Functional expression of the rat pancreatic islet glucose-dependent insulinotropic polypeptide receptor: ligand binding and intracellular signaling properties.

• DOI: 10.1210/endo.136.10.7664683
• Publication Date: 2014-01-08T11:06:52Z
• Authors: M B Wheeler; R W Gelling; C H McIntosh; J Georgiou; J C Brown; R A Pederson
• Keywords: Gastric inhibitory polypeptide

Incretins are endogenous peptides released from the gastrointestinal tract into circulation during a meal that potentiate glucose-stimulated insulin secretion. At present, there two established incretins: glucose-dependent insulinotropic polypeptide (GIP) and truncated glucagon-like (tGLPs), which now being investigated for use in treatment of diabetes mellitus. In present study we cloned rat islet GIP receptor complementary DNA (GIP-R1) to answer several important questions regarding ligand-binding intracellular signaling properties GP receptor. GIP-R1, when expressed transiently monkey kidney (COS-7) or stably Chinese hamster ovary (CHO-K1) cells, demonstrated comparable high affinity binding either synthetic porcine (sp) human (sh) GIP. The IC50 values displacement [125I]spGIP CHO-K1 cells were 2.6 +/- 0.8 3.1 0.9 nM different preparations shGIP, 3.7 1.5 3.6 0.4 spGIP. Saturation isotherms obtained with both intact membranes gave monophasic curves apparent Kd 204 17 334 94 pM, respectively. Cells 12-15 x 10(3) receptors/cell. COS-7 spGIP shGIP also exhibited similar (7.6 1.2 8.9 1.8 nM, respectively). bound GIP-(1-30) lower (IC50 = 39 nM), whereas fragments GIP-(19-30), GIP-(18-28), GIP-(21-26) showed no binding. specificity was further examined using structurally related peptides. Surprisingly, exendin-(9-39) [Ex-(9-39)], GLP-1 antagonist, Ex-4-(1-39), agonist, some receptor, 39% 21% [125I]spGIP, respectively, at 1 microM. Other members secretin/vasoactive intestinal peptide family tested interaction. GIP-R1 correlated activation adenylyl cyclase system, whereby evoked concentration-dependent increases cAMP accumulation EC50 8.7 10(-10)M 8.1 1.6 Increases presence 10 not dependent on ambient glucose concentration, 22- 18-fold 0.1 5.5 mM glucose,