Function and mechanism of the pyrin inflammasome.

Pyrin, encoded by the MEFV gene, is an intracellular pattern recognition receptor that assembles inflammasome complexes in response to pathogen infections. Mutations in the MEFV gene have been linked to autoinflammatory diseases such as familial Mediterranean fever (FMF) or pyrin-associated autoinflammation with neutrophilic dermatosis (PAAND). Recent insights have now revealed how pyrin is activated during infection, providing a molecular basis for the understanding of such disease-causing mutations in pyrin. Interestingly, pyrin does not directly recognize molecular patterns (pathogen- or host-derived danger molecules), but rather responds to disturbances in cytoplasmic homeostasis caused by the infection. In the case of pyrin, these perturbations, recently defined as 'homeostasis-altering molecular processes' (HAMPs), are processes leading to the inactivation of the RhoA GTPase. This review attempts to combine early observation and findings with the most recent discoveries on how pyrin detects inactivation of RhoA to shed light on the function and mechanism of pyrin activation.