Purification and identification of a BMP-like factor from bovine serum

Myogenic differentiation is suppressed in vitro by unknown factors present in fetal bovine serum (FBS). We found that specific inhibitors of bone morphogenetic proteins (BMPs) stimulated myogenic differentiation even in the presence of 20% FBS, which in turn activated specific BMP signaling. Moreover, these specific BMP inhibitors blocked maturation of osteoblastic cells induced by FBS, indicating that BMP-like factor(s) in serum regulate both myogenic and osteoblastic differentiation. The factor identified had an apparent molecular weight (Mw) of over 100 kDa on a Superdex 200 column for molecular sieving HPLC, but an apparent Mw of 33 kDa on SDS–PAGE under non-reducing conditions. Analysis of a purified preparation from FBS (5 L) by liquid chromatography-tandem mass spectrometry revealed the presence of an amino acid sequence conserved between mature human and murine BMP-4. This is the first study to show that BMP-4 is present in FBS as a large complex.