Grzymajlo, K. | Search bioRxiv

bioRxiv2025

Salmonella Effector SteE Reprogrammes the Macrophage Regulatory Network to Drive Specific Hyperactivation of STAT3 Target Genes

The ability of Salmonella Typhimurium to exploit macrophages as a niche for survival, replication and dissemination is central to its pathogenesis. The effector SteE, which polarises macrophages into an anti-inflammatory state, is critical during invasive disease. SteE operates via an unprecedented mechanism, reprogramming the host serine/threonine kinase GSK3 to perform tyrosyl-directed phosphorylation of neosubstrates, including the immune transcription factors STAT1 and STAT3. Here, we demonstrate that SteE-driven transcriptional reprogramming relies critically and specifically on STAT3 phosphorylation and DNA binding. By activating STAT3 via a non-canonical pathway, bypassing endogenous negative feedback mechanisms, SteE drives hyperactivation of STAT3 target genes, surpassing the effects of canonical IL10 signalling. Hyperactivation correlates with elevated phosphorylated STAT3 in the macrophage nucleus, facilitating opening of chromatin regions not accessible during endogenous cytokine signalling. Overall, our study illustrates how hijacking of a signalling pathway by SteE dramatically reshapes the macrophage gene regulatory network to enhance Salmonella immune evasion.

cell biology↗

bioRxiv2024

SanA is an inner membrane protein mediating the early stages of Salmonella infection

Bacterial membrane proteins, crucial for the interaction with the environment, encompass various functional molecules such as SanA. SanA is pivotal for the physicochemical properties of the bacterial membrane, influencing Salmonellas antibiotic resistance and infection phenotype. Previous studies identified a link between sanA mutation and increased Salmonella invasiveness, but the mechanisms underlying this phenomenon remain largely unexplored. Therefore, our research investigates SanAs role during Salmonella infection, examining its expression pattern, localization within the cell, and association with Salmonella Pathogenicity Island I (SPI-I). Using subcellular fractionation and Western Blotting we revealed that SanA is predominantly located in the inner membrane. Additionally, we utilized transcriptional fusion to monitor SanA expression under various environmental conditions. We observed that SanA plays a significant role during the late exponential and early stationary growth phase and remains important 24 hours after the bacteria enter host cells. Moreover, our invasion assays demonstrated that deletion of sanA in bacteria grown to early stationary phase significantly enhances their invasiveness, partly due to increased SPI-I expression, which is regulated in a nutrient availability-dependent manner. Our results highlight SanAs essential role in Salmonellas response to environmental stress, critical for its entry and survival in hostile environments. This research underscores the importance of inner membrane proteins in bacterial pathogenicity, particularly in the initial stages of infection.

microbiology↗