Mechanisms of 1α, 25‐Dihydroxyvitamin D regulation of hypoxia‐inducible factor‐1α in breast epithelial cells

The purpose of this study was to investigate 1α, 25‐dihydroxyvitamin (1,25(OH) 2 D) regulation of hypoxia inducible factor‐1α (HIF‐1α), an angiogenic transcriptional regulator, in untransformed MCF10A (10A) and H‐ ras transfected MCF10A (10A ‐ras ) breast epithelial cells, a model of cancer progression. In 10A cells, 1,25(OH) 2 D increased HIF‐1α mRNA abundance (64% ± 19 greater than vehicle control, p=0.01) and protein level (137% ± 30, p<0.001) at 12 hr. In contrast, 1,25(OH) 2 D treatment did not alter HIF‐1α mRNA abundance in 10A‐ ras although, similar to 10A cells, the protein level was increased at 12 hrs (108% ± 38, p=0.05). A transcriptional inhibitor prevented the 1,25(OH) 2 D‐mediated increase in HIF‐1α protein expression in 10A but not in 10A‐ ras cells. In contrast, inhibition of proteasomal degradation prevented the 1,25(OH) 2 D‐induced HIF‐1α protein level in 10A‐ ras but not in 10A cells. Knock‐down of VDR (siRNA) prevented 1,25(OH) 2 D‐mediated induction of HIF‐1α protein in 10A but not in 10A‐ ras cells and VDR was associated with a putative VDR response element on HIF‐1α gene promoter in 10A cells (chromatin IP assay). These results support that 1,25(OH) 2 D regulates HIF‐1α protein level in 10A cells via transcriptional regulation in contrast to through proteosomal degradation in 10A‐ ras cells, suggesting a differential mechanism in the two cell types. Grant Funding Source: Supported by NIH CA128770