Ferroptosis is a nonapoptotic form of cell death that can be induced by metabolic stress, such as glutathione (GSH) depletion
[28,99,100][69][70][71]. Recently defined as a newly discovered form of cell death, ferroptosis is different from apoptosis in that it does not involve caspase activation
[99][70]. Ferroptosis leads to an increase in ROS and malondialdehyde (MDA), which ultimately causes overwhelming lipid peroxidation and results in cell death
[99,101,102][70][72][73]. ATF3 is often involved in vital cellular activities such as metabolism. Currently, a large amount of research data indicates that ATF3 plays a significant role in the regulation of ferroptosis
[28,31,102,103,104,105,106,107][69][73][74][75][76][77][78][79]. Nuclear factor erythroid 2 related factor 2 (Nrf2) can promote the expression of SLC7A11 and GPX4 under oxidative stress, which is crucial to mediate the onset of ferroptosis
[108,109,110][80][81][82]. As an endogenous inhibitor of SLC7A11, ATF3 promotes erastin-induced ferroptosis by inhibiting the cystine/glutamate antiporter (system Xc-)
[28][69].
76. The Functions of ATF3 in the Pathogenic Microbial Infection Process
7.1. The Functions of ATF3 in Viral Infection
6.1. The Functions of ATF3 in Viral Infection
76.1.1. DNA Virus
The HBx protein, one of the seven proteins made by the Hepatitis B virus (HBV), is very toxic and can activate various genes in cells
[122,123][83][84]. This affects many cell processes, such as the regulation of intracellular gene transcription, signal transduction, protein degradation, the cell cycle, and apoptosis
[122,123][83][84]. Furthermore, HBx is a protein with a short half-life, primarily degraded in the cell via the ubiquitin-dependent proteasome pathway. Inhibiting HBx degradation and increasing the level of intracellular expression of HBx is one way HBV can cause liver cancer
[123][84]. IL-1β/ATF3 promotes HBx mRNA degradation by mediating the expression of Ski2, which helps prevent complications mediated by HBx
[122][83]. In particular, the level of Ski2 is also regulated by the HBx protein, forming a significant negative feedback loop to suppress HBx levels
[122][83]. This mechanism is likely crucial for the virus to maintain an optimal concentration of HBx to support viral replication without triggering apoptosis
[122,124][83][85]. Interestingly, HBx appears to induce
Ski2 promoter activity by interacting with ATF3
[121,122][83][86].
Murine cytomegalovirus (MCMV) is a virus particularly susceptible to control by IFN-γ, produced by NK cells. The viral load of MCMV in the liver is regulated by IFN-γ, which is secreted by NK cells in response to IL-12
[125,126,127][87][88][89]. Previous studies have shown that depletion of IFN-γ exacerbates infection, leading to an increase in liver MCMV viral load and the appearance of hepatitis
[126,128,129][88][90][91].
A key characteristic of the Herpes Simplex Virus (HSV) is its ability to establish latent infection in the autonomic ganglia and reactivate under physical, hormonal, or emotional stress
[131,132][92][93]. ATF3 is currently recognized as a significant stress-induced factor associated with the suppression of latent viral activation
[132][93]. ATF3 has been reported to play a role in maintaining the latent state of HSV
[132][93]. ATF3 is specifically expressed after neuronal injury, and it acts in synergy with STAT3 to induce the expression of downstream genes
[133][94]. The main function of ATF3 in cells infected with HSV-1 has been reported to be to maintain neuronal integrity
[132][93].
Human Papillomavirus (HPV) infection is a primary risk factor for cervical cancer
[134,135][95][96]. HPV facilitates the proteolytic degradation and inactivation of p53 through the expression of the E6 protein
[136,137][97][98]. Therefore, inhibiting the E6-promoted degradation of p53 appears to be an effective intervention against HPV-induced cervical cancer
[137,138,139][98][99][100].
76.1.2. RNA Virus
The binding of type I interferons (IFN) to their receptors leads to receptor dimerization, subsequently activating the IRF and STAT families of TF
[120,153][101][102]. STAT1 and STAT2 undergo dimerization and interact with IRF9, resulting in the formation of the interferon-stimulated gene factor 3 (ISGF3) complex
[120,153][101][102]. This complex then translocates to the nucleus and binds to the conserved interferon-stimulated response element, thus inducing a range of interferon-sensitive genes (ISGs) that inhibit the replication of the Japanese Encephalitis Virus (JEV) [
120
Interestingly, compared to its response to JEV infection, ATF3 exhibits a different function in hosts infected with the Zika virus (ZIKV). Research found that ATF3 inhibits ZIKV infection by differentially regulating the transcription of specific innate immune response and autophagy genes
[140][103]. During the infection with ZIKV of A549 cells, ATF3 promotes the transcription of the
RIG-I,
STAT1,
IRF9, and
ISG15 genes while simultaneously inhibiting the transcription levels of
IFNβ and
IFIT2 [140][103].
Viruses often need to inhibit host cell death in the early stages of infection to allow sufficient replication time for the production of adequate viral progeny
[159][104]. Later in the infection, promoting host cell death or utilizing budding mechanisms can facilitate viral dissemination
[159][104].
Infection with the Dengue virus (DENV) can induce a robust cytokine storm in the brain, leading to neurological symptoms or death in the host
[160][105]. An upregulation of ATF3 expression has been observed in blood samples of patients infected with DENV
[161][106]. Research has discovered that monocytes infected with DENV secrete extracellular vesicles (EV), which are internalized by microglia
[142][107]. The miR-148a carried within these EVs inhibits the expression level of the ubiquitin-specific peptidase 33 (USP33) protein. The reduction in USP33, in turn, decreases the stability of cellular ATF3 protein through deubiquitination, thereby promoting the expression of pro-inflammatory genes such as
TNF-α,
NF-κB, and
IFN-β [142][107]. This indicates that DENV manipulates the EV pathway to transfer miR-148a, thereby regulating the levels of USP33 and downstream ATF3 in human microglia and leading to neuroinflammation within the central nervous system.
In the context of the pathogenesis of integrated viruses, a pivotal aspect involves the exploitation of host cellular machinery for the expression of the viral genome during host infection. Specifically, the viral genome’s integration into the host’s chromatin architecture necessitates a strategic utilization of the host’s gene regulatory systems
[143,162][108][109]. This phenomenon is exemplified in the case of Human Immunodeficiency Virus Type 1 (HIV-1), where, post-infection, the viral genome becomes assimilated into the host genome as a component of chromatin
[143,162][108][109]. Central to this process is Nuc-1, a nucleosome situated immediately downstream of the HIV-1 transcription initiation site, which inherently inhibits the activity of the long-terminal repeat (LTR)
[143,162,163][108][109][110]. The initiation of LTR-driven transcription and consequent viral expression are contingent upon both epigenetic modifications and the disruption of nuc-1
[162][109]. Within this nucleosome, the presence of three AP1 sites is critical for the facilitation of viral transcription and replication
[164,165,166][111][112][113].
7.2. The Functions of ATF3 in Bacterial Infection
6.2. The Functions of ATF3 in Bacterial Infection
76.2.1. Gram-Positive Bacteria
During the infection process of
Staphylococcus aureus (
S. aureus), the host mediates the secretion of immune factors such as cytokines and chemokines through TLR-2, subsequently promoting the production of IL-17 to coordinate the host immune response
[14,169][114][115]. IL-17, together with IL-22/IL-23, modulates macrophage function, thus inducing the expression of antimicrobial peptides (AMP) that kill or inactivate the pathogen
[170,171][116][117]. Inactivation of IL-17, IL-22, and IL-23 leads to an increased
S. aureus load and exacerbates the disease
[170,172][116][118]. ATF3 has been reported to promote bacterial clearance by regulating the production of inflammatory cytokines, thus alleviating lethal
S. aureus pneumonia
[14][114]. ATF3 positively regulates the host’s resistance to
S. aureus infection by modulating macrophage Reg3 expression and AMPs gene-mediated bacterial clearance, as well as the recruitment of macrophages, thus playing a significant role in the early stages of
S. aureus infection
[14][114].
IL-17A is critical in the early defense against
Streptococcus pneumoniae (S. pneumoniae), as mice lacking IL-17A and IL-17RA show increased vulnerability to bacterial pathogens that incite lung diseases
[173,174,175][119][120][121]. ATF3 has been reported to facilitate the generation of IL-17A in γδ T cells through macrophage-mediated secretion of IL-1β, thus modulating the response to infection
[4]. ATF3 regulates the immune response by maintaining the intracellular balance of ROS and calcium ions (Ca
2+), influencing macrophage production of IL-1β and IL-23p19
[4]. This process is essential for stimulating the secretion of IL-17A, which is necessary for early defense against infections and crucial to eradicating
S. pneumoniae [4].
Wild-type mice demonstrate more effective bacterial clearance than ATF3-null mice during
Listeria monocytogenes (L. monocytogenes) infection
[15][122]. This suggests that ATF3 plays a critical role in resisting
L. monocytogenes infection. PLY induces ATF3 expression through the TLR4/MAPK pathway
[17][123]. Listeriolysin O (LLO), a member of the cytolysins released by
L. monocytogenes, is known to stimulate TLR4-dependent cytokine expression and acts as a TLR4 agonist
[176][124]. Furthermore, ATF3 significantly improves the expression levels of TNF-α, IL-1β, and IFN-γ during
L. monocytogenes infection
[15][122].
76.2.2. Gram-Negative Bacteria
During episodes of bacterial sepsis, the host modulates its response to infection by upregulating or suppressing cytokines through ATF3
[13,53][39][125]. LPS significantly induces ATF3, which functions as a negative regulator in the production of inflammatory cytokines
[19,53][13][39].
E. coli sepsis is currently one of the most important types of sepsis
[177][126]. ATF3 facilitates the progression of
E. coli sepsis by suppressing IL-6 transcription
[53][39]. Due to immunosuppression associated with ATF3-mediated sepsis, ATF3 knockout mice exhibit longer survival than wild-type mice after infection with
E. coli [53][39]. Post-infection with uropathogenic
Escherichia coli (UPEC), cytokines such as IL-1β, IL-6, and IFN-γ are significantly suppressed, while the bacterial load in the lungs and spleens of wild-type mice is substantially higher than in ATF3 knockout mice
[15][122]. This indicates that ATF3 exhibits a divergent mechanism in Gram-positive and Gram-negative bacterial infections. This contradictory result may be caused by the following reasons: (1) LPS-induced ATF3 competes with NF-κB for binding to the promoters of target cytokines, thus inhibiting the production of inflammatory cytokines
[15,19][13][122]. (2) LPS-induced ATF3 binds to cytokine promoters, and its interaction with HDAC leads to histone deacetylation. This process results in chromatin condensation, which suppresses cytokine gene transcription
[15,19][13][122]. (3) The regulation of TLR4 differs; in Gram-positive bacterial infections, ATF3 may positively regulate TLR4 expression and stimulate cytokine production
[13,15,17][122][123][125].
76.2.3. Other Bacteria
ATF3 expression is significantly upregulated during
Mycobacterium tuberculosis (Mtb) infection
[147][127]. ATF3 cooperates with BRG1 to activate the expression of the inflammatory cytokines IL-6, TNF-α, and IL-12p40 and increase the production of nitric oxide
[12,147][127][128]. Foamy macrophages, a subpopulation of macrophages, play a pivotal role in the pathogenesis of tuberculosis
[12][128]. They are characterized by an abundance of liposomes (LB), which may provide a survival environment for mycobacteria in granulomas
[12,180][128][129]. Mtb stimulates the formation of LB-rich foamy macrophages
[180,181][129][130]. ATF3 has been reported to inhibit liposome formation by regulating the expression of genes related to lipid metabolism
[12][128].
7.3. The Functions of ATF3 in Fungal and Parasite Infections
6.3. The Functions of ATF3 in Fungal and Parasite Infections
Patulin is a fungal toxin primarily released by
Aspergillus and
Penicillium species
[185][131]. Patulin exerts its toxic effect by covalently binding to reactive sulfhydryl groups in cellular proteins and by depleting glutathione, resulting in oxidative damage and the generation of reactive oxygen species (ROS)
[186,187][132][133]. Research has found that Patulin induces transcription factor EGR-1 phosphorylation through increased oxidative stress, thereby enhancing ATF3 expression and promoting apoptosis in colorectal cancer cells
[149][134]. Deoxynivalenol (DON), commonly known as vomitoxin, is a type B trichothecene mycotoxin predominantly produced by
Fusarium species, such as
F. culmorum and
F. graminearum [188][135].
87. Prospects for Clinical Applications
Considering the multifaceted role of ATF3 in the regulation of physiological functions, it presents a broad prospect as a clinical pharmacological target: (1) Treatments that target ATF3 to control inflammation, useful in autoimmune and other inflammatory diseases. (2) Exploiting ATF3 to develop treatments for neurological disorders and nerve damage. (3) Utilizing ATF3 expression levels as a diagnostic and prognostic tool, especially in cancer. However, we need to carefully consider ATF3’s dual functions to avoid adverse effects in treatment. Targeting ATF3 presents significant opportunities for novel therapeutic developments and improved disease management in clinical medicine. Its potential as a drug target and a biomarker can lead to advances in personalized medicine. However, the complexity of ATF3’s roles necessitates careful research and development to ensure the efficacy and safety of these new approaches.