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MuSK protein



muscle, skeletal, receptor tyrosine kinase
Identifiers
Symbol MUSK
Entrez 4593
HUGO 7525
OMIM 601296
RefSeq NM_005592
UniProt O15146
Other data
Locus Chr. 9 q31.3-q32

MuSK (for Muscle Specific Kinase) is a receptor tyrosine kinase important in neuromuscular development. It is activated by a proteoglycan called agrin.

Additional recommended knowledge

Contents

MuSK is required for formation of the Neuromuscular Junction

During development, the growing end of motor neuron axons secrete a protein called agrin.[1] This protein binds to several receptors on the surface of skeletal muscle. The receptor which seems to be required for formation of the neuromuscular junction (NMJ), which comprises the nerve-muscle synapse is called MuSK (Muscle specific kinase).[2] MuSK is a receptor tyrosine kinase - meaning that it induces cellular signaling by causing the addition of phosphate molecules to particular tyrosines on itself, and on proteins which bind the cytoplasmic domain of the receptor.

The requirement for MuSK in the formation of the NMJ was primarily demonstrated by mouse (transgenic|"knockout") studies. In mice which are deficient for either agrin or MuSK, the neuromuscular junction does not form. Many other proteins also comprise the NMJ, and are required to maintain its integrity. For example, MuSK also binds a protein called "dishevelled" (Dvl), which is in the Wnt signalling pathway. Dvl is additionally required for MuSK-mediated clustering of AChRs, since inhibtion of Dvl blocks clustering.

MuSK signaling

Upon activation by its ligand agrin, MuSK signals via the proteins called Casein kinase 2 (CK2),[3] Dok-7[4] and rapsyn, to induce "clustering" of acetylcholine receptors (AChR). Both CK2 and Dok-7 are required for MuSK induced formation of the neuromuscular junction, since mice lacking Dok-7 failed to form AChR clusters or neuromuscular synapses, and since downregulation of CK2 also impedes recruitment of AChR to the primary MuSK scaffold. In addition to the proteins mentioned, other proteins are then gathered, to form the endplate to the neuromuscular junction. The nerve terminates onto the endplate, forming the neuromuscular junction - a structure which is required to transmit nerve impulses to the muscle, and thus initiating muscle contraction.

MuSK's role in disease

Antibodies directed against this protein are found in those patients with myasthenia gravis who do not demonstrate antibodies to the acetylcholine receptor (sero-negative).[5] The phenotype of these patients appears to be different from many other myasthenic patients; more likely women, less eye involvement, more likely to have weakness of neck and oropharynx and more likely to be African-American in ethnicity.

References

  1. ^ Glass D et al (1996). "Agrin acts via a MuSK receptor complex". Cell 85 (4): 513-23. PMID 8653787.
  2. ^ DeChiara T et al (1996). "The receptor tyrosine kinase MuSK is required for neuromuscular junction formation in vivo". Cell 85 (4): 501-12. PMID 8653786.
  3. ^ Cheusova T et al (2006). "Casein kinase 2-dependent serine phosphorylation of MuSK regulates acetylcholine receptor aggregation at the neuromuscular junction". Genes Dev 20 (13): 1800-16. PMID 16818610.
  4. ^ Okada K et al (2006). "The muscle protein Dok-7 is essential for neuromuscular synaptogenesis". Science 312 (5781): 1802-5. PMID 16794080.
  5. ^ Hoch W et al (2001). "Auto-antibodies to the receptor tyrosine kinase MuSK in patients with myasthenia gravis without acetylcholine receptor antibodies". Nat Med 7 (3): 365-8. PMID 11231638.
 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "MuSK_protein". A list of authors is available in Wikipedia.
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