Inhibition of the potassium channel TREK-1 by S6 kinases: a mechanism for aberrant neuronal excitability in mTORpathies

The mammalian Target of Rapamycin (mTOR) kinase is a master regulator of cell metabolism. Genetic diseases in which mTOR activity is upregulated, such as Tuberous Sclerosis Complex (TSC), are classified as mTORopathies, and are characterized by severe neurological symptoms, including pharmacoresistant epilepsy. However, the mTORC1 downstream effectors responsible for seizure development remain unknown. Preliminary data identified the background K+ channel TREK-1 to be phosphorylated on Ser333 by the mTORC1 target S6 kinase (S6K) in a rapamycin-sensitive way, and it was demonstrated that this post-translational modification leads to the inhibition of the channel, possibly contributing to epileptogenesis in mTORopathies. Here, using a newly developed antibody against phosphor-TREK1(Ser333), we show that in vivo the channel is indeed phosphorylated by S6K. In the T47D cell line we observed that TREK-1 is phosphorylated in response to insulin in a torin 1- and U0126-sensitive, but rapamycin-insensitive fashion, suggesting the involvement of other kinases beside S6K. Finally, we observed that TREK-1 activity has a neuroprotective effect in models of acquired epilepsy. Indeed, S333X mice, in which the codon of TREK-1 encoding Ser333 is mutated to a stop codon, showed a distinctly less severe epileptic phenotype compared to wild type mice in response to kainic acid injection.