Jost Enninga

NF-κB driven cellular immunity is essential for both pro- and anti-inflammatory responses to microbes, which makes it one of the most frequently targeted pathways by bacteria during pathogenesis. How NF-κB tunes the epithelial response to Streptococcus pneumoniae across the spectrum of commensal to pathogenic outcomes is not fully understood. In this study, we compare a commensal-like 6B ST90 strain to an invasive TIGR4 strain and demonstrate, through comparative mass spectrometry of the p65 interactome, that TIGR4 challenge triggers interaction of COMMD2 with p65 and p62. Mechanistically, we show this complex mediates export of p65 for degradation and COMMD2 is necessary for altering host cellular immunity. With these results, we reveal a bacterial pathogenesis mechanism to repress host inflammatory response though COMMD2 and p65 degradation while presenting a paradigm for diverging NF-κB responses to pneumococcus.

Typhoid toxin, a genotoxin secreted by typhoidal Salmonella serovars, has been implicated in diverse host responses ranging from DNA damage to cellular senescence. In this Research Highlight, we discuss how recent findings reveal an unexpected link between toxin‐induced DNA damage and a noncanonical interferon‐like response centered on ISG15. Using transcriptomic profiling and functional infection models, a recent report by Stark and colleagues shows that intoxicated cells mount a type‐I interferon‐like transcriptional program independent of interferons. Instead, ISG15 is upregulated via a STING‐TBK1‐dependent pathway, likely triggered by cytosolic DNA sensing following toxin‐induced damage. Strikingly, ISG15 acts independently of its canonical ISGylation activity, remaining in its free form to promote host cell survival and antibacterial defense. Importantly, they demonstrate the role of ISG15 as a key regulator of cellular fate under genotoxic stress. This divergence from canonical interferon signaling does not only add a new flavor to our understanding of the STING pathway, it also points to alternatives for therapeutic intervention that bypass broad interferon activation. By promoting both host cell survival and antimicrobial defenses, this pathway may facilitate persistent infection and intracellular niche formation, revealing a nuanced strategy by which Salmonella exploits host responses to support long‐term colonization.

The primary cilium is a microtubule-based sensory organelle projecting from the plasma membrane of most mammalian cells. Genetic defects in ciliary components cause chronic kidney disease (CKD) characterized by heightened production of inflammatory and fibrogenic mediators by tubular epithelial cells. Yet, whether this reflects a physiological role of the primary cilium remains unknown. Here, we show that primary cilia on kidney tubular cells bind uropathogenic Escherichia coli and, in response to bacterial components, initiate a fibro-inflammatory program reminiscent of CKD. Integrating single-cell transcriptomics with conditional mouse models, we observed that epithelial cilia orchestrate a similar fibro-inflammatory response in the absence of infection during CKD. This convergence reveals a shared cilia-dependent signalling axis governing both host–pathogen responses and CKD progression. Mechanistically, cilia ablation selectively impairs tubular responses to ADP-heptose, a pathogen-associated molecular pattern that activates NF-κB via the cytosolic innate immune receptor ALPK1. In human kidney organoids, ADP-heptose induces robust fibro-inflammation, and genetic or pharmacological inhibition of ALPK1 attenuates this response in a rodent CKD model. Together, these findings identify primary cilia as central orchestrators of a fibro-inflammatory program linking pathogen detection to kidney disease progression.

The continuous emergence of antibody-escape variants of SARS-CoV-2 demands the identification of alternative methods of protection against infection that do not directly target viral proteins. Here, we generated heavy-chain-only antibody (VHHs) from an alpaca immunized with the human angiotensin-converting enzyme 2 (hACE2), the major entry receptor for SARS-CoV-2. The VHHs bind hACE2 without affecting its enzymatic activity, and two of them (B07 and B09) inhibit all SARS-CoV-2 isolates tested (Delta, BA.1, BQ1.1, XBB.1.5, XBB.1.16.1, EG.5.1.3, BA.2.86.1). Their X-ray structure in complex with hACE2 show that their epitope overlaps with the footprint of the receptor binding domain (RBD) of the SARS-CoV-2 spike on hACE2. A dimeric B07-Fc fusion construct avidly binds hACE2 with an apparent dissociation constant of 0.1 nM and inhibits in vitro infection of previously tested variants and, of JN.1.1 and KP.3.3 variants, with an IC50 ~ 1 nM. In vivo experiments using K18-hACE2 mice show that intranasal prophylactic administration of B07-Fc confer a dose-dependent protection against SARS-CoV-2 D614G and Omicron variants. These VHHs targeting hACE2 represent potential broad-spectrum therapeutic candidates against potential new emerging coronaviruses using hACE2 as a receptor.

Endomembrane breaching is a crucial strategy employed by intracellular pathogens enclosed within vacuoles to access the nutrient-rich cytosol for intracellular replication. While bacteria use various mechanisms to compromise host membranes, the specific processes and factors involved are often unknown. Shigella flexneri, a major human pathogen, accesses the cytosol relying on the Type Three Secretion System (T3SS) and secreted effectors. Using in-cell correlative light and electron microscopy, we tracked the sequential steps of Shigella host cell entry. Moreover, we captured the T3SS, which projects a needle from the bacterial surface, in the process of puncturing holes in the vacuolar membrane. This initial puncture ensures disruption of the vacuole. Together this introduces the concept of mechanoporation via a bacterial secretion system as a crucial process for bacterial pathogen-induced membrane damage.

S ummary: Endomembrane breaching is a crucial strategy employed by intracellular pathogens enclosed within vacuoles to access the nutrient-rich cytosol for intracellular replication. While bacteria use various mechanisms to compromise host membranes, the specific processes and factors involved are often unknown. Shigella flexneri, a major human pathogen, accesses the cytosol relying on the Type Three Secretion System (T3SS) and secreted effectors. Using in-cell correlative light and electron microscopy, we tracked the sequential steps of Shigella host cell entry. Moreover, we captured the T3SS, which projects a needle from the bacterial surface, in the process of puncturing holes in the vacuolar membrane. This initial puncture ensures disruption of the vacuolar membrane. Together this introduces the concept of mechanoporation via a bacterial secretion system as a crucial process for bacterial pathogen-induced membrane damage. G raphical A bstract:

Intracellular bacterial pathogens gain entry to mammalian cells inside a vacuole derived from the host membrane. Some of them escape the bacteria-containing vacuole (BCV) and colonize the cytosol. Bacteria replicating within BCVs coopt the microtubule network to position it within infected cells, whereas the role of microtubules for cyto-invasive pathogens remains obscure. Here, we show that the microtubule motor cytoplasmic dynein-1 and specific activating adaptors are hijacked by the enterobacterium Shigella flexneri. These host proteins were found on infection-associated macropinosomes (IAMs) formed during Shigella internalization. We identified Rab8 and Rab13 as mediators of dynein recruitment and discovered that the Shigella effector protein IpaH7.8 promotes Rab13 retention on moving BCV membrane remnants, thereby facilitating membrane uncoating of the Shigella-containing vacuole. Moreover, the efficient unpeeling of BCV remnants contributes to a successful intercellular spread. Taken together, our work demonstrates how a bacterial pathogen subverts the intracellular transport machinery to secure a cytosolic niche.