Role of Dicer Enzyme in the Regulation of Store Operated Calcium Entry (SOCE) in CD4+ T Cells

Abstract

Background/Aims: Activation of T cell receptors (TCRs) in CD4⁺ T cells leads to a cascade of signalling reactions including increase of intracellular calcium (Ca²⁺) levels with subsequent Ca²⁺ dependent stimulation of gene expression, proliferation, cell motility and cytokine release. The increase of cytosolic Ca²⁺ results from intracellular Ca²⁺ release with subsequent activation of store-operated Ca²⁺ entry (SOCE). Previous studies suggested miRNAs are required for the development and functions of CD4⁺ T cells. An enzyme called Dicer is required during the process of manufacturing mature miRNAs from the precursor miRNAs. In this study, we explored whether loss of Dicer in CD4⁺ T cells affects SOCE and thus Ca²⁺ dependent regulation of cellular functions. Methods: We tested the expression of Orai1 by q-RT-PCR and flow cytometry. Further, we measured SOCE by an inverted phase-contrast microscope with the Incident-light fluorescence illumination system using Fura-2. Intracellular Ca²⁺ was also measured by flow cytometry using Ca²⁺ sensitive dye Fluo-4. Results: We found that in Dicer deficient (Dicer^Δ^/Δ) mice Orai1 was downregulated at mRNA and protein level in CD4⁺ T cells. Further, SOCE was significantly smaller in Dicer^Δ^/Δ CD4⁺ T cells than in CD4⁺ T cells isolated from wild-type (Dicer^fl/fl) mice. Conclusion: Our data suggest that miRNAs are required for adequate Ca²⁺ entry into CD4⁺ T cells and thus triggering of Ca²⁺ sensitive immune functions.