Reduced Eukaryotic Initiation Factor 2Bε-Subunit Expression Suppresses the Transformed Phenotype of Cells Overexpressing the Protein

Eukaryotic initiation factor 213 (eIF2B), a five-subunit guanine nucleotide exchange factor, plays a key role in the regulation of mRNA translation. Expression of its e-subunit is specifically up-regulated in certain conditions associated with increased cell growth. Therefore, the purpose of the present study was to examine the effect of repressing elF2B epsilon expression on growth rate, protein synthesis, and other characteristics of two tumorigenic cell lines that display up-regulated expression of the epsilon-subunit. Experiments were designed to compare spontaneously transformed fibroblasts to transformed mouse embryonic fibroblasts infected with a lentivirus containing a short hairpin RNA directed against elF2B epsilon. Cells expressing the short hairpin RNA displayed a reduction in eIF2B epsilon abundance to 30% of the value observed in uninfected transformed mouse embryonic fibroblasts, with no change in the expression of any of the other four subunits. The repression of eIF2B epsilon expression was accompanied by reductions in guanine nucleotide exchange factor activity and global rates of protein synthesis. Moreover, repressed eIF2B epsilon expression led to marked reductions in cell growth rate in culture, colony formation in soft agar, and tumor progression in nude mice. Similar results were obtained in MCF-7 human breast cancer cells in which eIF2B epsilon expression was repressed through transient transfection with a small interfering RNA directed against the E-subunit. Overall, the results support a role for eIF2B epsilon in the regulation of cell growth and suggest that it might represent a therapeutic target for the treatment of human cancer. [Cancer Res 2008:68(21):8752-60]