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Identification of intracellular signaling pathways that induce myotonic dystrophy protein kinase expression during
Marta Carrasco1, Judith Canicio, Manuel Palacín
1Departament de Bioquímica i Biologia Molecular, Facultat de Biologia, Universitat de Barcelona, Avda. Diagonal 645, E-08028 Barcelona, Spain.
Abstract:
Myotonic dystrophy (DM) is the most common inherited adult neuromuscular disorder. DM is caused by a CTG expansion in the 3'-untranslated region of a protein kinase gene (DMPK). Decreased DMPK protein levels may contribute to the pathology of DM, as revealed by gene target studies. However, the postnatal regulation of DMPK expression and its pathophysiological role remain undefined. We studied the regulation of DMPK protein and mRNA expression during myogenesis in rat L6E9 myoblasts, mouse C2C12 myoblasts, and 10T1/2 fibroblasts stably expressing the myogenic transcription factor MyoD (10T1/2-MyoD). We detected DMPK as an 80-kDa protein mainly localized to the cytosolic fraction of skeletal muscle cells. DMPK expression and protein kinase activity were enhanced in IGF-II-differentiated cells. In L6E9 and C2C12 cells, DMPK expression was regulated through the same signaling pathways (i.e. phosphatidylinositol 3-kinase, nuclear factor-kappaB, nitric oxide synthase, and p38 mitogen-activated protein kinase) that had been described as being crucial for the myogenesis induced by either low serum or IGF-II. However, in 10T1/2-MyoD cells, p38 MAPK inhibition blocked cell fusion and caveolin-3 expression without affecting DMPK up-regulation. These results suggest that although DMPK is induced during myogenesis, its expression cannot be totally associated with the development of a fully differentiated phenotype.
Insights
Myotonic dystrophy (DM) involves a CTG expansion affecting the DMPK gene. DMPK protein is upregulated during muscle cell development, but its role in differentiation is complex and not fully understood.
Area of Science:
- Molecular Biology
- Muscle Development
- Neuromuscular Disorders
Background:
- Myotonic dystrophy (DM) is the most common inherited adult neuromuscular disorder.
- DM pathogenesis is linked to CTG expansion in the DMPK gene, with decreased DMPK protein potentially contributing to disease.
- Postnatal regulation and pathophysiological role of DMPK remain unclear.
Purpose of the Study:
- To investigate the regulation of DMPK protein and mRNA expression during myogenesis.
- To explore the pathophysiological role of DMPK in muscle differentiation.
Main Methods:
- Studied DMPK expression during myogenesis in rat L6E9 myoblasts, mouse C2C12 myoblasts, and 10T1/2-MyoD fibroblasts.
- Detected DMPK protein (80-kDa) primarily in the cytosolic fraction of skeletal muscle cells.
- Analyzed signaling pathways (PI3K, NF-κB, NOS, p38 MAPK) involved in DMPK regulation.
Main Results:
- DMPK expression and kinase activity were enhanced in IGF-II-differentiated cells.
- In L6E9 and C2C12 cells, DMPK regulation involved PI3K, NF-κB, NOS, and p38 MAPK pathways.
- In 10T1/2-MyoD cells, p38 MAPK inhibition affected cell fusion and caveolin-3 expression but not DMPK upregulation.
Conclusions:
- DMPK is induced during myogenesis, suggesting a role in muscle development.
- DMPK expression is regulated by conserved signaling pathways during myogenesis.
- DMPK upregulation is not entirely linked to the development of a fully differentiated phenotype.