Role of Dicer Enzyme in the Regulation of Store Operated Calcium Entry (SOCE) in CD4+ T Cells
Background/Aims: Activation of T cell receptors (TCRs) in CD4<sup>+</sup> T cells leads to a cascade of signalling reactions including increase of intracellular calcium (Ca<sup>2+</sup>) levels with subsequent Ca<sup>2+</sup> dependent stimulation of gene expression, proliferation, cell motility and cytokine release. The increase of cytosolic Ca<sup>2+</sup> results from intracellular Ca<sup>2+</sup> release with subsequent activation of store-operated Ca<sup>2+</sup> entry (SOCE). Previous studies suggested miRNAs are required for the development and functions of CD4<sup>+</sup> 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<sup>+</sup> T cells affects SOCE and thus Ca<sup>2+</sup> 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 Ca<sup>2+</sup> was also measured by flow cytometry using Ca<sup>2+</sup> sensitive dye Fluo-4. Results: We found that in Dicer deficient (Dicer<sup>Δ</sup><sup>/Δ</sup>) mice Orai1 was downregulated at mRNA and protein level in CD4<sup>+</sup> T cells. Further, SOCE was significantly smaller in Dicer<sup>Δ</sup><sup>/Δ</sup> CD4<sup>+</sup> T cells than in CD4<sup>+</sup> T cells isolated from wild-type (Dicer<sup>fl/fl</sup>) mice. Conclusion: Our data suggest that miRNAs are required for adequate Ca<sup>2+</sup> entry into CD4<sup>+</sup> T cells and thus triggering of Ca<sup>2+</sup> sensitive immune functions.