GDF-8 propeptide binds to GDF-8 and antagonizes biological activity by inhibiting GDF-8 receptor binding

GDF-8 is a new member of the TGF-beta superfamily which appears to be a neg ative regulator of skeletal muscle mass. Factors which regulate the biologi cal activity of GDF-8 have not yet been identified. However, the biological activities of TGF-beta superfamily members, TGF-beta1, -beta2 and -beta3, can be inhibited by noncovalent association with TGF-beta1, -beta2 and beta 3 propeptides cleaved from the amino-termini of the TGF-beta precursor prot eins. In contrast, the propeptides of other TGF-beta superfamily members do not appear to be inhibitory. In this investigation, we demonstrate that pu rified recombinant GDF-8 propeptide associates with purified recombinant GD F-8 to form a noncovalent complex, as evidenced by size exclusion chromatog raphy and chemical crosslinking analysis. Furthermore, we show that GDF-8 p ropeptide inhibits the biological activity of GDF-8 assayed on A204 rhabdom yosarcoma cells transfected with a (CAGA)(12) reporter construct. Finally, we demonstrate that GDF-8 propeptide inhibits specific GDF-8 binding to L6 myoblast cells. Collectively, these data identify the GDF-8 propeptide as a n inhibitor of GDF-8 biological activity.