New aspects of RpoE in Uropathogenic Proteus mirabilis
Date Issued
2014
Date
2014
Author(s)
Liu, Ming-Che
Abstract
Proteus mirabilis (P. mirabilis) is an opportunistic human pathogen causing urinary tract infection (UTI) in individuals with abnormalities or long-term catheterization. Innate immune responses induced or mediated by pattern recognition receptor signalling, antimicrobial peptides, and neutrophils are vital to clear bacteria during UTIs. Bacterial virulence and fitness factors include fimbriae and flagella that may function in immune evasion. The mechanism by which P. mirabilis sense the host environment and then trigger immune evasion is still unclear. In this study, we showed that sigma factor E (RpoE), which regulates expression of genes for survival in stresses, is important for host immune evasion. To investigate the role of P. mirabilis RpoE in immune evasion, we constructed rpoE mutant and rseA mutant (RseA, an anti-sigma E factor, rseA mutation causing RpoE overexpression). We found that the expression of mannose-resistant Proteus-like (MR/P) fimbriae of rseA mutant was higher than others, while the expression of flhDC and fliC1 of rseA mutant was the lowest in the three strains by qPCR assay. MrpI is a recombinase that control orientation of mrp operon promoter and we observe RpoE positively regulates mrpI by real-time PCR. The promoter invertible element (IE) assay also showed IE of wild-type and rseA mutant are largely on compared to rpoE mutant. Consistent with the results, rseA mutant had the best invasion ability and swarmed the least of all. Human urothelial cells have been known to secrete IL-8 cytokines to attract neutrophils to eliminate the pathogens. In this regard, we found NTUB1 produced more IL-8 and had the highest level of IL-8 mRNA after infecting with rpoE mutant by cytokine array and qPCR. The mouse UTI model further indicated almost no colonization of rpoE mutant in the bladder and kidney. Finally, we found that urea (the major component in urine) and polymyxin B (a kind of antimicrobial peptides) can induce high expression of rpoE in the wild-type. Altogether, our findings support that rseA mutant and rpoE mutant were phenotypically distinct and for the first time, we demonstrate that RpoE is important in sensing environmental cues and subsequently triggers expression of genes associated with virulence and fitness factors to evade host immunity and build up UTIs.
Subjects
Proteus mirabilis
Sigma factor E
virulence factor
immune evasion
Type
thesis
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