Phospholemman is a substrate for myotonic dystrophy protein kinase.

Abstract

The genetic abnormality in myotonic muscular dystrophy, multiple CTG repeats lie upstream of a gene that encodes a novel protein kinase, myotonic dystrophy protein kinase (DMPK). Phospholemman (PLM), a major membrane substrate for phosphorylation by protein kinases A and C, induces Cl currents (I(Cl(PLM))) when expressed in Xenopus oocytes. To test the idea that PLM is a substrate for DMPK, we measured in vitro phosphorylation of purified PLM by DMPK. To assess the functional effects of PLM phosphorylation we compared I(Cl(PLM)) in Xenopus oocytes expressing PLM alone to currents in oocytes co-expressing DMPK, and examined the effect of DMPK on oocyte membrane PLM expression. We found that PLM is indeed a good substrate for DMPK in vitro. Co-expression of DMPK with PLM in oocytes resulted in a reduction in I(Cl(PLM)). This was most likely a specific effect of phosphorylation of PLM by DMPK, as the effect was not present in oocytes expressing a phos(-) PLM mutant in which all potential phosphorylation had been disabled by Ser --> Ala substitution. The biophysical characteristics of I(Cl(PLM)) were not changed by DMPK or by the phos(-) mutation. Co-expression of DMPK reduced the expression of PLM in oocyte membranes, suggesting a possible mechanism for the observed reduction in I(Cl(PLM)) amplitude. These data show that PLM is a substrate for phosphorylation by DMPK and provide functional evidence for modulation of PLM function by phosphorylation.

• Authors: J P Mounsey, J E John 3rd, S M Helmke, E W Bush, J Gilbert, A D Roses, M B Perryman, L R Jones, J R Moorman
• Journal: The Journal of biological chemistry (J Biol Chem) Vol. 275 Issue 30 Pg. 23362-7 (Jul 28 2000) ISSN: 0021-9258 [Print] United States
• PMID: 10811636 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't, Research Support, U.S. Gov't, P.H.S.)

Chemical References

• Membrane Proteins
• Phosphoproteins
• RNA, Messenger
• phospholemman
• Myotonin-Protein Kinase
• Protein Serine-Threonine Kinases

Topics

• Animals
• Membrane Potentials
• Membrane Proteins (metabolism)
• Myotonic Dystrophy (enzymology)
• Myotonin-Protein Kinase
• Oocytes (metabolism, physiology)
• Phosphoproteins (metabolism)
• Protein Serine-Threonine Kinases (genetics, metabolism)
• RNA, Messenger (genetics, metabolism)
• Substrate Specificity
• Xenopus