAD7 and completely abrogated the effect of a SMAD7 mutant, which was defective in TGF-β receptor binding. In in vivo therapeutic studies, adoptive transfer of SMAD7-overexpressing NK cells showed superior antitumor efficacy against both pancreatic and liver cancers, and SMAD7 modification also significantly improved tumor control and prolonged survival in a chimeric antigen receptor (CAR)-NK cell therapeutic model for liver cancer. CONCLUSIONS: Our findings identify SMAD7 as a key enhancer of NK-cell antitumor activity through canonical inhibition of TGF-β signaling and non-canonical activation of STAT5A transcription. Modulating SMAD7 offers a promising approach to improve NK cell-based immunotherapy.