PKCθ and HIV-1 Transcriptional Regulator Tat Co-exist at the LTR Promoter in CD4+ T Cells

PKC theta is essential for the activation of CD4(+) T cells. Upon TCR/CD28 stimulation, PKC theta is phosphorylated and migrates to the immunological synapse, inducing the activation of cellular transcription factors such as NF-kappa B and kinases as ERK that are critical for HIV-1 replication. We previously demonstrated that PKC theta is also necessary for HIV-1 replication but the precise mechanism is unknown. Efficient HIV-1 transcription and elongation are absolutely dependent on the synergy between NF-kappa B and the viral regulator Tat. Tat exerts its function by binding a RNA stem-loop structure proximal to the viral mRNA cap site termed TAR. Besides, due to its effect on cellular metabolic pathways, Tat causes profound changes in infected CD4(+) T cells such as the activation of NF-kappa B and ERK. We hypothesized that the aberrant upregulation of Tat-mediated activation of NF-kappa B and ERK occurred through PKC theta signaling. In fact, Jurkat TetOff cells with stable and doxycycline-repressible expression of Tat (Jurkat-Tat) expressed high levels of mRNA for PKC theta. In these cells, PKC theta located at the plasma membrane was phosphorylated at T-538 residue in undivided cells, in the absence of stimulation. Treatment with doxycycline inhibited PKC theta phosphorylation in Jurkat-Tat, suggesting that Tat expression was directly related to the activation of PKC theta. Both NF-kappa B and Ras/Raf/MEK/ERK signaling pathway were significantly activated in Jurkat-Tat cells, and this correlated with high transactivation of HIV-1 LTR promoter. RNA interference for PKC theta inhibited NF-kappa B and ERK activity, as well as LTR-mediated transactivation even in the presence of Tat. In addition to Tat-mediated activation of PKC theta in the cytosol, we demonstrated by sequential ChIP that Tat and PKC theta coexisted in the same complex bound at the HIV-1 LTR promoter, specifically at the region containing TAR loop. In conclusion, PKC theta-Tat interaction seemed to be essential for HIV-1 replication in CD4(+) T cells and could be used as a therapeutic target.