Cannabinoid Receptor Type 1- and 2-mediated Increase in Cyclic AMP Inhibits T Cell Receptor-triggered Signaling

Christine Börner,Michal Smida,Volker Höllt,Burkhart Schraven,Jürgen Kraus

doi:10.1074/jbc.m109.006338

Christine Börner, Michal Smida + Show 3 more

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https://doi.org/10.1074/jbc.m109.006338

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Abstract

The aim of this study was to characterize inhibitory mechanisms on T cell receptor signaling mediated by the cannabinoid receptors CB1 and CB2. Both receptors are coupled to G(i/o) proteins, which are associated with inhibition of cyclic AMP formation. In human primary and Jurkat T lymphocytes, activation of CB1 by R(+)-methanandamide, CB2 by JWH015, and both by Delta9-tetrahydrocannabinol induced a short decrease in cyclic AMP lasting less than 1 h. However, this decrease was followed by a massive (up to 10-fold) and sustained (at least up to 48 h) increase in cyclic AMP. Mediated by the cyclic AMP-activated protein kinase A and C-terminal Src kinase, the cannabinoids induced a stable phosphorylation of the inhibitory Tyr-505 of the leukocyte-specific protein tyrosine kinase (Lck). By thus arresting Lck in its inhibited form, the cannabinoids prevented the dephosphorylation of Lck at Tyr-505 in response to T cell receptor activation, which is necessary for the subsequent initiation of T cell receptor signaling. In this way the cannabinoids inhibited the T cell receptor-triggered signaling, i.e. the activation of the zeta-chain-associated protein kinase of 70 kDa, the linker for activation of T cells, MAPK, the induction of interleukin-2, and T cell proliferation. All of the effects of the cannabinoids were blocked by the CB1 and CB2 antagonists AM281 and AM630. These findings help to better understand the immunosuppressive effects of cannabinoids and explain the beneficial effects of these drugs in the treatment of T cell-mediated autoimmune disorders like multiple sclerosis.

Highlights

Despite of a number of reports, it remains largely unresolved which types of cannabinoid receptors mediate IL-2 inhibition and what are the detailed molecular mechanisms
It is known that the activity of C-terminal Src kinase (Csk) to phosphorylate the negative regulatory site of leukocyte-specific protein tyrosine kinase (Lck) at Tyr-505 can be further enhanced by cAMP-dependent protein kinase A (PKA)
In line with the fact that only very small amounts of CB1 are present in naive Jurkat cells, the CB1-selective agonist metanandamide with a preference for CB1 (MAEA) had no significant effect on the anti-CD3/anti-CD28-induced IL-2 mRNA levels

Summary

Introduction

Despite of a number of reports, it remains largely unresolved which types of cannabinoid receptors mediate IL-2 inhibition and what are the detailed molecular mechanisms. With regard to the mechanisms of the cannabinoid-mediated inhibition of IL-2, it was shown that the drugs inhibit the T cell receptor (TCR)-induced activities of the transcription factors NF-␬B and NFAT (4, 16, 17). In nonactivated, resting T cells, this cascade is tonically repressed by constitutive phosphorylation of the negative regulatory site of the leukocyte-specific protein tyrosine kinase (Lck) at Tyr-505. Activated Zap 70 in turn phosphorylates the adaptor protein linker for activation of T cells (LAT), leading to the induction of calcium flux and activation of the MAPK cascades In this way, the signal is transduced, and the transcription factors AP-1, NF-␬B, and NFAT are activated and transactivate the IL-2 gene. We report on the molecular linkage between CB1 and CB2 and T cell signaling and present a mechanism by which cannabinoids inhibit IL-2 production of activated human T cells via these receptors

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