The CB(1)
cannabinoid receptor shows complex interactions with intracellular signalling partners, and responses to
cannabinoid ligands are likely to be influenced by concomitant inputs modifying the overall tone of signalling cascades. This appears even more relevant as we previously evidenced opposite regulations of
tyrosine hydroxylase (TH) expression by the two common
cannabinoid agonists HU 210 and CP 55,940. Therefore, we studied the consequences of manipulating
adenylyl cyclase activity with
forskolin on the regulation of TH gene transcription in
neuroblastoma cells (N1E-115). Reporter gene experiments performed with the
luciferase sequence cloned under the control of modified fragments of the TH gene promoter revealed that the
AP-1 consensus sequence is essential for
cannabinoid-mediated regulation of TH expression. Consistently, inhibition of PKC totally blocked the responses mediated by both
HU 210 and CP 55,940. In addition,
forskolin which boosts
adenylyl cyclase activity remarkably modified the responses to the
cannabinoid agonists. Thus, in these conditions, both agonists efficiently reduced TH gene promoter activity, a response requiring functional PKA/CRE-dependent signallings. Finally, the modulations of the promoter were inhibited in
pertussis toxin treated cells, suggesting that responses to both agonists are mediated through G(i/o)-dependent mechanisms. Emphasising on the importance of functional selectivity at GPCRs, these data demonstrate that the concomitant activation of
adenylyl cyclase by
forskolin strongly influences the biochemical responses triggered by distinct
cannabinoid agonists. Together our results suggest that the physiological modulation of TH expression by
cannabinoid agonists in dopaminergic neurons would be influenced by additional endogenous inputs.