Vitamin D analogue TX 527 down‐regulates the NF‐κB pathway and controls the proliferation of endothelial cells transformed by Kaposi sarcoma herpesvirus

Background and Purpose

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.

Experimental Approach

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.

Key Results

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)₂D₃, 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.

Conclusions and Implications

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.

DOI: 10.1111/bph.12219

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