Alterations in receptor expression or agonist concentration change the pathways gastrin-releasing peptide receptor uses to regulate extracellular signal-regulated kinase.
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.
Chen
Pei-Wen
PW
Department of Molecular Pharmacology, Albert Eistein College of Medicine, Bronx, New York 10461, USA.
Kroog
Glenn S
GS
D016475:3T3 Cells; D000818:Animals; D001839:Bombesin / Q000494:pharmacology; D002460:Cell Line; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000502:physiology*; D006801:Humans; D007211:Indoles / Q000494:pharmacology; D008301:Maleimides / Q000494:pharmacology; D051379:Mice; D018613:Microscopy, Confocal; D021381:Protein Transport; D018004:Receptors, Bombesin / Q000819:agonists / Q000502:physiology*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D004791:Enzyme Inhibitors; D007211:Indoles; D008301:Maleimides; D018004:Receptors, Bombesin; D048049:Extracellular Signal-Regulated MAP Kinases; C070515:bisindolylmaleimide I; D013755:Tetradecanoylphorbol Acetate; D001839:Bombesin