Phosphorylation and high level expression of Fra-2 in v-src transformed cells: a pathway of activation of endogenous AP-1.
Chicken embryo fibroblasts (CEF) transformed with v-src were previously reported to revert to normal phenotype after the introduction of dominant-negative mutants of Fos or Jun, indicating that endogenous AP-1 activity is essential for the cellular transformation. The major changes in the expression levels of fos and jun family genes induced by v-src were the elevation of fra-2 and c-jun transcripts. We show here that extensive phosphorylation of the AP-1 component Fra-2 is a major qualitative change in v-src transformed CEF and that several Ser and Thr residues in a C-terminal region of Fra-2 (amino acids 266-323) are phosphorylated specifically. The induced kinase activity was detected at the position of 42 kDa by in gel kinase assay using the Fra-2 C-terminal region as a substrate, and it was identified as chicken ERK2. JNK1 and JNK2, other members of the MAP kinase family, were not significantly activated in v-src transformed CEF and Fra-2 was not a good substrate for JNKs. fra-2 promoter analysis indicated that this promoter activity is elevated in v-src transformed CEF via two AP-1 binding sites and CRE-like sequence. We propose that phosphorylation of Fra-2 by ERK2 converts it from an inefficient transcriptional activator to an active one and further that fra-2 expression is autoregulated in response to the phosphorylation status of its gene product.
Murakami
M
M
Department of Gene Regulation, Institute of Medical Science, University of Tokyo, Minato-ku, Japan.
Sonobe
M H
MH
Ui
M
M
Kabuyama
Y
Y
Watanabe
H
H
Wada
T
T
Handa
H
H
Iba
H
H
D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D002461:Cell Line, Transformed; D002642:Chick Embryo; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004789:Enzyme Activation; D051921:Fos-Related Antigen-2; D016391:Genes, src; D048031:JNK Mitogen-Activated Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; D020928:Mitogen-Activated Protein Kinases; D010766:Phosphorylation; D018808:Transcription Factor AP-1 / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism*
D004268:DNA-Binding Proteins; D051921:Fos-Related Antigen-2; D018808:Transcription Factor AP-1; D014157:Transcription Factors; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D048031:JNK Mitogen-Activated Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; D020928:Mitogen-Activated Protein Kinases