1α,25-Dihydroxyvitamin D₃ regulates the expression of Id1 and Id2 genes and the angiogenic phenotype of human colon carcinoma cells

1α,25-Dihydroxyvitamin D₃ (1α,25(OH) ₂D₃) has antitumor activity in addition to its classical action on calcium metabolism and bone tissue biology. It is thought to regulate the expression of multiple target genes and thus modulate processes critical for tumor growth and metastases. Here we show that 1α,25(OH) ₂D₃ differentially regulates the expression of Id1 and Id2 genes, members of a family of transcriptional regulators of cell proliferation and differentiation. 1α,25(OH)₂D₃ induced epithelial differentiation in SW480-ADH human colon carcinoma cell line by promoting expression of the proteins implicated in adherent junction formation, including E-cadherin, and by inhibiting β-catenin transcriptional activity. 1α,25(OH)₂D₃ activated the human Id1 gene promoter and rapidly induced Id1 RNA and protein. Ectopic overexpression of Id1 was not sufficient to induce E-cadherin, which was critical for the morphological changes induced by 1α,25(OH)₂D₃ in SW480-ADH cells. Conversely, Id2 transcription rate, RNA and protein levels were decreased by 1α,25(OH)₂D₃. Id2 downregulation by 1α,25(OH)₂D₃ mediated the antiproliferative effect of 1α,25(OH)₂D₃ on SW480-ADH cells. In addition, we showed that 1α,25(OH)₂D₃ changed the levels of the inducer of angiogenesis, vascular endothelial growth factor and the potent antiangiogenic factor thrombospondin-1, leading to a balanced change in the angiogenic potential of SW480-ADH human colon carcinoma cells.