Vitamin D remodels the tumor microenvironment to suppress gastric cancer progression through cancer-associated fibroblasts-secreted exosomal miR-378c targeting KDSR.

Gastric cancer (GC) is a malignant neoplasm displaying highly cancer-related mortality globally. Although our previous studies have confirmed that vitamin D possessed a direct anti-cancer effect on GC cells, the regulatory role of vitamin D on gastric tumor microenvironment (TME) remains unexplored. This study aims to expound the modulation of vitamin D on TME especially on GC-associated fibroblasts (CAFs) and to further elucidate the essential role of the CAFs-derived exosomal ingredients in tumor-stroma crosstalk. Patient-derived primary CAFs enhanced the aggressive characteristics of GC cells. When co-cultured with GC cells, CAFs pretreated with 1,25(OH)2D3 (1,25D3), the active form of vitamin D exhibited a significant inhibitory effect on cancer cell invasion and migration. Additionally, exosomes isolated from 1,25D3-pretreated CAFs were found to mediate this inhibitory effect, significantly reducing the migratory and invasive capacity of GC cells. Exosomal RNA sequencing revealed a significant upregulation of miR-378c in CAF-derived exosomes following 1,25D3 treatment. Fluorescence tracing assays confirmed that this treatment augmented the transfer of CAF-derived exosomal miRNA-378c into GC cells. Mechanistically, this elevated miR-378c directly targeted ketodihydrosphinganine reductase (KDSR) in GC cells, further leading to the attenuation of tumor growth in a 615 mice model. Immunophenotypic analysis further revealed that treatment with ago-miR-378c significantly increased intratumoral Granzyme B and CD3 levels and downregulated Foxp3 expression, indicating an activated state of antitumor immunity and a relief from immune suppression within the TME. Correspondingly, the expression of TNF-α and IL-6 was found to be up-regulated, while the immunosuppressive factor IL-10 was reduced in the ago-miR-378c group in comparison to the control group. Moreover, systemic administration of vitamin D suppressed CAF-mediated promotion of in vivo tumor growth, concomitant with elevated intratumoral miR-378c and diminished KDSR expression in a nude mice model. Taken together, our results demonstrate that vitamin D reprograms CAFs to impede GC progression and to promote an anti-tumor immune microenvironment, which might be mediated by exosomal miR-378c/KDSR axis, highlighting a potential therapeutic strategy of using vitamin D to counteract CAF-driven oncogenesis in GC.