Salmonellaactively modulates TFEB in murine macrophages in a growth-phase and time-dependent manner
Authors: Inpanathan Subothan , Ospina-Escobar Erika , Li Vanessa Cruz , Adamji Zainab , Lackraj Tracy , Cho Youn Hee , Porco Natasha , Choy Christopher H. , McPhee Joseph B. , Botelho Roberto J. 
Published: December 2022

The transcription factor TFEB drives 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 likeMycobacteriumandSalmonellarepress TFEB. However,Salmonella entericasv. Typhimurium (S.Typhimurium) was reported to actively stimulate TFEB, implying a benefit toSalmonella. To better understand the relationship betweenS.Typhimurium and TFEB, we assessed ifS.Typhimurium regulated TFEB in macrophages in a manner dependent on infection conditions. We observed that macrophages that engulfed late-logarithmic grownSalmonellaaccumulated nuclear TFEB, comparable to macrophages that engulfedE. coli. In contrast, stationary-phaseS.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-phaseSalmonella, orSalmonellalacking functional SPI-1 and SPI-2 type three secretion systems.S.Typhimurium mutated in the master virulence regulatorphoPor the secreted effector genessifA, andsopDalso showed TFEB nuclear translocation. Interestingly, whileE. colisurvived better intfeb-/-macrophages,S.Typhimurium growth was similar in wild-type andtfeb-/-macrophages. Moreover,Salmonellasurvival was not readily affected by its growth phase in wild-type or knockout macrophages, though in HeLa cells late-logSalmonellabenefitted from the loss of TFEB. Priming macrophages with phagocytosis enhanced the killing ofSalmonellain wild-type, but not intfeb-/-macrophages. Collectively,S.Typhimurium orchestrate TFEB in a manner dependent on infection conditions, while disturbing this context-dependent control of TFEB may be detrimental toSalmonellasurvival.

Importance

Activation of the host transcription factor TFEB helps mammalian cells adapt to stresses such as starvation and infection by upregulating lysosome, autophagy, and immuno-protective gene expression. Thus, TFEB is generally thought to protect host cells. However, it may also be that pathogenic bacteria likeSalmonellaorchestrate TFEB in a spatio-temporal manner to harness its functions to grow intracellularly. Indeed, the relationship betweenSalmonellaand TFEB is controversial since some studies showed thatSalmonellaactively promotes TFEB, while others have observed thatSalmonelladegrades TFEB and that compounds that promote TFEB restrict bacterial growth. Our work provides a path to resolve these apparent discordant observations since we showed that stationary-grownSalmonellaactively delays TFEB after infection, while late-logSalmonellais permissive of TFEB activation. Nevertheless, the exact function of this manipulation remains unclear, but conditions that erase the conditional control of TFEB bySalmonellamay be detrimental to the microbe.