Loss of net as repressor leads to constitutive increased c-fos transcription in cervical cancer cells.
We have investigated the expression of c-fos in cervical carcinoma cells and in somatic cell hybrids derived therefrom. In malignant cells, c-fos was constitutively expressed even after serum starvation. Dissection of the c-fos promoter showed that expression was mainly controlled by the SRE motif, which was active in malignant cells, but repressed in their non-malignant counterparts. Constitutive SRE activity was not mediated by sustained mitogen-activated protein kinase activity but because of inefficient expression of the ternary complex factor Net, which was either very low or even barely discernible. Chromatin immunoprecipitation assays revealed that Net directly binds to the SRE nucleoprotein complex in non-tumorigenic cells, but not in malignant segregants. Small interfering RNA targeted against Net resulted in enhanced c-fos transcription, clearly illustrating its repressor function. Conversely, stable ectopic expression of Net in malignant cells negatively regulated endogenous c-fos, resulting in a disappearance of the c-Fos protein from the AP-1 transcription complex. These data indicate that loss of Net and constitutive c-fos expression appear to be a key event in the transformation of cervical cancer cells.
van Riggelen
Jan
J
Angewandte Tumorvirologie, Deutsches Krebsforschungszentrum, Im Neuenheimer Feld 242, 69120 Heidelberg, Germany.
Buchwalter
Gilles
G
Soto
Ubaldo
U
De-Castro Arce
Johanna
J
zur Hausen
Harald
H
Wasylyk
Bohdan
B
Rösl
Frank
F
D002471:Cell Transformation, Neoplastic / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D005260:Female; D005347:Fibroblasts / Q000166:cytology; D015972:Gene Expression Regulation, Neoplastic; D006367:HeLa Cells; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D008168:Lung / Q000166:cytology; D020935:MAP Kinase Signaling System / Q000502:physiology; D010766:Phosphorylation; D011401:Promoter Regions, Genetic / Q000502:physiology; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism; D016760:Proto-Oncogene Proteins c-fos / Q000235:genetics*; D034741:RNA, Small Interfering; D012097:Repressor Proteins / Q000235:genetics*; D027602:Serum Response Element / Q000502:physiology; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic / Q000502:physiology; D002583:Uterine Cervical Neoplasms / Q000235:genetics* / Q000503:physiopathology; D050807:ets-Domain Protein Elk-1; D050808:ets-Domain Protein Elk-4; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism; D000099169:Fos-Related Antigen 1
D004268:DNA-Binding Proteins; D048049:Extracellular Signal-Regulated MAP Kinases; D048031:JNK Mitogen-Activated Protein Kinases; D011518:Proto-Oncogene Proteins; D016760:Proto-Oncogene Proteins c-fos; D034741:RNA, Small Interfering; D012097:Repressor Proteins; D014157:Transcription Factors; D050807:ets-Domain Protein Elk-1; D050808:ets-Domain Protein Elk-4; D048051:p38 Mitogen-Activated Protein Kinases; D000099169:Fos-Related Antigen 1; C494193:ELK4 protein, human