Ubiquitination and degradation of eukaryotic translation initiation factor 4E result in toxicity and death in HeLa cells exposed to potassium dichromate.
Toxicologist 2006 Mar; 90(1):418
Exposure of HeLa cells to 6.0 uM potassium dichromate (Cr) resulted in cytotoxicity, cell death and a significant reduction in the cellular level of eukaryotic translation initiation factor 4E - the rate-limiting factor required for mRNA translation. Specific silencing of the eIF4E gene's expression with a small interfering RNA (siRNA) also resulted in significant cytotoxicity and cell death. Furthermore, the eIF4E silenced cells were significantly more susceptible to the Cr-induced cytotoxicity compared with the control cells suggesting that the Cr-induced toxicity in HeLa cells was, at least in part, due to the decreased cellular level of eIF4E protein. The Cr-induced reduction in the eIF4E protein level in HeLa cells was independent of the gene's transcription. Pre-exposure of the cells to ALLN and MG132 - inhibitors of proteasome activity, blocked the Cr-induced degradation of eIF4E protein. Inhibitors of PI3 kinase (LY294002), mTOR (rapamycin), and MAP kinase (SB203580, PD98059) blocked the Cr-induced degradation of eIF4E protein. Pretreatment of HeLa cells with insulin enhanced the phosphorylation as well as the Cr-induced degradation of the eIF4E protein. In addition, site-directed mutation at serine 209 - the phosphorylation site required for activation of the eIF4E protein, abolished its degradation induced by Cr in HeLa cells. These results confirmed that the phosphorylation of eIF4E protein is required for its ubiquitination and degradation in HeLa cells treated with Cr. The cellular level of cyclin D1 - a protein required for cell cycle progression was significantly lower in HeLa cells treated with chromium. Similarly, the siRNA-mediated silencing of the eIF4E gene's expression in HeLa cells also resulted in a significant reduction in the cellular level of cyclin D1 protein. In summary, our results demonstrate that the Cr-induced ubiquitination and degradation of the phosphorylated eIF4E protein in HeLa cells resulted in a decreased cellular level of cyclin D1 protein leading to cytotoxicity and cell death.
Cell-damage; Toxins; Toxic-effects; Potassium-compounds; Cytotoxicity; Cytotoxins; Cytotoxic-effects; Toxins; Toxic-effects; Proteins
Research Tools and Approaches: Cancer Research Methods
The Toxicologist. Society of Toxicology 45th Annual Meeting and ToxExpo, March 5-9, 2006, San Diego, California