SMAD3 activation in pancreatic stellate cells correlates with PTGDR2 expression and favorable stromal features in pancreatic cancer

BACKGROUND: Pancreatic cancer is characterized by a dense tumor microenvironment enriched with cancer-associated fibroblasts (CAFs), which display context-dependent tumor-promoting and tumor-restraining properties. However, the molecular basis of stromal heterogeneity remains incompletely understood. METHODS: We examined stromal responses of pancreatic stellate cells (PSCs), a major source of CAFs, using an orthotopic mouse co-implantation model, RNA sequencing, conditioned medium-based functional assays, and immunohistochemical analysis of resected pancreatic cancer specimens. RESULTS: Co-implantation of PSCs with pancreatic cancer cells was associated with smaller primary tumor volumes and selective activation of SMAD3 in PSCs. Cancer cell-derived conditioned medium activated SMAD3 signaling in PSCs but not in cancer cells, suggesting cell type-specific pathway activation. Transcriptomic analysis identified prostaglandin D2 receptor 2 (PTGDR2) as a gene upregulated in association with SMAD3 activation, and its expression decreased following SMAD3 inhibition. Functional assays showed that SMAD3 activation was associated with modulation of PTGDR2 and inflammatory gene expression in PSCs. In clinical samples, higher p-SMAD3 expression in CAFs correlated with favorable overall survival. CONCLUSIONS: SMAD3 activation in PSCs was observed in association with PTGDR2 expression, altered inflammatory profiles, and reduced tumor growth in vivo. These findings support the presence of distinct stromal phenotypes in pancreatic cancer and warrant further investigation into CAF modulation strategies.