The Impact of Phosphatidylinositol‐4,5‐bisophosphate (PIP2) on Serotonin Transport Function

The serotonin transporter (SERT) plays a key function in the termination of serotonergic neurotransmission. SERT is the main pharmacological target in treating depressive disorders and also a target for various drugs of abuse. Drugs like amphetamine‐type stimulants (ATS) reverse the direction of transport which finally leads to an increased serotonin concentration in the synaptic cleft. Transmembrane proteins get in close contact with the lipid environment and are partitioned in specific lipid microdomains. Our previous studies already implicated that the phosphatidylinositide phosphatidylinositol‐4,5‐bisophosphate (PIP2), an important signaling molecule, influences amphetamine effects at SERT. Furthermore, we elucidated a binding site on the intracellular face of SERT where PIP2 specifically attaches. However, upon mutation of the binding site, PIP2 interaction with SERT was largely reduced, i.e. more than 50%. The objective of this study was to further investigate the interaction between SERT and PIP2 and to explore other positively charged SERT areas. This was achieved by using a computational approach. We identified a putative second binding site which is close to the inner leaflet of the plasma membrane. Introduction of single point mutations and by pharmacological manipulation of cellular PIP2 levels led to a decrease of amphetamine‐induced substrate efflux. These results give rise to a better understanding of the PIP2 –SERT interactions and open up new possibilities to target SERT dependent amphetamine‐induced actions.