Received for publication April 24, 2006.
Revised August 25, 2006.
Accepted for publication August 25, 2006.

Cannabinoid receptor-mediated apoptosis induced by R(+)-methanandamide and Win55,212 is associated with ceramide accumulation and p38 activation in Mantle Cell Lymphoma

Abstract

We have recently shown that cannabinoids induce growth inhibition and apoptosis in mantle cell lymphoma (MCL), a malignant B-cell lymphoma that expresses high levels of cannabinoid receptors type 1 and 2 (CB₁ and CB₂). In the current study, the role of each receptor and the signal transduction triggered by receptor ligation were investigated. Induction of apoptosis following treatment with the synthetic agonists R(+)-methanandamide (R(+)-MA) and Win55,212-2 (Win55) was dependent on both cannabinoid receptors, as pre-treatment with SR141716A and SR144528, specific antagonists to CB₁ and CB₂, respectively, abrogated caspase-3 activity. Preincubation with the inhibitors SB203580 and SB202190 showed that phosphorylation of MAPK p38 was implicated in the signal transduction leading to apoptosis. Treatment with R(+)-MA and Win55 was associated with accumulation of ceramide, and pharmacological inhibition of ceramide synthesis de novo prevented both p38 activation and mitochondria depolarization assessed by binding of 3,3'- dihexyloxacarbocyanine iodide (DiOC6). In contrast, the pan-caspase inhibitor z-Val-Ala-Asp(Ome)-CH₂ (z-VAD-FMK) did not protect the mitochondrial integrity. Collectively, these results suggest that concurrent ligation of CB₁ and CB₂ with either R(+)-MA or Win55 induces apoptosis via a sequence of events in MCL cells: accumulation of ceramide, phosphorylation of p38, depolarization of the mitochondrial membrane and caspase activation. While induction of apoptosis was observed in both MCL cell lines and primary MCL, normal B-cells remained unaffected. The present data suggest that targeting CB₁/ CB₂ may have therapeutic potential in the treatment of mantle cell lymphoma.

Key words: Cannabinoid, Sphingolipids, MAP Kinase, P38 MAP Kinase, Mechanisms of cell killing/apoptosis

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