Functional selectivity at the CB1 receptor supports the complex modulation of tyrosine hydroxylase by cannabinoid agonists in neuroblastoma cells,
(2007) Neuroscience — Location: San Diego, CA, US (3.November.2007)
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- Acute and repeated administration of delta9-tetrahydrocannabinol (THC), the principal psychoactive constituent of Cannabis sativa, is associated with the modulation of motor and emotional behaviours. These effects frequently correlate with altered neuronal communication in particular at the level of dopamine transmission systems. Indeed, we recently reported a cannabinoid receptor (CB1)-mediated complex regulation of tyrosine hydroxylase (TH) gene expression in N1E-115 neuroblastoma cells (Bosier et al., J. Neurochemistry 2007). Indeed, the two typical CB1 receptor agonists HU 210 and CP 55,940 where shown to decrease and increase TH expression, respectively. We now further investigated the signalling pathways associated with the stimulation of the CB1 receptors in these cells using a TH promoter-driven luciferase reporter gene assay. Thus, PKC, PKA or MEK1/2 inhibitors totally prevented HU 210-induced reduction of luciferase activity while CP 55,940-induced activity was abolished using PKC, PI3K or JNK inhibitors. Besides, the opposite effects of HU 210 and CP 55,940 were both modified after pertussis toxin pretreatment, suggesting that Gi/o-proteins are involved in the regulation of these signalling pathways. Given the crucial regulatory role of the cis-enhancer elements CRE and AP1 within the TH promoter, luciferase reporter gene assays were repeated with constructs in which these sequences were specifically mutated. Both agonists displayed a reduced efficacy when tested on the CRE mutated construct while AP1 mutation totally prevented the CP 55,940-induced increase in transcription. These data suggest that the CRE element regulates the strength of CB1 receptor mediated effects whereas the AP1 element is essential to observe a dual response. Finally, the assays were repeated in the presence of forskolin, in order to boost adenylyl cyclase activity and favour the detection of Gi/o-mediated responses. Our data show that in these conditions, both agonists decreased luciferase activity, a response that was totally prevented using PKA inhibitors. This suggests that the concomitant activation of cellular effectors or alteration in the cellular environment could strongly influence cannabinoid responses to selected agonists. Together, these data confirm a functional selectivity of drugs acting at the CB1 receptor which explains the complex regulation of TH expression through a variety of signalling pathways. In vivo studies are in progress to specifically investigate the influence of CB1 agonists on TH expression in the striatum of rats as well as on striatal dopamine content and dopamine related motor behaviours.
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Bosier, B., & et al. (2007). Functional selectivity at the CB1 receptor supports the complex modulation of tyrosine hydroxylase by cannabinoid agonists in neuroblastoma cells,. Neuroscience, San Diego, CA, US. https://hdl.handle.net/2078.5/86566