title: Suppressor of cytokine signaling 1 regulates an endogenous inhibitor of a mast cell protease.
abstract: Suppressor of cytokine signaling 1 (SOCS1) is a negative regulator of c-Kit and interleukin-3 (IL-3) receptor signaling. We examined the role of SOCS1 in regulating IL-3-induced cell growth of primary bone marrow-derived mast cells (BMMCs) from SOCS1-/- mice. Instead of showing increased proliferation, SOCS1-deficient BMMCs responded poorly to IL-3 and stem cell factor. SOCS1-/- BMMCs showed increased apoptosis and defective cell cycle entry. We show that the growth retardation of SOCS1-/- BMMCs was due to a cell intrinsic defect. Protein tyrosine phosphorylation following IL-3 stimulation was markedly diminished in SOCS1-/- BMMCs. Intriguingly, JAK2 and STAT5 proteins were selectively diminished in SOCS1-/- BMMCs, which also showed lower molecular mass products of p85 and Vav suggesting proteolytic degradation. Incubation of the SOCS1-/- BMMC lysate with STAT5, p85, and Vav immunoprecipitated from SOCS1+/+ cells directly demonstrated the dysregulated proteolytic activity in SOCS1-/- BMMCs. The proteolytic activity in SOCS1-/- BMMCs was selectively inhibited by phenylmethylsulfonyl fluoride and soybean trypsin inhibitor, suggesting that the protease regulated by SOCS1 is a tryptase. The dysregulated tryptase in SOCS1-/- BMMCs is unlikely to be mMCP6 or mMCP7, because the enzyme activity was not inhibited by Polybrene but was inhibited by normal mouse plasma. SOCS1+/+ BMMC lysate inhibited the proteolytic activity present in SOCS1-/- BMMC lysate, indicating that SOCS1-/- BMMCs lack an endogenous protease inhibitor. These results show that SOCS1 is required for the expression and/or stability of an endogenous protease inhibitor, which protects mast cells from their own proteolytic enzymes.
authors.affiliation: Ontario Cancer Institute, Princess Margaret Hospital, University Health Network, 610 University Avenue, Toronto M5G 2M9, Canada.
authors.forename: Subburaj
authors.initials: S
authors.lastname: Ilangumaran
authors.forename: Dina
authors.initials: D
authors.lastname: Finan
authors.forename: Jason
authors.initials: J
authors.lastname: Raine
authors.forename: Robert
authors.initials: R
authors.lastname: Rottapel
mesh_terms: D000818:Animals; D017209:Apoptosis; D001854:Bone Marrow Cells / Q000166:cytology; D002352:Carrier Proteins / Q000235:genetics / Q000502:physiology*; D002453:Cell Cycle; D002455:Cell Division / Q000187:drug effects; D010450:Endopeptidases / Q000378:metabolism; D007377:Interleukin-3 / Q000494:pharmacology; D008407:Mast Cells / Q000166:cytology* / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D011480:Protease Inhibitors / Q000378:metabolism; D012097:Repressor Proteins; D012697:Serine Endopeptidases / Q000378:metabolism*; D015398:Signal Transduction; D019089:Stem Cell Factor / Q000494:pharmacology; D000071222:Suppressor of Cytokine Signaling 1 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D053802:Tryptases
chemical_list: D002352:Carrier Proteins; D007377:Interleukin-3; D011480:Protease Inhibitors; D012097:Repressor Proteins; C491590:Socs1 protein, mouse; D019089:Stem Cell Factor; D000071222:Suppressor of Cytokine Signaling 1 Protein; D050826:Suppressor of Cytokine Signaling Proteins; C509190:Tpsb2 protein, mouse; D010450:Endopeptidases; D012697:Serine Endopeptidases; C509222:Tpsab1 protein, mouse; D053802:Tryptases