SGK3 Regulates Ca2+ Entry and Migration of Dendritic Cells
Background/Aims: Dendritic cells (DCs) are antigen-presenting cells linking innate and adaptive immunity. DC maturation and migration are governed by alterations of cytosolic Ca<sup>2+</sup> concentrations ([Ca<sup>2+</sup>]<sub>i</sub>). Ca<sup>2+</sup> entry is in part accomplished by store-operated Ca<sup>2+</sup> (SOC) channels consisting of the membrane pore-forming subunit Orai and the ER Ca<sup>2+</sup> sensing subunit STIM. Moreover, DC functions are under powerful regulation of the phosphatidylinositol-3-kinase (PI3K) pathway, which suppresses proinflammatory cytokine production but supports DC migration. Downstream targets of PI3K include serum- and glucocorticoid-inducible kinase isoform SGK3. The present study explored, whether SGK3 participates in the regulation of [Ca<sup>2+</sup>]<sub>i</sub> and Ca<sup>2+</sup>-dependent functions of DCs, such as maturation and migration. Methods/ Results: Experiments were performed with bone marrow derived DCs from gene targeted mice lacking SGK3 (sgk3<sup>-/-</sup>) and DCs from their wild type littermates (sgk3<sup>+/+</sup>). Maturation, phagocytosis and cytokine production were similar in sgk3<sup>-/-</sup> and sgk3<sup>+/+</sup> DCs. However, SOC entry triggered by intracellular Ca<sup>2+</sup> store depletion with the endosomal Ca<sup>2+</sup> ATPase inhibitor thapsigargin (1 µM) was significantly reduced in sgk3<sup>-/-</sup> compared to sgk3<sup>+/+</sup> DCs. Similarly, bacterial lipopolysaccharide (LPS, 1 µg/ml)- and chemokine CXCL12 (300 ng/ml)- induced increase in [Ca<sup>2+</sup>]<sub>i</sub> was impaired in sgk3<sup>-/-</sup> DCs. Moreover, currents through SOC channels were reduced in sgk3<sup>-/-</sup> DCs. STIM2 transcript levels and protein abundance were significantly lower in sgk3<sup>-/-</sup> DCs than in sgk3<sup>+/+</sup> DCs, whereas Orai1, Orai2, STIM1 and TRPC1 transcript levels and/or protein abundance were similar in sgk3-/- and sgk3<sup>+/+</sup> DCs. Migration of both, immature DCs towards CXCL12 and LPS-matured DCs towards CCL21 was reduced in sgk3<sup>-/-</sup> as compared to sgk3<sup>+/+</sup> DCs. Migration of sgk3<sup>+/+</sup> DCs was further sensitive to SOC channel inhibitor 2-APB (50 µM) and to STIM1/STIM2 knock-down. Conclusion: SGK3 contributes to the regulation of store-operated Ca<sup>2+</sup> entry into and migration of dendritic cells, effects at least partially mediated through SGK3-dependent upregulation of STIM2 expression.