title: Suppression of normal and malignant kit signaling by a bispecific antibody linking kit with CD300a.
abstract: Through its receptor Kit (CD117), stem cell factor (SCF) critically regulates human mast cell (MC) differentiation, survival, priming, and activation. The dominance of SCF in setting these parameters compels stringent contra-regulation to maintain a balanced MC phenotype. We have synthesized a library of bispecific Ab fragments to examine the effect of linking Kit with CD300a. In this study, we report that CD300a exerts a strong inhibitory effect on Kit-mediated SCF-induced signaling, consequently impairing MC differentiation, survival, and activation in vitro. This effect derives from Kit-mediated tyrosine phosphorylation of CD300a and recruitment of the SHIP-1 but not of SH2-containing protein phosphatase 1. CD300a inhibits the constitutive activation of the human leukemic HMC-1 cells but not their survival. Finally, CD300a abrogates the allergic reaction induced by SCF in a murine model of cutaneous anaphylaxis. Our findings highlight CD300a as a novel regulator of Kit in human MC and suggest roles for this receptor as a suppressor of Kit signaling in MC-related disorders.
authors.affiliation: Department of Pharmacology and Experimental Therapeutics, School of Pharmacy, Faculty of Medicine, The Hebrew University of Jerusalem, Israel.
authors.forename: Ido
authors.initials: I
authors.lastname: Bachelet
authors.forename: Ariel
authors.initials: A
authors.lastname: Munitz
authors.forename: Beata
authors.initials: B
authors.lastname: Berent-Maoz
authors.forename: David
authors.initials: D
authors.lastname: Mankuta
authors.forename: Francesca
authors.initials: F
authors.lastname: Levi-Schaffer
mesh_terms: D000707:Anaphylaxis / Q000276:immunology; D000818:Animals; D018033:Antibodies, Bispecific / Q000276:immunology / Q000494:pharmacology*; D015703:Antigens, CD / Q000276:immunology*; D002454:Cell Differentiation / Q000187:drug effects / Q000276:immunology; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects / Q000276:immunology; D004195:Disease Models, Animal; D006801:Humans; D007152:Immunologic Capping / Q000187:drug effects* / Q000276:immunology; D008407:Mast Cells / Q000276:immunology*; D051379:Mice; D010766:Phosphorylation / Q000187:drug effects; D019009:Proto-Oncogene Proteins c-kit / Q000276:immunology*; D011971:Receptors, Immunologic / Q000276:immunology*; D015398:Signal Transduction / Q000187:drug effects* / Q000276:immunology; D019089:Stem Cell Factor / Q000276:immunology
chemical_list: D018033:Antibodies, Bispecific; D015703:Antigens, CD; C515070:CD300A protein, human; D011971:Receptors, Immunologic; D019089:Stem Cell Factor; D019009:Proto-Oncogene Proteins c-kit