Major secretory product of the mesometrial decidua in the rat, a variant of alpha-2-macroglobulin, binds insulin-like growth factor I via a protease-dependent mechanism.
Decidualization-associated protein (DAP), the quantitatively major secretory product of the mesometrial decidua in the rat, is a pl variant of the liver-derived acute-phase reactant, alpha-2-macroglobulin (alpha 2M). Alpha 2M, a broad spectrum protease inhibitor, has been demonstrated in the human to bind a variety of cytokines and growth factors. In humans, the quantitatively major secretory product of decidual tissue is an insulin-like growth factor (IGF) binding protein. In this study, we have therefore tested the ability of liver- and decidual-derived alpha 2M in the rat to bind IGF-I. Alpha 2M purified from acute-phase plasma and DAP purified from cytosolic extracts of decidual tissue and medium from tissue incubations both bound radiolabeled IGF-I. The binding of IGF-I was principally dependent upon the coincubation of the protein with a proteinase. Therefore, it occurred during the conversion of the "slow" to the "fast" form of alpha 2M. Pretreatment with proteinase to produce the fast form before addition of the IGF-I reduced the binding. Binding was enhanced at a ratio protein:proteinase of 1:1. Results from gel electrophoretic analysis were consistent with the covalent linkage of IGF-I to alpha 2M during the cleavage of the "bait region." A saturable displacement by increasing concentrations of unlabeled IGF-I suggested high affinity interaction. Under conditions of demonstrated binding to purified proteins binding in acute-phase plasma, decidual tissue extracts and tissue incubation medium were associated with a high molecular weight species which was confirmed to represent alpha 2M and DAP, respectively. Our studies demonstrate that IGF-I may now be added to the list of regulatory peptides which alpha 2M may bind and that, in rat decidua, DAP may represent the functional homolog of decidual IGFBP-1 in the human and regulate growth factor function during placental development.
da Silva
G C
GC
Department of Biochemistry, Faculty of Pharmacy, Oporto University, Portugal.
Teixeira
N
N
Bell
S C
SC
D000818:Animals; D003656:Decidua / Q000378:metabolism*; D005260:Female; D006023:Glycoproteins / Q000378:metabolism*; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D008099:Liver / Q000378:metabolism; D008297:Male; D011257:Pregnancy Proteins / Q000378:metabolism*; D045384:Pregnancy-Associated alpha 2-Macroglobulins; D011480:Protease Inhibitors / Q000378:metabolism*; D011485:Protein Binding; D051381:Rats; D017208:Rats, Wistar; D000511:alpha-Macroglobulins / Q000378:metabolism*
D006023:Glycoproteins; D011257:Pregnancy Proteins; D045384:Pregnancy-Associated alpha 2-Macroglobulins; D011480:Protease Inhibitors; D000511:alpha-Macroglobulins; C020881:decidualization-associated protein, rat; D007334:Insulin-Like Growth Factor I