title: Bcl-2-mediated drug resistance: inhibition of apoptosis by blocking nuclear factor of activated T lymphocytes (NFAT)-induced Fas ligand transcription.
abstract: Bcl-2 inhibits apoptosis induced by a variety of stimuli, including chemotherapy drugs and glucocorticoids. It is generally accepted that Bcl-2 exerts its antiapoptotic effects mainly by dimerizing with proapoptotic members of the Bcl-2 family such as Bax and Bad. However, the mechanism of the antiapoptotic effects is unclear. Paclitaxel and other drugs that disturb microtubule dynamics kill cells in a Fas/Fas ligand (FasL)-dependent manner; antibody to FasL inhibits paclitaxel-induced apoptosis. We have found that Bcl-2 overexpression leads to the prevention of chemotherapy (paclitaxel)-induced expression of FasL and blocks paclitaxel-induced apoptosis. The mechanism of this effect is that Bcl-2 prevents the nuclear translocation of NFAT (nuclear factor of activated T lymphocytes, a transcription factor activated by microtubule damage) by binding and sequestering calcineurin, a calcium-dependent phosphatase that must dephosphorylate NFAT to move to the nucleus. Without NFAT nuclear translocation, the FasL gene is not transcribed. Thus, it appears that paclitaxel and other drugs that disturb microtubule function kill cells at least in part through the induction of FasL. Furthermore, Bcl-2 antagonizes drug-induced apoptosis by inhibiting calcineurin activation, blocking NFAT nuclear translocation, and preventing FasL expression. The effects of Bcl-2 can be overcome, at least partially, through phosphorylation of Bcl-2. Phosphorylated Bcl-2 cannot bind calcineurin, and NFAT activation, FasL expression, and apoptosis can occur after Bcl-2 phosphorylation.
authors.affiliation: Laboratory of Immunology, National Institute on Aging, National Institutes of Health, Baltimore, Maryland 21224-6825, USA. rakeshs@vax.grc.nia.nih.gov
authors.forename: R K
authors.initials: RK
authors.lastname: Srivastava
authors.forename: C Y
authors.initials: CY
authors.lastname: Sasaki
authors.forename: J M
authors.initials: JM
authors.lastname: Hardwick
authors.forename: D L
authors.initials: DL
authors.lastname: Longo
mesh_terms: D017209:Apoptosis / Q000187:drug effects / Q000235:genetics* / Q000502:physiology*; D001665:Binding Sites; D001693:Biological Transport, Active; D019703:Calcineurin / Q000378:metabolism; D002467:Cell Nucleus / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004351:Drug Resistance / Q000235:genetics; D053222:Fas Ligand Protein; D019254:Genes, bcl-2; D006801:Humans; D019169:Jurkat Cells; D008213:Lymphocyte Activation; D008562:Membrane Glycoproteins / Q000235:genetics* / Q000378:metabolism; D008954:Models, Biological; D050778:NFATC Transcription Factors; D009687:Nuclear Proteins; D017239:Paclitaxel / Q000494:pharmacology; D011401:Promoter Regions, Genetic; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000737:chemistry / Q000378:metabolism; D015398:Signal Transduction; D013601:T-Lymphocytes / Q000166:cytology / Q000276:immunology* / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured
chemical_list: D004268:DNA-Binding Proteins; C505661:FASLG protein, human; D053222:Fas Ligand Protein; D008562:Membrane Glycoproteins; D050778:NFATC Transcription Factors; D009687:Nuclear Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D014157:Transcription Factors; D019703:Calcineurin; D017239:Paclitaxel