ASCC3 promotes chemosensitivity in colorectal cancer cells.

The activating signal co-integrator 1 complex subunit 3 (ASCC3), a multifunctional protein, has been implicated as a prognostic marker in several types of cancer. However, mechanisms underlying its prognostic value are not fully understood. Here, we report that ASCC3 promotes sensitivity to chemotherapeutic drugs that induce replication stress, such as 5-fluorouracil, cisplatin, and hydroxyurea, in colorectal cancer (CRC) cells, likely in a cancer type dependent manner. Increased chemoresistance resulting from ASCC3 loss is not due to reduced genomic instability as evidenced by enhanced accumulation of DNA damage and micronuclei following exposure to these drugs. RNA-seq analysis reveals that ASCC3 stimulates the expression of gene sets associated with mTORC1 signaling, glycolysis, and protein folding pathways in CRC cells. While promoting the serine biosynthesis pathway, we demonstrate, through extracellular flux assays and stable isotopes tracer analysis, that ASCC3 reprograms energy metabolism, favoring glycolysis over oxidative phosphorylation. Furthermore, we find that ASCC3 is required for PERK production upon ER stress. Impaired PERK production is associated with reduced levels of CHOP and caspase 3 following treatment with 5-fluorouracil, indicating that ASCC3 promotes PERK production to enhance cell death upon chemotherapy. Collectively, our work reveals an unexpected role of ASCC3 in connecting replication stress to both metabolic reprogramming and PERK-mediated signaling in CRC cells.