Constitutively expressed c-myb abrogates the requirement for insulinlike growth factor 1 in 3T3 fibroblasts.
The proto-oncogene c-myb, whose expression is usually limited to cells of the hematopoietic lineages, can be expressed in fibroblasts if placed under the control of a constitutive promoter, such as the simian virus SV40 early promoter. 3T3 cells carrying a constitutively expressed human c-myb were found to grow in 1% serum or in a serum-free, platelet-derived growth factor-supplemented medium, whereas the parent cell line, BALB/c 3T3, needed insulinlike growth factor 1 (IGF-1) in addition to platelet-derived growth factor for growth. myb-carrying cells, however, could not grow in platelet-poor plasma. In fibroblasts, therefore, a constitutively expressed c-myb can abrogate the requirement for platelet-poor plasma or IGF-1. When 3T3 cells constitutively expressed both c-myc and c-myb, they could grow in serum-free medium without added growth factors. The ability of c-myb to abrogate in fibroblasts the IGF-1 requirement seems to be due to its ability to induce overexpression of IGF-1, as indicated by an increase in steady-state levels of IGF-1 mRNA. These results have some important implications; for instance, they suggest a commonality of pathways for entry into S phase in different cell types and the possibility of a myb-like or myb-equivalent gene product of critical importance for entry of fibroblasts into S phase.
Travali
S
S
Department of Pathology, Temple University Medical School, Philadelphia, Pennsylvania 19140.
Reiss
K
K
Ferber
A
A
Petralia
S
S
Mercer
W E
WE
Calabretta
B
B
Baserga
R
R
D000818:Animals; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D007700:Kinetics; D051379:Mice; D008807:Mice, Inbred BALB C; D010957:Plasmids; D011505:Protein-Tyrosine Kinases / Q000235:genetics; D000090063:Proto-Oncogene Mas; D011518:Proto-Oncogene Proteins / Q000235:genetics* / Q000302:isolation & purification; D020598:Proto-Oncogene Proteins c-myb; D011519:Proto-Oncogenes; D014162:Transfection
C000715470:MAS1 protein, human; D000090063:Proto-Oncogene Mas; D011518:Proto-Oncogene Proteins; D020598:Proto-Oncogene Proteins c-myb; D007334:Insulin-Like Growth Factor I; D011505:Protein-Tyrosine Kinases