Abstract
Cannabinol (CBN), an immunosuppressive cannabinoid and ligand for the peripheral cannabinoid receptor CB2, inhibits the cAMP signaling cascade in forskolin-stimulated thymocytes. The objective of the present studies was to further characterize the mechanism of CBN immune modulation by investigating its effects on interleukin-2 (IL-2) secretion, cAMP response element (CRE), and κB DNA binding activity in phorbol ester (phorbol-12-myristate-13-acetate, PMA) plus calcium ionophore (PMA/Io)-activated thymocytes. PMA/Io treatment induced CRE and κB DNA binding activity that was attenuated in the presence of CBN. A concomitant and concentration-related inhibition of IL-2 also was produced by CBN in PMA/Io-activated thymocytes. PMA/Io induced two CRE DNA binding complexes, a major complex consisting of a cAMP response element-binding protein (CREB)-1 homodimer, and a minor CREB-1/activating transcription factor (ATF)-2 complex. Both CRE complexes were inhibited by CBN. Conversely, two κB DNA binding complexes were observed, but only one was PMA/Io-inducible. However, the DNA binding activity of both complexes was diminished in the presence of CBN. The PMA/Io-inducible κB complex was a p65/c-Rel heterodimer. Analysis of up-stream regulation revealed a decrease in phosphorylated CREB/ATF nuclear proteins in PMA/Io-activated thymocytes after CBN treatment. Similarly, CBN prevented the phosphorylation-dependent degradation of the nuclear factor-κB inhibitory protein IκB-α. These results provide a potential link between the CBN-mediated inhibition of thymocyte function, including IL-2 production, and the inhibition of two critical transcription factor families, CREB/ATF and NF-κB/Rel.
Footnotes
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Send reprint requests to: Norbert E. Kaminski, Department of Pharmacology and Toxicology, 315 Food Safety and Toxicology Building, Michigan State University, East Lansing, MI 48824. E-mail:kamins11{at}pilot.msu.edu
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↵1 This work was supported by National Institute on Drug Abuse Grant DA07908.
- Abbreviations:
- CB
- cannabinoid receptor
- CBN
- cannabinol
- PKA
- protein kinase A
- CRE
- cAMP response element
- CREB
- cAMP response element-binding protein
- ATF
- activating transcription factor
- IL-2
- interleukin-2
- NF
- nuclear factor
- AT
- activated T cells
- AP-1
- activator protein-1
- PMA
- phorbol-12-myristate-13 acetate
- THC
- tetrahydrocannabinol
- EMSA
- electrophoretic mobility shift assay
- ELISA
- enzyme-linked immunosorbent assay
- MAPK
- mitogen-activated protein kinase
- PAGE
- polyacrylamide gel electrophoresis
- ECL
- enhanced chemiluminescence
- PKAc
- protein kinase A catalytic subunit
- Received February 16, 1999.
- Accepted August 10, 1999.
- The American Society for Pharmacology and Experimental Therapeutics
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Cannabinol-Mediated Inhibition of Nuclear Factor-κB, cAMP Response Element-Binding Protein, and Interleukin-2 Secretion by Activated Thymocytes
