epidermal-growth-factor and Adenoma--Islet-Cell

Foregut neuroendocrine tumors [NETs] usually pursuit a benign course, but some show aggressive behavior. The treatment of patients with advanced NETs is marginally effective and new approaches are needed. In other tumors, transactivation of the EGF receptor (EGFR) by growth factors, gastrointestinal (GI) hormones and lipids can stimulate growth, which has led to new treatments. Recent studies show a direct correlation between NET malignancy and EGFR expression, EGFR inhibition decreases basal NET growth and an autocrine growth effect exerted by GI hormones, for some NETs. To determine if GI hormones can stimulate NET growth by inducing transactivation of EGFR, we examined the ability of EGF, TGFα and various GI hormones to stimulate growth of the human foregut carcinoid,BON, the somatostatinoma QGP-1 and the rat islet tumor,Rin-14B-cell lines. The EGFR tyrosine-kinase inhibitor, AG1478 strongly inhibited EGF and the GI hormones stimulated cell growth, both in BON and QGP-1 cells. In all the three neuroendocrine cell lines studied, we found EGF, TGFα and the other growth-stimulating GI hormones increased Tyr(1068) EGFR phosphorylation. In BON cells, both the GI hormones neurotensin and a bombesin analogue caused a time- and dose-dependent increase in EGFR phosphorylation, which was strongly inhibited by AG1478. Moreover, we found this stimulated phosphorylation was dependent on Src kinases, PKCs, matrix metalloproteinase activation and the generation of reactive oxygen species. These results raise the possibility that disruption of this signaling cascade by either EGFR inhibition alone or combined with receptor antagonists may be a novel therapeutic approach for treatment of foregut NETs/PETs.

Topics: Adenoma, Islet Cell; Animals; Blotting, Western; Cell Proliferation; Epidermal Growth Factor; ErbB Receptors; Gastrointestinal Hormones; Humans; Neuroendocrine Tumors; Pancreatic Neoplasms; Phosphorylation; Rats; Reactive Oxygen Species; Signal Transduction; Somatostatinoma; Transcriptional Activation; Transforming Growth Factor alpha; Tumor Cells, Cultured; Tyrosine

Information about the mechanism of beta-cell growth and regeneration may be obtained by studies of insulinoma cells. In the present study the growth and function of the rat insulinoma cell lines RINm5F and 5AH were evaluated by addition of serum, hormones, and growth factors. It was found that transferrin is the only obligatory factor whereas growth hormone, epidermal growth factor, fibroblast growth factor, and TRH had modulating effects. A heat-labile heparin binding serum factor which stimulated thymidine incorporation but not cell proliferation was demonstrated in human serum. Measurements of insulin mRNA content showed that the insulinoma cells only contained about 2% of that of normal rat beta-cells. These results are discussed in relation to the role of growth factors, oncogenes, and differentiation in the growth and regeneration of beta-cells.

Topics: Adenoma, Islet Cell; Animals; Cell Division; Cell Line, Transformed; Cell Transformation, Neoplastic; Epidermal Growth Factor; Fibroblast Growth Factors; Growth Hormone; Insulin; Insulinoma; Islets of Langerhans; Pancreas; Pancreatic Neoplasms; Rats; Regeneration; RNA, Messenger; Thymidine; Thyrotropin-Releasing Hormone; Transferrin; Tumor Cells, Cultured

The peptide somatostatin (SRIF) is secreted by delta cells of the endocrine pancreas and inhibits the secretion of insulin from pancreatic beta cells. We have previously shown that [125I-Tyr11]SRIF binds to specific, high affinity receptors on RINm5F insulinoma cells and that these receptors mediate the action of SRIF to inhibit insulin release. In the present study we investigated the processing of receptor-bound [125I-Tyr11]SRIF in this clonal cell line. Surface-bound and internalized peptides were distinguished by the ability of an acid/salt solution (0.2 M acetic acid, 0.5 M NaCl, pH 2.5) to dissociate only exposed ligand-receptor complexes. Surprisingly, greater than 80% of saturably bound [125I-Tyr11]SRIF was removed by this acid wash independent of the time or temperature of the binding incubation. In contrast, the processing of receptor-bound [125I]EGF (epidermal growth factor) in RINm5F cells was markedly temperature-dependent. Although over 90% of saturably bound [125I]EGF was dissociated by acid after a 4 degrees C binding incubation, less than 10% was removed by acid treatment after 37 degrees C binding. The radioactivity released upon dissociation of receptor-bound [125I-Tyr11]SRIF was analyzed by high performance liquid chromatography and shown to consist of a mixture of intact peptide (40%) and [125I]tyrosine (60%). However, neither the rate of [125I-Tyr11]SRIF dissociation nor its degradation were affected by NH4Cl, methylamine, or leupeptin at concentrations which inhibited the lysosomal degradation of [125I] EGF. Of 11 other protease inhibitors tested, only the metalloendoprotease inhibitor, phosphoramidon, substantially reduced the degradation of receptor-bound [125I-Tyr11]SRIF. These data indicate that, unlike [125I] EGF, receptor-bound [125I-Tyr11]SRIF is not rapidly internalized by RINm5F cells and is degraded by a nonlysosomal process which may involve a metalloendoprotease.

Topics: Adenoma, Islet Cell; Ammonium Chloride; Animals; Cells, Cultured; Deoxyglucose; Epidermal Growth Factor; Glycopeptides; Insulinoma; Iodine Radioisotopes; Lysosomes; Methylamines; Pancreatic Neoplasms; Protease Inhibitors; Rats; Receptors, Cell Surface; Receptors, Somatostatin; Somatostatin; Temperature