Anticoagulant effects of 1α,25-dihydroxyvitamin D₃ on human myelogenous leukemia cells and monocytes

The hormonally active form of vitamin D is 1α,25-dihydroxyvitamin D₃ [1,25(OH)2D₃], which is a principal regulator of calcium homeostasis. It also affects hormone secretion, cell differentiation, and proliferation a mode of action that involves stereospecific interaction with an intracellular vitamin D receptor (VDR). We recently found that retinoids, which are vitamin A derivatives, exert anticoagulant effects upregulating thrombomodulin (TM) and downregulating tissue factor (TF) expression in acute promyelocytic leukemia cells and monoblastic leukemia cells. Both the VDR and retinoid receptors belong to the same family of receptors. A heterodimer consisting of the retinoid X receptor end the VDR binds to vitamin D responsive elements on genes regulated vitamin D. To determine whether 1,25(OH)₂D₃ would exhibit anticoagulant effects similar to retinoids, we measured the antigen level, activity, and mRNA level of TM and TF in human leukemic cells, vascular endothelial cells, and monocytes treated with 1,25(OH)₂D₃. We found that 1,25(OH)₂D₃ upregulates antigen expression, activity, and mRNA levels of TM and downregulates antigen expression, activity, and mRNA levels of TF in human monocytic leukemia cells, some acute myelogenous leukemia cells, and monocytes, but not in umbilical vein endothelial cells. Transient transfection studies with reporter plasmids in monocytic leukemia cells and mobility gel-shift assay showed interaction with 1,25(OH)₂D₃ and functional retinoic acid responsive elements present in the 5'-flanking region of the TM gene. However, auxiliary factors or other elements in the TM gene may contribute to VDR specificity and transactivation of the gene in specific target cells. These findings indicate that 1,25(OH)₂D₃ resembles the retinoids in its control of the transcription of the TM and TF genes in human monocytic cells. Analogs of 1,25(OH)₂D₃ with anticoagulant activity may serve as adjunctive antithrombotic agents in monocytic leukemia and atherosclerotic disease.