SGK3 regulates Ca 2+ entry and migration of dendritic cells

Abstract

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 2+ concentrations ([Ca 2+ ]i). Ca 2+ entry is in part accomplished by store-operated Ca 2+ (SOC) channels consisting of the membrane pore-forming subunit Orai and the ER Ca 2+ sensing subunit STIM. Moreover, DC functions are under powerful regulation of the phosphatidylinositol-3-kinase (PI3K) pathway, which suppresses proinfammatory 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 2+ ]i and Ca 2+ -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 -/- ) and DCs from their wild type littermates (sgk3 +/+ ). Maturation, phagocytosis and cytokine production were similar in sgk3 -/- and sgk3 +/+ DCs. However, SOC entry triggered by intracellular Ca 2+ store depletion with the endosomal Ca 2+ ATPase inhibitor thapsigargin (1 μM) was signifcantly reduced in sgk3 -/- compared to sgk3 +/+ DCs. Similarly, bacterial lipopolysaccharide (LPS, 1 μg/ml)- and chemokine CXCL12 (300 ng/ml)-induced increase in [Ca 2+ ]i was impaired in sgk3 -/- DCs. Moreover, currents through SOC channels were reduced in sgk3 -/- DCs. STIM2 transcript levels and protein abundance were signifcantly lower in sgk3 -/- DCs than in sgk3 +/+ DCs, whereas Orai1, Orai2, STIM1 and TRPC1 transcript levels and/or protein abundance were similar in sgk3 -/- and sgk3 +/+ DCs. Migration of both, immature DCs towards CXCL12 and LPS-matured DCs towards CCL21 was reduced in sgk3 -/- as compared to sgk3 +/+ DCs. Migration of sgk3 +/+ 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 2+ entry into and migration of dendritic cells, effects at least partially mediated through SGK3-dependent upregulation of STIM2 expression. Copyright © 2012 S. Karger AG, Basel.