Vitamin D regulates CXCL12/CXCR4 and epithelial-to-mesenchymal transition in a model of breast cancer metastasis to lung

Vitamin D deficiency is associated with poor cancer outcome in humans, and administration of vitamin D or its analogs decreases tumor progression and metastasis in animal models. Using the mouse MMTV-PyMT model of mammary cancer, we previously demonstrated a significant acceleration of carcinogenesis in animals on a low vitamin D diet and a reduction in spontaneous lung metastases when mice received vitamin D through perfusion. We investigate here the action mechanism for vitamin D in lung metastasis in the same non-immunodeficient model and demonstrate it involves the control of epithelial to mesenchymal transition as well as interactions between chemokine CXCL12 and its receptor CXCR4. In vitro, 10 -9M vitamin D treatment modifies the phenotype of MMTV-PyMT primary mammary tumor cells and significantly decreases their invasiveness and mammosphere formation capacity by 40 and 50% respectively. Vitamin D treatment also inhibits p-STAT3, Zeb1 and vimentin by 52%, 75% and 77% respectively, and increases E-cadherin by 87%. In vivo, dietary vitamin D deficiency maintains high levels of Zeb1 and p-STAT3 in cells from primary mammary tumors, and increases CXCL12 expression in lung stroma by 64%. In lung metastases, vitamin D deficiency increases CXCL12/CXCR4 co-localization by a factor of 2.5. These findings indicate an involvement of vitamin D in mammary cancer ”seed” (primary tumor cell) and ”soil” (metastatic site), and link vitamin D deficiency to epithelial-to-mesenchymal transition (EMT), CXCL12/CXCR4 signaling and accelerated metastasis, suggesting vitamin D-repleteness in breast cancer patients could enhance the efficacy of co-administered therapies in preventing spread to distant organs.