Interleukin-2-dependent phosphorylation of the retinoblastoma-susceptibility-gene product p110-115RB in human T-cells.
The state of phosphorylation of the retinoblastoma-susceptibility gene product, p110-115RB, is thought to have fundamental importance in controlling the progression of the cell through the cell cycle. We have studied RB phosphorylation in human T-cells in the context of T-cell activation, stimulated by phytohaemagglutinin (PHA) and interleukin-2 (IL-2). We show that, of the signals associated with T-cell activation, only signals that directly lead to movement into S phase of the cell cycle are capable of stimulating RB phosphorylation. Cyclosporin A (CsA), a potent inhibitor of IL-2 synthesis and cellular proliferation, blocked RB phosphorylation, and this was recovered with exogenous IL-2, indicating a direct involvement of IL-2 in controlling RB phosphorylation. We found that PHA did not stimulate RB phosphorylation within 10 h of treatment, but IL-2 could effectively stimulate RB phosphorylation within 2 h, and this approached a maximum within 8-10 h of IL-2 treatment. Further, by using actinomycin D to inhibit new gene transcription following IL-2 stimulation, we found that early-cell-cycle phosphorylation of RB required IL-2-stimulated gene transcription. From these data we conclude that, in human T-cells, RB phosphorylation is not directly associated with T-cell receptor-mediated events, but requires the interaction of IL-2 and new gene transcription following IL-2 stimulation.
Evans
G A
GA
Program Resources Inc./DynCorp, National Cancer Institute, Frederick, MD 21702-1201.
Wahl
L M
LM
Farrar
W L
WL
D002453:Cell Cycle / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D016572:Cyclosporine / Q000494:pharmacology; D003609:Dactinomycin / Q000494:pharmacology; D016161:Genes, Retinoblastoma / Q000235:genetics; D006801:Humans; D007376:Interleukin-2 / Q000494:pharmacology* / Q000502:physiology; D008213:Lymphocyte Activation / Q000187:drug effects / Q000502:physiology; D008934:Mitogens / Q000494:pharmacology; D009687:Nuclear Proteins / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D016160:Retinoblastoma Protein / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D013268:Stimulation, Chemical; D013601:T-Lymphocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*
D007376:Interleukin-2; D008934:Mitogens; D009687:Nuclear Proteins; D016160:Retinoblastoma Protein; D003609:Dactinomycin; D016572:Cyclosporine