Abstract

In multiple myeloma (MM), resistance to B-cell maturation antigen (BCMA)-targeted chimeric antigen receptor T-cell (CAR-T) treatment continues to limit therapeutic benefit, whereas the tumor-intrinsic factors governing sensitivity to CAR-T remain poorly understood. Here, integrating public single-cell RNA-seq data with transcriptomic profiling of MM cells before and after CAR-T exposure, we identified the mitochondrial protein PPTC7 as a key modulator linking tumor mitophagy to innate immune activation and CAR-T efficacy. Mechanistically, PPTC7 acted as a negative regulator of tumor-intrinsic mitophagy by promoting SCF^FBXL4-dependent ubiquitination and proteasomal degradation of the mitophagy receptors BNIP3 and NIX, thereby suppressing mitophagic flux. Consistent with this, PPTC7 overexpression inhibited mitophagy, caused mitochondrial dysfunction, and increased cytosolic leakage of mitochondrial DNA (mtDNA), whereas PPTC7 knockdown stabilized BNIP3/NIX, enhanced mitophagy, and reduced cytosolic mtDNA. The accumulated cytosolic mtDNA consequent to mitophagy suppression activated the cGAS/STING pathway, induced a senescence-associated secretory phenotype, and remodeled the inflammatory tumor microenvironment. Functionally, PPTC7-mediated mitophagy repression markedly enhanced CAR-T cytotoxicity in vitro and promoted CAR-T infiltration and tumor control in vivo. Rescue experiments further supported this axis: restoring mitophagy via NIX attenuated mtDNA leakage and dampened cGAS/STING signaling and CAR-T activity, whereas re-activating cGAS reinstated inflammatory signaling and CAR-T effector function. Collectively, our findings define a tumor-intrinsic PPTC7-BNIP3/NIX-mtDNA-cGAS/STING circuit in which suppression of mitophagy increases tumor immunogenicity and sensitizes MM to CAR-T therapy, highlighting PPTC7 as a potential immune-sensitizing target to overcome CAR-T resistance.