Viry, A. | Search bioRxiv

bioRxiv2025

Virulence priming of Listeria monocytogenes inside replication-permissive endolysosomes

Listeria monocytogenes (Lm), the foodborne pathogen responsible for listeriosis, is well-known for its intracellular lifestyle. After entering epithelial cells, it can evade within minutes from its internalization vacuole into the cytosol, or transiently co-opt and replicate within endomembrane compartments termed epithelial Spacious ListeriA-containing Phagosomes (eSLAPs). Although eSLAPs display endolysosomal features, we bring evidence that they lack cathepsin D activity and are permeated. Indeed, sustained eSLAP membrane perforation by listeriolysin O is crucial for accommodating bacterial growth and vacuole expansion. Conversely, we show that Lm broad range phospholipase C PlcB is the main escape factor from eSLAPs. Unexpectedly, we find that Lm PrfA-dependent cytosolic virulence program is primed inside eSLAPs. As a consequence, the bacteria released from eSLAPs are pre-equipped with the actin assembly-inducing protein ActA and can recruit actin faster. We propose that a delayed access to the cytosol benefit eSLAP-transiting bacteria by favoring their dissemination or evasion from xenophagy.

microbiology↗

bioRxiv2023

Alternative splicing of the stress-sensitive regulator CIRBP sharpens the cellular response to bacterial infection

Cell autonomous responses to intracellular bacteria largely depend on gene expression reorganization. To gain isoform-level resolution into these regulations, we combined long- and short-read transcriptomic analyses of the response of intestinal epithelial cells to infection by the foodborne pathogen Listeria monocytogenes. Among the most striking isoform-based regulations, expression of the cellular stress response regulator CIRBP (cold-inducible RNA-binding protein) and of several SRSFs (serine/arginine-rich splicing factors) switched from canonical transcripts to nonsense-mediated decay-sensitive isoforms by inclusion of "poison exons". We showed that damage to host cell membranes caused by bacterial pore-forming toxins (listeriolysin O, perfringolysin, streptolysin, or aerolysin) led to the dephosphorylation of SRSF proteins via the inhibition of the kinase activity of CLK1, thereby driving CIRBP alternative splicing. CIRBP isoform usage was found to have consequences on infection, since selective repression of canonical CIRBP reduced intracellular bacterial load while that of the poison exon-containing isoform exacerbated it. Consistently, CIRBP-bound mRNAs were shifted towards stress-relevant transcripts in infected cells, with increased mRNA levels or reduced translation efficiency for some targets. Our results thus generalize the alternative splicing of CIRBP and SRSFs as a common response to biotic or abiotic stresses by extending its relevance to the context of bacterial infection.

molecular biology↗