Inactivation of a c-Myb/estrogen receptor fusion protein in transformed primary cells leads to granulocyte/macrophage differentiation and down regulation of c-kit but not c-myc or cdc2.
Primary murine fetal hemopoietic cells were transformed with a fusion protein consisting of the ligand-binding domain of the estrogen receptor and a carboxyl-terminally truncated c-Myb protein (ERMYB). The ERMYB-transformed hemopoietic cells exhibit an immature myeloid phenotype when grown in the presence of beta-estradiol. Upon removal of beta-estradiol, the ERMYB cells display increased adherence, decreased clonogenicity and differentiate to cells exhibiting granulocyte or macrophage morphology. The expression of the c-myc, c-kit, cdc2 and bcl-2 genes, which are putatively regulated by Myb, was investigated in ERMYB cells grown in the presence or absence of beta-estradiol. Neither c-myc nor cdc2 expression was down-regulated after removal of beta-estradiol demonstrating that differentiation is not a consequence of decreased transactivation of these genes by ERMYB. While bcl-2 expression was reduced by 50% in ERMYB cells grown in the absence of beta-estradiol, there was no increase in DNA laddering, suggesting that Myb was not protecting ERMYB cells from apoptosis. In contrast, a substantial (200-fold) decrease in c-kit mRNA level was observed following differentiation of ERMYB cells, and c-kit mRNA could be partially re-induced by the re-addition of beta-estradiol. Furthermore, a reporter construct containing the c-kit promoter was activated when cotransfected with a Myb expression vector, providing further evidence of a role for Myb in the regulation of c-kit.
Hogg
A
A
Hanson Centre for Cancer Research, Institute of Medical and Veterinary Science, Adelaide, South Australia.
Schirm
S
S
Nakagoshi
H
H
Bartley
P
P
Ishii
S
S
Bishop
J M
JM
Gonda
T J
TJ
D000818:Animals; D017209:Apoptosis; D002454:Cell Differentiation / Q000187:drug effects / Q000235:genetics; D002455:Cell Division / Q000187:drug effects; D002461:Cell Line, Transformed; D004247:DNA / Q000096:biosynthesis / Q000737:chemistry; D015536:Down-Regulation / Q000235:genetics*; D004958:Estradiol / Q000172:deficiency / Q000502:physiology; D005333:Fetus; D018816:Genes, cdc; D016259:Genes, myc; D005822:Genetic Vectors / Q000138:chemical synthesis; D006098:Granulocytes / Q000166:cytology*; D006412:Hematopoietic Stem Cells; D008264:Macrophages / Q000166:cytology*; D051379:Mice; D008808:Mice, Inbred CBA; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism; D019009:Proto-Oncogene Proteins c-kit / Q000235:genetics*; D020598:Proto-Oncogene Proteins c-myb; D012333:RNA, Messenger / Q000096:biosynthesis / Q000737:chemistry; D011960:Receptors, Estrogen / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis / Q000378:metabolism*; D012190:Retroviridae / Q000235:genetics; D015534:Trans-Activators / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism
D011518:Proto-Oncogene Proteins; D020598:Proto-Oncogene Proteins c-myb; D012333:RNA, Messenger; D011960:Receptors, Estrogen; D011993:Recombinant Fusion Proteins; D015534:Trans-Activators; D004958:Estradiol; D004247:DNA; D019009:Proto-Oncogene Proteins c-kit