Resistance to apoptosis in CTLL-2 cells constitutively expressing c-Myb is associated with induction of BCL-2 expression and Myb-dependent regulation of bcl-2 promoter activity.
c-Myb, the cellular homologue of the transforming gene of the avian myeloblastosis virus, is preferentially expressed in all hematopoietic lineages, including T and B lymphocyte lineages. In T lymphocytes, c-Myb expression appears to be required for cell cycle progression and proliferation. To further investigate the role of c-Myb in T cell proliferation and survival, interleukin (IL) 2-dependent CTLL-2 cells were transfected with a constitutively active c-myb or with a c-myb antisense construct able to down-regulate endogenous Myb levels, and the transfectants were assessed for proliferation and survival in low concentrations of IL-2 and for susceptibility to dexamethasone-induced apoptosis. Compared with control cells, CTLL-2 cells constitutively expressing c-Myb proliferate in low concentrations of IL-2 and are less susceptible to apoptosis induced by IL-2 deprivation or treatment with dexamethasone. In contrast, cells transfected with an antisense c-myb construct do not proliferate in low concentrations of IL-2 and undergo apoptosis upon IL-2 deprivation or dexamethasone treatment more rapidly than parental cells. Overexpression of c-Myb was accompanied by up-regulation of BCL-2 expression. In transient transfection assays, the murine bcl-2 promoter was efficiently transactivated by c-Myb, but such effect was observed also in cells transfected with a DNA binding-deficient c-myb construct. Moreover, in gel retardation assays, a 38-bp oligomer in the shortest bcl-2 promoter segment regulated by c-Myb formed a specific complex with nuclear extracts from c-Myb-transfected CTLL-2 cells. Thus, these results strongly suggest that c-Myb, in addition to regulating T cell proliferation, protects T lymphocytes from apoptosis by induction of BCL-2 expression, which involves a c-Myb-dependent mechanism of promoter regulation.
Salomoni
P
P
Department of Microbiology and Immunology, Thomas Jefferson University, Philadelphia, PA 19107-6799, USA.
Perrotti
D
D
Martinez
R
R
Franceschi
C
C
Calabretta
B
B
D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000235:genetics*; D002460:Cell Line; D015500:Chloramphenicol O-Acetyltransferase / Q000235:genetics; D006224:Cricetinae; D003907:Dexamethasone / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000235:genetics*; D019254:Genes, bcl-2; D007376:Interleukin-2 / Q000378:metabolism; D016376:Oligonucleotides, Antisense; D009857:Oncogenes; D011401:Promoter Regions, Genetic; D015398:Signal Transduction; D015533:Transcriptional Activation; D014162:Transfection
D007376:Interleukin-2; D016376:Oligonucleotides, Antisense; D003907:Dexamethasone; D015500:Chloramphenicol O-Acetyltransferase