The Shigella E3 ubiquitin ligase IpaH7.8 reprograms host kinase signaling to suppress NOX2-dependent oxidative burst responses in human monocytes

Abstract

Bacterial effector proteins manipulate host signalling cascades, including immune responses, to facilitate infection. While most effectors of Gram-negative bacteria rely on a secretion system for intracellular delivery, some possess intrinsic cell-penetrating capabilities. Here, we characterize the Shigella flexneri LPX effector IpaH7.8, which combines autonomous cell entry with enzymatic modulation of immunomodulatory host signaling pathways through distinct structural domains. We show that recombinant IpaH7.8 (rIpaH7.8) enters human cells independent of Shigellas type III secretion system (T3SS) via lipid raft-mediated endocytosis and escapes the endosome through a conserved N-terminal domain composed of two -helices. In the cytosol, the C-terminal E3 ubiquitin ligase domain of the cell-penetrating effector protein targets the pore-forming protein gasdermin D (GSDMD), suppressing inflammasome-induced IL-1{beta} release. Beyond inflammasome inhibition, integrated transcriptomic and kinome profiling in primary human monocytes revealed that IpaH7.8 induces a coordinated reprogramming of host signaling networks. Cluster-resolved gene expression analysis demonstrated selective suppression of immune effector pathways alongside induction of regulatory programs and interference with vesicular trafficking. These transcriptional changes converged with kinase activity remodeling, characterized by attenuation of PKC- and PKA-dependent signaling pathways. Notably, both datasets identified the NOX2 complex as a central target of IpaH7.8 activity. The NOX2 subunit NCF1 was downregulated at the transcriptional level and showed reduced phosphorylation at regulatory sites, indicating impaired activation. Consistently, IpaH7.8 significantly reduced reactive oxygen species production in primary human monocytes, demonstrating functional suppression of oxidative burst responses. Together, our findings reveal that IpaH7.8 acts as a multi-layered regulator of host immunity that integrates ubiquitination and kinase signaling to suppress both inflammatory and antimicrobial responses. By converging on the NOX2 axis, this effector uncovers a central vulnerability in host defense and highlights bacterial effector proteins as modulators of complex signaling networks with potential therapeutic relevance. Author SummaryBacterial pathogens like Shigella flexneri manipulate host immune responses to survive and spread within human cells. The Shigella effector protein IpaH7.8 is known to block inflammatory cell death by targeting gasdermin D. Here, we show that IpaH7.8 can enter human cells without a bacterial secretion system. It uses a specialized protein domain to cross the membrane and reach the cytoplasm. Once inside, IpaH7.8 alters host cell signaling by both attaching ubiquitin to immune proteins and reprogramming phosphorylation pathways. This dual function allows Shigella to suppress inflammation and promotes its escape from immune defenses. Our findings reveal how IpaH7.8 combines cell entry, immune evasion, and cytoskeletal control in a single protein, and highlight its potential as a tool to modulate inflammation in disease contexts.