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 themyotonic dystrophy protein kinase (DMPK) and its localization withintissues. We have used a new panel of monoclonal antibodies (mAbs) to beginto resolve these issues, which are important for understanding the possiblerole of DMPK in myotonic dystrophy. Antisera raised against the catalyticand coil domains of DMPK recognized a major 55 kDa protein and a minor72-80 kDa doublet on western blots of human skeletal muscle. Ten mAbs, fiveagainst the catalytic domain and five against the coil region, recognizedonly the 72-80 kDa doublet. The 72 kDa protein was present in all tissuestested, whereas the 80 kDa component was variably expressed, mainly inskeletal and cardiac muscles. The 72 kDa protein was absent in a DMPKknockout mouse and was greatly increased in a transgenic mouseoverexpressing human DMPK, confirming its identity as authentic DMPK. TwomAbs against the catalytic domain recognized only the more abundant 55 kDaprotein, which was found only in skeletal muscle. Nine out of 10 mAbslocated DMPK to intercalated discs in human heart, an affected tissue inmyotonic dystrophy. However, co-localization of DMPK with acetylcholinereceptors at neuromuscular junctions was not observed with any of the mAbs.Subcellular fractionation and sedimentation analysis suggest that a majorproportion of the DMPK in skeletal muscle and brain is cytosolic.