PKC inhibitors reveal PKC isoforms involved in HIV latency reversal and immunomodulation

The reservoir of persistently latently infected cells is a major barrier to a cure for HIV infection. Protein kinase C (PKC) modulators can reverse HIV latency and could thus be useful "Kick" components in "Kick and Kill" approaches to a cure. However, PKC modulators also affect immune cell function, potentially limiting their clinical safety and utility. Here, using PKC isoform inhibitors in models of HIV latency and HIV-negative mononuclear cells, we determined the PKC isoforms involved in PKC modulator-mediated HIV latency reversal and immunomodulation (CD69 and CD4 expression, and inflammatory cytokine production). We found that inhibition of PKC α, β, γ, δ, or θ limited PKC-mediated HIV latency reversal to varying degrees. We also found that combinatorial PKC isoform inhibition significantly limited robust PKC modulator-mediated immune cell surface expression of CD69 and cytokine production. None of the pharmacologic PKC inhibitors affected PKC modulator-mediated downmodulation of T-cell surface CD4 expression. These results provide important insight into the isoforms involved in the various PKC modulator-mediated activities, including HIV latency reversal. Design of next-generation PKC modulators that are more selective for PKC α, β, and θ may allow for the partial functional decoupling of HIV latency reversal from immunomodulatory effects, and lead to safer and more effective PKC modulator-based latency-reversing regimens.IMPORTANCEHIV persists in long-lived, latently infected cellular reservoirs, which prevents the cure of the infection using currently available antiretroviral therapy alone. The "Kick and Kill" strategy proposes the use of latency-reversing agents (LRAs) to induce viral reactivation leading to reservoir elimination. Protein kinase C (PKC) modulators are one of the most potent classes of LRAs and operate through the activation of several PKC isoforms. Here, we demonstrate the contribution of various PKC isoforms to PKC modulator-mediated HIV latency reversal and immunomodulation. We identified PKC α, β, and θ as the isoforms important for latency reversal, while other isoforms, especially broad PKC isoform activation, had greater relative effects on immune cell activation and cytokine release. Together, these results define the pathways required for PKC-mediated HIV latency reversal and other important immunomodulatory effects and will thus inform the development of next-generation isoform-selective PKC modulator LRAs.