ELK1/NOL3/GRP78 axis regulates proliferation and stemness in TP53-mutant colon cancer by enhancing adaptive endoplasmic reticulum stress.

[BACKGROUND] Colon cancer harboring TP53 mutations is highly aggressive and associated with short survival. Adaptive, rather than apoptotic, endoplasmic reticulum (ER) stress endows TP53-mutant tumor cells with enhanced protein-folding capacity, metabolic plasticity, and chemoresistance. However, the upstream regulators that selectively drive this cytoprotective program within the cancer stem cell compartment remain elusive.

[METHODS] Single-cell RNA-seq analysis of TP53-mutant versus wild-type tumors was performed to identify ER stress- and mitochondrial metabolism-related differentially expressed genes (EMRDEGs). A four-gene prognostic signature was constructed from TCGA-COAD and GEO cohorts using DESeq2 and LASSO regression. Functional analyses included gain- and loss-of-function studies in TP53-mutant (SW480, HT-29) and TP53-wild-type (HCT116) colon cancer cells, followed by CCK-8, colony formation, microsphere formation, xenograft, dual-luciferase reporter, coimmunoprecipitation and western blot assays.

[RESULTS] TP53-mutant tumor stem cells exhibited synchronized activation of ER stress and mitochondrial metabolic pathways, guiding EMRDEG selection. Among the signature genes, nucleolar protein 3 (NOL3) emerged as an independent adverse prognostic factor that correlated with advanced stage, nodal positivity and shorter overall survival. NOL3 enhanced proliferation and cancer stem cell properties in a TP53-mutant-dependent manner. Mechanistically, ELK1 transcriptionally upregulated NOL3, which physically interacted with GRP78 to activate the PERK/CHOP branch of the unfolded protein response, thereby amplifying adaptive ER stress.

[CONCLUSION] The ELK1/NOL3/GRP78 axis promotes the progression of TP53-mutant colon cancer by increasing adaptive ER stress and stemness. NOL3 serves as a valuable prognostic biomarker and a potential therapeutic target.