Susceptibility to Anthrax Lethal Toxin-Induced Rat Death Is Controlled by a Single Chromosome 10 Locus That Includes rNlrp1

Zachary L Newman,Morton P Printz,Shihui Liu,Mahtab Moayeri,Laura Breen,Devorah Crown,Pamela Flodman,Sharmina Miller-Randolph,Stephen H Leppla,Theresa Koehler

doi:10.1371/journal.ppat.1000906

Abstract

Anthrax lethal toxin (LT) is a bipartite protease-containing toxin and a key virulence determinant of Bacillus anthracis. In mice, LT causes the rapid lysis of macrophages isolated from certain inbred strains, but the correlation between murine macrophage sensitivity and mouse strain susceptibility to toxin challenge is poor. In rats, LT induces a rapid death in as little as 37 minutes through unknown mechanisms. We used a recombinant inbred (RI) rat panel of 19 strains generated from LT-sensitive and LT-resistant progenitors to map LT sensitivity in rats to a locus on chromosome 10 that includes the inflammasome NOD-like receptor (NLR) sensor, Nlrp1. This gene is the closest rat homolog of mouse Nlrp1b, which was previously shown to control murine macrophage sensitivity to LT. An absolute correlation between in vitro macrophage sensitivity to LT-induced lysis and animal susceptibility to the toxin was found for the 19 RI strains and 12 additional rat strains. Sequencing Nlrp1 from these strains identified five polymorphic alleles. Polymorphisms within the N-terminal 100 amino acids of the Nlrp1 protein were perfectly correlated with LT sensitivity. These data suggest that toxin-mediated lethality in rats as well as macrophage sensitivity in this animal model are controlled by a single locus on chromosome 10 that is likely to be the inflammasome NLR sensor, Nlrp1.

Highlights

Anthrax lethal toxin (LT), a major virulence factor of Bacillus anthracis, is composed of two proteins, lethal factor (LF) and protective antigen (PA)
Mouse Nlrp1b has five alleles that correlate with LT sensitivity or resistance in macrophages, and it is one of three tandem Nlrp1 paralogs on chromosome 11 [3]. mNlrp1b, the paralog controlling LT sensitivity, is a NOD-like receptor (NLR) which, when activated, leads to assembly of the inflammasome, a multiprotein complex responsible for the activation of caspase-1 [4]
Inflammasomes are multiprotein cytoplasmic complexes that respond to a variety of danger signals by activating the host innate immune response

Summary

Introduction

Anthrax lethal toxin (LT), a major virulence factor of Bacillus anthracis, is composed of two proteins, lethal factor (LF) and protective antigen (PA). LF is a protease which cleaves and inactivates members of the mitogenactivated protein kinase kinase (MAPKK or MEK) family, resulting in proliferation arrest in most cell types and a unique, rapid (,90 min), caspase-1 dependent lysis of mouse macrophages from certain inbred strains through poorly characterized mechanisms (for review see [2]). Sensitivity to LT-mediated lysis is a dominant trait that maps to the highly polymorphic Nlrp1b (Nalp1b) gene on chromosome 11 [3]. Mouse Nlrp1b (mNlrp1b) has five alleles that correlate with LT sensitivity or resistance in macrophages, and it is one of three tandem Nlrp paralogs on chromosome 11 [3]. MNlrp1b, the paralog controlling LT sensitivity, is a NOD-like receptor (NLR) which, when activated, leads to assembly of the inflammasome, a multiprotein complex responsible for the activation of caspase-1 [4]. Expression of mNlrp1b from LT-sensitive macrophages together with caspase-1 is sufficient to render other cell types sensitive to the effects of LT [8]

Methods

Results

Discussion

Conclusion