Caspase crosstalk: integration of apoptotic and innate immune signalling pathways

• Individual caspases can regulate both cell death and inflammatory processes.
• Caspases can no longer be classified as being ‘apoptotic’ or ‘inflammatory’.
• Cell death and inflammation are processes on a common axis, regulated by caspases.

The caspase family of cysteine proteases has been functionally divided into two groups: those involved in apoptosis and those involved in innate immune signalling. Recent findings have identified ‘apoptotic’ caspases within inflammasome complexes and revealed that ‘inflammatory’ caspases are capable of inducing cell death, suggesting that the earlier view of caspase function may have been overly simplistic. Here, I review evidence attributing nonclassical functions to many caspases and propose that caspases serve as critical mediators in the integration of apoptotic and inflammatory pathways, thereby forming an integrated signalling system that regulates cell death and innate immune responses during development, infection, and homeostasis.