p120-v-Abl expression overcomes TGF-beta1 negative regulation of c-myc transcription but not cell growth.
Transformation of interleukin-3 dependent (IL-3) 32D-123 myeloid cells by p120-v-Abl produced the factor-independent 32D-abl cell line. In 32D-abl cells, myc expression was found to be significantly higher than in the parental cells and was correlated with increased E2F-1 protein expression and DNA binding ability. Surprisingly, in 32D-abl cells, TGF-beta1, a potent G1/S inhibitor of 32D-123 and 32D-abl cell growth, increased E2F transactivation as shown by increased c-myc promoter-CAT and GAL4-E2F-1 activity. In addition, TGF-beta1 was also found to increase E2F-1 protein levels but had no effect on steady-state retinoblastoma (RB) protein levels or phosphorylation state. In the absence of TGF-beta1, transient expression of RB in v-Abl expressing cells resulted in decreased c-myc transcription, inhibition of GAL4-E2F-1 driven transactivation and inhibition of cellular proliferation. RB and v-Abl were found to physically associate in vivo and in vitro via v-Abl's ATP binding region. In summary, these studies established that in myeloid cells: (1) v-Abl binds RB resulting in increased E2F-1-driven c-myc transcription, and (2) an alternative pathway exists for TGF-beta1-mediated growth inhibition of v-Abl-transformed cells, in which increased rather than decreased E2F-mediated c-myc transcription is observed.
Birchenall-Roberts
M C
MC
Intramural Research Support Program, SAIC Frederick, Maryland 21702, USA.
Kim
S J
SJ
Bertolette
D C
DC
Turley
J M
JM
Fu
T
T
Bang
O S
OS
Kasper
J J
JJ
Yoo
Y D
YD
Ruscetti
F W
FW
D000818:Animals; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D002461:Cell Line, Transformed; D004247:DNA / Q000378:metabolism*; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; D051379:Mice; D016271:Proto-Oncogene Proteins c-myc / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D016160:Retinoblastoma Protein / Q000235:genetics / Q000378:metabolism*; D056465:Retinoblastoma-Binding Protein 1; D050680:Transcription Factor DP1; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000502:physiology*
C533431:Arid4a protein, mouse; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; C493754:E2f1 protein, mouse; D016271:Proto-Oncogene Proteins c-myc; D011993:Recombinant Fusion Proteins; D016160:Retinoblastoma Protein; D056465:Retinoblastoma-Binding Protein 1; D050680:Transcription Factor DP1; D014157:Transcription Factors; D016212:Transforming Growth Factor beta; D004247:DNA