A genetic analysis of mouse macrophage susceptibility to anthrax lethal factor

Anthrax is an infectious disease caused by the Gram-positive organism Bacillus anthracis. The lethal effects of systemic anthrax can be mimicked in animal models by the administration of anthrax Lethal Toxin (LeTx), which is produced at high levels during systemic infection. LeTx is made up of two polypeptides: protective antigen (PA), and lethal factor (LF). PA mediates the delivery of LF into the cytosol of all cell types that have been tested, where LF exerts a cytolytic effect that is specific to macrophages.; It has previously been shown that inbred strains of the mouse exhibit striking differences in the susceptibility of their cultured macrophages to killing by LeTx. In an attempt to clarify the molecular mechanism by which LF induces macrophage cytolysis, we have exploited this genetic difference to isolate one gene that determines mouse macrophage susceptibility to anthrax LeTx. We mapped a single genetic locus that controls this phenotype, called Ltxs1, to a 0.51 cM interval on mouse chromosome 11. In collaboration with the Whitehead Institute for Genome Research, we then generated virtually complete genomic sequence for the entire Ltxs1 interval. Analysis of all genes in the Ltxsl interval revealed that only one gene showed any polymorphisms between resistant and susceptible strains. This gene, Kif1C, encodes an 1100 amino acid protein that is a member of the kinesin UNC104 subfamily. We show that Kif1C sequence correlates with the LeTx susceptibility phenotype in all cases. We also show that treatments that disrupt Kif1C function induce susceptibility in normally resistant cells, while ectopic expression of a resistance allele of Kif1C in susceptible cells rescues them from LeTx-induced cytolysis.; Taken together, these results show that Kif1C function is required for macrophages to survive LeTx treatment, and that haploinsufficiency of Kif1C function is responsible for the susceptibility of heterozygous macrophages. Our data also suggest that Kif1C acts downstream in the LeTx cytolytic pathway. The discovery that a molecular motor is involved in susceptibility to LeTx provides new insight into a poorly understood aspect of anthrax pathogenesis.