Dopamine and norepinephrine transporter-dependent c-Fos production in vitro: relevance to neuroadaptation

Abstract

Cocaine, methylphenidate and other drugs that block dopamine transport indirectly promote immediate early gene expression, via dopamine-mediated activation of D1 dopamine receptors. Increased expression of the immediate early gene (IEG) c-fos, initiates a cascade of intracellular events that may underlie neuroadaptive changes following repeated exposure to the drugs. We investigated whether substrates (dopamine, norepinephrine) of the human dopamine (hDAT) and norepinephrine (hNET) transporters can directly induce c-Fos protein in HEK-293 (HEK) cells transfected with the hDAT and hNET and whether PKC modulators affect this process. Dopamine and norepinephrine robustly induced c-Fos immunofluorescence in both hDAT and hNET cells, but not in untransfected HEK-293 cells, demonstrating that catecholamine-induced c-Fos induction was DAT- and NET-dependent. The PKC activator PMA induced c-Fos in hDAT, hNET and HEK cell lines indicating that PKC stimulated c-Fos independent of transporters. The PKC inhibitor bisindolylmaleimide I (BIS) significantly increased c-Fos expression in hDAT cells, but not in hNET or HEK-293 cells, suggesting that inhibition of DAT-mediated phosphorylation results in c-Fos induction. BIS pretreatment abolished norepinephrine-induced c-Fos expression hNET but not dopamine-induced c-Fos induction in hDAT cells. In conclusion, induction of c-Fos by dopamine and norepinephrine requires the presence of hDAT and hNET but the contributions of hDAT and hNET to c-Fos induction is distinguishable on the basis of differing responses to a PKC inhibitor. These findings present a cell system and methodology for investigating the potential contribution of monoamine transporters to pre-synaptic neuroadaptation.