title: Serum- and glucocorticoid-inducible kinase SGK1 regulates reorganization of actin cytoskeleton in mast cells upon degranulation.
abstract: Aggregation of the high-affinity IgE receptor (FcεRI) on mast cells (MCs) causes MC degranulation, a process that involves cortical F-actin disassembly. Actin depolymerization may be triggered by increase of cytosolic Ca(2+). Entry of Ca(2+) through the Ca(2+) release-activated Ca(2+) (CRAC) channels is under powerful regulation by the serum- and glucocorticoid-inducible kinase SGK1. Moreover, FcεRI-dependent degranulation is decreased in SGK1-deficient (sgk1(-/-)) MCs. The present study addressed whether SGK1 is required for actin cytoskeleton rearrangement in MCs and whether modulation of actin architecture could underlie decreased degranulation of sgk1(-/-) MCs. Confirming previous results, release of β-hexosaminidase reflecting FcεRI-dependent degranulation was impaired in sgk1(-/-) MCs compared with sgk1(+/+) MCs. When CRAC channels were inhibited by 2-aminoethoxydiphenyl borate (2-APB; 50 μM), MC degranulation was strongly decreased in both sgk1(+/+) and sgk1(-/-) MCs and the difference between genotypes was abolished. Moreover, degranulation was impaired by actin-stabilizing (phallacidin) and enhanced by actin-disrupting (cytochalasin B) agents to a similar extent in sgk1(+/+) MCs and sgk1(-/-) MCs, implying a regulatory role of actin reorganization in this event. In line with this, measurements of monomeric (G) and filamentous (F) actin content by FACS analysis and Western blotting of detergent-soluble and -insoluble cell fractions indicated an increase of the G/F-actin ratio in sgk1(+/+) MCs but not in sgk1(-/-) MCs upon FcεRI ligation, an observation reflecting actin depolymerization. In sgk1(+/+) MCs, FcεRI-induced actin depolymerization was abolished by 2-APB. The observed actin reorganization was confirmed by confocal laser microscopic analysis. Our observations uncover SGK1-dependent Ca(2+) entry in mast cells as a novel mechanism regulating actin cytoskeleton.
authors.affiliation: Dept. of Physiology, University of Tübingen, Gmelinstr. 5, D-72072 Tübingen, Germany.
authors.forename: Evi
authors.initials: E
authors.lastname: Schmid
authors.forename: Shuchen
authors.initials: S
authors.lastname: Gu
authors.forename: Wenting
authors.initials: W
authors.lastname: Yang
authors.forename: Patrick
authors.initials: P
authors.lastname: Münzer
authors.forename: Martin
authors.initials: M
authors.lastname: Schaller
authors.forename: Florian
authors.initials: F
authors.lastname: Lang
authors.forename: Christos
authors.initials: C
authors.lastname: Stournaras
authors.forename: Ekaterina
authors.initials: E
authors.lastname: Shumilina
mesh_terms: D008841:Actin Cytoskeleton / Q000187:drug effects / Q000201:enzymology*; D000199:Actins / Q000097:blood / Q000378:metabolism; D000818:Animals; D001854:Bone Marrow Cells / Q000166:cytology / Q000187:drug effects / Q000201:enzymology; D001896:Boron Compounds / Q000494:pharmacology; D002118:Calcium / Q000097:blood / Q000378:metabolism; D015220:Calcium Channels / Q000097:blood; D015550:Cell Degranulation / Q000187:drug effects / Q000235:genetics*; D002478:Cells, Cultured; D005938:Glucocorticoids / Q000097:blood / Q000502:physiology*; D017874:Immediate-Early Proteins / Q000097:blood / Q000172:deficiency / Q000378:metabolism*; D008407:Mast Cells / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D017346:Protein Serine-Threonine Kinases / Q000097:blood / Q000172:deficiency / Q000378:metabolism*; D000099184:Serum-Glucocorticoid Regulated Kinases
chemical_list: D000199:Actins; D001896:Boron Compounds; D002118:Calcium; D015220:Calcium Channels; D005938:Glucocorticoids; D017874:Immediate-Early Proteins; D017346:Protein Serine-Threonine Kinases; D000099184:Serum-Glucocorticoid Regulated Kinases; C109986:2-aminoethoxydiphenyl borate