The myostatin propeptide and the follistatin-related gene are inhibitory binding proteins of myostatin in normal serum.
Myostatin, also known as growth and differentiation factor 8, is a member of the transforming growth factor beta 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.
Department of Protein Chemistry and Proteomics, Wyeth Research, 87 Cambridge Park Drive, Cambridge, MA 02140, USA. jhill@wyeth.com
Jennifer J
JJ
Hill
Monique V
MV
Davies
Adele A
AA
Pearson
Jack H
JH
Wang
Rodney M
RM
Hewick
Neil M
NM
Wolfman
Yongchang
Y
Qiu
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015153:Blotting, Western; D017931:DNA Primers; D038702:Follistatin-Related Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D017930:Genes, Reporter; D006801:Humans; D013058:Mass Spectrometry; D051379:Mice; D008969:Molecular Sequence Data; D055435:Myostatin; D011485:Protein Binding; D016212:Transforming Growth Factor beta / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics / Q000502:physiology*
D017931:DNA Primers; D038702:Follistatin-Related Proteins; C525911:MSTN protein, human; C525912:Mstn protein, mouse; D055435:Myostatin; D016212:Transforming Growth Factor beta