J Biol Chem, Vol. 273, Issue 11, 6402-6409, March 13, 1998

A Novel Site, Mt, in the Human Desmin Enhancer Is Necessary for Maximal Expression in Skeletal Muscle

Jie Gao, Zhenlin Li^¶, and Denise Paulin^¶

From the  Laboratoire de Biologie Moléculaire de la Différentiation Cellulaire, Université Paris VII and ^¶ SCME Institut Pasteur, 25 rue du Dr. Roux, Paris cedex 15, France

Previous investigations have shown that expression of the muscle-specific intermediate filament desmin gene in skeletal muscle is controlled in part by a 5' muscle-specific enhancer. This enhancer activity can be divided into myoblast-specific and myotube-specific activation domains. The myotube-specific region contains a MyoD and MEF2 sites, whereas the myoblast-specific region contains Sp1, Krox, and Mb sites. In the present study, we designed mutations in the conserved portion of the myotube-specific region; transfection analysis of these mutations showed that a novel site located between the MyoD and MEF2 sites, named Mt (GGTATTT), is required for full transcriptional activity of the desmin enhancer in skeletal muscle. Although gel mobility shift assays demonstrate that myotube, myoblast, fibroblast, and HeLa nuclear extracts contain a nuclear factor that binds specifically to Mt, four copies of the Mt site function as the native enhancer only in myotubes. Functional synergism among the MyoD, MEF2, and Mt sites in myotubes has been demonstrated. These results show that the novel Mt site cooperates with MyoD and MEF2 to give maximal expression of the desmin gene.