Calpain-dependent cytoskeletal rearrangement exploited for anthrax toxin endocytosis.
The protective antigen component of Bacillus anthracis toxins can interact with at least three distinct proteins on the host cell surface, capillary morphogenesis gene 2 (CMG2), tumor endothelial marker 8, and β1-integrin, and, with the assistance of other host proteins, enters targeted cells by receptor-mediated endocytosis. Using an antisense-based phenotypic screen, we discovered the role of calpains in this process. We show that functions of a ubiquitous Ca(2+)-dependent cysteine protease, calpain-2, and of the calpain substrate talin-1 are exploited for association of anthrax toxin and its principal receptor, CMG2, with higher-order actin filaments and consequently for toxin entry into host cells. Down-regulated expression of calpain-2 or talin-1, or pharmacological interference with calpain action, did not affect toxin binding but reduced endocytosis and increased the survival of cells exposed to anthrax lethal toxin. Adventitious expression of wild-type talin-1 promoted toxin endocytosis and lethality, whereas expression of a talin-1 mutant (L432G) that is insensitive to calpain cleavage did not. Disruption of talin-1, which links integrin-containing focal adhesion complexes to the actin cytoskeleton, facilitated association of toxin bound to its principal cell-surface receptor, CMG2, with higher-order actin filaments undergoing dynamic disassembly and reassembly during endocytosis. Our results reveal a mechanism by which a bacterial toxin uses constitutively occurring calpain-mediated cytoskeletal rearrangement for internalization.
['Jeong|Sun-Young|SY|', 'Martchenko|Mikhail|M|', 'Cohen|Stanley N|SN|']
D019943:Amino Acid Substitution D000818:Animals D000942:Antigens, Bacterial D001408:Bacillus anthracis D001427:Bacterial Toxins D002154:Calpain D002460:Cell Line D003599:Cytoskeleton D015536:Down-Regulation D004705:Endocytosis D022001:Focal Adhesions D005786:Gene Expression Regulation D051379:Mice D020125:Mutation, Missense D021381:Protein Transport D018000:Receptors, Peptide D016608:Talin
MDL28170 calpastatin lethal factor