Salmonella effector SteE reprograms 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 polarizes 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 IL-10 signaling. Hyperactivation correlates with elevated phosphorylated STAT3 in the macrophage nucleus and coordinated chromatin remodeling at STAT3 target loci. Overall, our study illustrates how hijacking of a signaling pathway by SteE dramatically reshapes the macrophage gene regulatory network to enhance Salmonella immune evasion.