Fibroblast growth factor-2 inhibits the maturation of pro-insulin-like growth factor-II (Pro-IGF-II) and the expression of insulin-like growth factor binding protein-2 (IGFBP-2) in the human adrenocortical tumor cell line NCI-H295R.
The IGF system is thought to play a major role in adrenocortical tumorigenesis. In this study, we used the NCI H295R cell line as a model to investigate the effects of fibroblast growth factor-2 (FGF-2), a potent mitogen for normal adrenal cells, on the proliferation and on the expression of the IGF system in cultured adrenocortical tumor cells. Three immunoreactive FGF-2 isoforms of molecular masses 18, 22, and 24 kDa were detected in H295R cell extracts. Recombinant human FGF-2 stimulated the proliferation of adrenocortical tumor cells in a dose- and time-dependent manner, with a maximal effect at a concentration of about 1 ng/ml. Treatment of H295R cells with 10 ng/ml FGF-2 for 7 days had no significant effect on IGF-II messenger RNA levels. However, a marked increase in levels of intracellular IGF-II protein was detected by immunoblotting. In contrast, FGF-2 induced a marked decrease in the amount of IGF-II protein secreted, with the disappearance of mature IGF-II and secretion of higher molecular forms of the growth factor, suggesting modifications of IGF-II processing. Cell cultures in the presence of brefeldin A (1 microg/ml), a specific inhibitor of protein secretion, suggested that FGF-2 did not increase IGF-II synthesis but instead inhibited the secretion of pro-IGF-II from H295R cells, thereby impairing the final steps of IGF-II processing to the mature 7.5-kDa peptide. At the same concentrations, FGF-2 also decreased both IGFBP-2 messenger RNA and secreted protein, which might increase IGF-II bioavailability. No proteolysis of IGFBP-2 was detected in FGF-2-conditioned medium. Altogether, these results indicate that FGF-2 is mitogenic for NCI H295R tumor cells and regulates the expression of both IGF-II and IGFBP-2 in this tumor model. Moreover, this study shows a novel effect of FGF-2, by which this growth factor modulates the processing of pro-IGF-II.
Boulle
N
N
Laboratoire d'Explorations Fonctionnelles Endocriniennes, Hôpital Trousseau, Paris, France. lab.endoc@trs.ap-hop-paris.fr
Gicquel
C
C
Logié
A
A
Christol
R
R
Feige
J J
JJ
Le Bouc
Y
Y
D000306:Adrenal Cortex Neoplasms / Q000378:metabolism / Q000473:pathology; D015152:Blotting, Northern; D015153:Blotting, Western; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D003720:Densitometry; D004591:Electrophoresis, Polyacrylamide Gel; D016222:Fibroblast Growth Factor 2 / Q000494:pharmacology*; D006801:Humans; D018971:Insulin-Like Growth Factor Binding Protein 2 / Q000096:biosynthesis*; D007335:Insulin-Like Growth Factor II / Q000096:biosynthesis*; D008934:Mitogens / Q000494:pharmacology; D011498:Protein Precursors / Q000096:biosynthesis*; D012313:RNA / Q000096:biosynthesis; D013936:Thymidine / Q000378:metabolism; D014407:Tumor Cells, Cultured
D018971:Insulin-Like Growth Factor Binding Protein 2; D008934:Mitogens; D011498:Protein Precursors; C066038:proinsulin-like growth factor II; D016222:Fibroblast Growth Factor 2; D012313:RNA; D007335:Insulin-Like Growth Factor II; D013936:Thymidine