SPEG interacts with myotubularin, and its deficiency causes centronuclear myopathy with dilated cardiomyopathy

Am J Hum Genet. 2014 Aug 7;95(2):218-26. doi: 10.1016/j.ajhg.2014.07.004. Epub 2014 Jul 31.

Abstract

Centronuclear myopathies (CNMs) are characterized by muscle weakness and increased numbers of central nuclei within myofibers. X-linked myotubular myopathy, the most common severe form of CNM, is caused by mutations in MTM1, encoding myotubularin (MTM1), a lipid phosphatase. To increase our understanding of MTM1 function, we conducted a yeast two-hybrid screen to identify MTM1-interacting proteins. Striated muscle preferentially expressed protein kinase (SPEG), the product of SPEG complex locus (SPEG), was identified as an MTM1-interacting protein, confirmed by immunoprecipitation and immunofluorescence studies. SPEG knockout has been previously associated with severe dilated cardiomyopathy in a mouse model. Using whole-exome sequencing, we identified three unrelated CNM-affected probands, including two with documented dilated cardiomyopathy, carrying homozygous or compound-heterozygous SPEG mutations. SPEG was markedly reduced or absent in two individuals whose muscle was available for immunofluorescence and immunoblot studies. Examination of muscle samples from Speg-knockout mice revealed an increased frequency of central nuclei, as seen in human subjects. SPEG localizes in a double line, flanking desmin over the Z lines, and is apparently in alignment with the terminal cisternae of the sarcoplasmic reticulum. Examination of human and murine MTM1-deficient muscles revealed similar abnormalities in staining patterns for both desmin and SPEG. Our results suggest that mutations in SPEG, encoding SPEG, cause a CNM phenotype as a result of its interaction with MTM1. SPEG is present in cardiac muscle, where it plays a critical role; therefore, individuals with SPEG mutations additionally present with dilated cardiomyopathy.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Cardiomyopathy, Dilated / genetics*
  • Child
  • Child, Preschool
  • Disease Models, Animal
  • Female
  • Humans
  • Infant, Newborn
  • Male
  • Mice
  • Mice, Knockout
  • Muscle Proteins / genetics*
  • Muscle Proteins / metabolism
  • Mutation
  • Myocardium / cytology
  • Myofibrils / genetics
  • Myopathies, Structural, Congenital / genetics*
  • Phosphatidylinositol Phosphates / biosynthesis
  • Protein Tyrosine Phosphatases, Non-Receptor / genetics*
  • Protein Tyrosine Phosphatases, Non-Receptor / metabolism
  • Protein-Serine-Threonine Kinases / genetics*
  • Protein-Serine-Threonine Kinases / metabolism
  • Sarcoplasmic Reticulum / genetics
  • Sarcoplasmic Reticulum / pathology
  • Sequence Alignment
  • Sequence Analysis, DNA
  • Turkey
  • Two-Hybrid System Techniques

Substances

  • Muscle Proteins
  • Phosphatidylinositol Phosphates
  • phosphatidylinositol 3-phosphate
  • Protein-Serine-Threonine Kinases
  • SPEG protein, human
  • Protein Tyrosine Phosphatases, Non-Receptor
  • myotubularin