Submitted to: Journal of Biological Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 10, 1999
Publication Date: N/A
Interpretive Summary: Growth of domestic birds is influenced by many factors, including a very important group of protein hormones, the insulin-like growth factors. The action of these growth factors are modulated to a great extent by another group of proteins, the insulin-like growth factor binding proteins. Recently this laboratory identified a unique protein in the blood of chickens which binds insulin-like growth factor-2. This protein is not found in mammalian blood. This study was conducted to identify this protein in chicken blood. It was determined that this protein is chicken vitronectin, a protein important to cell motility and growth. This is the first report of an interaction between vitronectin and a growth factor. These results will be of interest to other scientists.
We have previously reported the presence of a 70 kDa insulin-like growth factor (IGF1)-II-specific binding protein in chicken serum using Western ligand blotting approaches. Indeed, this protein appears to be a major carrier of IGF-II in chicken serum. In order to ascertain the identity of this 70 kDa IGF-II binding species, the protein has been purified from chicken serum using a combination of ion-exchange and gel-permeation chromatography. Interestingly, amino acid sequencing of the purified protein revealed that it has the same N-terminal sequence as chicken vitronectin. The protein has the ability to specifically bind IGF- II and not IGF-I as determined by ligand blotting, cross-linking and competitive binding assay approaches. In addition, the protein binds 125I-des(1-6)-IGF-II, suggesting that the interaction with IGF- II is different to those with other IGF-binding proteins. Moreover, we have ascertained that both human and bovine vitronectin also specifically bind IGF-II. These results are particularly relevant in the light of the recent report that the urokinase-type plasminogen activator receptor, a protein that also binds vitronectin, has been shown to associate with the cation- independent mannose-6-phosphate/IGF-II receptor and suggests a possible role for IGF-II in cell adhesion and invasion.