Activator protein-1 mediates induced but not basal epidermal growth factor receptor gene expression.
BACKGROUND
The epidermal growth factor receptor (EGFR) is expressed at different levels in many cell types and found overexpressed in many cancers. EGFR expression is increased or decreased in response to extracellular stimuli. We examined the effect of increased c-Jun expression on EGFR promoter activity.


METHODS
We used DNAse I foot-printing analysis to determine the binding of activator protein 1 (AP-1) to the promoter region. We also used cotransfection experiments and western blotting analysis to determine the effect of AP-1 family members on EGFR expression.


RESULTS
AP-1 was able to bind to at least seven sites in the EGFR promoter region. Cotransfection of MCF-7 cells with a c-Jun expression vector and the EGFR promoter reporter resulted in a 7-fold increase in promoter activity. JunB, but not c-fos, also enhanced the EGFR promoter activity. An A-Fos-dominant negative shown to inhibit Jun-dependent transactivation was able to prevent c-Jun induction of the promoter activity, but only slightly decreased the basal activity of the promoter. Furthermore, the A-Fos dominant negative was able to inhibit phorbol ester induction of the EGFR promoter. Examination of EGFR expression of MCF-7 stable cell lines that overexpress c-Jun revealed an increase in EGFR expression. Additionally, a cisplatin-resistant cell line, A2780/CP70, which has an increase in AP-1 activity compared with the parental cell line, A2780, was found to have an increase in EGFR level.


CONCLUSIONS
These results indicate that AP-1 can act to increase the expression of EGFR and may play a role in upregulation of EGFR in cancer cells.
Johnson
A C
AC
Laboratory of Molecular Biology, Division of Basic Sciences, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892-4255, USA. aj2e@nih.gov
Murphy
B A
BA
Matelis
C M
CM
Rubinstein
Y
Y
Piebenga
E C
EC
Akers
L M
LM
Neta
G
G
Vinson
C
C
Birrer
M
M
D016475:3T3 Cells; D000818:Animals; D001943:Breast Neoplasms / Q000235:genetics; D018983:DNA Footprinting; D003850:Deoxyribonuclease I; D066246:ErbB Receptors / Q000096:biosynthesis / Q000235:genetics*; D005260:Female; D005786:Gene Expression Regulation; D006801:Humans; D051379:Mice; D010703:Phorbol Esters / Q000494:pharmacology; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D016760:Proto-Oncogene Proteins c-fos / Q000235:genetics; D016755:Proto-Oncogene Proteins c-jun / Q000235:genetics; D018808:Transcription Factor AP-1 / Q000378:metabolism*
D010703:Phorbol Esters; D016760:Proto-Oncogene Proteins c-fos; D016755:Proto-Oncogene Proteins c-jun; D018808:Transcription Factor AP-1; D066246:ErbB Receptors; D003850:Deoxyribonuclease I