title: Commitment point during G0-->G1 that controls entry into the cell cycle.
abstract: Initiation of T-lymphocyte-mediated immune responses involves two cellular processes: entry into the cell cycle (G(0)-->G(1)) for clonal proliferation and coordinated changes in surface and secreted molecules that mediate effector functions. However, a point during G(0)-->G(1) beyond which T cells are committed to enter the cell cycle has not been defined. We define here a G(0)-->G(1) commitment point that occurs 3 to 5 h after CD3 and CD28 stimulation of human CD4 or CD8 T cells. Transition through this point requires cdk6/4-cyclin D, since inhibition with TAT-p16(INK4A) during the first 3 to 5 h prevents cell cycle entry and maintains both naive and memory T cells in G(0). Transition through the G(0)-->G(1) commitment point is also necessary for T cells to increase in size, i.e., to enter the cellular growth cycle. However, transition through this point is not required for the induction of effector functions. These can be initiated while cells are maintained in G(0) with TAT-p16(INK4A). We have termed this quiescent, activated state G(0(A)). Our data provide proof of the principle that entry of T cells into the cell cycle and cellular growth cycles are coupled at the G(0)-->G(1) commitment point but that these processes can be uncoupled from the early expression of molecules of effector functions.
authors.affiliation: Department of Haematological Medicine, Leukaemia Sciences Laboratories, Guy's, King's and St. Thomas' School of Medicine, London SE5 9NU, United Kingdom.
authors.forename: Nicholas C
authors.initials: NC
authors.lastname: Lea
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Orr
authors.forename: Kai
authors.initials: K
authors.lastname: Stoeber
authors.forename: Gareth H
authors.initials: GH
authors.lastname: Williams
authors.forename: Eric W-F
authors.initials: EW
authors.lastname: Lam
authors.forename: Mohammad A A
authors.initials: MA
authors.lastname: Ibrahim
authors.forename: Ghulam J
authors.initials: GJ
authors.lastname: Mufti
authors.forename: N Shaun B
authors.initials: NS
authors.lastname: Thomas
mesh_terms: D000906:Antibodies / Q000494:pharmacology; D018106:CD28 Antigens / Q000378:metabolism; D017252:CD3 Complex / Q000378:metabolism; D015496:CD4-Positive T-Lymphocytes / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D018414:CD8-Positive T-Lymphocytes / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D002453:Cell Cycle / Q000187:drug effects / Q000502:physiology*; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology; D002455:Cell Division / Q000187:drug effects / Q000502:physiology; D002469:Cell Separation; D002478:Cells, Cultured; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000235:genetics; D004791:Enzyme Inhibitors / Q000494:pharmacology; D016193:G1 Phase / Q000187:drug effects / Q000502:physiology; D015696:Gene Products, tat / Q000235:genetics; D006801:Humans; D007376:Interleukin-2 / Q000096:biosynthesis; D008213:Lymphocyte Activation / Q000187:drug effects / Q000502:physiology; D008934:Mitogens / Q000494:pharmacology; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis / Q000235:genetics / Q000494:pharmacology; D016192:Resting Phase, Cell Cycle / Q000187:drug effects / Q000502:physiology; D014161:Transduction, Genetic / Q000379:methods
chemical_list: D000906:Antibodies; D018106:CD28 Antigens; D017252:CD3 Complex; D019941:Cyclin-Dependent Kinase Inhibitor p16; D004791:Enzyme Inhibitors; D015696:Gene Products, tat; D007376:Interleukin-2; D008934:Mitogens; D011993:Recombinant Fusion Proteins