The PYHIN Protein p205 Regulates the Inflammasome by Controlling Asc Expression

Members of the IFN-inducible PYHIN protein family, such as absent in melanoma-2 and IFN-γ-inducible protein (IFI)16, bind dsDNA and form caspase-1-activating inflammasomes that are important in immunity to cytosolic bacteria, DNA viruses, or HIV. IFI16 has also been shown to regulate transcription of type I IFNs during HSV infection. The role of other members of the PYHIN protein family in the regulation of immune responses is much less clear. In this study, we identified an immune-regulatory function for a member of the murine PYHIN protein family, p205 (also called Ifi205). Examination of immune responses induced by dsDNA and other microbial ligands in bone marrow-derived macrophages lacking p205 revealed that inflammasome activation by dsDNA, as well as ligands that engage the NLRP3 inflammasome, was severely compromised in these cells. Further analysis revealed that p205-knockdown cells showed reduced expression of apoptosis-associated speck-like molecule containing CARD domain (Asc) at the protein and RNA levels. p205 knockdown resulted in reduced binding of actively transcribing RNA polymerase II to the endogenous Asc gene, resulting in decreased transcription and processing of Asc pre-mRNA. Deletion of p205 in B16 melanoma cells using CRISPR/Cas9 showed a similar loss of Asc expression. Ectopic expression of p205 induced expression of an Asc promoter-luciferase reporter gene. Together, these findings suggest that p205 controls expression of Asc mRNA to regulate inflammasome responses. These findings expand on our understanding of immune-regulatory roles for the PYHIN protein family.