Anthrax lethal factor cleaves regulatory subunits of phosphoinositide-3 kinase to contribute to toxin lethality.

Cellular targets of anthrax lethal factor are identified to reveal the molecular basis of toxin-induced death. Anthrax lethal toxin (LT), produced byBacillus anthracis, comprises a receptor-binding moiety, protective antigen and the lethal factor (LF) protease(1,2). Although LF is known to cleave mitogen-activated protein kinase kinases (MEKs/MKKs) and some variants of the NLRP1 inflammasome sensor, targeting of these pathways does not explain the lethality of anthrax toxin(1,2). Here we report that the regulatory subunits of phosphoinositide-3 kinase (PI3K)-p85 alpha (PIK3R1) and p85 beta (PIK3R2)(3,4)-are substrates of LF. Cleavage of these proteins in a proline-rich region between their N-terminal Src homology and Bcr homology domains disrupts homodimer formation and impacts PI3K signalling. Mice carrying a mutated p85 alpha that cannot be cleaved by LF show a greater resistance to anthrax toxin challenge. The LF(W271A) mutant cleaves p85 alpha with lower efficiency and is non-toxic to mice but can regain lethality when combined with PI3K pathway inhibitors. We provide evidence that LF targets two signalling pathways that are essential for growth and metabolism and that the disabling of both pathways is likely necessary for lethal anthrax infection.