Regulation of bone morphogenetic protein activity by pro domains and proprotein convertases

Bone morphogenetic proteins (BMPs) are derived from inactive precursor prot eins by endoproteolytic cleavage. Here we show that processing of Nodal and Myc-tagged BMP4 is significantly enhanced by SPC1/Furin or SPC4/PACE4, pro viding direct evidence that regulation of BMP signaling is likely to be con trolled by subtilisin-like proprotein convertase (SPC) activities. Nodal pr ocessing is dramatically enhanced if two residues adjacent to the precursor cleavage site are substituted with amino acids found at the equivalent pos itions of Activin, demonstrating that structural constraints at the precurs or cleavage site limit the processing efficiency. However, in transfection assays, mature Nodal is undetectable either in culture supernatants or in c ell lysates, despite efficient cleavage of the precursor protein, suggestin g that mature Nodal is highly unstable. Domain swap experiments support thi s conclusion since mature BMP4 or Dorsalin are also destabilized when expre ssed in conjunction with the Nodal pro domain. By contrast, mature Nodal is stabilized by the Dorsalin pro domain, which mediates the formation of sta ble complexes. Collectively, these data show that the half-life of mature B MPs is greatly influenced by the identity of their pro regions.