The Ifi 200 genes: an emerging family of IFN-inducible genes.

The biological activities of interferons (IFNs) are mediated by IFN-induced proteins. One family is encoded by several structurally related genes located on murine chromosome 1 (Ifi 200 cluster) and three homologous genes (MNDA, IFI 16 and AIM2) located on human chromosome 1 as well, within a linkage group highly conserved between mouse and human. All the proteins of this family contain at least one copy of a conserved 200 amino acid domain, in addition to other regions that are different or missing among the various family members. Conservation of the 200 amino acid segment, therefore, may be responsible for a common function, while individually expressed domains may afford other tissue- or cell-specific functions. The data available demonstrate that at least two members of the Ifi 200 protein family, p202 and p204, inhibit cell proliferation in vitro. Moreover, high constitutive levels of p204 expression impair normal embryo development in transgenic animals. Here, we will review the principal features of murine and human proteins belonging to this family and their function in the cell growth-regulatory activities mediated by IFNs.