EXPANDED CTG REPEATS IN MYOTONIN PROTEIN-KINASE SUPPRESSES MYOGENIC DIFFERENTIATION

A full-length mutant human myotonin protein kinase (MtPK) cDNA having a 46 expanded CTG-repeat size or a wild type containing 5 CTG repeats was stably transfected into mouse C2C12 cell line in order to explore the effects of the expansion mutation of trinucleotide repeats in the 3' untranslated region on developing myogenic cells. Each established clone expressed a human 70 kDa MtPK protein without proteolytic proces sing. Differentiation experiments indicated that stable mutant MtPK cD NA-transformants suppressed myogenic differentiation, whereas wild-typ e transformants exhibited almost normal myogenesis. The disturbance of the expression of neuronal nitric oxide synthase, a mediator of myobl ast fusion, suggests that signal transduction system might be involved in the muscle manifestations of mutant MtPK.