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N‐terminally and C‐terminally truncated forms of glucose‐dependent insulinotropic polypeptide are high‐affinity competitive antagonists of the human GIP receptor
Author(s) -
Hansen L S,
SparreUlrich A H,
Christensen M,
Knop F K,
Hartmann B,
Holst J J,
Rosenkilde M M
Publication year - 2016
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/bph.13384
Subject(s) - agonist , medicine , endocrinology , gastric inhibitory polypeptide , receptor , chemistry , schild regression , biology , biochemistry , insulin , glucagon
Background and Purpose Glucose‐dependent insulinotropic polypeptide (GIP) affects lipid, bone and glucose homeostasis. High‐affinity ligands for the GIP receptor are needed to elucidate the physiological functions and pharmacological potential of GIP in vivo . GIP(1–30)NH 2 is a naturally occurring truncation of GIP(1–42). Here, we have characterized eight N‐terminal truncations of human GIP(1–30)NH 2 . Experimental Approach COS‐7 cells were transiently transfected with human GIP receptors and assessed for cAMP accumulation upon ligand stimulation or competition binding with 125 I‐labelled GIP(1–42), GIP(1–30)NH 2 , GIP(2–30)NH 2 or GIP(3–30)NH 2 . Key Results GIP(1–30)NH 2 displaced 125 I‐GIP(1–42) as effectively as GIP(1–42) (K i 0.75 nM), whereas the eight truncations displayed lower affinities (K i 2.3–347 nM) with highest affinities for GIP(3–30)NH 2 and GIP(5–30)NH 2 (5–30)NH 2 . Only GIP(1–30)NH 2 (E max 100% of GIP(1–42)) and GIP(2–30)NH 2 (E max 20%) were agonists. GIP(2‐ to 9–30)NH 2 displayed antagonism (IC 50 12–450 nM) and Schild plot analyses identified GIP(3–30)NH 2 and GIP(5–30)NH 2 as competitive antagonists (K i 15 nM). GIP(3–30) NH 2 was a 26‐fold more potent antagonist than GIP(3–42). Binding studies with agonist ( 125 I‐GIP(1–30)NH 2 ), partial agonist ( 125 I‐GIP(2–30)NH 2 ) and competitive antagonist ( 125 I‐GIP(3–30)NH 2 ) revealed distinct receptor conformations for these three ligand classes. Conclusions and Implications The N‐terminus is crucial for GIP agonist activity. Removal of the C‐terminus of the endogenous GIP(3–42) creates another naturally occurring, more potent, antagonist GIP(3–30)NH 2 , which like GIP(5–30)NH 2 , was a high‐affinity competitive antagonist. These peptides may be suitable tools for basic GIP research and future pharmacological interventions.