Nuclear Transit and HIV LTR Binding of NF-κB Subunits Held by IκB Proteins: Implications for HIV-1 Activation

No effective therapy to eliminate the HIV latently infected cell reservoir has been developed. One approach, "shock and kill", employs agents that activate HIV, subsequently killing the activated infected cells and/or virus. Shock and kill requires agents that safely and effectively activate HIV. One class of activation agents works through classical NF-kappa B pathways, but global NF-kappa B activators are non-specific and toxic. There exist two major I kappa Bs: I kappa B alpha, and I kappa B epsilon, which hold activating NF-kappa B subunits in the cytoplasm, releasing them for nuclear transit upon cell stimulation. I kappa B alpha was considered the main I kappa B responsible for gene expression regulation, including HIV activation. I kappa B epsilon is expressed in cells constituting much of the latent HIV reservoir, and I kappa B epsilon knockout mice have a minimal phenotype, suggesting that I kappa B epsilon could be a valuable target for HIV activation and reservoir depletion. We previously showed that targeting I kappa B epsilon yields substantial increases in HIV expression. Here, we show that I kappa B epsilon holds c-Rel and p65 activating NF-kappa B subunits in the cytoplasm, and that targeting I kappa B epsilon with siRNA produces a strong increase in HIV expression associated with enhanced c-Rel and p65 transit to the nucleus and binding to the HIV LTR of the activating NF-kappa Bs, demonstrating a mechanism through which targeting I kappa B epsilon increases HIV expression. The findings suggest that it may be helpful to develop HIV activation approaches, acting specifically to target I kappa B epsilon and its interactions with the NF-kappa Bs.