Proteasomes control caspase-1 activation in anthrax lethal toxin-mediated cell killing

Area of Science:

• Immunology
• Cell Biology

Background:

• Anthrax lethal toxin (LT) induces necrosis in macrophages.
• Caspase-1 activation, regulated by Nalp1b inflammasome, is crucial for LT-induced cell death.
• The precise mechanisms controlling caspase-1 activation and macrophage death by LT are not fully understood.

Purpose of the Study:

• To investigate the physiological changes governed by caspase-1 in LT-treated murine macrophages.
• To elucidate the relationship between caspase-1 activation, proteasome activity, and plasma membrane integrity following LT exposure.

Main Methods:

• Treatment of J774A.1 macrophages with anthrax lethal toxin (LT).
• Application of caspase-1 inhibitor (Boc-D-cmk) and proteasome inhibitor (MG132) at various time points post-LT exposure.
• Assessment of caspase-1 activity, plasma membrane integrity, and metabolic activity.

Main Results:

• Caspase-1 inhibition by Boc-D-cmk rescued LT-treated macrophages, restoring membrane integrity and metabolic activity, even when added late.
• Proteasome inhibitor MG132 also rescued LT-treated macrophages, mirroring the effects of Boc-D-cmk.
• Proteasome inhibitors abrogated caspase-1 activity in LT-treated cells, suggesting they act upstream of caspase-1 activation, but did not affect LPS/nigericin-induced cell death.

Conclusions:

• Caspase-1-mediated necrosis in macrophages is tightly controlled by upstream events regulated by proteasomes in response to LT.
• Proteasome inhibitors do not directly inhibit caspase-1 but rather modulate an upstream pathway crucial for LT-induced caspase-1 activation and subsequent cell death.
• The regulation of caspase-1 activity by proteasomes is specific to LT-induced cytolysis, highlighting differential control mechanisms depending on the death stimulus.