High error rates in selenocysteine insertion in mammalian cells treated with the antibiotic doxycycline, chloramphenicol, or geneticin.

Antibiotics target bacteria by interfering with essential processes such as translation, but their effects on translation in mammalian cells are less well characterized. We found that doxycycline, chloramphenicol, and Geneticin (G418) interfered with insertion of selenocysteine (Sec), which is encoded by the stop codon, UGA, into selenoproteins in murine EMT6 cells. Treatment of EMT6 cells with these antibiotics reduced enzymatic activities and Sec insertion into thioredoxin reductase 1 (TR1) and glutathione peroxidase 1 (GPx1). However, these proteins were differentially affected due to varying errors in Sec insertion at UGA. In the presence of doxycycline, chloramphenicol, or G418, the Sec-containing form of TR1 decreased, whereas the arginine-containing and truncated forms of this protein increased. We also detected antibiotic-specific misinsertion of cysteine and tryptophan. Furthermore, misinsertion of arginine in place of Sec was commonly observed in GPx1 and glutathione peroxidase 4. TR1 was the most affected and GPx1 was the least affected by these translation errors. These observations were consistent with the differential use of two Sec tRNA isoforms and their distinct roles in supporting accuracy of Sec insertion into selenoproteins. The data reveal widespread errors in inserting Sec into proteins and in dysregulation of selenoprotein expression and function upon antibiotic treatment.