Background:

Glycogen synthase kinase GSK3 has been recently identified as a central regulator of both innate and adaptive immune responses. In dendritic cells (DCs), GSK3β has been demonstrated to mediate secretion of high levels of proinlfammatory cytokines. Since cytokine secretion in DCs also depends on Ca²⁺ signalling, the present project investigates the possible involvement of GSK3 in the regulation of cytosolic Ca²⁺ and in further Ca²⁺-dependent functions.

Methods/Results:

DCs were isolated from the bone marrow of gene targeted knockin mice carrying mutated and thus PKB/SGK-resistant GSK3α,ß ( gsk3^KI ) and of their wild type littermates ( gsk3^+/+ ). Western blot analysis revealed that GSK3 phosphorylation could be detected in DCs from gsk3^+/+ but not from gsk3^KI mice. Maturation markers, MHC II and costimulatory molecule CD86, were similarly expressed on CD11c-positive immature and lipopolysaccharide (LPS)-matured gsk3^+/+ and gsk3^KI DCs, as analyzed by FACS. Production of cytokines IL-12, IL-6, IL-10 and TNFα, as analyzed by ELISA, was also unaffected in mature gsk3^KI DCs. However, migration of gsk3^KI towards the chemokine CXCL12 (50 ng/ml) was strongly enhanced compared to gsk3^+/+ DCs. Moreover, increase of cytosolic Ca²⁺ concentrations ([Ca²⁺]_i) upon stimulation with CXCL12 (300 ng/ml) or with LPS (1 µg/ml) was also significantly increased in gsk3^KI DCs. On the other hand, inhibition of GSK3 with SB216763 (10 µM, 30 min) led to a significant impairment of LPS-induced [Ca²⁺]_i increase in gsk3^+/+ DCs.

Conclusions:

The observations disclose a completely novel role of GSK3 in the regulation of cytosolic Ca²⁺ in DCs.