The Pyrin and HIN200 domain-containing (PYHIN) protein family consists of AIM2, IFI16, MNDA, PYHIN1 and POP3 in humans and at least 13 proteins in mouse. Mouse AIM2 and p204 have been previously described to be intracellular dsDNA sensors leading to caspase-1 activation and STING-dependent IFN-β induction respectively. However the function of most mouse PYHIN proteins remains unknown. Here we characterized one such mouse PYHIN protein, p207.

P207 contains an N-terminal Pyrin and a C-terminal HINB domain that share strong sequence similarity with the corresponding domains of p204 (85% and 92% respectively). P207 is highly expressed in BMDMs and BMDCs and its expression is further enhanced after dsDNA stimulation of cells in an IFN-dependent manner. In contrast to p204, reduction of p207 expression by shRNA had no effect on DNA-induced IFN-β. Rather, p207 shRNA studies in macrophage cell lines showed an impairment in TNF mRNA induction following stimulation with dsDNA, transfected poly(I:C) or LPS as well as after infection with HSV. Induction of other LPS-dependent genes including CCL5, IL-1, IL-12 or IL-6 was not p207-dependent. Further, ectopic expression of p207 induced a murine TNF promoter reporter, while p207 shRNA inhibited LPS-stimulated RNA polymerase II recruitment to the TNF promoter. Furthermore, p207 interactome analysis by mass spectrometry revealed a list of potential interaction partners involved in transcription. These candidates and their involvement in p207-mediated effects on TNF induction are being currently pursued.

These results demonstrate the existence of a novel PYHIN-dependent mechanism of regulation of TNF induction during pattern recognition receptor responses. Thus mouse p207 is another PYHIN protein involved in mediating innate immune responses. Further, the requirement for a PYHIN protein for maximal TNF responses may be conserved in humans.