Functional characterization of insulin and IGF-I receptors in chicken lens epithelial and fiber cells.

Abstract

Insulin and insulin-like growth factor I (IGF-I) play a role in lens cell growth and development. The binding of these hormones to their respective receptors with its concomitant signal transduction is an important step in these cellular processes. Hormone binding to adult chicken lens insulin and IGF-I receptors, partially purified from epithelial and fiber cells, was studied to examine this activity in lens. The associated stimulation of receptor-mediated tyrosine kinase by the hormones was also studied. At an insulin concentration of 0.02 nM, specific binding was similar for epithelial and fiber receptor preparations (Epi = 0.23 +/- 0.03 fmol, Fib = 0.19 +/- 0.02 fmol). Displacement studies revealed that there was also no difference between epithelial and fiber receptor preparations in the concentration of insulin necessary for half maximal displacement of specific [125I]-insulin binding (IC50: Epi = 0.32 nM +/- 0.07 nM, Fib = 0.31 nM +/- 0.05 nM). Comparison of IGF-I (0.02 nM) binding to receptor preparations from epithelial and fiber cells demonstrated that specific binding was similar in the two preparations (Epi = 0.50 +/- 0.05 fmol, Fib = 0.42 +/- 0.05 fmol). Also, there was no difference in the concentration of IGF-I necessary for half maximal displacement of specific [125I]-IGF-I binding (IC50 = Epi: 0.27 +/- 0.05 nM, Fib: 0.28 +/- 0.04 nM). The ability of IGF-I to displace bound [125I]-insulin was also examined. The IC50 for IGF-I binding to the insulin receptors isolated from epithelial and fiber cells was 37.4 +/- 2.4 nM, and 35.4 +/- 2.8 nM, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)