Gastric inhibitory peptide human

Abstract

G protein-coupled receptors activate extracellular signal-regulated kinases (ERKs) via different pathways in different cell types. In this study, we demonstrate that gastrin-releasing peptide receptor (GRPr) regulates ERK through multiple pathways in a single cell type depending upon receptor expression and agonist concentration. We examined stably transfected BALB/c 3T3 fibroblasts expressing GRPr constructs at different levels and treated the cells with several concentrations of bombesin (BN, a GRPr agonist) to activate a variable number of GRPr per cell. GRPr induced two waves of ERK activation and one wave of ERK inhibition. One wave of activation required an intact GRPr carboxyl-terminal domain (CTD). It peaked 6 min after addition of high BN concentration ([BN]) in cells with high GRPr expression. Another wave of activation was CTD-independent. It peaked 2 to 4 min after BN addition in cells when [BN] and/or GRPr expression were lower. The early wave of ERK activation was more sensitive than the later one to pretreatment with Bisindolylmaleimide I (GF 109203X) (a protein kinase C inhibitor) or hypertonic sucrose. Because these two waves of activation differ in time course, dose-response curve, requirement for GRPr CTD, and sensitivity to inhibitors, they result from different signaling pathways. A third pathway in these cells inhibited ERK phosphorylation 2 min after addition of high [BN] in cells with high GRPr expression. Furthermore, a GRPr-expressing human duodenal cancer cell line showed differential sensitivity to GF 109203X throughout BN-induced ERK activation, indicating that GRPr may activate ERK via multiple pathways in cells expressing endogenous GRPr.

Materials

Dulbecco’s modified Eagle’s medium (DMEM), fetal bovine serum, penicillin/streptomycin, G-418, and LipofectAMINE reagent were from Invitrogen (Carlsbad, CA). BN was from Bachem California (Torrance, CA). [D-Phe 6]BN(6-13) methyl ester ([D-Phe 6]BN(6-13) ME) was a gift from Dr. David Coy (Tulane University, New Orleans, LA). 125 I-Labeled BN (125 I-BN; 2200 Ci/mmol) and HuTu 80 cells were obtained from Sam Mantey and Dr. Robert Jensen (National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, MD).

The Carboxyl-Terminal Domain of GRPr Is Required for Bombesin-Induced ERK Activation in BALB/c 3T3 Mouse Fibroblasts Expressing High Levels of GRPr

To determine whether the CTD of GRPr is involved in BN-induced ERK activation, we studied stably transfected BALB/c 3T3 fibroblast cell lines expressing high levels (240,000-950,000 receptors/cell) of either wild-type or CTD mutant GRPr (Ally et al., 2003). The cell lines studied were myc-GRPr, expressing myc-tagged wild-type GRPr; Δ346, expressing CTD truncation of GRPr afterLeu 345; and S/T-mut, expressing GRPr with 12 of 13 Ser and Thr residues distal to Leu 345 (all except Thr 371) replaced with Ala.

Discussion

GPCRs activate MAPK via cell type-specific mechanisms (Liebmann, 2001). In this study, we demonstrate that GRPr activation enhances or diminishes the level of ERK phosphorylation through three distinct pathways in a single cell type. The amplitude of each pathway was a function of both concentration of added BN and number of GRPr per cell. Evidence for two pathways that increase ERK phosphorylation was provided by differences in time course, dose-response curve, requirement for CTD, and sensitivity to inhibitors.

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• Molecular mechanisms mediating gastrin-releasing peptide receptor modulation of memory consolidation in the hippocampus 2006, Neuropharmacology Show abstract Although the gastrin-releasing peptide-preferring bombesin receptor (GRPR) has been implicated in memory formation, the underlying molecular events are poorly understood. In the present study, we examined interactions between the GRPR and cellular signaling pathways in influencing memory consolidation in the hippocampus. Male Wistar rats received bilateral infusions of bombesin (BB) into the dorsal hippocampus immediately after inhibitory avoidance (IA) training. Intermediate doses of BB enhanced, whereas a higher dose impaired, 24-h IA memory retention. The BB-induced memory enhancement was prevented by pretraining infusions of a GRPR antagonist or inhibitors of protein kinase C (PKC), mitogen-activated protein kinase (MAPK) kinase and protein kinase A (PKA), but not by a neuromedin B receptor (NMBR) antagonist. We next further investigated the interactions between the GRPR and the PKA pathway. BB-induced enhancement of consolidation was potentiated by coinfusion of activators of the dopamine D1/D5 receptor (D1R)/cAMP/PKA pathway and prevented by a PKA inhibitor. We conclude that memory modulation by hippocampal GRPRs is mediated by the PKC, MAPK, and PKA pathways. Furthermore, pretraining infusion of BB prevented beta-amyloid peptide (25–35)-induced memory impairment, supporting the view that the GRPR is a target for the development of cognitive enhancers for dementia.
• Gastrin-releasing peptide receptors in the central nervous system: Role in brain function and as a drug target 2012, Frontiers in Endocrinology
• Regulation of survival, proliferation, and migration of cancer cells by bombesin/gastrin-releasing peptide signaling pathways 2010, Current Opinion in Endocrinology, Diabetes and Obesity