Abstract
The decision between survival and death in cells exposed to TNF relies on a highly regulated equilibrium between proapoptotic and antiapoptotic factors. The TNF-activated antiapoptotic response depends on several transcription factors, including NF-κB and its RelA/p65 subunit, that are activated through phosphorylation-mediated degradation of IκB inhibitors, a process controlled by the IκB kinase complex. Genetic studies in mice have identified the IκB kinase-related kinase TANK-binding kinase 1 (TBK1; also called NAK or T2K) as an additional regulatory molecule that promotes survival downstream of TNF, but the mechanism through which TBK1 exerts its survival function has remained elusive. Here we show that TBK1 triggers an antiapoptotic response by controlling a specific RelA/p65 phosphorylation event. TBK1-induced RelA phosphorylation results in inducible expression of plasminogen activator inhibitor-2 (PAI-2), a member of the serpin family with known antiapoptotic activity. PAI-2 limits caspase-3 activation through stabilization of transglutaminase 2 (TG2), which cross-links and inactivates procaspase-3. Importantly, Tg2(-/-) mice were found to be more susceptible to apoptotic cell death in two models of TNF-dependent acute liver injury. Our results establish PAI-2 and TG2 as downstream mediators in the antiapoptotic response triggered upon TBK1 activation.