TANK-binding kinase 1 (TBK1) controls cell survival through PAI-2/serpinB2 and transglutaminase 2.

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.

Cooperative functions of Chk1 and Chk2 reduce tumour susceptibility in vivo.

Although the linkage of Chk1 and Chk2 to important cancer signalling suggests that these kinases have functions as tumour suppressors, neither Chk1+/- nor Chk2-/- mice show a predisposition to cancer under unperturbed conditions. We show here that Chk1+/-Chk2-/- and Chk1+/-Chk2+/- mice have a progressive cancer-prone phenotype. Deletion of a single Chk1 allele compromises G2/M checkpoint function that is not further affected by Chk2 depletion, whereas Chk1 and Chk2 cooperatively affect G1/S and intra-S phase checkpoints. Either or both of the kinases are required for DNA repair depending on the type of DNA damage. Mouse embryonic fibroblasts from the double-mutant mice showed a higher level of p53 with spontaneous DNA damage under unperturbed conditions, but failed to phosphorylate p53 at S23 and further induce p53 expression upon additional DNA damage. Neither Chk1 nor Chk2 is apparently essential for p53- or Rb-dependent oncogene-induced senescence. Our results suggest that the double Chk mutation leads to a high level of spontaneous DNA damage, but fails to eliminate cells with damaged DNA, which may ultimately increase cancer susceptibility independently of senescence.

Identification of NAP1, a regulatory subunit of IkappaB kinase-related kinases that potentiates NF-kappaB signaling.

The IkappaB kinase (IKK)-related kinase NAK (also known as TBK or T2K) contributes to the activation of NF-kappaB-dependent gene expression. Here we identify NAP1 (for NAK-associated protein 1), a protein that interacts with NAK and its relative IKK epsilon (also known as IKKi). NAP1 activates NAK and facilitates its oligomerization. Interestingly, the NAK-NAP1 complex itself effectively phosphorylated serine 536 of the p65/RelA subunit of NF-kappaB, and this activity was stimulated by tumor necrosis factor alpha (TNF-alpha). Overexpression of NAP1 specifically enhanced cytokine induction of an NF-kappaB-dependent, but not an AP-1-dependent, reporter. Depletion of NAP1 reduced NF-kappaB-dependent reporter gene expression and sensitized cells to TNF-alpha-induced apoptosis. These results define NAP1 as an activator of IKK-related kinases and suggest that the NAK-NAP1 complex may protect cells from TNF-alpha-induced apoptosis by promoting NF-kappaB activation.

The Cytokine Odyssey 2001, a joint meeting of the Society of Leukocyte Biology and the International Cytokine Society. 8-11 November 2001, Maui, Hawaii, USA.

The Cytokine Odyssey 2001 was held at the Outrigger Wailea Resort in Maui, Hawaii, USA. The meeting, jointly sponsored by the International Cytokine Society (ICS, 9th Annual Meeting) and the Society of Leukocyte Biology (SLB, 35th Annual Meeting), was organised by Carl Ware (Chair) from the La Jolla Institute for Allergy and Immunology (La Jolla, USA) and Thomas Hamilton (Co-Chair) from the Cleveland Clinic Foundation (Cleveland, USA). This international conference was designed to bring together leading investigators in molecular and cellular biology, physiology and genetics, interested in cytokines and cells of the immune system. This forum was aimed to assess the impact of this expanding science on new approaches to disease intervention [1].

CK2 Is a C-Terminal IkappaB Kinase Responsible for NF-kappaB Activation during the UV Response.

NF-kappaB is activated in response to proinflammatory stimuli, infections, and physical stress. While activation of NF-kappaB by many stimuli depends on the IkappaB kinase (IKK) complex, which phosphorylates IkappaBs at N-terminal sites, the mechanism of NF-kappaB activation by ultraviolet (UV) radiation remained enigmatic, as it is IKK independent. We now show that UV-induced NF-kappaB activation depends on phosphorylation of IkappaBalpha at a cluster of C-terminal sites that are recognized by CK2 (formerly casein kinase II). Furthermore, CK2 activity toward IkappaB is UV inducible through a mechanism that depends on activation of p38 MAP kinase. Inhibition of this pathway prevents UV-induced IkappaBalpha degradation and increases UV-induced cell death. Thus, the p38-CK2-NF-kappaB axis is an important component of the mammalian UV response.

The lymphotoxin-beta receptor induces different patterns of gene expression via two NF-kappaB pathways.

The lymphotoxin-beta receptor (LTbetaR) plays critical roles in inflammation and lymphoid organogenesis through activation of NF-kappaB. In addition to activation of the classical NF-kappaB, ligation of this receptor induces the processing of the cytosolic NF-kappaB2/p100 precursor to yield the mature p52 subunit, followed by translocation of p52 to the nucleus. This activation of NF-kappaB2 requires NIK and IKKalpha, while NEMO/IKKgamma is dispensable for p100 processing. IKKbeta-dependent activation of canonical NF-kappaB is required for the expression but not processing of p100 and for the expression of proinflammatory molecules including VCAM-1, MIP-1beta, and MIP-2 in response to LTbetaR ligation. In contrast, IKKalpha controls the induction by LTbetaR ligation of chemokines and cytokines involved in lymphoid organogenesis, including SLC, BLC, ELC, SDF1, and BAFF.