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

The transcription factor TFEB drives the expression of lysosomal, autophagic, and immune-responsive genes in response to LPS and phagocytosis. Interestingly, compounds that promote TFEB activity enhance bactericidal activity, while intracellular pathogens like Mycobacterium and Salmonella repress TFEB. However, Salmonella enterica sv. Typhimurium (S. Typhimurium) was reported to actively stimulate TFEB, implying a benefit to Salmonella. To better understand the relationship between S. Typhimurium and TFEB, we assessed if S. Typhimurium regulated TFEB in macrophages in a manner dependent on infection conditions. We observed that macrophages that engulfed late-logarithmic grown Salmonella accumulated nuclear TFEB, comparable to macrophages that engulfed Escherichia coli. In contrast, stationary-phase S. Typhimurium infection of macrophages actively delayed TFEB nuclear mobilization. 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 3 secretion systems. S. Typhimurium mutated in the master virulence regulator phoP or the secreted effector genes sifA, and sopD also showed TFEB nuclear translocation. Interestingly, while E. coli survived better in tfeb-/- macrophages, S. Typhimurium growth was similar in wild-type and tfeb-/- macrophages. Moreover, Salmonella survival was not readily affected by its growth phase in wild-type or knockout macrophages, though in HeLa cells late-log Salmonella benefitted from the loss of TFEB. Priming macrophages with phagocytosis enhanced the killing of Salmonella in wild-type, but not in tfeb-/- macrophages. Collectively, S. Typhimurium orchestrate TFEB in a manner dependent on infection conditions, while disturbing this context-dependent control of TFEB may be detrimental to Salmonella survival.