EVIDENCE FOR LOCALIZATION OF THE MYOTONIC-DYSTROPHY PROTEIN-KINASE TOTHE TERMINAL CISTERNAE OF THE SARCOPLASMIC-RETICULUM

Myotonic dystrophy is an autosomal dominant multisystem disease primar ily affecting skeletal muscle and is characterized by the presence of an amplified trinucleotide repeat in the 3' untranslated region of the myotonic dystrophy protein kinase gene. In this study, the subcellula r localization of the myotonic dystrophy protein kinase in muscle tiss ues has been investigated at both morphological and biochemical level, by using antibodies against the myotonic dystrophy protein kinase. Im munofluorescence studies and Western-blot analysis were carried out wi th antibodies raised against both a synthetic peptide and a recombinan t fusion protein fragment specific for the myotonic dystrophy protein kinase. The kinase is localized both to the surface membranes, and wit hin the skeletal fibres in the region of the A-I band boundary. Consis tent with the A-I location of the kinase is that Western-blot analysis of purified fractions from sarcoplasmic reticulum show that triads an d sarcoplasmic reticulum terminal cisternae are immunoreactive for two myotonic dystrophy protein kinase proteins of different molecular wei ght (85 and 54 kDa). The relative amount of these two proteins is diff erent in relation to the muscle type, the 85 kDa protein being more ev ident in skeletal than in cardiac fibres. In addition, immunofluoresce nce studies of cardiac muscle reveal a heavy concentration of DM-PK lo calized to the intercalated discs, as well as a weaker reaction in the sarcoplasm. These results taken together suggest that multiple isofor ms of the DM-PK may exist and that they may be differentially located in muscle tissues.