Serum factors inhibit melanoma cell surface expression of type I and type II IGF receptors.
We have identified one class of IGF-I-binding sites and two classes of IGF-II-binding sites at the surface of the melanoma cell line IGR39. By means of affinity labeling with 125I-IGF-I, 290-300 kDa form was characterized. Using 125I-IGF-II, a 270 kDa polypeptide was labeled, corresponding to the type II IGF receptor. In the two serials of experiments, the order of potency in inhibiting 125I-IGF-I or 125I-IGF-II labeling of IGF-related peptides and alpha IR3, an antibody directed against type I receptor alpha subunit, was the same as in competition experiments. When IGR39 cells were cultured in a serum-free medium, the number of both high affinity IGF-II and IGF-I binding sites was increased, by 8- and 5-fold respectively, without any significant change in Kd values. In both culture conditions, we found IGFBP-2, -3 -4 and a 30 kDa form which Mr was consistent with IGFBP-5 or -6. Except for IGFBP-2, the amount of secreted IGFBPs was modified depending on culture conditions: in conditioned medium from cells cultured with 10% FCS, the amount of IGFBP-3 or -4 was higher, and the amount of the 30 kDa IGFBP was lower when compared to conditioned medium from cells cultured in serum-free medium.
Bellan
C
C
Laboratoire de biochimie cellulaire URA CNRS 1924, Faculté de Pharmacie, Marseille.
Remacle-Bonnet
M
M
Garrouste
F
F
Secchi
J
J
Luis
J
J
Pommier
G
G
Marvaldi
J
J
D000345:Affinity Labels / Q000378:metabolism; D001665:Binding Sites; D001667:Binding, Competitive; D001798:Blood Proteins / Q000494:pharmacology*; D015153:Blotting, Western; D002460:Cell Line; D016895:Culture Media, Serum-Free; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects*; D006801:Humans; D008545:Melanoma / Q000378:metabolism*; D017526:Receptor, IGF Type 1 / Q000096:biosynthesis*; D017527:Receptor, IGF Type 2 / Q000096:biosynthesis*
D000345:Affinity Labels; D001798:Blood Proteins; D016895:Culture Media, Serum-Free; D017527:Receptor, IGF Type 2; D017526:Receptor, IGF Type 1