ENHANCED EXPRESSION OF AMYLOID PRECURSOR PROTEIN IN RESPONSE TO DIBUTYRYL-CYCLIC-AMP IS NOT MEDIATED BY THE TRANSCRIPTION FACTOR AP-2

The gene for amyloid precursor protein (APP) is expressed almost ubiqu itously, with high levels of mRNA being detected in brain. The basal e xpression level of the APP gene can be modulated by physiological stim uli, and in this report we demonstrate that the second messenger cycli c AMP can regulate APP mRNA through transcriptional mechanisms. Northe rn blot analysis showed a 1.8-fold increase in steady-state levels of APP mRNA when the neuroblastoma x glioma hybrid cell line NG108-15 was treated with dibutyryl cyclic AMP. Although the upstream sequences of the APP gene do not contain a canonical cyclic AMP response element, transient transfection assays in NG108-15 cells using different portio ns of the APP promoter showed an increase in reporter gene activity me diated by sequences located between -303 to -204 and -488 to -2991. Co transfection assays carried out in HepG2 cells with AP-2, a cyclic AMP -regulated transcription factor, failed to activate the APP promoter t hrough the AP-2 consensus sequence (GCCNNNCGG) located at position -20 5. Electrophoretic mobility shift analysis revealed that the AP-2 bind ing activity present in HeLa nuclear extracts fails to recognize the A PP AP-2 consensus sequence. We conclude that increases in cyclic AMP l evels can lead to an up-regulation of APP gene transcription through a t least two different regions of the APP promoter. This increase does not involve the AP-2 consensus sequence present in the APP promoter lo cated at position -205, and, moreover, this putative site is not recog nized by the transcription factor AP-2.