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Evasion of IFN-? signaling by Francisella novicida is dependent upon Francisella outer membrane protein C.

ABSTRACT:

Background

Francisella tularensis is a Gram-negative facultative intracellular bacterium and the causative agent of the lethal disease tularemia. An outer membrane protein (FTT0918) of F. tularensis subsp. tularensis has been identified as a virulence factor. We generated a F. novicida (F. tularensis subsp. novicida) FTN_0444 (homolog of FTT0918) fopC mutant to study the virulence-associated mechanism(s) of FTT0918.

Methods and findings

The ?fopC strain phenotype was characterized using immunological and biochemical assays. Attenuated virulence via the pulmonary route in wildtype C57BL/6 and BALB/c mice, as well as in knockout (KO) mice, including MHC I, MHC II, and µmT (B cell deficient), but not in IFN-? or IFN-?R KO mice was observed. Primary bone marrow derived macrophages (BMDM) prepared from C57BL/6 mice treated with rIFN-? exhibited greater inhibition of intracellular ?fopC than wildtype U112 strain replication; whereas, IFN-?R KO macrophages showed no IFN-?-dependent inhibition of ?fopC replication. Moreover, phosphorylation of STAT1 was downregulated by the wildtype strain, but not the fopC mutant, in rIFN-? treated macrophages. Addition of NG-monomethyl-L-arginine, an NOS inhibitor, led to an increase of ?fopC replication to that seen in the BMDM unstimulated with rIFN-?. Enzymatic screening of ?fopC revealed aberrant acid phosphatase activity and localization. Furthermore, a greater abundance of different proteins in the culture supernatants of ?fopC than that in the wildtype U112 strain was observed.

Conclusions

F. novicida FopC protein facilitates evasion of IFN-?-mediated immune defense(s) by down-regulation of STAT1 phosphorylation and nitric oxide production, thereby promoting virulence. Additionally, the FopC protein also may play a role in maintaining outer membrane stability (integrity) facilitating the activity and localization of acid phosphatases and other F. novicida cell components.

SUBMITTER: Nallaparaju KC

PROVIDER: S-EPMC3069069 | biostudies-literature | 2011 Mar

REPOSITORIES: biostudies-literature

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Publications

Evasion of IFN-γ signaling by Francisella novicida is dependent upon Francisella outer membrane protein C.

Nallaparaju Kalyan C KC Yu Jieh-Juen JJ Rodriguez Stephen A SA Zogaj Xhavit X Manam Srikanth S Guentzel M Neal MN Seshu Janakiram J Murthy Ashlesh K AK Chambers James P JP Klose Karl E KE Arulanandam Bernard P BP

PloS one 20110331 3

<h4>Background</h4>Francisella tularensis is a Gram-negative facultative intracellular bacterium and the causative agent of the lethal disease tularemia. An outer membrane protein (FTT0918) of F. tularensis subsp. tularensis has been identified as a virulence factor. We generated a F. novicida (F. tularensis subsp. novicida) FTN_0444 (homolog of FTT0918) fopC mutant to study the virulence-associated mechanism(s) of FTT0918.<h4>Methods and findings</h4>The ΔfopC strain phenotype was characterized ...[more]

PMID: 21483828

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