cAMP antagonizes interleukin 2-promoted T-cell cycle progression at a discrete point in early G1.
T lymphocytes are stimulated to proliferate in an autocrine/paracrine manner by the lymphokine interleukin 2 (IL-2). In seeking further insight into the mechanisms by which IL-2 induces progression of T cells through the G1 phase of the cell cycle, studies were performed with agents that increase cellular adenosine 3',5'-cyclic monophosphate (cAMP), a well-known inhibitor of lymphocyte growth. The addition of dibutyryl-cAMP, cholera toxin, forskolin, or 3-isobutyl-1-methylxanthine to an IL-2-dependent murine T-cell line evoked a dose-related suppression of S-phase transition without affecting cellular viability. Moreover, elevation of cAMP levels led to an accumulation of uniformly small cells, suggesting an arrest in early G1. Consistent with these findings, dibutyryl-cAMP inhibited the incorporation of both [3H]-uridine and [3H]thymidine by IL-2-stimulated, synchronized normal human T cells. Furthermore, maximal inhibition occurred during early G1, as indicated by experiments where the addition of dibutyryl-cAMP was delayed with respect to IL-2 stimulation. Quantitative flow cytometric analysis of RNA and DNA content of IL-2-stimulated cells affirmed that increased cAMP inhibits RNA accumulation and S-phase transition. In addition, exposure of IL-2-dependent, asynchronously proliferating normal human T cells to dibutyryl-cAMP resulted in uniform growth arrest in early G1, the point at which cycling T cells accumulate when they are deprived of IL-2. These results indicate that increased cAMP inhibits G1 progression stimulated by IL-2 and provide a rationale for the use of cAMP analogues as pharmacologic probes for the dissection of molecular events occurring during IL-2 signaling and T-cell G1 transit. They also suggest the possibility of therapeutic immunosuppression by a combination of agents that act at different stages of the T-cell cycle.
Johnson
K W
KW
Department of Medicine, Dartmouth Medical School, Hanover, NH 03756.
Davis
B H
BH
Smith
K A
KA
D003994:Bucladesine / Q000494:pharmacology; D002455:Cell Division / Q000187:drug effects; D000242:Cyclic AMP / Q000502:physiology*; D005434:Flow Cytometry; D006801:Humans; D007376:Interleukin-2 / Q000494:pharmacology*; D007399:Interphase / Q000187:drug effects*; D011971:Receptors, Immunologic / Q000032:analysis; D015375:Receptors, Interleukin-2
D007376:Interleukin-2; D011971:Receptors, Immunologic; D015375:Receptors, Interleukin-2; D003994:Bucladesine; D000242:Cyclic AMP