Calpain-dependent cytoskeletal rearrangement exploited for anthrax toxin endocytosis

Area of Science:

• Cell Biology
• Microbiology
• Biochemistry

Background:

• Bacillus anthracis toxin enters host cells via receptor-mediated endocytosis.
• The protective antigen component binds host cell receptors like CMG2.
• The mechanism of toxin internalization involving host cell proteins is not fully understood.

Purpose of the Study:

• To identify host cell factors involved in Bacillus anthracis toxin entry.
• To elucidate the role of calpains and their substrates in toxin internalization.
• To investigate the mechanism of toxin association with the actin cytoskeleton.

Main Methods:

• Antisense-based phenotypic screening to identify host factors.
• Assessing the effect of calpain-2 and talin-1 down-regulation on toxin entry.
• Using pharmacological inhibitors to interfere with calpain activity.
• Expressing wild-type and mutant talin-1 to study its function.
• Analyzing toxin binding, endocytosis, and cell survival.

Main Results:

• Calpain-2 and its substrate talin-1 are essential for anthrax toxin internalization.
• Down-regulation of calpain-2 or talin-1, or calpain inhibition, reduced toxin endocytosis but not binding.
• Interference with calpain activity or talin-1 function increased cell survival against anthrax lethal toxin.
• Talin-1 cleavage by calpain is crucial for toxin entry, as a non-cleavable mutant did not promote entry.
• Toxin-bound CMG2 associated with dynamic actin filaments during endocytosis, facilitated by talin-1 disruption.

Conclusions:

• Bacterial toxins exploit host cell calpain-mediated cytoskeletal rearrangements for internalization.
• Calpain-2 and talin-1 play a critical role in facilitating the association of anthrax toxin with the actin cytoskeleton for entry.
• Targeting calpain activity or talin-1 function represents a potential strategy to inhibit anthrax toxin entry and protect host cells.