Stimulation of Ca ²⁺ ‐channel Orai1/STIM1 by serum‐and glucocorticoid‐inducible kinase 1 (SGK1)

Abstract

Ca(2+) signaling includes store-operated Ca(2+) entry (SOCE) following depletion of endoplasmic reticulum (ER) Ca(2+) stores. On store depletion, the ER Ca(2+) sensor STIM1 activates Orai1, the pore-forming unit of Ca(2+)-release-activated Ca(2+) (CRAC) channels. Here, we show that Orai1 is regulated by serum- and glucocorticoid-inducible kinase 1 (SGK1), a growth factor-regulated kinase. Membrane Orai1 protein abundance, I(CRAC), and SOCE in human embryonic kidney (HEK293) cells stably expressing Orai1 and transfected with STIM1 were each significantly enhanced by coexpression of constitutively active (S422D)SGK1 (by+81, +378, and+136%, respectively) but not by inactive (K127N)SGK1. Coexpression of the ubiquitin ligase Nedd4-2, an established negatively regulated SGK1 target, down-regulated SOCE (by -48%) and I(CRAC) (by -60%), an effect reversed by expression of (S422D)SGK1 (by +175 and +173%, respectively). Orai1 protein abundance and SOCE were significantly lower in mast cells from SGK1-knockout (sgk1(-/-)) mice (by -37% and -52%, respectively) than in mast cells from wild-type (sgk1(+/+)) littermates. Activation of SOCE by sarcoplasmic/endoplasmic reticulum Ca(2+)-ATPase-inhibitor thapsigargin (2 μM) stimulated migration, an effect significantly higher (by +306%) in (S422D)SGK1-expressing than in (K127N)SGK1-expressing HEK293 cells, and also significantly higher (by +108%) in sgk1(+/+) than in sgk1(-/-) mast cells. SGK1 is thus a novel key player in the regulation of SOCE.

The serum- and glucocorticoid-inducible kinase 1 (SGK1) influences platelet calcium signaling and function by regulation of Orai1 expression in megakaryocytes

“…MEG-01 and human embryonic kidney (HEK293) cells were transiently transfected for 48 hours with the constitutively active SGK1 mutant S422D SGK1 (hSGK1 SD in pCDNA3.1), which does not require activation by phosphoinositide-dependent kinase PDK1, 19 or the inactive mutant K127N SGK1 (hSGK1 KN in pCDNA3.1), which lacks catalytic activity. 19 Transfections were performed as described previously 24 using FuGENE HD transfection reagent (Roche Diagnostics) according to the manufacturer's instructions. For experiments with pharmacologic inhibition of SGK1 or IB kinase (IKK), 1M GSK650394 (Solvay) or 10M BMS-345541 (Sigma-Aldrich) was added.…”

“…17 Most recently, SGK1 has been shown to be critically important for the Ca 2ϩ entry into mast cells after activation of the IgE receptor, 18 an effect mediated by regulation of Orai1. 19 Furthermore, SGK1 participates in the regulation of renal tubular Na ϩ reabsorption, salt appetite, and thus blood pressure. 17 A gain-of-function SGK1 gene variant, the combined presence of single nucleotide polymorphism in intron 6 (rs1743966) and in exon 8 (rs1057293), is associated with enhanced blood pressure.…”

Serum- and glucocorticoid-inducible kinase SGK1 regulates reorganization of actin cytoskeleton in mast cells upon degranulation

“…The process of F-actin disassembly was shown to be dependent on the increase of intracellular Ca 2ϩ (16,23). On the other hand, a powerful regulator of Ca 2ϩ entry and exocytosis in MCs is the serum-and glucocorticoidinducible kinase SGK1 (9,10,33). SGK1-deficient (sgk1 Ϫ/Ϫ ) MCs have a decreased FcεRI-dependent Ca 2ϩ entry and degranulation, and sgk1 Ϫ/Ϫ mice are thus protected against anaphylactic reaction, pointing to a strongly impaired MC function in vivo (33).…”

“…We have recently demonstrated that SGK1 acts through upregulating the Ca 2ϩ release-activated Ca 2ϩ (CRAC) channel in the plasma membrane (9, 10), which in MCs consists of the pore-forming subunit Orai1 (36) and the endoplasmatic Ca 2ϩ -sensing subunit STIM1 (3). SGK1 is partially effective through phosphorylation of the ubiquitin ligase Nedd4-2 (neuronal precursor cells expressed developmentally downregulated), which ubiquitinates Orai1, thus preparing the channel protein for degradation (9). Moreover, SGK1 activates the transcription factor NF-B, which is required for Orai1 and STIM1 transcription (10).…”

Pivotal Role of Serum- and Glucocorticoid-Inducible Kinase 1 in Vascular Inflammation and Atherogenesis

“…17,18 There is growing evidence indicating that SGK1 is heavily expressed in macrophages and plays an important role in cellular migration. 28,30 Although inflammatory infiltration of the vascular wall by immigrating monocytes and monocytederived macrophages is critical to the development of atherosclerosis and although SGK1 is considered a candidate gene fostering the development of atherosclerosis, 31 nothing is hitherto known about the influence of SGK1 in atherogenesis.…”