Rictor negatively regulates high-affinity receptors for IgE-induced mast cell degranulation.
Rictor is a regulatory component of the mammalian target of rapamycin (mTOR) complex 2 (mTORC2). We have previously demonstrated that rictor expression is substantially downregulated in terminally differentiated mast cells as compared with their immature or transformed counterparts. However, it is not known whether rictor and mTORC2 regulate mast cell activation. In this article, we show that mast cell degranulation induced by aggregation of high-affinity receptors for IgE (FcεRI) is negatively regulated by rictor independently of mTOR. We found that inhibition of mTORC2 by the dual mTORC1/mTORC2 inhibitor Torin1 or by downregulation of mTOR by short hairpin RNA had no impact on FcεRI-induced degranulation, whereas downregulation of rictor itself resulted in an increased sensitivity (∼50-fold) of cells to FcεRI aggregation with enhancement of degranulation. This was linked to a similar enhancement in calcium mobilization and cytoskeletal rearrangement attributable to increased phosphorylation of LAT and PLCγ1. In contrast, degranulation and calcium responses elicited by the G protein-coupled receptor ligand, C3a, or by thapsigargin, which induces a receptor-independent calcium signal, was unaffected by rictor knockdown. Overexpression of rictor, in contrast with knockdown, suppressed FcεRI-mediated degranulation. Taken together, these data provide evidence that rictor is a multifunctional signaling regulator that can regulate FcεRI-mediated degranulation independently of mTORC2.
Laboratory of Allergic Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892; and daniel.smrz@lfmotol.cuni.cz.
Daniel
D
Smrz
Laboratory of Allergic Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892; and.
Glenn
G
Cruse
Laboratory of Molecular Immunology, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892.
Michael A
MA
Beaven
Laboratory of Allergic Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892; and.
Arnold
A
Kirshenbaum
Laboratory of Allergic Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892; and.
Dean D
DD
Metcalfe
Laboratory of Allergic Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892; and.
Alasdair M
AM
Gilfillan
D000199:Actins / Q000378:metabolism; D020013:Calcium Signaling; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D015550:Cell Degranulation / Q000235:genetics / Q000276:immunology*; D002460:Cell Line; D004789:Enzyme Activation; D055785:Gene Knockdown Techniques; D006801:Humans; D008407:Mast Cells / Q000276:immunology* / Q000378:metabolism*; D066329:Protein Aggregates; D021381:Protein Transport; D034622:RNA Interference; D000076226:Rapamycin-Insensitive Companion of mTOR Protein; D017455:Receptors, IgE / Q000378:metabolism*; D015398:Signal Transduction; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism
D000199:Actins; D002352:Carrier Proteins; D066329:Protein Aggregates; C492571:RICTOR protein, human; D000076226:Rapamycin-Insensitive Companion of mTOR Protein; D017455:Receptors, IgE; D058570:TOR Serine-Threonine Kinases