Suppression of apoptosis in a cytotoxic T-cell line by interleukin 2-mediated gene transcription and deregulated expression of the protooncogene bcl-2.
Absence of interleukin 2 (IL-2) from IL-2-dependent cells, such as the cytotoxic T-cell line CTLL2, causes DNA fragmentation and programmed cell death (apoptosis). We found that, upon initiation, DNA degradation proceeds rapidly. IL-2-deprived CTLL2 cells can be rescued from apoptosis by the addition of IL-2 2 h prior to the onset of detectable DNA breakdown. Addition of inhibitors of transcription with IL-2 abolished the IL-2-mediated rescue of CTLL2 cells. Thus it appears that IL-2-mediated gene transcription is necessary for survival. Deregulated expression of a protooncogene, bcl-2, inhibits apoptosis of cells dependent on other hematopoietic growth factors. To determine whether bcl-2 was active in CTLL2 cells, we transfected CTLL2 cells with a plasmid containing bcl-2 cDNA expressed under the metallothionein promoter and observed prolonged survival of the transfected cells upon IL-2 deprivation. Cell growth, however, was arrested in the G0/G1 or G2/M phases of the cell cycle. The prolonged survival of bcl-2 transfectants allowed the analysis of endogenous bcl-2 mRNA levels by Northern blot analysis. The expression of endogenous bcl-2 was down-regulated within 8 h of IL-2 withdrawal and was not detected after 3 days. Addition of IL-2 induced endogenous bcl-2 expression within 8 h. Full recovery of bcl-2 expression was achieved by 24 h after IL-2 addition. We conclude that the survival of death-prone CTLL2 cells may be viewed as IL-2-dependent suppression of suicide, probably by the IL-2-induced expression of the cellular bcl-2 gene.
Deng
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Department of Microbiology and Immunology, University of Miami School of Medicine, FL 33101.
Podack
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D000199:Actins / Q000235:genetics; D000546:Amanitins / Q000494:pharmacology; D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D001483:Base Sequence; D015152:Blotting, Northern; D002453:Cell Cycle; D002460:Cell Line; D003513:Cycloheximide / Q000494:pharmacology; D003609:Dactinomycin / Q000494:pharmacology; D015870:Gene Expression / Q000187:drug effects; D016259:Genes, myc / Q000187:drug effects; D007376:Interleukin-2 / Q000494:pharmacology*; D007700:Kinetics; D051379:Mice; D008969:Molecular Sequence Data; D009838:Oligodeoxyribonucleotides; D016133:Polymerase Chain Reaction / Q000379:methods; D011505:Protein-Tyrosine Kinases / Q000235:genetics / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000235:genetics* / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2; D011519:Proto-Oncogenes / Q000187:drug effects*; D011994:Recombinant Proteins / Q000494:pharmacology; D013602:T-Lymphocytes, Cytotoxic / Q000187:drug effects / Q000276:immunology / Q000502:physiology*; D013997:Time Factors; D014158:Transcription, Genetic / Q000187:drug effects*; D014162:Transfection
D000199:Actins; D000546:Amanitins; D007376:Interleukin-2; D009838:Oligodeoxyribonucleotides; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D011994:Recombinant Proteins; D003609:Dactinomycin; D003513:Cycloheximide; D011505:Protein-Tyrosine Kinases