Alternative splicing of the locus AbetaH-J-J generates three functionally 
distinct proteins: an enzyme, AbetaH (aspartyl-beta-hydroxylase), a structural 
protein of the sarcoplasmic reticulum membrane (junctin), and an integral 
membrane calcium binding protein (junctate). Junctin and junctate are two 
important proteins involved in calcium regulation in eukaryotic cells. To 
understand the regulation of these two proteins, we identified and functionally 
characterized one of the two promoter sequences of the AbetaH-J-J locus. We 
demonstrate that the P2 promoter of the AbetaH-J-J locus contains (i) a minimal 
sequence localized within a region -159 bp from the transcription initiation 
site, which is sufficient to activate transcription of both mRNAs; (ii) 
sequences which bind known transcriptional factors such as those belonging to 
the myocyte enhancer factor 2 (MEF-2), MEF-3, and NF-kappaB protein families; 
and (iii) sequences bound by unknown proteins. The functional characterization 
of the minimal promoter in C2C12 cells and in the rat soleus muscle in vivo 
model indicates the existence of cis elements having positive and negative 
effects on transcription. In addition, our data demonstrate that in striated 
muscle cells the calcium-dependent transcription factor MEF-2 is crucial for the 
transcription activity directed by the P2 promoter. The transcription directed 
by the AbetaH-J-J P2 promoter is induced by high expression of MEF-2, further 
stimulated by calcineurin and Ca2+/calmodulin-dependent protein kinase I, and 
inhibited by histone deacetylase 4.