Antidepressants Accumulate in Lipid Rafts and Modify the Acylation State of G alpha S

Depression is a significant public health problem for which currently available medications are often ineffective while their physiological effects are routinely delayed. Previous studies from our laboratory have shown that the protein responsible for increasing cyclic adenosine monophosphate (Gαs) is increasingly localized to lipid rafts in depressed patients and that chronic antidepressant treatment mediates its translocation out of lipid rafts. Translocation of Gαs presents a potential biochemical explanation for the delayed onset of therapeutic action. Recent evidence from our laboratory suggests that localization of Gαs to lipid rafts is augmented through N-terminal palmitoylation and that antidepressants accumulate over time to mediate the depalmitoylation of Gαs. We have stably transfected C6 glioma cells, which lack the canonical monoamine transport system, with Gαs-GFP N-terminal acylation mutants to affect the palmitoylation (Cys3Ser) and myristoylation (Asn6Ser) state, respectively. Modification of Cys3 impairs palmitoylation of Gαs and mutation of Asn6Ser provides the recognition sequence necessary for myristoylation of Gαs (Gαi like). These acylation mutant Gαs constructs display clear differences in their subcellular localization and are invaluable tools for evaluating the effects of antidepressants on the localization of Gαs. Deacylation of Gαs abrogates membrane localization and chronic antidepressant treatment potentiates depalmitoylation of Gαs. Taken together, these results provide new molecular insights into the biochemistry of antidepressant signaling cascade(s) and present an explanation for the therapeutic latency of antidepressants.