CELL TYPE-DEPENDENT AND DIFFERENTIATION-DEPENDENT EXPRESSION FROM THEMOUSE ACETYLCHOLINE-RECEPTOR EPSILON-SUBUNIT PROMOTER

The nicotinic acetylcholine receptor (AChR) in adult skeletal muscle i s composed of alpha-, beta-, epsilon-, and delta-subunits and is local ized at the neuromuscular junction; in contrast, the more diffusely di stributed fetal form is composed of alpha-, beta-, gamma-, and delta-s ubunits. To define sequences necessary for the transcriptional regulat ion of the mouse epsilon-subunit gene, we sequenced and analyzed 1036 bp upstream of the transcription start site. Using deletion analysis o f the 5'-flanking region linked to the bacterial chloramphenicol acety ltransferase (CAT) gene and transfection of the resulting constructs i nto established cell lines, we demonstrate that a 151 bp fragment exhi bits cell type- and differentiation-specific promoter activity. This a ctivity was independent of a myogenic factor putative binding site (E- box). However, transactivation experiments with recombinant myoD, myog enin, or MRF4 showed that the E-box was functional and that MRF4 prefe rentially transactivates the epsilon-promoter. Thus, like other AChR p romoters, the proximal region of the epsilon-promoter contains informa tion for cell type-specific and developmental regulation of CAT and ca n be transactivated by myogenic factors in cultured cell lines. Unlike the other AChR promoters characterized to date, epsilon-promoter func tion can be partially independent of myogenic factors of the helix-loo p-helix class. (C) 1993 Wiley-Liss, Inc.