Multivalent cations and ligand affinity of the type 1 insulin-like growth factor receptor on P2A2-LISN muscle cells

✍ Scribed by Robert H. McCusker; Mike Kaleko; Rebecca L. Sackett

• Publisher: John Wiley and Sons
• Year: 1998
• Tongue: English
• Weight: 237 KB
• Volume: 176
• Category: Article
• ISSN: 0021-9541
• DOI: 10.1002/(sici)1097-4652(199808)176:2<392::aid-jcp18>3.0.co;2-5

✦ Synopsis

Mouse P 2 A 2 -LISN myoblasts are transfected cells that overexpress the human type 1 insulin-like growth factor (IGF) receptor. Because the type 1 IGF receptor is the major binding site for both IGF-I and IGF-II, this cell line is an excellent model to determine the effect of multivalent cations on ligand binding specifically to this type of receptor. Competitive binding assays were performed to characterize IGF binding and Scatchard analysis to quantify affinity (K a ). 125 I-IGF-I, 125 I-IGF-II, and 125 I-R 3 -IGF-I bind only to the type 1 IGF receptor on these cells. Zn 2/ increased binding of the three ligands to the type 1 IGF receptor by 17 to 35%. Cd 2/ significantly increased binding of 125 I-IGF-I, although by only 8%. La 3/ and Cr 3/ did not effect binding. Au 3/ decreased IGF binding by approximately 56%. Scatchard analysis produced nonlinear concave-down plots yielding binding constants for high and low affinity sites. Zn 2/ increased the strength of only the high affinity sites. Au 3/ decreased the affinity of both high and low affinity sites. Zn 2/ increased binding with a half-maximal effect between 40 mM and 60 mM. Halfmaximal dose of Au 3/ was ú130 mM. Zinc, gold, and cadmium bind to similar regions within proteins (a zinc-binding motif) and only these cations were found to affect receptor binding indicating similar mechanisms of action. Thus, multivalent cations may alter IGF binding to cell surface receptors ultimately controlling growth. Physiologically this may be especially important for the growth promoting effects of Zn 2/ .