Analysis of AP-1 function in cellular transformation pathways.
To understand the role of endogenous AP-1 activity in cellular transformation induced by oncogenes, we have made use of a fos mutant (supfos-1) and a jun mutant (supjun-1), either of which can function as a transdominant inhibitor of AP-1-mediated transcriptional regulation. Chicken embryo fibroblasts (CEF) infected with a series of transforming retroviruses were doubly infected with retrovirus carrying supfos-1 or supjun-1, and suppression of cellular transformation was monitored in terms of reversion to normal cellular morphology or acquisition of anchorage-dependent growth. Cellular transformation induced by several exogenously expressed transforming genes of the fos or jun family was efficiently suppressed, as expected. CEF transformed by v-src, v-yes, v-fps, c-Ha-ras, and N-terminally truncated c-raf were also induced to revert to the normal phenotype by these transdominant mutants, suggesting that functional transcription factor AP-1 activity is essential for the cellular transformation induced by these oncogenes. The suppression is not attributable to nonspecific inhibition of cellular proliferation, because CEF transformed by v-ros or v-myc were not induced to revert to the normal phenotype. We next analyzed changes in all known components of chicken AP-1 induced by v-src, c-Ha-ras, or activated c-raf transformation. The levels of both Fra-2 and c-Jun expression were elevated two- to fourfold, and hyperphosphorylation of Fra-2 was also observed. We further showed that Fra-2-c-Jun heterodimer is mainly responsible for the elevated AP-1 DNA-binding activity in these transformed cells, and we propose that this heterodimer play a crucial role in the transformation induced by these oncogenes.
Suzuki
T
T
Department of Tumor Virus Research, University of Tokyo, Japan.
Murakami
M
M
Onai
N
N
Fukuda
E
E
Hashimoto
Y
Y
Sonobe
M H
MH
Kameda
T
T
Ichinose
M
M
Miki
K
K
Iba
H
H
D000818:Animals; D001483:Base Sequence; D002461:Cell Line, Transformed; D002471:Cell Transformation, Neoplastic / Q000235:genetics*; D002642:Chick Embryo; D017931:DNA Primers / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D051921:Fos-Related Antigen-2; D015870:Gene Expression; D006801:Humans; D008969:Molecular Sequence Data; D009154:Mutation; D009857:Oncogenes; D016755:Proto-Oncogene Proteins c-jun / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D011519:Proto-Oncogenes; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic
D017931:DNA Primers; D004268:DNA-Binding Proteins; C497872:FOSL2 protein, human; D051921:Fos-Related Antigen-2; D016755:Proto-Oncogene Proteins c-jun; D014157:Transcription Factors