Abstract
Hemokinin-1 (HK-1) is a newly identified tachykinin, originating from the immune system rather than neurons, and may participate in the immune and inflammatory response. In colonic mucosa of patients with inflammatory bowel disease (IBD), up-regulation of the TAC4 gene encoding HK-1 and increased production of prostaglandin E2 (PGE2) occur. Our aim was to examine the mechanistic link between human HK-1 and PGE2 production in normal human colon. Exogenous HK-1 (0.1 μM) for 4 h evoked an increased PGE2 release from colonic mucosal and muscle explants by 10- and 3.5-fold, respectively, compared with unstimulated time controls. The HK-1-stimulated PGE2 release was inhibited by the tachykinin receptor antagonists (S)1–2-[3-(3,4-dichlorophenyl)-1-(3-isopropoxyphenylacetyl)piperidin-3-yl]ethyl-4-phenyl-l azonia-bicyclo[2.2.2]octane (SR140333) [neurokinin-1 (NK1)] and N-[(2S)-4-(4-acetamido-4-phenylpiperidin-1-yl)-2-(3,4-dichlorophenyl)butyl]-N-methylbenzamide (SR48968) [neurokinin-2 (NK2)] and was also inhibited by the cyclooxygenase (COX)-2 inhibitor N-(2-cyclohexyloxy-4-nitrophenyl)methanesulfonamide) (NS-398) but not by the COX-1 inhibitor 5-(4-chlorophenyl)-1-(4-methoxyphenyl)-3-trifluoromethylpyrazole (SC-560). A parallel study with substance P showed similar results. Molecular studies with HK-1-treated explants demonstrated a stimulatory effect on COX-2 expression at both transcription and protein levels. It is noteworthy that this was coupled with HK-1-induced down-regulation of 15-hydroxyprostaglandin dehydrogenase (15-PGDH) mRNA and protein expression. Immunoreactivity for 15-PGDH occurred on inflammatory cells, epithelial cells, platelets, and ganglia. This finding provides an additional mechanism for HK-1-evoked PGE2 increase, in which HK-1 may interfere with the downstream metabolism of PGE2 by suppressing 15-PGDH expression. In conclusion, our results uncover a novel inflammatory role for HK-1, which signals via NK1 and NK2 receptors to regulate PGE2 release from human colonic tissue, and may further explain a pathological role for HK-1 in IBD when abnormal levels of PGE2 occur.
Footnotes
This study was supported by the National Health and Medical Research Council of Australia [Grant ID 568861]. B.R.S. was supported by the Victorian Government's Operational Infrastructure Support Program.
This article represents partial fulfillment for L.D.'s Ph.D thesis in pharmacology.
Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
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ABBREVIATIONS:
- SP
- substance P
- HK-1
- hemokinin-1
- PGE2
- prostaglandin E2
- COX
- cyclooxygenase
- IR
- immunoreactivity
- 15-PGDH
- 15-hydroxyprostaglandin dehydrogenase
- NK
- neurokinin
- IBD
- inflammatory bowel disease
- GAPDH
- glyceraldehyde-3-phosphate dehydrogenase
- HKG
- housekeeping gene
- ANOVA
- analysis of variance
- ELISA
- enzyme-linked immunosorbent assay
- PCR
- polymerase chain reaction
- qPCR
- quantitative PCR
- TTX
- tetrodotoxin
- fp
- forward primer
- rp
- reverse primer
- SR140333
- (S)1–2-[3-(3,4-dichlorophenyl)-1-(3-isopropoxyphenylacetyl)piperidin-3-yl]ethyl-4-phenyl-l azonia-bicyclo[2.2.2]octane
- SR48968
- N-[(2S)-4-(4-acetamido-4-phenylpiperidin-1-yl)-2-(3,4-dichlorophenyl)butyl]-N-methylbenzamide
- SC-560
- 5-(4-chlorophenyl)-1-(4-methoxyphenyl)-3-trifluoromethylpyrazole
- NS-398
- N-(2-cyclohexyloxy-4-nitrophenyl)methanesulfonamide).
- Received July 25, 2011.
- Accepted September 27, 2011.
- Copyright © 2012 by The American Society for Pharmacology and Experimental Therapeutics
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