Human bone morphogenetic protein 4 (BMP4) fused to the collagen-binding domain (CBD) of fbronectin was constructed and expressed in a silkworm-baculovirus expression system. When recombinant BmNPV was injected into the silkworm larvae and harvested after approximately 4 days, 0.22 mg/ml (0.1 mg/larva) of recombinant CBD-BMP4 was secreted into the silkworm haemolymph. Interestingly, cultured silkworm cells infected with the same recombinant virus could not secrete the recombinant CBD-BMP4 into culture media. The purifed rCBD-BMP4 showed Smad- and MAPK-stimulating activities in human UET-13 cells.
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