Glucose-dependent insulinotropic polypeptide stimulated insulin release from a tumor-derived β-cell line (βTC3)

Abstract

The beta TC3 tumor cell line was examined for the presence of functional glucose-dependent insulinotropic polypeptide (GIP) receptors. Increasing amounts of natural porcine GIP decreased the binding of HPLC-purified [125I]GIP to beta TC3 cells in a concentration-dependent manner. Displacement of GIP was significant at concentrations as low as 500 pM, and the radioligand was fully displaced at 100 nM. GIP(1-30) produced a displacement of [125I]GIP comparable with that produced by GIP(1-42), and glucagon yielded 20% displacement at a concentration of 1 microM but was without effect at 100 mM. Incubation of beta TC3 cells in the presence of glucose concentrations of 2-20 mM yielded a concentration-dependent stimulation of immunoreactive insulin (IRI) release. GIP and glucagon-like peptide-I(7-36) amide (tGLP-I) at concentrations of 1 nM or greater significantly stimulated IRI release in the presence of 2 mM glucose. The threshold glucose concentration for GIP-stimulated IRI release from beta TC3 cells was 0.5 mM, and maximal potentiation of IRI release by GIP occurred at 5 mM glucose. Somatostatin significantly inhibited GIP-stimulated IRI release in the presence of 5 mM glucose. It is concluded that beta TC3 cells have functional GIP receptors and may provide a useful model for the study of IRI secretion at the cellular level.

Role of glucose in chronic desensitization of isolated rat islets and mouse insulinoma (betaTC-3) cells to glucose-dependent insulinotropic polypeptide

“…In confirmation of previous work (Kieffer et al 1993, Jia et al 1995, GIP was shown in the current study to exert its insulin-potentiating effects only in the presence of increased glucose, with both perifused islets and TC-3 cells (Figs 1 and 4). Chronic exposure of islets to 11 mM glucose resulted in an insulin secretory profile characterized by desensitization of the response over time (Fig.…”

“…Both glucose and GIP produced changes in insulin release from TC-3 cells similar to those previously published (Kieffer et al 1993). Parallel experiments on desensitization of insulin release show that the same procedure used for the cAMP studies yields a significant reduction in insulin release.…”

“…The degree of glucose-stimulated insulin release from TC-3 cells in KRB was similar to that previously observed (Kieffer et al 1993), with significant insulin released by 5·5 and 11 mM glucose (163 16% and 182 21% basal release in 0 mM glucose respectively; P<0·05 and P<0·01 compared with basal) (Fig. 4A).…”

“…GIP receptors have been demonstrated to be expressed in this cell line, and stimulation of insulin release by GIP is glucosedependent (Kieffer et al 1993). cAMP production in response to GIP was found to increase in a concentrationdependent manner ( Fig.…”

Postprandial stimulation of insulin release by glucose-dependent insulinotropic polypeptide (GIP). Effect of a specific glucose-dependent insulinotropic polypeptide receptor antagonist in the rat.

“…GLP(7-37) and porcine GIP (5 g each) were iodinated by the chloramine-T method and were purified using C-18 cartridges (model Sep-Pak; Millipore Corp., Waters Chromatography, Milford, MA) using an acetonitrile gradient of 30-45%. The specific activity of radiolabeled peptides was 10-50 Ci/mg (18,19). Aliquots were lyophilized and reconstituted in assay buffer at 4 Њ C to a concentration of 3 ϫ 10 5 cpm/100 l. Binding studies were performed in desegregated stably transfected L293 or ␤ TC3 cells, the latter a generous gift from Dr. S. Efrat (Diabetes Center, Albert Einstein College of Medicine, NY).…”