Salmonella actively modulates TFEB in murine macrophages in a growth-phase and time-dependent manner

The transcription factor TFEB promotes lysosomal and autophagic capacity in response to stresses like amino acid depletion. Additionally, TFEB drives expression of immune-responsive and immuno-protective genes in response to LPS, phagocytosis, and bacteria such as Escherichia coli (E. coli) and Staphylococcus aureus. Consistent with a role for TFEB in promoting immunity and bactericidal activity, intracellular pathogens like Mycobacterium and Salmonella appear to repress TFEB, whereas compounds that promote TFEB production or activity enhance macrophage killing of Salmonella. Intriguingly, Salmonella enterica sv. Typhimurium (S. Typhimurium) was observed to actively stimulate TFEB, implying a benefit to Salmonella during infection. To better understand the relationship between S. Typhimurium infection and TFEB, we assessed if S. Typhimurium regulated TFEB in murine macrophages in a manner dependent on infection conditions. Here, we show that macrophages that engulfed late-logarithmic grown Salmonella accumulated and maintained nuclear TFEB, comparable to macrophages that engulfed E. coli. In contrast, stationary-phase S. Typhimurium infection of macrophages actively delayed TFEB nuclear mobilization over the first hour of infection. The delay in TFEB nuclear mobilization was not observed in macrophages that engulfed heat-killed stationary-phase Salmonella, or Salmonella lacking functional SPI-1 and SPI-2 type three secretion systems. S. Typhimurium mutated in the master virulence regulator phoP or the secreted effector genes sifA, and sopD also showed normal TFEB nuclear translocation. Interestingly, while E. coli survived better in Tfeb-/- macrophages, S. Typhimurium growth was similar in wild-type and Tfeb-/-macrophages. Yet, priming macrophages with phagocytosis enhanced the killing of Salmonella in wild-type, but not in Tfeb-/- macrophages. Collectively, S. Typhimurium seems to orchestrate TFEB in a manner dependent on infection conditions, while conditions that disturb this context-dependent control of TFEB, such as forcing activation of TFEB seems to be detrimental to Salmonella survival.