Dj. Pillion et al., EXPRESSION OF IGF-II MAN-6-P RECEPTORS ON RAT, RABBIT, AND HUMAN COLON EPITHELIAL-CELLS, The American journal of physiology, 264(6), 1993, pp. 1101-1110
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.