AJP - Regulatory, Integrative and Comparative Physiology, Vol 264, Issue 6 1101-R1110, Copyright © 1993 by American Physiological Society
Expression of IGF-II/Man-6-P receptors on rat, rabbit, and human colon epithelial cells
D. J. Pillion, W. E. Grizzle, M. Yang, E. Meezan, C. R. Stockard, V. Ganapathy, F. H. Leibach, R. B. Myers and J. F. Haskell
Metabolic Diseases Research Laboratory/Department of Pharmacology, University of Alabama, Birmingham 35294.
Previous experiments from this laboratory have established the presence of
receptors for insulin and insulin-like growth factor I (IGF-I) on apical
membranes prepared from rabbit colon epithelial cells; however, no
receptors for multiplication-stimulating activity (MSA), the rat peptide
hormone equivalent of human IGF-II, were found in this tissue. In the
current studies, radioligand binding assays, covalent cross-linking
experiments, and immunoblot analyses using a polyclonal rabbit antiserum
that recognizes the IGF-II/mannose 6-phosphate (Man-6-P) receptor, all
confirmed the presence of IGF-II/Man-6-P receptors on membranes prepared
from rat and human colon epithelial cells. Exposure of rat colon epithelial
cell membrane fractions to 5 mM Man-6-P before incubation with 125I-labeled
IGF-II increased radioligand binding. Immunoblot analysis indicated that
IGF-II/Man-6-P receptors were present in both unfractionated rat colon
membranes and fractions enriched with apical membranes. Rabbit and human
colon epithelial cells displayed a different pattern of receptor
distribution than rat colon epithelial cells, with more insulin receptors
but relatively few IGF-II/Man-6-P receptors. Immunohistochemical studies
using a rabbit polyclonal antiserum confirmed that IGF-II/Man-6-P receptors
were present on both the apical and the basolateral surfaces of colon
epithelial cells.
