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

Abstract

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-κB pathways, but global NF-κB activators are non-specific and toxic. There exist two major IκBs: IκBα, and IκBε, which hold activating NF-κB subunits in the cytoplasm, releasing them for nuclear transit upon cell stimulation. IκBα was considered the main IκB responsible for gene expression regulation, including HIV activation. IκBε is expressed in cells constituting much of the latent HIV reservoir, and IκBε knockout mice have a minimal phenotype, suggesting that IκBε could be a valuable target for HIV activation and reservoir depletion. We previously showed that targeting IκBε yields substantial increases in HIV expression. Here, we show that IκBε holds c-Rel and p65 activating NF-κB subunits in the cytoplasm, and that targeting IκBε 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-κBs, demonstrating a mechanism through which targeting IκBε increases HIV expression. The findings suggest that it may be helpful to develop HIV activation approaches, acting specifically to target IκBε and its interactions with the NF-κBs.

Pharmacological Inhibition of IKK to Tackle Latency and Hyperinflammation in Chronic HIV-1 Infection

“…We demonstrate that IKKis have the capacity to reverse HIV-1 latency in lymphoid and myeloid cellular models. Accordingly, NF-κB modulation, through siRNA silencing of IkBα and NF-κB binding to the kB sites of the HIV-LTR, was previously described to activate HIV in latently infected monocytic U1 and lymphoid J-Lat 10.6 [ 10 , 25 ]. These results were confirmed in ex vivo CD4+ T cells from HIV+ individuals by ultra-sensitive semi-nested qPCR that revealed high IKKis-induced viral transcription comparable to PMA and ionomycin reactivation, as previously reported [ 26 ].…”

“…Although Pam3CSK4 showed less potency compared to the HDACi panobinostat, this finding lends credence to the possibility of harnessing immune modulation as a strategy to reverse HIV-1 latency and circumvent immune cell activation. The modulation of NF-κB by cytokines/chemokines or PKC agonists has been discouraged due to drug tolerability concerns [ 25 , 32 , 33 ]. Alternatively, the LRA activity of IKKis had minimal impact on cell activation markers in primary CD4+ T cells.…”

Viral-Host Dependency Factors as Therapeutic Targets to Overcome Antiviral Drug-Resistance: A Focus on Innate Immune Modulation

“…Interestingly, IKK -TBK1/IKKϵ interplay is a confluent downstream regulator of multiple pathogen sensing pathways as described in Figure 2 (see (170,171) for review). As examples of the potential of IKK modulation as HDT, siRNA of IkBa has been shown to induce HIV reactivation in latently infected cells (172,173). Similarly, TBK-1/IKKϵ inhibitors have been reported to inhibit HIV replication in human primary macrophages (174) as well as a broad antiviral activity against diverse sort of virus including HSV-1 and HSV2 (175), HCV (176), RVFV (177) or Venezuelan equine encephalitis virus infection (VEEV) (178).…”

NF-κB sub-pathways and HIV cure: A revisit

“…In contrast, low expression of cNF-κB or impaired translocation of cNF-κB into nucleus is associated with HIV latency [31] . When IκBs were knocked down, latent HIV was reactivated [ 48 , 49 ], indicating that this pathway can be modulated to achieve latency disruption. By mimicking the physiologic ligand diacylglycerol, protein kinase C agonist binds to the regulatory domains of PKC isoforms, targets PKC/cNF-κB pathway to degrade IκBs, and activates HIV transcription from latency [31] .…”