Pharmacological-based translational induction of transgene expression in mammalian cells

In the quest for the development of pharmacological switches that control gene expression, no system has been reported that regulates at the translational level. To permit small-molecule control of transgene translation, we have constructed a farnesyl transferase inhibitor-responsive translation initiation factor. This artificial protein is a three-component chimaera consisting of the ribosome recruitment core of the eIF4G1 eukaryotic translation initiation factor, the RNA-binding domain of the R17 bacteriophage coat protein and the plasma membrane localization CAAX motif of farnesylated H-Ras. This membrane-delocalized translation factor is inactive unless liberated in the cytosol. Farnesyl transferase inhibitor FTI-277 prevents the membrane association of the CAAX motif and thus increases the cytoplasmic levels of the eIF4G fusion protein, which is then capable of inducing translation of the second cistron of a bicistronic messenger RNA containing an R17-binding site in its intercistronic space. Such direct translational control by farnesyl transferase inhibitors provides a system for fast, graded and reversible regulation of transgene expression.