In a microarray screen for genes regulated by Toll-like receptor (TLR) signaling, Matsushita et al. found Zc3h12a and proceeded to create knockout mice to explore the function of this gene in immune responses. The knockout mice developed severe, lethal autoimmune disease associated with hyperimmunoglobulemia, excessive plasma cells, excessive production of effector and memory T cells with increased production of interferon-γ (IFN-γ), and increased production of inflammatory cytokines, such as interleukin-6 (IL-6) and IL-12p40, from macrophages. Cytokine production in response to stimulation with ligands for TLR2, TLR3, TLR4, TLR7, or TLR9 was increased in macrophages from the knockout mice compared with that in macrophages from wild-type mice. The authors showed that the half-life of the Il6 transcript, but not Tnf (encoding tumor necrosis factor–α), was prolonged in the knockout cells, and experiments with transfected cells showed that the destabilization by Zc3h12a required the 3′-untranslated region (UTR) of Il6. Although mutation of the CCCH zinc finger domain decreased the mRNA destabilizing activity of Zc3h12a, it did not abolish its activity, and another region with homology to RNases was identified. In vitro assays confirmed the RNase activity of Zc3h12a; however, the activity in vitro was not sequence-specific, which suggests that in cells there is a mechanism to achieve specificity, for example, by interactions with other proteins or mRNA structure under certain conditions. Thus, TLR signaling appears to be held in check through the induction of an RNase that targets specific cytokine transcripts to limit production of inflammatory mediators.
K. Matsushita, O. Takeuchi, D. M. Standley, Y. Kumagai, T. Kawagoe, T. Miyake, T. Satoh, H. Kato, T. Tsujimura, H. Nakamura, S. Akira, Zc3h12a is an RNase essential for controlling immune responses by regulating mRNA decay. Nature 458, 1185–1190 (2009). [PubMed]