title: Suppressor of cytokine signaling 1 regulates IL-15 receptor signaling in CD8+CD44high memory T lymphocytes.
abstract: T lymphocyte survival, proliferation, and death in the periphery are dependent on several cytokines. Many of these cytokines induce the expression of suppressor of cytokine signaling-1 (SOCS1), a feedback inhibitor of JAK kinases. However, it is unclear whether the cytokines that regulate T lymphocyte homeostasis are critically regulated by SOCS1 in vivo. Using SOCS1(-/-)IFN-gamma(-/-) mice we show that SOCS1 deficiency causes a lymphoproliferative disorder characterized by decreased CD4/CD8 ratio due to chronic accumulation of CD8+CD44(high) memory phenotype T cells. SOCS1-deficient CD8+ T cells express elevated levels of IL-2Rbeta, show increased proliferative response to IL-15 and IL-2 in vitro, and undergo increased bystander proliferation and vigorous homeostatic expansion in vivo. Sorted CD8+CD44(high) T cells from SOCS1(-/-)IFN-gamma(-/-) mice respond 5 times more strongly than control cells, indicating that SOCS1 is a critical regulator of IL-15R signaling. Consistent with this idea, IL-15 stimulates sustained STAT5 phosphorylation in SOCS1-deficient CD8+ T cells. IL-15 strongly induces TNF-alpha production in SOCS1-deficient CD8+ T cells, indicating that SOCS1 is also a critical regulator of CD8+ T cell activation by IL-15. However, IL-15 and IL-2 induce comparable levels of Bcl-2 and Bcl-x(L) in SOCS1-deficient and SOCS1-sufficient CD8+ T cells, suggesting that cytokine receptor signals required for inducing proliferation and cell survival signals are not identical. These results show that SOCS1 differentially regulates common gamma-chain cytokine signaling in CD8+ T cells and suggest that CD8+ T cell homeostasis is maintained by distinct mechanisms that control cytokine-mediated survival and proliferation signals.
authors.affiliation: Ontario Cancer Institute, Princess Margaret Hospital, University Health Network, 610 University Avenue, Toronto, Ontario, Canada M5G 2M9.
authors.forename: Subburaj
authors.initials: S
authors.lastname: Ilangumaran
authors.forename: Sheela
authors.initials: S
authors.lastname: Ramanathan
authors.forename: Jose
authors.initials: J
authors.lastname: La Rose
authors.forename: Philippe
authors.initials: P
authors.lastname: Poussier
authors.forename: Robert
authors.initials: R
authors.lastname: Rottapel
mesh_terms: D000818:Animals; D024201:Bystander Effect / Q000235:genetics / Q000276:immunology; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology / Q000378:metabolism* / Q000473:pathology; D002352:Carrier Proteins / Q000235:genetics / Q000502:physiology*; D002455:Cell Division / Q000235:genetics / Q000276:immunology; D002999:Clone Cells; D004306:Dose-Response Relationship, Immunologic; D018398:Homeodomain Proteins / Q000235:genetics; D006706:Homeostasis / Q000235:genetics / Q000276:immunology; D018960:Hyaluronan Receptors / Q000096:biosynthesis*; D007156:Immunologic Memory / Q000235:genetics; D016130:Immunophenotyping; D007371:Interferon-gamma / Q000172:deficiency / Q000235:genetics; D019409:Interleukin-15 / Q000494:pharmacology; D008232:Lymphoproliferative Disorders / Q000235:genetics / Q000276:immunology / Q000473:pathology; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D053647:Receptors, Interleukin-15; D015375:Receptors, Interleukin-2 / Q000037:antagonists & inhibitors* / Q000502:physiology*; D012097:Repressor Proteins; D015398:Signal Transduction / Q000235:genetics / Q000276:immunology*; D000071222:Suppressor of Cytokine Signaling 1 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D016176:T-Lymphocyte Subsets / Q000276:immunology / Q000378:metabolism* / Q000473:pathology
chemical_list: D002352:Carrier Proteins; D018398:Homeodomain Proteins; D018960:Hyaluronan Receptors; C508025:Il15ra protein, mouse; D019409:Interleukin-15; D053647:Receptors, Interleukin-15; D015375:Receptors, Interleukin-2; D012097:Repressor Proteins; C491590:Socs1 protein, mouse; D000071222:Suppressor of Cytokine Signaling 1 Protein; D050826:Suppressor of Cytokine Signaling Proteins; C064658:RAG-1 protein; D007371:Interferon-gamma