Gene regulation of amyloid precursor protein during differentiation of neuroblastoma cells

Abstract

Expression of APP (amyloid precursor protein) during brain development, specific expression of APP 695 isoform in neurons, and the degeneration of cholinergic neurons in Alzheimer's disease point to the important physiological function of APP in nervous system development and metabolism. We studied the regulation of APP mRNA expression in NG108-15 neuroblastoma x glioma cells which had been induced to differentiate in the presence of dibutyryl cAMP. APP mRNA levels gradually increased concomitant with the appearance of differentiated features. In the present studies, Northern blot analysis showed a 3.1 fold increase in APP expression at day 6 of dibutyryl cAMP treatment along with increase in expression of the neuronal markers, GAP-43 and NF-L. Run-on assay experiments confirmed a 2-fold increase in the rate of APP mRNA transcription. Although the half-life of APP mRNA was long, differentiated and nondifferentiated cells showed the same half-life of about 21h. The presence of APP mRNA binding proteins was also investigated. We found that RNA binding proteins were present in both differentiated and non-differentiated cells. These experiments strongly suggest that APP mRNA induction is due to increase in transcription rate. Studies of mRNA decay in the presence of actinomycin D, an inhibitor of transcription, in primary cultures revealed large differences in APP mRNA half-life between fetal neurons and fetal astrocytes without any qualitative changes in APP mRNA binding proteins