Abstract 5718: Convergence of vitamin D and PPARγ signaling in human breast cancer cell lines

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Abstract Previous studies have demonstrated a positive interaction between vitamin D and peroxisome proliferator- activated receptor γ (PPARγ) mediated signaling while other studies have shown an inverse relationship between these two pathways. Therefore, we sought to determine the functional interaction between the vitamin D receptor (VDR) and PPARγ in human breast cancer cells. We report the physical interaction and nuclear colocalization of VDR and PPARγ in the T47D human breast cancer cell line as determined by co-immunoprecipitation and immunofluorescence respectively. Furthermore, 1alpha,25-dihydroxyvitamin D3 (1,25D3) treatment of MCF-7 and T47D cells significantly upregulated PPARγ protein expression in a dose and time dependent manner. Conversely, knockdown of unliganded VDR also upregulated PPARγ protein expression, suggesting that it is a potential VDR target gene. Thus, VDR itself in the absence of ligand, can suppress PPARγ basal expression. This paradoxical effect may be due to the differential binding of VDR to its coactivators or corepressors during the liganded and unliganded state. Consistent with this, the basal expression of PPARγ mRNA was inversely correlated with VDR mRNA expression in several human breast cancer cell lines. Reciprocally, a PPARγ agonist attenuated vitamin D mediated upregulation of vitamin D target genes CYP24 and p21. Similarly, the activity of VDRE, a vitamin D responsive reporter was decreased by 2 fold in the presence of the PPARγ agonist. Together, these observations infer that VDR and PPARγ protein interactions negatively influence their respective pathways. (This work was supported by NCI predoctoral fellowship 1F31CA132619 (F.A.) and NCI R03 CA121365 (X.P). Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5718.