The Myostatin Propeptide and the Follistatin-related Gene Are Inhibitory Binding Proteins of Myostatin in Normal Serum

• Published in: The Journal of biological chemistry Vol. 277; no. 43; pp. 40735 - 40741
• Main Authors: Hill, Jennifer J, Davies, Monique V, Pearson, Adele A, Wang, Jack H, Hewick, Rodney M, Wolfman, Neil M, Qiu, Yongchang
• Format: Journal Article
• Language: English
• Published: United States American Society for Biochemistry and Molecular Biology 25-10-2002
• Subjects: Amino Acid Sequence; Animals; Base Sequence; Blotting, Western; DNA Primers; Follistatin-Related Proteins - genetics; Follistatin-Related Proteins - metabolism; Follistatin-Related Proteins - physiology; Genes, Reporter; Humans; Mass Spectrometry; Mice; Molecular Sequence Data; Myostatin; Protein Binding; Transforming Growth Factor beta - antagonists & inhibitors; Transforming Growth Factor beta - chemistry; Transforming Growth Factor beta - genetics; Transforming Growth Factor beta - physiology
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M206379200

Myostatin, also known as growth and differentiation factor 8, is a member of the transforming growth factor β superfamily
that negatively regulates skeletal muscle mass ( 1 ). Recent experiments have shown that myostatin activity is detected in serum by a reporter gene assay only after activation
by acid, suggesting that native myostatin circulates as a latent complex ( 2 ). We have used a monoclonal myostatin antibody, JA16, to isolate the native myostatin complex from normal mouse and human
serum. Analysis by mass spectrometry and Western blot shows that circulating myostatin is bound to at least two major proteins,
the myostatin propeptide and the follistatin-related gene (FLRG). The myostatin propeptide is known to bind and inhibit myostatin
in vitro ( 3 ). Here we show that this interaction is relevant in vivo , with a majority (>70%) of myostatin in serum bound to its propeptide. Studies with recombinant V5-His-tagged FLRG protein
confirm a direct interaction between mature myostatin and FLRG. Functional studies show that FLRG inhibits myostatin activity
in a reporter gene assay. These experiments suggest that the myostatin propeptide and FLRG are major negative regulators of
myostatin in vivo .