In vitro studies revealed a downregulation of Wnt/β-catenin cascade by active vitamin D and TX 527 analog in a Kaposi's sarcoma cellular model.

The Kaposi's sarcoma-associated herpesvirus G-protein-coupled receptor (vGPCR) is a key molecule in the pathogenesis of Kaposi's sarcoma. We have previously demonstrated that 1α,25(OH)2D3 or its less calcemic analog TX 527 exerts antiproliferative effects in endothelial cells stable expressing vGPCR. Since it is well documented that vGPCR activates the canonical Wnt/β-catenin signaling pathway, the aim of this study was to evaluate if Wnt/β-catenin cascade is target of 1α,25(OH)2D3 or TX 527 as part of their antineoplastic mechanism. Firstly, Western blot studies showed an increase in β-catenin protein levels in a dose and time dependent manner; and when VDR was knockdown, β-catenin protein levels were significantly decreased. Secondly, β-catenin localization, investigated by immunofluorescence and subcellular fractionation techniques, was found increased in the nucleus and plasma membrane after 1α,25(OH)2D3 treatment. VE-cadherin protein levels were also increased in the plasma membrane fraction. Furthermore, β-catenin interaction with VDR was observed by co-immunoprecipitation and mRNA expression of β-catenin target genes was found decreased. Finally, DKK-1, the extracellular inhibitor of Wnt/β-catenin pathway, showed an initial upregulation of mRNA expression. Altogether, the results obtained by different techniques revealed a downregulation of Wnt/β-catenin cascade after 1α,25(OH)2D3 or TX 527 treatment, showing the foundation for a potential chemotherapeutic agent.