Abstract A52: Mechanisms of 1,25-dihdyroxyvitamin D-mediated growth arrest and apoptosis in transformed mammary cells

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Abstract 1,25-Dihdyroxyvitamin D (1,25D), the biologically active form of vitamin D, exerts pro-differentiating and anti-proliferative actions on epithelial cells, but the exact role of the vitamin D receptor (VDR) in mediating these effects remains to be defined. The goal of this project is to link specific functional domains of the VDR with regulation of cancer cell proliferation, invasion, and apoptosis. Epithelial cell lines derived from DMBA induced mammary tumors generated in VDR knock-out (KO) mice and their wild-type (WT) littermates were characterized for growth arrest and apoptosis following 1,25D treatment. Cells derived from WT tumors expressed VDR and exhibited growth arrest and apoptosis in response to 1,25D. In VDR positive cells, 1,25D mediated apoptosis was associated with activation of multiple caspases and calpain, resulting in PARP cleavage. In contrast, cells derived from KO tumors lacked VDR and failed to undergo growth arrest and apoptosis upon 1,25D treatment. To recreate VDR signaling in KO cells, human VDR was stably expressed in the KO240 cell line, generating the KOhVDR cell line. KOhVDR cells expressed transcriptionally active VDR protein at levels comparable to that of WT cells. Re-introduction of VDR did not affect doubling time of KOhVDR cells in the absence of ligand, but did sensitize cells to growth arrest and apoptosis in response to VDR agonists. PCR screening arrays and independent qPCR validation were used to identify VDR target genes in this model system. In WT cells, 6-24h treatment with 100nM 1,25D induced PDGF-B (up to 10 fold) and VEGF-A (up to 5 fold). No changes in PDGF-B or VEGF-A expression were observed in KO cells treated with 1,25D, but both genes were inducible by 1,25D in KOhVDR cells stably expressing hVDR. Thus, 1,25D can activate either human or murine VDR to induce endogenous PDGF-B and VEGF-A gene expression in these murine cells. In summary, these data indicate that VDR does not exert ligand-independent effects on mammary cell growth, but is essential to trigger gene expression, growth arrest and apoptosis in response to 1,25D. Supported by NIH CA69700. Citation Information: Cancer Res 2009;69(23 Suppl):A52.