Myocyte Enhancer Factor 2 Activates Promoter Sequences of the Human AβH-J-J Locus, Encoding Aspartyl-β-Hydroxylase, Junctin, and Junctate

Abstract

Alternative splicing of the locus AβH-J-J generates three functionally distinct proteins: an enzyme, AβH (aspartyl-β-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 AβH-J-J locus. We demonstrate that the P2 promoter of the AβH-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-κB 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 AβH-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.

ACKNOWLEDGMENTS

This work was supported in part by grants from FIRB and Ministero Università e Ricerca Scientifica e Tecnologica (60 and 40%), the Department of Anesthesia, Kantosspital, Basel, Switzerland, HPRN-CT-2002-00331 from the European Union, the Italian Space Agency, and the Swiss Muscle Foundation. R.G. is supported by grants from the Associazione Italiana per la Ricerca sul Cancro. S.F. is supported by Telethon grant GP0210Y01.

We thank Anemone Gunther and Maria Luisa Piaggio for help in the ChIP procedure.