Kynurenic acid is a potent endogenous aryl hydrocarbon receptor ligand that synergistically induces interleukin-6 in the presence of inflammatory signaling.
Inflammatory signaling plays a key role in tumor progression, and the pleiotropic cytokine interleukin-6 (IL-6) is an important mediator of protumorigenic properties. Activation of the aryl hydrocarbon receptor (AHR) with exogenous ligands coupled with inflammatory signals can lead to synergistic induction of IL6 expression in tumor cells. Whether there are endogenous AHR ligands that can mediate IL6 production remains to be established. The indoleamine-2,3-dioxygenase pathway is a tryptophan oxidation pathway that is involved in controlling immune tolerance, which also aids in tumor escape. We screened the metabolites of this pathway for their ability to activate the AHR; results revealed that kynurenic acid (KA) is an efficient agonist for the human AHR. Structure-activity studies further indicate that the carboxylic acid group is required for significant agonist activity. KA is capable of inducing CYP1A1 messenger RNA levels in HepG2 cells and inducing CYP1A-mediated metabolism in primary human hepatocytes. In a human dioxin response element-driven stable reporter cell line, the EC(25) was observed to be 104nM, while in a mouse stable reporter cell line, the EC(25) was 10muM. AHR ligand competition binding assays revealed that KA is a ligand for the AHR. Treatment of MCF-7 cells with interleukin-1beta and a physiologically relevant concentration of KA (e.g., 100nM) leads to induction of IL6 expression that is largely dependent on AHR expression. Our findings have established that KA is a potent AHR endogenous ligand that can induce IL6 production and xenobiotic metabolism in cells at physiologically relevant concentrations.
DiNatale
Brett C
BC
Center for Molecular Toxicology and Carcinogenesis, Department of Veterinary and Biomedical Sciences, Pennsylvania State University, University Park, Pennsylvania 16803, USA.
Murray
Iain A
IA
Schroeder
Jennifer C
JC
Flaveny
Colin A
CA
Lahoti
Tejas S
TS
Laurenzana
Elizabeth M
EM
Omiecinski
Curtis J
CJ
Perdew
Gary H
GH
D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins; D001943:Breast Neoplasms / Q000188:drug therapy / Q000378:metabolism; D045744:Cell Line, Tumor; D019363:Cytochrome P-450 CYP1A1 / Q000096:biosynthesis / Q000235:genetics; D004785:Environmental Pollutants / Q000633:toxicity; D004790:Enzyme Induction / Q000187:drug effects; D018691:Excitatory Amino Acid Antagonists / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology; D005260:Female; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D050503:Indoleamine-Pyrrole 2,3,-Dioxygenase / Q000378:metabolism; D015850:Interleukin-6 / Q000096:biosynthesis*; D007736:Kynurenic Acid / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology; D008024:Ligands; D051379:Mice; D000072317:Polychlorinated Dibenzodioxins / Q000633:toxicity; D012333:RNA, Messenger / Q000378:metabolism; D018336:Receptors, Aryl Hydrocarbon / Q000819:agonists* / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D013329:Structure-Activity Relationship
D051792:Basic Helix-Loop-Helix Proteins; D019363:Cytochrome P-450 CYP1A1; D004785:Environmental Pollutants; D018691:Excitatory Amino Acid Antagonists; D050503:Indoleamine-Pyrrole 2,3,-Dioxygenase; D015850:Interleukin-6; D007736:Kynurenic Acid; D008024:Ligands; D000072317:Polychlorinated Dibenzodioxins; D012333:RNA, Messenger; D018336:Receptors, Aryl Hydrocarbon; C111235:AHR protein, human