Calcitriol decreases expression of importin ?3 and attenuates RelA translocation in human bronchial smooth muscle cells.
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ABSTRACT: A potent immunomodulatory role of Vitamin D in both innate and adaptive immunity has recently been appreciated. In allergic asthma, activation of NF-?B induces transcription of various cytokines and chemokines involved in allergic airway inflammation. The nuclear import of activated NF-?B p50/RelA subunit is dependent on importin ?3 (KPNA4) and importin ?4 (KPNA3). In this study, we examined the role of importin ?3 in immunomodulatory effect of calcitriol in human bronchial smooth muscle cells (HBSMCs).Cultured HBSMCs were stimulated with calcitriol in the presence and absence of cytokines, TNF-?, IL-1?, and IL-10. The mRNA transcripts of importin ?3 and ?4 were analyzed using qPCR while protein expression of importin ?3, ?4 and nuclear RelA was analyzed by immunoblotting.Calcitriol significantly decreased mRNA and protein expression of importin ?3 as well as nuclear protein expression of NF-?B p65 (RelA). The decreased activation of RelA by calcitriol was confirmed by decreased release of RelA-inducible molecules, including IL-5, IL-6 and IL-8, by HBSMCs upon calcitriol treatment. Calcitriol attenuated the effect of TNF-? and IL-1? to upregulate mRNA and protein expression of importin ?3. IL-10 significantly decreased the TNF-? induced expression of importin ?3 and this effect was further potentiated by calcitriol.These data suggest that under inflammatory conditions, calcitriol decreases the expression of importin ?3 resulting in decreased nuclear import of activated RelA. This could be a novel mechanism by which calcitriol could exert its immunomodulatory effects to reduce allergic airway inflammation and thus may alleviate the symptoms in allergic asthma.
SUBMITTER: Agrawal T
PROVIDER: S-EPMC3444658 | biostudies-literature | 2012 Oct
REPOSITORIES: biostudies-literature
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