Evasion of CARD8 activation during HIV-1 assembly.

As intracellular parasites, viruses must devise sophisticated mechanisms to produce and assemble viral components while suppressing activation of innate immune effectors. Here, we report that coordination of HIV-1 assembly by the viral polyprotein Gag suppresses inappropriately timed protease (PR) activity to evade the PR activity sensor, caspase recruitment domain-containing protein 8 (CARD8). Using mutants of Gag, we show that disruption of domains controlling viral assembly site [matrix (MA)] or virus particle release (nucleocapsid and p6) leads to premature activation of PR and the CARD8 inflammasome, resulting in interleukin-1β (IL-1β) secretion and pyroptotic cell death. Further, we demonstrate that previously observed host-adaptive mutations in HIV-1 MA (M30K) and p6 (PTAP duplication) associated with greater fitness in humans improve infected CD4+ T cell survival in a PR-dependent manner, which may be regulated by CARD8. Together, this work reveals virus-encoded mechanistic control over PR activation and CARD8 sensing by HIV-1 Gag.