BACKGROUND: Recently, an increased incidence of allergic diseases has been associated with vitamin D deficiency. We demonstrated previously that calcitriol, the active form of vitamin D, inhibits ε germline transcription, a prerequisite for IgE production. However, the underlying mechanisms remain unexplored. OBJECTIVE: We sought to investigate whether the ε germline gene promoter (Iε) represents a primary vitamin D receptor (VDR) target. Therefore we investigated VDR binding to Iε, analyzed VDR-complex composition in more detail, and delineated its functional consequences. METHODS: The VDR binding to Iε in human B cells, the composition of the VDR-recruited complex, and the acetylation pattern were investigated by means of chromatin immunoprecipitation. The calcitriol-mediated action on Iε was analyzed by using a reporter gene assay. RESULTS: We demonstrate that Iε is a possible VDR target. Calcitriol-activated VDR binds together with retinoid X receptor α to the Iε region. The heterodimer interacts with silencing mediator for retinoid and thyroid hormone receptors, which recruits histone deacetylase (HDAC) 1 and HDAC3. The inhibition of silencing mediator for retinoid and thyroid hormone receptors or HDACs reversed the site-specific deacetylation of histones 3 and 4 and the calcitriol-driven inhibition of the ε germline transcription. The VDR-complex transrepressive actions on Iε were confirmed in a reporter assay. CONCLUSION: We show here that inhibition of IgE production by calcitriol is mediated by its transrepressive activity through the VDR-corepressor complex affecting chromatin compacting around the Iε region. Our findings shed new light on mechanisms of VDR transrepression and understanding of IgE regulation.
BACKGROUND: Recently, an increased incidence of allergic diseases has been associated with vitamin D deficiency. We demonstrated previously that calcitriol, the active form of vitamin D, inhibits ε germline transcription, a prerequisite for IgE production. However, the underlying mechanisms remain unexplored. OBJECTIVE: We sought to investigate whether the ε germline gene promoter (Iε) represents a primary vitamin D receptor (VDR) target. Therefore we investigated VDR binding to Iε, analyzed VDR-complex composition in more detail, and delineated its functional consequences. METHODS: The VDR binding to Iε in human B cells, the composition of the VDR-recruited complex, and the acetylation pattern were investigated by means of chromatin immunoprecipitation. The calcitriol-mediated action on Iε was analyzed by using a reporter gene assay. RESULTS: We demonstrate that Iε is a possible VDR target. Calcitriol-activated VDR binds together with retinoid X receptor α to the Iε region. The heterodimer interacts with silencing mediator for retinoid and thyroid hormone receptors, which recruits histone deacetylase (HDAC) 1 and HDAC3. The inhibition of silencing mediator for retinoid and thyroid hormone receptors or HDACs reversed the site-specific deacetylation of histones 3 and 4 and the calcitriol-driven inhibition of the ε germline transcription. The VDR-complex transrepressive actions on Iε were confirmed in a reporter assay. CONCLUSION: We show here that inhibition of IgE production by calcitriol is mediated by its transrepressive activity through the VDR-corepressor complex affecting chromatin compacting around the Iε region. Our findings shed new light on mechanisms of VDR transrepression and understanding of IgE regulation.
Authors: Lauren L Ritterhouse; Rufei Lu; Hemangi B Shah; Julie M Robertson; Dustin A Fife; Holden T Maecker; Hongwu Du; Charles G Fathman; Eliza F Chakravarty; R Hal Scofield; Diane L Kamen; Joel M Guthridge; Judith A James Journal: PLoS One Date: 2014-04-11 Impact factor: 3.240