cholecalciferol and Sarcoma--Kaposi

We have previously shown that 1α,25(OH)2-Vitamin D3 [1α,25(OH)2D3] and its less calcemic analog TX 527 inhibit the proliferation of endothelial cells transformed by the viral G protein-coupled receptor associated to Kaposi sarcoma (vGPCR) and this could be partially explained by the inhibition of the NF-κB pathway. In this work, we further explored the mechanism of action of both vitamin D compounds in Kaposi sarcoma. We investigated whether the cell cycle arrest and subsequent apoptosis of endothelial cells (SVEC) and SVEC transformed by vGPCR (SVEC-vGPCR) elicited by 1α,25(OH)2D3 and TX 527 were mediated by the vitamin D receptor (VDR). Cell cycle analysis of SVEC and SVEC-vGPCR treated with 1α,25(OH)2D3 (10nM, 48h) revealed that 1α,25(OH)2D3 increased the percentage of cells in the G0/G1 phase and diminished the percentage of cells in the S phase of the cell cycle. Moreover, the number of cells in the S phase was higher in SVEC-vGPCR than in SVEC due to vGPCR expression. TX 527 exerted similar effects on growth arrest in SVEC-vGPCR cells. The cell cycle changes were suppressed when the expression of the VDR was blocked by a stable transfection of shRNA against VDR. Annexin V-PI staining demonstrated apoptosis in both SVEC and SVEC-vGPCR after 1α,25(OH)2D3 and TX 527 treatment (10nM, 24h). Cleavage of caspase-3 detected by Western blot analysis was increased to a greater extent in SVEC than in SVEC-vGPCR cells, and this effect was also blocked in VDR knockdown cells. Altogether, these results suggest that 1α,25(OH)2D3 and TX 527 inhibit the proliferation of SVEC and SVEC-vGPCR and induce apoptosis by a mechanism that involves the VDR.

Topics: Alkynes; Animals; Apoptosis; Bone Density Conservation Agents; Calcitriol; Cell Cycle Checkpoints; Cholecalciferol; Gene Expression Regulation, Neoplastic; Humans; Receptors, Calcitriol; Sarcoma, Kaposi

The Kaposi sarcoma (KS)-associated herpesvirus GPCR (vGPCR) is a key molecule in the pathogenesis of KS, where it increases NF-κB gene expression and activates the NF-κB pathway. We investigated whether the less calcemic vitamin D analogue TX 527 inhibited the proliferation of endothelial cells transformed by vGPCR by modulation of the NF-κB pathway.. Endothelial cells transformed by vGPCR (SVEC-vGPCR) were treated with TX 527. Proliferation was measured by 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium, inner salt (MTS) and cell cycle by flow cytometry. mRNA and protein levels were measured by real-time quantitative reverse transcriptase-PCR (qRT-PCR) and immunoblot analysis respectively.. TX 527, similar to bortezomib (0.5 nM), a proteasome inhibitor that inhibits the activation of NF-κB, reduced proliferation and induced G0/G1 cell cycle arrest in SVEC-vGPCR. TX 527 like 1α,25(OH)2 D3 , biological active form of vitamin D, decreased the activity of NF-κB comparable with the effect of bortezomib. Time-response studies showed that TX 527 significantly decreased NF-κB and increased IκBα mRNA and protein levels. The increase of IκBα was accompanied by a reduction in p65/NF-κB translocation to the nucleus. These responses were abolished when vitamin D receptor (VDR) expression was suppressed by stable transfection of shRNA against VDR. In parallel with NF-κB inhibition, there was a down-regulation of inflammatory genes such as IL-6, CCL2/MCP and CCL20/MIP3α.. These results suggest that the anti-proliferative effects of the vitamin D analogue TX 527 in SVEC-vGPCR occur by modulation of the NF-κB pathway and are VDR dependent.

Topics: Alkynes; Animals; Antineoplastic Agents; Boronic Acids; Bortezomib; Cell Cycle; Cell Line, Transformed; Cell Proliferation; Cholecalciferol; Endothelial Cells; Gene Expression Regulation; Herpesvirus 8, Human; I-kappa B Proteins; Mice; NF-kappa B; Pyrazines; Sarcoma, Kaposi; Signal Transduction; Vitamin D