Deregulation of specific E2F complexes by the v-mos oncogene.
The product of the c-mos proto-oncogene is a protein kinase that is normally expressed in germ cells and functions during oocyte maturation. It has been shown, however, that inappropriate expression of either the viral or cellular mos gene can induce neoplastic progression in somatic cells. Furthermore, v-mos-transformed NIH3T3 cells will undergo arrest of proliferation in early G1 upon serum withdrawal but are unable to appropriately down-regulate cell cycle regulatory proteins, such as cyclin and cdc2 proteins, that normally are down-regulated in quiescent, untransformed NIH3T3 cells. Since the levels of these proteins are partially transcriptionally controlled, we investigated whether there were alterations in the expression of E2F and AP-1 transcription factor complexes. Indeed, the putative G0/G1-specific p130-E2F complex that is normally observed during low serum-induced cell cycle arrest in NIH3T3 cells is not present in serum starved v-mos-transformed cells. Instead, G1-phase arrested v-mos-transformed cells stably express two E2F protein complexes that are normally observed only during S-phase in untransformed cells. The elevation of these complexes in arrested v-mos-transformed cells may be the cause of the transcriptional activation of the E2F-regulated genes cdc2, DHFR, cyclin A, and E2F1 seen in serum starved v-mos-transformed cells. In addition, there are high levels of AP-1 DNA binding activity in serum starved v-mos-transformed cells compared to very low amounts in nontransformed cells. This altered regulation of transcription factor complexes and cell cycle control proteins upon serum withdrawal may provide a mechanism for the uncontrolled cell growth associated with neoplastic transformation induced by certain proto-oncogenes.
Afshari
C A
CA
Duke University Medical Center, Department of Medicine and Center for the Study of Aging and Human Development and Durham VA a Veterans Administration Medical Center, North Carolina 27705, USA.
Rhodes
N
N
Paules
R S
RS
Mudryj
M
M
D016475:3T3 Cells / Q000502:physiology; D000818:Animals; D042846:CDC2-CDC28 Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002352:Carrier Proteins; D002453:Cell Cycle / Q000235:genetics*; D018797:Cell Cycle Proteins; D002455:Cell Division / Q000235:genetics; D002461:Cell Line, Transformed; D016895:Culture Media, Serum-Free; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D016213:Cyclins / Q000378:metabolism; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; D016193:G1 Phase / Q000235:genetics; D017930:Genes, Reporter; D016258:Genes, mos; D051379:Mice; D009687:Nuclear Proteins / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D000090063:Proto-Oncogene Mas; D056465:Retinoblastoma-Binding Protein 1; D050720:Retinoblastoma-Like Protein p107; D016196:S Phase / Q000502:physiology; D018808:Transcription Factor AP-1 / Q000378:metabolism; D050680:Transcription Factor DP1; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic
C533431:Arid4a protein, mouse; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D016895:Culture Media, Serum-Free; D016213:Cyclins; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; C493754:E2f1 protein, mouse; C000715470:MAS1 protein, human; D009687:Nuclear Proteins; D000090063:Proto-Oncogene Mas; C489485:Rbl1 protein, mouse; D056465:Retinoblastoma-Binding Protein 1; D050720:Retinoblastoma-Like Protein p107; D018808:Transcription Factor AP-1; D050680:Transcription Factor DP1; D014157:Transcription Factors; D017346:Protein Serine-Threonine Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D042846:CDC2-CDC28 Kinases; C495893:Cdk2 protein, mouse; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases