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Interleukin-2 Suppression by 2-Arachidonyl Glycerol Is Mediated through Peroxisome Proliferator-Activated Receptor Independently of Cannabinoid Receptors 1 and 2

Department of Pharmacology & Toxicology and the Center of Integrative Toxicology, Michigan State University, East Lansing, Michigan (C.E.R., N.T.S., N.E.K.); and Department of Veterinary Science and Center for Molecular Toxicology and Carcinogenesis, Pennsylvania State University, University Park, Pennsylvania (J.T.T., J.P.V.H.)

2-Arachidonyl glycerol (2-AG) is an endogenous arachidonic acid derivative that binds cannabinoid receptors CB1 and CB2 and is hence termed an endocannabinoid. 2-AG also modulates a variety of immunological responses, including expression of the autocrine/paracrine T cell growth factor interleukin (IL)-2. The objective of the present studies was to determine the mechanism responsible for IL-2 suppression by 2-AG. Because of the labile properties of 2-AG, 2-AG ether, a nonhydrolyzable analog of 2-AG, was also used. Both 2-AG and 2-AG ether suppressed IL-2 expression independently of CB1 and CB2, as demonstrated in leukocytes derived from CB1/CB2-null mice. Moreover, we demonstrated that both 2-AG and 2-AG ether treatment activated peroxisome proliferator-activated receptor (PPAR), as evidenced by forced differentiation of 3T3-L1 cells into adipocytes, induction of aP2 mRNA levels, and activation of a PPAR-specific luciferase reporter in transiently transfected 3T3-L1 cells. Consequently, the putative role of PPAR in IL-2 suppression by 2-AG and 2-AG ether was examined in Jurkat T cells. Concordant with PPAR involvement, the PPAR-specific antagonist 2-chloro-5-nitro-N-(4-pyridyl)-benzamide (T0070907) blocked 2-AG- and 2-AG ether-mediated IL-2 suppression. Likewise, 2-AG suppressed the transcriptional activity of two transcription factors crucial for IL-2 expression, nuclear factor of activated T cells and nuclear factor B, in the absence but not in the presence of T0070907. 2-AG treatment also induced PPAR binding to a PPAR response element in activated Jurkat T cells. Together, the aforementioned studies identify PPAR as a novel intracellular target of 2-AG, which mediates the suppression of IL-2 by 2-AG in a manner that is independent of CB1 and/or CB2.

Address correspondence to: Dr. Norbert Kaminski, Department of Pharmacology and Toxicology, Michigan State University, 315 National Food Safety and Toxicology Building, East Lansing, MI 48824-1317. E-mail: kamins11{at}msu.edu

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