PROMOTER ELEMENTS OF THE MOUSE ACETYLCHOLINESTERASE GENE - TRANSCRIPTIONAL REGULATION DURING MUSCLE DIFFERENTIATION

The increase in acetylcholinesterase expression during muscle differen tiation from myoblasts to myotubes was shown previously to reflect pri marily a greater stability of the messenger RNA (mRNA). Here, we inves tigate the regulation of the acetylcholinesterase gene during early de termination of the muscle phenotype. (i) We employ myogenic transcript ion factors to transform non-muscle cells into myoblasts in order to a ssess the role of the myogenic transcription factors in this regulatio n. (ii) We analyze the Ache promoter region by deletion analysis, poin t mutagenesis, and gel mobility shift assays, The myogenic transcripti on factors do not accelerate transcription of the Ache gene in spite o f the presence of E-boxes at -335 base pairs from the start of transcr iption and in the first intron, and they are not able to trigger stabi lization of the Ache mRNA when constitutively expressed in 10T1/2 fibr oblasts. A GC-rich region (at -105 to -59 base pairs from the start of transcription) containing overlapping binding sites for the transcrip tion factors Sp1 and Egr-1 is essential for promoter activity, Mutatio n of the Sp1 sites dramatically reduces the promoter activity while mu tation of the Egr-1 sites has little effect. Sp1 and Egr-1 compete for binding to overlapping sites and an increase in Egr-1 decreases the e xpression of the Ache gene.