Interleukin-1α mediates the antiproliferative effects of 1,25-dihydroxyvitamin D3 in prostate progenitor/stem cells.

Vitamin D(3) is a promising preventative and therapeutic agent for prostate cancer, but its implementation is hampered by a lack of understanding about its mechanism of action. Upon treatment with 1α,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3), vitamin D(3)], the metabolically active form of vitamin D(3), adult prostate progenitor/stem cells (PrP/SC) undergo cell-cycle arrest, senescence, and differentiation to an androgen receptor-positive luminal epithelial cell fate. Microarray analyses of control- and vitamin D(3)-treated PrP/SCs revealed global gene expression signatures consistent with induction of differentiation. Interestingly, one of the most highly upregulated genes by vitamin D(3) was the proinflammatory cytokine interleukin-1α (IL-1α). Systems biology analyses supported a central role for IL-1α in the vitamin D(3) response in PrP/SCs. siRNA-mediated knockdown of IL-1α abrogated vitamin D(3)-induced growth suppression, establishing a requirement for IL-1α in the antiproliferative effects of vitamin D(3) in PrP/SCs. These studies establish a system to study the molecular profile of PrP/SC differentiation, proliferation, and senescence, and they point to an important new role for IL-1α in vitamin D(3) signaling in PrP/SCs.