Medizinische Universität Graz Austria/Österreich - Forschungsportal - Medical University of Graz
Gewählte Publikation:
Poparic, I.
Mutations in FHL1 impair expression and functionality of potassium voltage-gated channel Kv1.5 in myopathy patients
[ Dissertation ] Medical University of Graz; 2011. pp. 99
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- Autor*innen der Med Uni Graz:
- Poparic Ivana
- Betreuer*innen:
- Wagner Klaus
- Windpassinger Christian
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- Abstract:
- Four-and-a-half LIM domain protein 1 (FHL1) is expressed predominantly in skeletal but also in cardiac muscle. It is suggested to play a role in sarcomere synthesis and assembly. Three alternatively-spliced isoforms of FHL1 exist (FHL1A, FHL1B and FHL1C), which differ in amino acid sequence, localization, expression patterns and protein interactions. Mutations in FHL1 were identified as causative in four different myopathies including X-linked myopathy with postural muscle atrophy, termed XMPMA. Mutations in patients with XMPMA affect variants A and B, isoform C remaining intact. Recently FHL1A was identified as a possible regulator of the human atrial potassium voltage-gated channel Kv1.5. Here we describe the physical and functional interaction between Kv1.5 and FHL1 proteins. Quantitative PCR experiments showed altered mRNA expression for Kv1.5 and FHL1 variants in myoblasts of XMPMA patients compared to controls. Western blot analysis further confirmed absence of FHL1A protein and reduction/absence of Kv1.5 in these cells. Patient myoblasts showed a decreased proliferation rate compared to controls and a higher number of cells in the G0/G1 phase. Colocalization of FHL1 and Kv1.5 in the cell cytoplasm and plasma membrane was confirmed in HL-1 cells. Two-electrode voltage clamp experiments demonstrated that Xenopus oocytes expressing Kv1.5 and FHL1 variants exerted markedly reduced currents when compared to oocytes expressing Kv1.5 only, FHL1C variant having the most prominent effect. Potential physical interaction between FHL1C and Kv1.5 was proven in vitro by a pull down assay. In conclusion, we have described the functional interaction of FHL1 and Kv1.5.. Since Kv1.5 expression and functionality are altered in XMPMA patients we propose FHL1 might regulate this channel in both cardiac and skeletal muscle. Absence of FHL1 could result in lack of regulation of the channel and explain the pathophysiology found in our patients.