EXPRESSION OF IGF-II MAN-6-P RECEPTORS ON RAT, RABBIT, AND HUMAN COLON EPITHELIAL-CELLS

Previous experiments from this laboratory have established the presenc e 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-li nking experiments, and immunoblot analyses using a polyclonal rabbit a ntiserum that recognizes the IGF-II/mannose 6-phosphate (Man-6-P) rece ptor, all confirmed the presence of IGF-II/Man-6-P receptors on membra nes prepared from rat and human colon epithelial cells. Exposure of ra t colon epithelial cell membrane fractions to 5 mM Man-6-P before incu bation with I-125-labeled IGF-II increased radioligand binding. Immuno blot analysis indicated that IGF-II/Man-6-P receptors were present in both unfractionated rat colon membranes and fractions enriched with ap ical membranes. Rabbit and human colon epithelial cells displayed a di fferent pattern of receptor distribution than rat colon epithelial cel ls, with more insulin receptors but relatively few IGF-II/Man-6-P rece ptors. Immunohistochemical studies using a rabbit polyclonal antiserum confirmed that IGF-II/Man-6-P receptors were present on both the apic al and the basolateral surfaces of colon epithelial cells.