Type-II insulin-like growth-factor receptor in conditioned medium from HT-29 human colon carcinoma cell line.
The HT-29 human colon cancer cell line has previously been shown to secrete high amounts of insulin-like growth factor II (IGF-II). The recent demonstration that soluble IGF-II/mannose 6-phosphate receptor was present in fetal serum prompted us to search for a release of type-II IGF receptor by these human colonic carcinoma cells. Serum-free conditioned medium from the HT-29 cell line was gel filtered on Sephadex G-200. There was significant binding of [125I]IGF-II to the void volume fractions in addition to binding to the 40-kDa IGF-binding protein (IGF-BP) fractions. Competitive binding studies using [125I]IGF-II and the void volume pool showed a pattern typical of the type-II receptor. It exhibited a high affinity for IGF-II (KD = 0.4 nM), but had a low affinity for IGF-I (KD = 6.8 nM), and no detectable affinity for insulin. Additional evidence was provided by affinity cross-linking of [125I]IGF-II to the same high-molecular-weight material which demonstrated a major specific band at 250 kDa after reduction of disulfide bonds. In contrast, the type-I IGF receptor was undetectable. The extracellular type-II IGF receptor was not a significant carrier for IGF-II since virtually all IGF-II secreted by HT-29 cells was associated with IGF-BP. The presence of a soluble IGF-II/mannose 6-phosphate receptor in the culture medium from colonic cancer cells suggests that it may play an important role in tumor pathogenesis.
Garrouste
F
F
Laboratoire d'Immunologie, Faculté de Médecine, Marseilles, France.
Remacle-Bonnet
M
M
Culouscou
J M
JM
Marvaldi
J
J
Pommier
G
G
D000230:Adenocarcinoma / Q000378:metabolism*; D001667:Binding, Competitive; D002850:Chromatography, Gel; D003110:Colonic Neoplasms / Q000378:metabolism*; D003470:Culture Media; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D007335:Insulin-Like Growth Factor II / Q000378:metabolism; D017527:Receptor, IGF Type 2; D011956:Receptors, Cell Surface / Q000378:metabolism*; D017451:Receptors, Somatomedin; D014407:Tumor Cells, Cultured
D003470:Culture Media; D017527:Receptor, IGF Type 2; D011956:Receptors, Cell Surface; D017451:Receptors, Somatomedin; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II