Calcitriol-mediated reduction in IFN-? output in T cell large granular lymphocytic leukemia requires vitamin D receptor upregulation.

ABSTRACT: Constitutively activated STAT1 and elevated IFN-? are both characteristic of T cell large granular lymphocytic leukemia (T-LGLL), a rare incurable leukemia with clonal expansion of cytotoxic T cells due to defective apoptosis. Interferon gamma (IFN-?) is an inflammatory cytokine that correlates with worse progression and symptomology in multiple autoimmune diseases and cancers. In canonical IFN-?-STAT1 signaling, IFN-? activates STAT1, a transcription factor, via phosphorylation of tyrosine residue 701 (p-STAT1). p-STAT1 then promotes transcription of IFN-?, creating a positive feedback loop. We previously found that calcitriol treatment of the TL-1 cell line, a model of T-LGLL, significantly decreased IFN-? secretion and p-STAT1 while increasing the vitamin D receptor (VDR) protein. Here we further explore these observations. Using TL-1 cells, IFN-? decreased starting at 4h following calcitriol treatment, with a reduction in the intracellular and secreted protein levels as well as the mRNA content. A similar reduction in IFN-? transcript levels was observed in primary T-LGLL patient peripheral blood mononuclear cells (PBMCs). p-STAT1 inhibition followed a similar temporal pattern and VDR upregulation inversely correlated with IFN-? levels. Using EB1089 and 25(OH)D3, which have high or low affinity for VDR, respectively, we found that the decrease in IFN-? correlated with the ability of EB1089, but not 25(OH)D3, to upregulate VDR. However, both compounds inhibited p-STAT1; thus the reduction of p-STAT1 is not solely responsible for IFN-? inhibition. Conversely, cells treated with VDR siRNA exhibited decreased basal IFN-? production upon VDR knockdown in a dose-dependent manner. Calcitriol treatment upregulated VDR and decreased IFN-? regardless of initial VDR knockdown efficiency, strengthening the connection between VDR upregulation and IFN-? reduction. Our findings suggest multiple opportunities to further explore the clinical relevance of the vitamin D pathway and the potential role for vitamin D supplementation in T-LGLL.

SUBMITTER: Kulling PM 

PROVIDER: S-EPMC5775933 | biostudies-literature | 2018 Mar

REPOSITORIES: biostudies-literature