Protein Kinase Activity in Erythrocyte Ghosts of Patients with Myotonic Muscular Dystrophy

Abstract

Myotonic muscular dystrophy is a disorder of humans that involves many organ systems. Physiological studies have suggested that the fundamental defect is of membrane origin. Heretofore, no reproducible metabolic abnormalities have been demonstrated. In the present studies we used erythrocyte ghosts as a convenient source of purified membranes that do not possess changes of denervation, dystrophy, and fibrosis that might complicate the interpretation of muscle membrane changes. Our experiments demonstrated a significant difference in the phosphorylation of erythrocyte ghost protein by [y_32PJATP, with endogenous protein kinase of erythrocyte membrane as the enzyme source. After ghosts were kept for 1 week at -20°, phosphorylation of membrane protein in eight controls was twice as high as endogenous protein kinase activity measured in fresh preparations. No stimulation was seen in preparations from seven myotonic dystrophy patients from three different families. This reproducible difference in normal and myotonic membranes may represent an important new approach to studies of this debilitating inborn error of metabolism.

Modulation of skeletal muscle sodium channels by human myotonin protein kinase.

“…This work extends the original observations of Roses and Appel linking DM to membrane protein phosphorylation (13)(14)(15) and reconfirms the role of HMPK as the active agent in DM (5,36,37). Moreover, these findings link the pathophysiology of DM (altered Na channel kinetics to the genetic abnormality) a mutation in a gene whose product has sequence similarity to protein kinases.…”

“…This finding substantiates earlier biochemical studies of protein phosphorylation in erythrocytes and muscle isolated from DM patients (13)(14)(15). It has therefore been suggested that HMPK normally regulates ion channel function (16,17).…”

Myotonic muscular dystrophy: defective phospholipid metabolism in the erythrocyte plasma membrane.

“…(c) A reduction of diacylglycerol kinase activity necessary for the conversion of diacylglycerol to phosphatidic acid. Additional experimental data will be necessary to decide among these possibilities as well as to determine the relationship of these data to altered band 3 phosphorylation (2,(4)(5)(6) or the other disturbances in membrane function that have been previously described in this disorder (7)(8)(9)(10)(11).…”

“…It is characterized by variable penetrance and expression (1). The involvement of multiple organ systems has led to a suspicion that the disease results from a generalized defect in cellular membrane function (2,3). This hypothesis has been supported by observations in muscle from MyD patients indicating a decreased membrane protein phosphorylation associated with no differences in protein content or other membrane marker enzymes (4).…”

“…MyD patients show an altered [32P]phosphorylation of membrane band 3, an altered stoichiometry of the sodium-potassium pump and differences in membrane properties measured by electron spin resonance spectroscopy (2,(5)(6)(7)(8). When erythrocytes from MyD patients are depleted of ATP by exposure to iodoacetic acid and adenosine (9,10), a diminished calcium-induced potassium efflux is observed.…”