Abstract
Pseudomonas aeruginosa is an opportunistic pathogen that causes life-threatening infections in cystic fibrosis patients and immunocompromised individuals. A tightly regulated immune response possessed by healthy individuals can effectively control P. aeruginosa infections, whereas the patients with dysregulated immune response are susceptible to this bacterial pathogen. Early growth response 1 (Egr-1) is a zinc-finger transcription factor involved in regulation of various cellular functions, including immune responses. We previously identified that Egr-1 was deleterious to host in a mouse model of acute P. aeruginosa pneumonia by promoting systemic inflammation and impairing bacterial clearance in lung, which associated with reduced phagocytosis and bactericidal ability of leucocytes, including macrophages and neutrophils. However, the molecular mechanisms underlying the Egr-1-suppressed phagocytosis of P. aeruginosa are incompletely understood. Herein, we investigated whether the Egr-1-regulated autophagy play a role in macrophage phagocytosis during P. aeruginosa infection by overexpression or knockdown of Egr-1. We found that overexpression of Egr-1 inhibited the phagocytic activity of macrophages, and the autophagy activator rapamycin and inhibitor chloroquine could reverse the effects of Egr-1 knockdown and Egr-1 overexpression on phagocytosis of P. aeruginosa, respectively. Furthermore, the Egr-1-overexpressing macrophages displayed upregulated expression of autophagy-related proteins LC3A, LC3B and Atg5, and decreased levels of p62 in macrophages. Further studies revealed that the macrophages with Egr-1 knockdown displayed enhanced activation of transcription factor NRF2 and expression of scavenger receptors MACRO and MSR1. Altogether, these findings suggest that Egr-1 suppresses the phagocytosis of P. aeruginosa by macrophages through upregulation of autophagy and inhibition of NRF2 signaling.
Highlights
Pseudomonas aeruginosa is an environmental ubiquitous bacterium that is harmless to healthy individuals but causes life-threatening acute infections in immunocompromised individuals and chronic infections in cystic fibrosis (CF) patients (Moradali et al, 2017)
We identified that the mRNA and protein expression of Early growth response 1 (Egr-1) in RAW264.7 cells were rapidly and transiently induced by P. aeruginosa (Figures 1A–C), suggesting Egr-1 may play a role in regulation of P. aeruginosa-induced immune responses
Initiation of autophagy is characterized by conversion of cytosolic form of microtubule-associated protein 1A/1B light chain 3 (LC3-I) to a LC3-phosphatidylethanolamine (PE) form (LC3-II), which is correlated with the number of autophagosomes (Mizushima and Yoshimori, 2007)
Summary
Pseudomonas aeruginosa is an environmental ubiquitous bacterium that is harmless to healthy individuals but causes life-threatening acute infections in immunocompromised individuals and chronic infections in cystic fibrosis (CF) patients (Moradali et al, 2017). Growth response 1 (Egr-1), known as NGFI-A, Krox, Tis, Zif268, and ZENK, is a zinc-finger transcription factor that is rapidly and transiently induced by a broad range of extracellular stimuli, including bacterial infections, growth factors, cytokines, stresses, and injury (Dieckgraefe and Weems, 1999; Jones and Agani, 2003; Hoffmann et al, 2008; de Klerk et al, 2017). Egr-1 translocates to nucleus and binds to a GC-rich consensus sequence, GCG(G/T)GGGCG, in the promotor of target genes, important for immune responses, cell growth, migration, differentiation and apoptosis (Dinkel et al, 1998; Abdel-Malak et al, 2009; Boone et al, 2011; Ten Hoeve et al, 2019). By contrast, binding of transcriptional corepressors NGFI-A binding protein 1 (NAB1) and NAB2 to the inhibitory domain of Egr-1 can repress Egr-1 transcriptional activity (Thiel and Cibelli, 2002)
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call