AJP - Endocrinology and Metabolism, Vol 257, Issue 1 E27-E34, Copyright © 1989 by American Physiological Society
Receptors for IGF-I, but not for IGF-II, on proximal colon epithelial cell apical membranes
D. J. Pillion, J. F. Haskell, J. A. Atchison, V. Ganapathy and F. H. Leibach
Department of Pharmacology, University of Alabama, Birmingham 35294.
Rabbit proximal colon epithelial cell apical membranes, which are known to
contain receptors for insulin, were isolated by a Ca2+-precipitation
technique. Binding assays with 125I-insulin-like growth factor I (IGF-I)
revealed the presence of specific high-affinity binding sites, with 50%
inhibition of binding observed at a concentration of 13.7 ng/ml IGF-I. In
contrast, 50% inhibition of 125I-IGF-I binding was observed at an insulin
concentration of 1.37 micrograms/ml, suggesting that 125I-IGF-I was not
binding to insulin receptors present in this tissue. Cross-linking studies
revealed an 125I-IGF-I binding subunit of relative molecular weight (Mr) of
130,000 under reducing conditions on docecyl sulfate-polyacrylamide gel
electrophoresis that was similar to the IGF-I binding subunit in human
placental membranes (Mr 140,000). Binding and cross-linking studies with
125I-insulin-like growth factor II (IGF-II), however, failed to reveal a
specific receptor for this peptide in colon epithelial cell membranes.
These results establish the coexistence of receptors for IGF-I and insulin,
but not IGF-II, on rabbit proximal colon epithelial cell apical membranes
and demonstrate that colon epithelial cells are capable of selective
synthesis of various peptide hormone receptors.
