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A molecular defect in virally transformed muscle cells that cannot cluster acetylcholine receptors
D T Anthony1, R J Jacobs-Cohen, G Marazzi
1Laboratory of Neurobiology, Rockefeller University, New York, New York 10021-6399.
Abstract:
Muscle cells infected at the permissive temperature with temperature-sensitive mutants of Rous sarcoma virus and shifted to the non-permissive temperature form myotubes that are unable to cluster acetylcholine receptors (Anthony, D. T., S. M. Schuetze, and L. L. Rubin. 1984. Proc. Natl. Acad. Sci. USA. 81:2265-2269). Work described in this paper demonstrates that the virally-infected cells are missing a 37-kD peptide which reacts with an anti-tropomyosin antiserum. Using a monoclonal antibody specific for the missing peptide, we show that this tropomyosin is absent from fibroblasts and is distinct from smooth muscle tropomyosins. It is also different from the two previously identified striated muscle myofibrillar tropomyosins (alpha and beta). We suggest that, in normal muscle, this novel, non-myofibrillar, tropomyosin-like molecule is an important component of a cytoskeletal network necessary for cluster formation.
Insights
Viral infection of muscle cells prevents acetylcholine receptor clustering by causing the loss of a novel tropomyosin. This tropomyosin is crucial for cytoskeletal networks in normal muscle cell function.
Area of Science:
- Cell Biology
- Molecular Biology
- Muscle Physiology
Background:
- Temperature-sensitive Rous sarcoma virus mutants infect muscle cells.
- Viral infection at non-permissive temperatures inhibits acetylcholine receptor clustering in myotubes.
Purpose of the Study:
- Investigate the molecular basis for the loss of acetylcholine receptor clustering in virally infected muscle cells.
- Identify the missing peptide in infected cells and characterize its role in muscle cell structure.
Main Methods:
- Utilized temperature-sensitive Rous sarcoma virus mutants to infect muscle cells.
- Employed anti-tropomyosin antiserum and a specific monoclonal antibody to detect and characterize a missing 37-kD peptide.
- Compared the novel tropomyosin to known smooth and striated muscle tropomyosins.
Main Results:
- Virally infected muscle cells lack a specific 37-kD peptide that reacts with anti-tropomyosin antiserum.
- This novel tropomyosin is absent in fibroblasts and distinct from smooth and striated muscle tropomyosins.
- The identified molecule is non-myofibrillar.
Conclusions:
- A novel tropomyosin-like molecule, distinct from myofibrillar tropomyosins, is essential for cytoskeletal networks.
- This molecule plays a critical role in the formation of acetylcholine receptor clusters in muscle cells.
- Viral infection disrupts this cytoskeletal component, leading to impaired receptor clustering.