LINKING CHROMATIN REMODELING TO MITOCHONDRIAL DYSFUNCTION: A ROLE FOR THE SMARCA5-MYC-TFAM AXIS IN HEPATOCELLULAR CARCINOMA

Hepatocellular carcinoma (HCC) is an aggressive primary liver malignancy characterized by poor prognosis, limited therapeutic options, and frequent resistance to conventional treatments. Metabolic reprogramming, particularly involving mitochondria, is a hallmark of cancer and represents a potential therapeutic vulnerability. In this study, a CRISPR/Cas9-based reverse genetic screen targeting novel mitochondrial regulators identified Smarca5 (SWI/SNF Related, Matrix Associated, Actin Dependent Regulator of Chromatin, Subfamily A, Member 5), an ATP-dependent chromatin remodeler of the ISWI family, as essential gene for maintaining mitochondrial function, proliferation, and viability in HCC cells. Depletion of SMARCA5 led to severe impairments in mitochondrial respiration, reduced ATP production, and widespread disruption of bioenergetic and biosynthetic pathways. These effects included impaired β-oxidation of fatty acids, diminished nucleotide synthesis, and defective amino acid catabolism, indicating a collapse in mitochondrial biosynthetic processes, leading to cancer cell death. Mechanistically, loss of SMARCA5 emerged as a major driver of MYC signaling impairment, resulting in reduced expression of MYC target genes. Notably, SMARCA5 depletion decreased the level of MYC binding to chromatin and promoted its cytoplasmatic localization. In this context, MYC aberrantly interacts with TFAM, a key regulator of mitochondrial DNA transcription, thereby blocking its import into mitochondria. Supporting this model, our findings showed a reduction of mitochondrial TFAM protein levels together with an increased MYC–TFAM interactions in the cytoplasm, which likely contribute to the mitochondrial dysfunction observed upon SMARCA5 downregulation. Together, these results establish SMARCA5 as a critical regulator of mitochondrial function by modulating a MYC–TFAM signaling axis. This work provides new insight into nuclear-mitochondrial crosstalk in HCC and opens potential therapeutic strategies for targeting metabolic vulnerabilities in cancers.