Tumor suppressor candidate 1 (TUSC1) drives oxidative phosphorylation and tumor cell death in colorectal cancer.

Tumor Suppressor Candidate-1 (TUSC1), located at chromosome 9p21.2, resides within a region frequently deleted in human malignancies, yet its role in colorectal cancer (CRC) remains undefined. We investigated TUSC1 expression and function using integrated clinical, transcriptomic, metabolic, and in-vivo approaches. Immunohistochemical analysis of 145 CRC specimens revealed a significant loss of TUSC1 protein compared to normal colon, concordant with TCGA-COAD/READ RNA-Seq datasets. DepMap CRISPR fitness screens demonstrated that TUSC1 is non-essential for baseline proliferation, supporting a tumor suppressor-like profile. Lentiviral re-expression of TUSC1 in low-expressing CRC cell lines (HCT116, SW480) induced broad transcriptomic remodeling, including suppression of PI3K-Akt-mTOR signaling and stemness programs, with concomitant enrichment of oxidative phosphorylation (OXPHOS) pathways. Quantitative proteomics and phospho-western analyses confirmed attenuation of PI3K-Akt signaling. TUSC1 overexpression led to increased mitochondrial respiration, Complex I activity, and mitochondrial mass without significant changes in glycolytic flux. It also led to elevated mitochondrial ROS levels and induced G2/M arrest and apoptosis. Antioxidants partially rescued mitochondrial ROS-dependent cytotoxicity in HCT116 cells, whereas SW480 cells displayed a more limited redox rescue. TUSC1 also reduced cancer stem cell markers, impaired clonogenicity, enhanced 5-fluorouracil sensitivity, and suppressed tumor growth in xenograft models. These findings establish TUSC1 as a metabolic tumor suppressor in CRC that attenuates PI3K-Akt signaling, enhances mitochondrial oxidative metabolism, and promotes ROS-mediated tumor cell death. This study provides the first mechanistic insight into TUSC1's function in cancer, and its restoration or therapeutic induction of oxidative metabolic stress may represent a strategy for targeting CRCs.