Cloning and sequence determination of bovine insulin-like growth factor binding protein-2 (IGFBP-2): comparison of its structural and functional properties with IGFBP-1.
Insulin-like growth factor binding proteins (IGFBPs) are secreted by several cell types and can modify IGF actions. Mandin-Darby Bovine Kidney (MDBK) cells have been shown to secrete a 34,000 Da form of IGF binding protein whose N-terminal sequence is similar to a form of IGFBP purified from rat BRL-3A cells that has recently been named IGFBP-2. These studies report the complete amino acid sequence of bovine IGFBP-2 and compare its functional properties with human IGFBP-1. The protein is 81% identical to rat IGFBP-2. When compared with both rat IGFBP-2 and human IGFBP-1, the positions of all 18 cysteine residues are conserved. Similarly an RGD sequence is present near the carboxyl terminus in both proteins. IGFBP-2 has a higher affinity for IGF-II than for IGF-I and its affinity for both forms of IGF is greater than for human IGFBP-1. Like IGFBP-1 the protein can enhance the DNA synthesis response of porcine aortic smooth muscle cells to IGF-I; however, IGFBP-2 was much less potent. The maximum potentiation of the IGF-mediated mitogenic response that could be achieved was approximately 42% that of IGFBP-1. This potentiation is dependent upon a factor contained in platelet poor plasma and if this factor is omitted from the incubation medium, IGFBP-2 inhibits DNA synthesis. The purification of IGFBP-2 will allow more detailed comparisons to be made between it and other forms of IGFBPs in physiologic test systems.
Bourner
M J
MJ
Department of Medicine, University of North Carolina School of Medicine, Chapel Hill 27599.
Busby
W H
WH
Siegel
N R
NR
Krivi
G G
GG
McCusker
R H
RH
Clemmons
D R
DR
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002352:Carrier Proteins / Q000737:chemistry* / Q000235:genetics* / Q000502:physiology; D002417:Cattle; D003001:Cloning, Molecular; D006801:Humans; D018970:Insulin-Like Growth Factor Binding Protein 1; D018971:Insulin-Like Growth Factor Binding Protein 2; D008969:Molecular Sequence Data; D051381:Rats; D012689:Sequence Homology, Nucleic Acid
D002352:Carrier Proteins; D018970:Insulin-Like Growth Factor Binding Protein 1; D018971:Insulin-Like Growth Factor Binding Protein 2