Question:

Dendritic cells (DCs) are antigen-presenting cells linking innate and adaptive immunity. DC maturation and migration are governed by alterations of cytosolic Ca²⁺ concentrations ([Ca²⁺]_i). Ca²⁺ entry is in part accomplished by store-operated Ca²⁺ (SOC) channels. 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 SGK3. The present study explored, whether SGK3 participates in the regulation of [Ca²⁺]_i and Ca²⁺-dependent functions of DCs.

Methods/Results:

Experiments were performed with bone marrow derived DCs from mice lacking SGK3 ( sgk3^-/- ) and their wild type littermates ( sgk3^+/+ ). Maturation, phagocytosis and cytokine production were similar in sgk3^-/- DCs and sgk3^+/+ DCs. However, SOC entry triggered by intracellular Ca²⁺ store depletion with thapsigargin (1 µM) was significantly reduced in sgk3^-/- DCs compared to sgk3^+/+ DCs. Similarly, bacterial lipopolysaccharide (LPS, 1 µg/ml)- and chemokine CXCL12 (300 ng/ml)- induced increase in [Ca²⁺]_i was impaired in sgk3^-/- DCs. Moreover, currents through SOC channels were reduced in sgk3^-/- DCs. STIM2 transcript and protein abundance were significantly lower in sgk3^-/- DCs, whereas Orai1, Orai2, STIM1 and TRPC1 transcript levels and/or protein abundance were similar in sgk3^-/- DCs and sgk3^+/+ DCs. Chemokine-induced migration of immature and LPS-matured DCs was reduced in sgk3^-/- DCs 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.

Conclusions:

SGK3 contributes to the regulation of SOC entry into and migration of DCs, effects at least partially mediated through SGK3-dependent upregulation of STIM2 expression.