| Abstract |
It is unclear whether local anesthetics, such as tetracaine, and antipsychotics, such as phenothiazines, act on lipids or proteins. In Saccharomyces cerevisiae, these drugs inhibit growth, translation initiation, and actin polarization, and induce cell lysis at high concentrations. These activities are likely due to the cationic amphiphilic structure common to these agents. Although drug-induced translational inhibition is conserved in mammalian cells, other mechanisms, including the phosphorylation of eIF2α, a eukaryotic translational initiation factor, remain poorly understood. At a concentration of 10 mM, tetracaine rapidly inhibited translation initiation and lysed cells, whereas, at 2.5 mM, it slowly induced inhibition without lysis. The pat1 disruptant defective in mRNA decapping and the xrn1 disruptant defective in 5'-3' exoribonuclease were partially resistant to translational inhibition by tetracaine at each concentration, but the gcn2 disruptant defective in the eIF2α kinase was not. Phosphorylation of eIF2α was induced by 10 mM but not by 2.5 mM tetracaine, whereas processing bodies (P-bodies) were formed at 2.5 mM in Pat1-dependent and -independent manners. Therefore, administration of tetracaine inhibits translation initiation with P-body formation at both concentrations but acts via the Gcn2-eIF2α system only at the higher concentration. Because other local anesthetics and phenothiazines induced Pat1-dependent P-body formation, the mechanisms involved in translational inhibition by these cationic amphiphiles are similar. These results suggest that this dose-dependent biphasic translational inhibition by tetracaine results from an increase in membrane proteins that are indirectly inhibited by nonspecific interactions of cationic amphiphiles with membrane lipids.
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