GLG1 in cancer-associated fibroblasts promotes bladder cancer growth while limiting tumor apoptosis

Cancer-associated fibroblasts (CAFs) shape bladder cancer progression, but functionally relevant CAF-associated drivers remain insufficiently characterized. This study aimed to identify CAF-enriched genes with translational relevance and to determine whether GLG1 mediates tumor-stromal crosstalk in bladder cancer. Single-cell RNA sequencing from bladder cancer tissues was integrated with Mendelian randomization, Bayesian colocalization, correlation analyses, immunostaining of clinical specimens, CAF-conditioned medium assays, GLG1 knockdown/overexpression, TGF-β1/Smad2/3 assessment, and xenograft modeling. Single-cell profiling of nine bladder cancer samples retained 60,561 cells and identified fibroblast-enriched transcriptional programs. Among 960 fibroblast-enriched genes, Mendelian randomization identified 22 genes whose genetically predicted expression was associated with bladder cancer risk, and colocalization prioritized GLG1, HES4, and HSP90B1. GLG1 was selected for validation because it showed fibroblast-enriched expression, genetic support for bladder cancer association, and shared cis-eQTL/GWAS signals. GLG1 expression was higher in tumor tissues than in adjacent normal tissues, consistent with a stromal localization pattern, and GLG1 positivity was associated with tumor invasiveness. Tumor-derived TGF-β1/Smad2/3 signaling contributed to GLG1 upregulation in fibroblasts. CAF-conditioned medium enhanced EJ-1 cell viability, migration, and Matrigel invasion; these effects were weakened by GLG1 silencing and strengthened by GLG1 overexpression in CAFs. In xenografts, CAFs-shGLG1 reduced tumor growth and Ki-67 positivity and increased TUNEL-positive tumor cells relative to CAFs-shNC, whereas CAFs-OE-GLG1 showed the opposite Ki-67 and TUNEL staining pattern. CAF-associated GLG1 promotes bladder cancer cell viability, migration, Matrigel invasion, and xenograft growth while limiting tumor-cell apoptosis, likely by reinforcing tumor-stromal crosstalk. These findings support GLG1 as a stromal factor involved in bladder cancer progression and provide a basis for further evaluation of its biomarker potential and therapeutic relevance.