Transdominant Mutants of IkBa Block Tat-Tumor Necrosis Factor Synergistic Activation of Human Immunodeficiency Virus Type 1 Gene Expression and Virus Multiplication

The human immunodeficiency virus type 1 (HIV-1) long terminal repeat (LTR) contains two binding sites for the NF-kB/Rel family of transcription factors which are required for the transcriptional activation of viral genes by inflammatory cytokines such as tumor necrosis factor alpha (TNF-a) and interleukin-1. In the present study, we examined the effect of transdominant mutants of IkBa on the synergistic activation of the HIV-1 LTR by TNF-a and the HIV-1 transactivator, Tat, in Jurkat T cells. The synergistic induction of HIV-1 LTR-driven gene expression represented a 50to 70-fold stimulation and required both an intact HIV-1 enhancer and Tat-TAR element interaction, since mutations in Tat protein (R52Q, R53Q) or in the bulge region of the TAR element that eliminated Tat binding to TAR were unable to stimulate LTR expression. Coexpression of IkBa inhibited Tat-TNF-a activation of HIV LTR in a dose-dependent manner. Transdominant forms of IkBa, mutated in critical serine or threonine residues required for inducer-mediated (S32A, S36A) and/or constitutive (S283A, T291A, T299A) phosphorylation of IkBa were tested for their capacity to block HIV-1 LTR transactivation. IkBamolecules mutated in the N-terminal sites were not degraded following inducer-mediated stimulation (t1/2, >4 h) and were able to efficiently block HIV-1 LTR transactivation. Strikingly, the IkBa (S32A, S36A) transdominant mutant was at least five times as effective as wild-type IkBa in inhibiting synergistic induction of the HIV-1 LTR. This mutant also effectively inhibited HIV-1 multiplication in a single-cycle infection model in Cos-1 cells, as measured by Northern (RNA) blot analysis of viral mRNA species and viral protein production. These experiments suggest a strategy that may contribute to inhibition of HIV-1 gene expression by interfering with the NF-kB/Rel signaling pathway.