Differentiation and polarity alter the binding of IGF-I to human intestinal epithelial (Caco-2) cells.
This study examined whether insulin-like growth factor-I (IGF-I) bound to specific functioning IGF receptors on the surface of Caco-2 cells and how this binding was affected by the differentiation and polarity of these cells. IGF-I, which increased cell proliferation in a dose-dependent manner, bound to a specific receptor on the surface of Caco-2 cells. Affinity cross-linking with labeled IGF-I followed by reducing sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE) showed M(r)s at 135,000, 270,000 and 355,000 bands, which was inhibited by unlabeled IGF-I. A Scatchard analysis of radioligand-receptor binding showed the presence of a single class of receptors with high affinity for IGF-I. This class of receptors was specific for IGF-I, the affinity of IGF-I to the receptor being four and 150 times greater than IGF-II and insulin, respectively. There was no difference in the affinity of IGF-I to type 1 IGF receptors between less-differentiated [dissociation constant (Kd) = 3.81 nM] and well-differentiated cells (Kd = 3.78 nM); however, well-differentiated cells showed a 2.4-fold higher maximum number of binding sites (Bmax) than less-differentiated cells (3.45 vs. 1.44 x 10(4) sites/cell), indicating an increase in the density of IGF-I receptors with differentiation.(ABSTRACT TRUNCATED AT 250 WORDS)
Oguchi
S
S
Developmental Gastroenterology Laboratory, Massachusetts General Hospital, Charlestown 02129-2060, USA.
Walker
W A
WA
Sanderson
I R
IR
D000230:Adenocarcinoma; D002454:Cell Differentiation; D002455:Cell Division; D016764:Cell Polarity; D003432:Cross-Linking Reagents; D004847:Epithelial Cells; D004848:Epithelium / Q000378:metabolism; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000378:metabolism* / Q000494:pharmacology; D007413:Intestinal Mucosa / Q000378:metabolism*; D007414:Intestinal Neoplasms; D007422:Intestines / Q000166:cytology; D007457:Iodine Radioisotopes; D008970:Molecular Weight; D017526:Receptor, IGF Type 1 / Q000737:chemistry / Q000378:metabolism; D014407:Tumor Cells, Cultured
D003432:Cross-Linking Reagents; D007457:Iodine Radioisotopes; D007334:Insulin-Like Growth Factor I; D017526:Receptor, IGF Type 1