DOXORUBICIN INHIBITS TAT-DEPENDENT TRANSACTIVATION OF HIV TYPE-1 LTR

Tat, the human immunodeficiency virus (HIV)-encoded transcription fact or, is vital for HIV replication and transcription, Any drug that inhi bits Tat's activity is a valuable candidate for chemotherapeutic appli cations, We show here that doxorubicin (Dox), a well-known anticancer drug and its derivative, daunomycin, inhibit the ability of Tat to act ivate the HIV-1 LTR, We cotransfected HeLa cells with pSV40TAT and a c hloramphenicol acetyltransferase gene driven by an HIV LTR promoter, C AT transcription was vigorously stimulated many fold by Tat production but the effect of Tat was inhibited by Dox in a dose-dependent manner , The transcriptional activation domain of Tat, located in its 67 amin o terminal residues, remains Dox sensitive, A TAR-deleted reporter gen e with a Gal binding domain is transactivated by a Gal-Tat fusion prot ein, This transcription complex retains a high level of activity in th e presence of Dox, suggesting that Dox primarily affects RNA-Tat, rath er than DNA-Tat, mediated transactivation. RNA gel mobility analysis r eveals that Dox does not affect the binding of Tat to TAR-RNA in vitro but does increase the binding activity of cellular nuclear proteins w ith TAR-RNA, Induction or activation of such TAR-binding proteins in c ells that might interfere with the activity of Tat could explain the o bserved inhibitory effects of Dox on Tat-activated transcription, Thes e results suggest that Dox may have chemotherapeutic effects on HIV ex pression mediated through TAR RNA.