Biomedical subjects

Changchuan Xie

Publications and source records attributed to Changchuan Xie.

3 recordsLinked to original sources

PubMed2006

Determinants that control the specific interactions between TAB1 and p38alpha.

Previous studies have revealed that transforming growth factor-beta-activated protein kinase 1 (TAB1) interacts with p38alpha and induces p38alpha autophosphorylation. Here, we examine the sequence requirements in TAB1 and p38alpha that drive their interaction. Deletion and point mutations in TAB1 reveal that a proline residue in the C terminus of TAB1 (Pro412) is necessary for its interaction with p38alpha. Furthermore, a cryptic D-domain-like docking site was identified adjacent to the N terminus of Pro412, putting Pro412 in the phi(B)+3 position of the docking site. Through mutational analysis, we found that the previously identified hydrophobic docking groove in p38alpha is involved in this interaction, whereas the CD domain and ED domain are not. Furthermore, chimeric analysis with p38beta (which does not bind to TAB1) revealed a previously unidentified locus of p38alpha comprising Thr218 and Ile275 that is essential for specific binding of p38alpha to TAB1. Converting either of these residues to the corresponding amino acid of p38beta abolishes p38alpha interaction with TAB1. These p38alpha mutants still can be fully activated by p38alpha upstream activating kinase mitogen-activated protein kinase kinase 6, but their basal activity and activation in response to some extracellular stimuli are reduced. Adjacent to Thr218 and Ile275 is a site where large conformational changes occur in the presence of docking-site peptides derived from p38alpha substrates and activators. This suggests that TAB1-induced autophosphorylation of p38alpha results from conformational changes that are similar but unique to those seen in p38alpha interactions with its substrates and activating kinases.

Adaptor Proteins, Signal Transducing↗

PubMed2005

Distinct roles of basal steady-state and induced H-ferritin in tumor necrosis factor-induced death in L929 cells.

Tumor necrosis factor (TNF) alpha is a cytokine capable of inducing caspase-dependent (apoptotic) cell death in some cells and caspase-independent (necrosis-like) cell death in others. Here, using a mutagenesis screen for genes critical in TNF-induced death in L929 cells, we have found that H-ferritin deficiency is responsible for TNF resistance in a mutant line and that, upon treatment with TNF, this line fails to elevate levels of labile iron pool (LIP), critical for TNF-induced reactive oxygen species (ROS) production and ROS-dependent cell death. Since we found that TNF-induced LIP in L929 cells is primarily furnished by intracellular storage iron, the lesser induction of LIP in H-ferritin-deficient cells results from a reduction of intracellular iron storage caused by less H-ferritin. Different from some other cell lines, the H-ferritin gene in L929 cells is not TNF inducible; however, when H-ferritin is expressed in L929 cells under a TNF-inducible system, the TNF-induced LIP and subsequent ROS production and cell death were all prevented. Thus, LIP is a common denominator of ferritin both in the enhancement of cell death by basal steady-state H-ferritin and in protection against cell death by induced H-ferritin, thereby acting as a key determinant of TNF-induced cell death.

Animals↗

PubMed2004

Beta-actin is required for mitochondria clustering and ROS generation in TNF-induced, caspase-independent cell death.

Tumor necrosis factor (TNF)-alpha induces caspase-independent cell death in the fibrosarcoma cell line L929. This cell death has a necrotic phenotype and is dependent on production of reactive oxygen species (ROS) in the mitochondria. To identify genes involved in this TNF-induced, ROS-dependent cell death pathway, we utilized retrovirus insertion-mediated random mutagenesis to generate TNF-resistant L929 cell lines and we subsequently identified genes whose mutations are responsible for the TNF-resistant phenotype. In one such resistant line, beta-actin was disrupted by viral insertion, and subsequent reconstitution of beta-actin expression levels in the mutant line Actin(mut) restored its sensitivity to TNF. Resistance to TNF in Actin(mut) cells is signal specific since the sensitivity to other death stimuli is either unchanged or even increased. Comparable NF-kappaB activation and p38 phosphorylation in TNF-treated wild-type and Actin(mut) cells also indicates that reduced expression of actin only selectively blocked some of the TNF-induced cellular changes. Actin cleavage involved in apoptosis does not occur in TNF-treated L929 cell death, as in HeLa cells. Consistent over-expression of a caspase-cleaved product, a 15 kDa actin fragment, had no effect on TNF-induced necrosis of L929 cell. By contrast, TNF-induced mitochondria clustering and ROS production were dramatically reduced in Actin(mut) cells, indicating that actin-deficiency-mediated TNF resistance is most likely due to impaired mitochondrial responses to TNF stimulation. Our findings suggest that a full complement of actin is required for transduction of a cell death signal to mitochondria in TNF-treated L929 cells.

Actins↗