Transforming Growth Factor-β-activated Kinase 1 Research Articles

Pellino2 activates the mitogen activated protein kinase pathway

Engagement of the interleukin-1 (IL1) and Toll receptors, which are part of the innate immune system, facilitates activation of the transcription factors NF-κB, Elk-1 and AP-1. Pellino1 and Pellino2 have recently been shown to be intermediates in the pathway leading to activation of NF-κB. Here we demonstrate for the first time that human Pellino2 interacts with TRAF6 (tumor necrosis factor receptor associated factor 6) and that both Pellino1 and Pellino2 also interact with TAK1 (transforming growth factor-β activated kinase 1). We also show that Pellino2, but not Pellino1, can activate the mitogen activated protein kinase pathway leading to activation of AP-1 and Elk-1. These observations suggest a role for the Pellino proteins in the IL1/Toll signaling cascades as scaffold proteins that may regulate signaling branch-points.

Erratum: NF-κB regulation in the immune system

Nature Reviews Immunology 2, 725–734 (2002) On page 728 of this article, the following incorrect sentence was published: 'The complex of transforming-growth-factor-β-activated kinase 1 (TAK1), TAK1-binding protein 1 (TAB1) and TAB2 was thought to be an integral component that relays the signals to IKK complexes downstream of TRAF6 (REF.

Helicobacter pylori lipopolysaccharide induces apoptosis of cultured guinea pig gastric mucosal cells.

Helicobacter pylori lipopolysaccharide (LPS) is generally accepted as a low-toxicity virulence. Primary cultures of guinea pig gastric mucosal cells expressed the Toll-like receptor 4 and were sensitive to H. pylori LPS as well as Escherichia coli LPS. H. pylori LPS stimulated phosphorylation of transforming growth factor-beta-activated kinase 1 (TAK1), TAK1-binding protein 1 (TAB1), and c-Jun NH(2)-terminal kinase (JNK) 2. H. pylori LPS at >2.1 endotoxin unit/ml (>1 ng/ml) activated caspase-8, stimulated cytochrome c release from mitochondria, and subsequently activated caspases-9 and -3, leading to apoptosis. Epidermal growth factor blocked all of these apoptotic processes and inhibited apoptosis, whereas it did not modify the phosphorylation of TAK1, TAB1, and JNK2. A comparatively specific inhibitor of caspase-8 or -9 blocked apoptosis, whereas cytochrome c release was prevented only with a caspase-8-like inhibitor. Our results suggest that caspase-8 and mitochondria may play crucial roles in H. pylori LPS-induced apoptosis and that this accelerated apoptosis may be involved in abnormal cell turnover of H. pylori-infected gastric mucosa.

TAK1 regulates multiple protein kinase cascades activated by bacterial lipopolysaccharide

During inflammation the balance between cell activation and cell death is determined by the tight regulation of multiple intracellular enzyme cascades. Key regulatory steps often involve protein kinases. We show that the prototypical pro-inflammatory molecule, bacterial lipopolysaccharide, activates multiple protein kinases such as p38, JNK, IKK-beta, and PKB/Akt via transforming growth factor beta-activated kinase-1 (TAK1). We also show that TAK1 plays an important role in similar activation pathways triggered by interleukin-1. Thus TAK1 must be considered as an important component of intracellular pathways in cells involved in host responses to physiological and/or environmental stress signals during inflammation.

TAK1 mediates an activation signal from toll-like receptor(s) to nuclear factor-κB in lipopolysaccharide-stimulated macrophages

Stimulation of monocytes/macrophages with lipopolysaccharide (LPS) results in activation of nuclear factor-κB (NF-κB), which plays crucial roles in regulating expression of many genes involved in the subsequent inflammatory responses. Here, we investigated roles of transforming growth factor-β activated kinase 1 (TGF-TAK1), a mitogen-activated protein kinase kinase kinase (MAPKKK), in the LPS-induced signaling cascade. A kinase-negative mutant of TAK1 inhibited the LPS-induced NF-κB activation both in a macrophage-like cell line, RAW 264.7, and in human embryonic kidney 293 cells expressing toll-like receptor 2 or 4. Furthermore, we demonstrated that endogenous TAK1 is phosphorylated upon simulation of RAW 264.7 cells with LPS. These results indicate that TAK1 functions as a critical mediator in the LPS-induced signaling pathway.

NLK TAKs onto the Wnt signalling pathway

The Wnt signalling pathway regulates cell-fate decisions in development through a complex of β-catenin and the TCF/LEF family of transcription factors. In most experimental systems, Wnt signalling stabilizes cytosolic β-catenin, which then binds to TCF and acts as a transcriptional co-activator. Thus, the loss of β-catenin and TCF results in similar phenotypes. However, in Caenorhabditis elegans, the loss of WRM-1 (a β-catenin homologue) has the opposite effect to the loss of POP-1 (a TCF-related protein). These papers reveal that a novel mitogen-activated protein (MAP) kinase-like pathway converges with the Wnt signalling pathway to regulate TCF-mediated gene transcription1xMAP kinase and Wnt pathways converge to downregulate an HMG-domain repressor in Caenorhabditis elegans. Meneghini, M.D. et al. Nature. 1999; 399: 793–797Crossref | PubMed | Scopus (218)See all References, 2xWRM-1 activates the LIT-1 protein kinase to transduce anterior/posterior polarity signals in C. elegans. Rocheleau, C.E. et al. Cell. 1999; 97: 717–726Abstract | Full Text | Full Text PDF | PubMed | Scopus (202)See all References, 3xThe TAK1–NLK–MAPK-related pathway antagonises signalling between β-catenin and transcription factor TCF. Ishitani, T. et al. Nature. 1999; 399: 798–802Crossref | PubMed | Scopus (423)See all References. This pathway might be the basis for the apparent discrepancy between the role of β-catenin in C. elegans and vertebrates.In C. elegans, Wnt signalling polarizes the embryo by downregulating POP-1 activity in posterior daughter cells. The proteins MOM-1 and LIT-1 are also required to downregulate POP-11xMAP kinase and Wnt pathways converge to downregulate an HMG-domain repressor in Caenorhabditis elegans. Meneghini, M.D. et al. Nature. 1999; 399: 793–797Crossref | PubMed | Scopus (218)See all References, 2xWRM-1 activates the LIT-1 protein kinase to transduce anterior/posterior polarity signals in C. elegans. Rocheleau, C.E. et al. Cell. 1999; 97: 717–726Abstract | Full Text | Full Text PDF | PubMed | Scopus (202)See all References and are homologous to TAK1 (transforming-growth-factor-β-activated kinase 1) and NLK (nemo-like kinase) respectively, which are components of the MAP kinase pathway. Ishitani and colleagues3xThe TAK1–NLK–MAPK-related pathway antagonises signalling between β-catenin and transcription factor TCF. Ishitani, T. et al. Nature. 1999; 399: 798–802Crossref | PubMed | Scopus (423)See all References3 found that TAK1 and NLK negatively regulate β-catenin/TCF-mediated transcription in mammalian cells. TAK1 stimulates the kinase activity of NLK, and this in turn phosphorylates hTCF4. Phosphorylated hTCF4 can still bind to β-catenin, but NLK phosphorylation interferes with the binding of the β-catenin–TCF complex to DNA, thereby negatively regulating β-catenin–TCF-mediated transcription. NLK immunoprecipitates contain hTCF4, but the interaction does not appear to be direct and might require β-catenin3xThe TAK1–NLK–MAPK-related pathway antagonises signalling between β-catenin and transcription factor TCF. Ishitani, T. et al. Nature. 1999; 399: 798–802Crossref | PubMed | Scopus (423)See all References3. Consistent with this, in C. elegans, WRM-1 (β-catenin) was found in a stable complex with LIT-1 (NLK), where it activated LIT-1-dependent kinase activity to hyperphosphorylate POP-1 (TCF). However, unlike the situation in vertebrates, WRM-1 did not form a stable complex with POP-12xWRM-1 activates the LIT-1 protein kinase to transduce anterior/posterior polarity signals in C. elegans. Rocheleau, C.E. et al. Cell. 1999; 97: 717–726Abstract | Full Text | Full Text PDF | PubMed | Scopus (202)See all References2. Interestingly, POP-1 was normally found in the nucleus of vertebrate cells (as it is in C. elegans embryos), but coexpression of POP-1 with LIT-1 and WRM-1 resulted in a redistribution of POP-1 to the cytoplasm2xWRM-1 activates the LIT-1 protein kinase to transduce anterior/posterior polarity signals in C. elegans. Rocheleau, C.E. et al. Cell. 1999; 97: 717–726Abstract | Full Text | Full Text PDF | PubMed | Scopus (202)See all References2. Thus, in C. elegans, the accumulation of WRM-1 due to Wnt signalling might promote the inactivation of POP-1 through LIT-1 rather than promoting the coactivation of POP-1-mediated transcription.

Mitogen-activated protein kinase cascade and cell cycle-related genes in the kidney

Recent studies have shown that mitogen-activated protein kinase (MAPK) consists of at least 3 subfamilies, including the classical MAPK, stress-activated protein kinase/c-Jun N-terminal kinase, and p38 kinase. Transforming growth factor (TGF)-β-activating kinase-1 (TAK1) is a novel MAP kinase kinase (MAPKK) that is reported to stimulate the p38 kinase and/or c-Jun N-terminal kinase pathway. TAKdN, the active form of TAK1, inhibits [3H]-thymidine uptake, and reduces the percentages of cells in the S and G2/M phases of the cell cycle. TAKK63W, the negative, or inactive form of TAK1, ameliorates the inhibition of3H-thymidine uptake and the percentages of cells in S and G2/M phases induced by TGF-β. Overexpression of TAKdN inhibits cyclin D1 gene promoter activity and protein expression. In contrast, constitutive active MKK1, the classical p42/44 MAPK activator, increases cyclin D1 promoter activity and protein level. Overexpression of the active form of MKK1 increases [3H]-thymidine uptake, while the inactive form decreases the uptake. To elucidate the mechanisms of the cell cycle of mesangial cells, we produced adenovirus vectors containing the coding sequences of cyclin D1 (AxCAD1), p16INK4 (AxCAp16), and p21CIP1 (AxCAp21), and investigated whether transfer of these genes changes platelet-derived growth factor-and endothelin-1-induced proliferation of rat mesangial cells. AxCAp16 and AxCAp21 inhibits [3H]-thymidine incorporation and the mitogen-induced increase in cyclin-dependent kinase-4 activity, and reduces the percentage of cells in the S phase as well. Overexpression of cyclin D1 increases the percentage of the cells in the S and G2 phases, and reduces cell size. These findings suggest that p16INK4 and p21CIP1 function as inhibitors of the proliferation of mesangial cells, induced by growth-promoting factors, and that deregulated expression of cyclin D1 causes disturbances in the cell cycle.