A binary adenoviral vector system for expressing high levels of the proapoptotic gene bax

The bar gene plays a critical role in signaling apoptosis and expression th rough gene transfer may be valuable in the treatment of a variety of apopto sis-related diseases such as cancer. However, constructing an adenoviral ve ctor expressing a bar gene driven by a constitutive promoter has been diffi cult, presumably because of the gene's high proapoptotic activity Here we r eport a system that induces the expression of the bar gene safely by adenov irus-mediated gene cotransfer. Briefly, the system involves an adenoviral v ector containing a human bar cDNA driven by a synthetic promoter consisting of five GAL4-binding sites and a TATA box (GT). This vector expresses a mi nimal background level of bar protein in cultured mammalian cells thus prev enting apoptosis of packaging cells, however, expression of the bar gene ca n be induced substantially in vitro and in vivo by transferring it into tar get cells along with an adenoviral vector expressing the transactivator, fu sion protein GAL4/VP16. Extensive apoptosis was observed after induction of the bar gene both in cultured human lung carcinoma cells and in the livers of Balb/c mice. Our results suggest that this GAL4 gene regulatory system provides an alternative approach to constructing viral vectors that express potentially toxic genes.