REACTIVATION OF SILENCED, VIRALLY TRANSDUCED GENES BY INHIBITORS OF HISTONE DEACETYLASE

Retroviral and adeno-associated viral sequences can dramatically silen ce transgene expression in mice. We now report that this repression al so occurs in stably infected HeLa cells when the cells are grown witho ut selection, Expression of a transduced lacZ gene (rAAV/CMVlacZ) is s ilenced in greater than 90% of cells after 60 days in culture, Surpris ingly, high-level expression can be reactivated by treating the cells with sodium butyrate or trichostatin A but not with 5-azacytidine. Whe n cell clones with integrated copies of rAAV/CMVlacZ were isolated, la cZ expression was silenced in 80% of the clones; however, lacZ express ion was reactivated in all of the silenced clones by treatment with bu tyrate or trichostatin A. The two drugs also reactivated a silenced gl obin gene construct (rAAV/HS2 alpha beta(AS3)) in stably infected K562 cells, Trichostatin A is a specific inhibitor of histone deacetylase; therefore, we propose that hyperacetylation of histones after drug tr eatment changes the structure of chromatin on integrated viral sequenc es and relieves repression of transduced genes, The reactivation of si lenced, transduced genes has implications for gene therapy, Efficient viral gene transfer followed by drug treatment to relieve suppression may provide a powerful combination for treatment of various genetic an d infectious diseases.