title: Mixed lineage kinase 3 (MLK3)-activated p38 MAP kinase mediates transforming growth factor-beta-induced apoptosis in hepatoma cells.
abstract: Although transforming growth factor beta1 (TGF-beta1) acts via the Smad signaling pathway to initiate de novo gene transcription, the TGF-beta1-induced MAPK kinase activation that is involved in the regulation of apoptosis is less well understood. Even though the p38 MAP kinase and c-Jun NH(2)-terminal kinases (JNKs) are involved in TGF-beta1-induced cell death in hepatoma cells, the upstream mediators of these kinases remain to be defined. We show here that the members of the mixed lineage kinase (MLK) family (including MLK1, MLK2, MLK3, and dual leucine zipper-bearing kinase (DLK)) are expressed in FaO rat hepatoma cells and are likely to act between p38 and TGF-beta receptor kinase in death signaling. TGF-beta1 treatment leads to an increase in MLK3 activity. Overexpression of MLK3 enhances TGF-beta1-induced apoptotic death in FaO cells and Hep3B human hepatoma cells, whereas expression of the dominant-negative forms of MLK3 suppresses cell death induced by TGF-beta1. The dominant-negative forms of MLK1 and -2 also suppress TGF-beta1-induced cell death. In MLK3-overexpressing cells, ERK, JNKs, and p38 MAP kinases were further activated in response to TGF-beta1 compared with the control cells. In contrast, overexpression of the dominant-negative MLK3 resulted in suppression of TGF-beta1-induced MAP kinase activation and TGF-beta1-induced caspase-3 activation. We also show that only the inhibition of the p38 pathway suppressed TGF-beta1-induced apoptosis. These observations support a role for MLKs in the TGF-beta1-induced cell death mechanism.
authors.affiliation: Laboratory of Cell Regulation and Carcinogenesis, NCI, National Institutes of Health, Bethesda, Maryland 20892, USA.
authors.forename: Ki-Yong
authors.initials: KY
authors.lastname: Kim
authors.forename: Byung-Chul
authors.initials: BC
authors.lastname: Kim
authors.forename: Zhiheng
authors.initials: Z
authors.lastname: Xu
authors.forename: Seong-Jin
authors.initials: SJ
authors.lastname: Kim
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D006528:Carcinoma, Hepatocellular / Q000378:metabolism*; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D045744:Cell Line, Tumor; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000378:metabolism; D006801:Humans; D008113:Liver Neoplasms / Q000378:metabolism*; D020930:MAP Kinase Kinase Kinases; D020929:Mitogen-Activated Protein Kinase Kinases; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D011506:Proteins / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D014158:Transcription, Genetic; D016212:Transforming Growth Factor beta / Q000378:metabolism*; D053773:Transforming Growth Factor beta1; D048051:p38 Mitogen-Activated Protein Kinases; D000097767:Mitogen-Activated Protein Kinase Kinase Kinase 11
chemical_list: D053148:Caspase 3; D020169:Caspases; D004791:Enzyme Inhibitors; D020930:MAP Kinase Kinase Kinases; D020929:Mitogen-Activated Protein Kinase Kinases; D020928:Mitogen-Activated Protein Kinases; D017346:Protein Serine-Threonine Kinases; D011506:Proteins; D011993:Recombinant Fusion Proteins; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; D048051:p38 Mitogen-Activated Protein Kinases; D000097767:Mitogen-Activated Protein Kinase Kinase Kinase 11; C508960:TGFB1 protein, human; C508962:Tgfb1 protein, rat; C490205:Sprk protein, rat; C505407:CASP3 protein, human; C505410:Casp3 protein, rat