Augmenting transgene expression from carcinoembryonic antigen (CEA) promoter via a GAL4 gene regulatory system

Though extensively studied, the use of tissue- or cell-type-specific promoters to target transgene expression is hampered by their weak activity. We hypothesized that this problem could be addressed by using a GAL4 gene regulatory system, wherein a weak, tissue-specific promoter would drive expression of the GAL4/VP16 fusion protein (GV16), which in turn would transactivate a minimal synthetic promoter, GAL4/TATA (GT), upstream of a transgene. To test this hypothesis, we constructed adenoviral vectors expressing a lacZ or GV16 gene driven by a carcinoembryonic antigen (CEA) promoter (Ad/CEA-LacZ or Ad/CEA-GV16) and evaluated levels of transgene expression they produced in cultured cells and in subcutaneous tumors after intratumoral administration. In CEA-positive cells, treatment with Ad/CEA-GV16 + Ad/GT-LacZ versus Ad/CEA-LacZ increased transgene expression 20- to 100-fold. In CEA-negative cells, treatment with Ad/CEA-GV16 + Ad/GT-LacZ increased transgene expression to a much lower degree (6- to 8-fold). In addition, analysis of Bax gene-mediated cell death revealed that this system can be used to avoid Bax's toxic effects on CEA-negative cells without compromising its ability to kill CEA-positive cells in vitro and in vivo. Thus, the combination of a tissue-specific promoter with the GAL4 gene regulatory system could be useful for targeting transgene expression.