LOCALIZATION OF MYOTONIC-DYSTROPHY PROTEIN-KINASE IN HUMAN AND RABBIT-TISSUES USING A NEW PANEL OF MONOCLONAL-ANTIBODIES

There is considerable confusion in the literature about the size of th e myotonic dystrophy protein kinase (DMPK) and its localization within tissues, We have used a new panel of monoclonal antibodies (mAbs) to begin to resolve these issues, which are important for understanding t he possible role of DMPK in myotonic dystrophy. Antisera raised agains t the catalytic and coil domains of DMPK recognized a major 55 kDa pro tein and a minor 72-80 kDa doublet on western blots of human skeletal muscle. Ten mAbs, five against the catalytic domain and five against t he coil region, recognized only the 72-80 kDa doublet, The 72 kDa prot ein was present in all tissues tested, whereas the 80 kDa component wa s variably expressed, mainly in skeletal and cardiac muscles, The 72 k Da protein was absent in a DMPK knockout mouse and was greatly increas ed in a transgenic mouse overexpressing human DMPK, confirming its ide ntity as authentic DMPK, Two mAbs against the catalytic domain recogni zed only the more abundant 55 kDa protein, which was found only in ske letal muscle. Nine out of 10 mAbs located DMPK to intercalated discs i n human heart, an affected tissue in myotonic dystrophy, However, co-l ocalization of DMPK with acetylcholine receptors at neuromuscular junc tions was not observed with any of the mAbs, Subcellular fractionation and sedimentation analysis suggest that a major proportion of the DMP K in skeletal muscle and brain is cytosolic.