Salmonella
actively 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 2023

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.

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 like
Salmonella
orchestrate TFEB in a spatio-temporal manner to harness its functions to grow intracellularly. Indeed, the relationship between
Salmonella
and TFEB is controversial since some studies showed that
Salmonella
actively promotes TFEB, while others have observed that
Salmonella
degrades 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-grown
Salmonella
actively delays TFEB after infection, while late-log
Salmonella
is permissive of TFEB activation. Nevertheless, the exact function of this manipulation remains unclear, but conditions that erase the conditional control of TFEB by
Salmonella
may be detrimental to the microbe.