Anthrax lethal toxin paralyzes actin-based motility by blocking Hsp27 phosphorylation

Abstract

Inhalation of anthrax causes fatal bacteremia, indicating a meager host immune response. We previously showed that anthrax lethal toxin (LT) paralyzes neutrophils, a major component of innate immunity. Here, we have found that LT also inhibits actin-based motility of the intracellular pathogen Listeria monocytogenes. LT inhibition of actin assembly is mediated by blockade of Hsp27 phosphorylation, and can be reproduced by treating cells with the p38 mitogen-activated protein (MAP) kinase inhibitor SB203580. Nonphosphorylated Hsp27 inhibits Listeria actin-based motility in cell extracts, and binds to and sequesters purified actin monomers. Phosphorylation of Hsp27 reverses these effects. RNA interference knockdown of Hsp27 blocks LT inhibition of Listeria actin-based motility. Rescue with wild-type Hsp27 accelerates Listeria speed in knockdown cells, whereas introduction of Hsp27 mutants incapable of phosphorylation or dephosphorylation causes slowing down. We propose that Hsp27 facilitates actin-based motility through a phosphorylation cycle that shuttles actin monomers to regions of new actin filament assembly. Our findings provide a previously unappreciated mechanism for LT virulence, and emphasize a central role for p38 MAP kinase-mediated phosphorylation of Hsp27 in actin-based motility and innate immunity.

Endothelium-targeted overexpression of heat shock protein 27 ameliorates blood–brain barrier disruption after ischemic brain injury

“…S6). These results are consistent with previous findings that HSP27 is a direct inhibitor of actin polymerization (20,21).…”

“…It is well established that HSP27 directly inhibits actin polymerization by capping the barbed end of actin (20), where rapid addition of actin monomers occurs. Additionally, HSP27 can sequester G-actin monomers (21). As a consequence of either action, G-actin cannot bind to the plus end of F-actin and be further aggregated by myosin to form contractile stress fibers.…”

“…However, HSP27 exerts additional actions on ECs (14). For example, HSP27 can directly inhibit actin polymerization by capping the barbed end of filamentous actin (F-actin) (19,20) and by sequestering globular actin (G-actin) (21). Thus, the present study sought to test the hypothesis that HSP27 suppresses I/R-induced early onset BBB leakage through inhibiting actin polymerization and the disassembly of junctional proteins in cerebral ECs.…”

Global Impact of Salmonella Pathogenicity Island 2-secreted Effectors on the Host Phosphoproteome

“…S5), whereas one of HSP27's natural kinases in humans, MAPKAP2, can phosphorylate only three sites (Ser-15, Ser-78, and Ser-82) (56). This system differs from that used by Listeria monocytogenes, which manipulates the host p38 MAPK pathway to indirectly cause the phosphorylation of HSP27 to affect actin remodeling (54). More recently, two groups showed that SteC targets Cdc24 in yeast (57) and MEK in mammalian cells (9).…”

“…How this might occur at the atomic level is still an open question in the HSP27 field, although it seems likely that phosphorylation of HSP27 induces its disassociation from actin monomers, resulting in promotion of F-actin assembly from the newly freed actin monomers (54,55). One prediction of this would then be that multiply phosphorylated forms of HSP27 could further accelerate actin polymerization.…”