Abstract
Vasoactive intestinal peptide receptors 1 (VPAC1) and 2 (VPAC2) have been identified in humans. Cell lines expressing only VPAC1 (HT-29) or VPAC2 (Molt-4b) were identified using real-time reverse transcriptase polymerase chain reaction. Vasoactive intestinal peptide (VIP) and related peptides, VIP–6–28, VIP4–28, and VIP10–28, previously isolated from cultures of human leukocytes, were evaluated for their ability to bind to VPAC1 and VPAC2 and to increase the levels of cAMP in HT-29 and Molt-4b cells. VIP bound to membranes of HT-29 colon carcinoma cells and Molt-4b lymphoblasts with high affinity (KD = 1.6 ± 0.2 and 1.7 ± 0.9 nM, respectively). VIP4–28 also demonstrated high-affinity binding (KD = 1.7 ± 0.2 and 1.7 ± 0.7 nM in HT-29 and Molt-4b, respectively). VIP and VIP4–28 are potent VPAC1 agonists, inducing maximal 200- and 400-fold increases in cAMP, respectively. VIP demonstrated weak VPAC2 agonist activity, inducing a maximal 14-fold increase in cAMP. VIP4–28 had no VPAC2 agonist activity but demonstrated potent VPAC2 antagonist activity. VIP4–28 inhibited VPAC2-mediated increases in cAMP in Molt-4b cells up to 95%, but had no antagonistic effect on VPAC1. Lymphoblasts did not hydrolyze VIP4–28 to a form with VPAC1 antagonist activity. VIP4–28 thus is a lymphocyte-generated VIP fragment with potent agonist activity for VPAC1 and potent antagonist activity for VPAC2.
Footnotes
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This research was supported by National Cancer Institute funding R01 CA41997 and R01 CA90236 (to M.S.O.).
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DOI: 10.1124/jpet.103.050583.
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ABBREVIATIONS: VIP, vasoactive intestinal peptide; RT-PCR, reverse transcriptase-polymerase chain reaction; PCR, polymerase chain reaction; TAMRA, 6-carboxytetramethylrhodamine; TCA, trichloroacetic acid; HPLC, high-pressure liquid chromatography; PAC1, pituitary adenylate cyclase-activating peptide receptor 1.
- Received March 7, 2003.
- Accepted May 9, 2003.
- The American Society for Pharmacology and Experimental Therapeutics
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