BIOCHEMICAL-PROPERTIES OF AMPHIBIAN BONE MORPHOGENETIC PROTEIN-4 EXPRESSED IN CHO CELLS

The biochemical properties of recombinant amphibian bone morphogenetic protein-4 (BMP4), the cDNA of which has been cloned recently by scree ning of a Xenopus cDNA library, was characterized. The protein was exp ressed by the transfection of Chinese hamster ovary (CHO) cells with t he cDNA cloned into expression vectors bearing a cytomegalovirus promo ter or a simian virus 40 promoter. Northern-blot analysis showed that the latter vector was more efficient for Xenopus BMP-4 expression. Spe cific antiserum against Xenopus BMP-4 peptide demonstrated that the pr otein is synthesized as a large precursor, processed to the mature for m and then secreted from the cells as a homodimer. Analysis of the bio logical activity in the conditioned medium revealed that Xenopus BMP-4 has a potent alkaline phosphatase-inducing activity on mouse osteobla stic cells.