Human serotonin transporter: regulation by the neuroprotective agent aurintricarboxylic acid and by epidermal growth...

The influence of aurintricarboxylic acid (ATA), a neuroprotective compound, on the serotonin transporter expressed in JAR human placental choriocarcinoma cells was investigated. Treatment of the cells with ATA for 16 h led to a significant stimulation of the serotonin transporter activity. This effect was not observed, however, when the treatment was done for 1-2 h. The stimulatory effect was associated with an increase in the maximal velocity of the transport process with no significant change in the Michaelis-Menten constant. Northern blot hybridization revealed that ATA treatment caused a marked increase in the steady-state levels of serotonin transporter-specific transcripts. Treatment of the cells with ATA was found to increase tyrosine phosphorylation of a 180-kDa protein. The phosphotyrosine content of a protein of a similar molecular size increased dramatically when the cells were exposed to epidermal growth factor (EGF), suggesting that this protein may be the EGF receptor. Treatment of the cells with EGF for 24 h could reproduce the stimulatory effects of ATA on the serotonin transporter activity, the maximal velocity of the transport process, and the steady-state levels of the transporter-specific mRNAs. Genistein, a tyrosine kinase inhibitor, was able to block the stimulatory effect of ATA and EGF. It is concluded that EGF increases the serotonin transporter expression in JAR cells and that the neuroprotective compound ATA produces similar effects on the transporter most likely by activating the EGF receptor through tyrosine phosphorylation.