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Kazuo Tatebayashi

Publications and source records attributed to Kazuo Tatebayashi.

8 recordsLinked to original sources
PubMed2006

Adaptor functions of Cdc42, Ste50, and Sho1 in the yeast osmoregulatory HOG MAPK pathway.

The yeast high osmolarity glycerol (HOG) signaling pathway can be activated by either of the two upstream pathways, termed the SHO1 and SLN1 branches. When stimulated by high osmolarity, the SHO1 branch activates an MAP kinase module composed of the Ste11 MAPKKK, the Pbs2 MAPKK, and the Hog1 MAPK. To investigate how osmostress activates this MAPK module, we isolated both gain-of-function and loss-of-function alleles in four key genes involved in the SHO1 branch, namely SHO1, CDC42, STE50, and STE11. These mutants were characterized using an HOG-dependent reporter gene, 8xCRE-lacZ. We found that Cdc42, in addition to binding and activating the PAK-like kinases Ste20 and Cla4, binds to the Ste11-Ste50 complex to bring activated Ste20/Cla4 to their substrate Ste11. Activated Ste11 and its HOG pathway-specific substrate, Pbs2, are brought together by Sho1; the Ste11-Ste50 complex binds to the cytoplasmic domain of Sho1, to which Pbs2 also binds. Thus, Cdc42, Ste50, and Sho1 act as adaptor proteins that control the flow of the osmostress signal from Ste20/Cla4 to Ste11, then to Pbs2.

Enzyme Activation↗
PubMed2005

Conserved docking site is essential for activation of mammalian MAP kinase kinases by specific MAP kinase kinase kinases.

Mammalian mitogen-activated protein kinase (MAPK) cascades control various cellular events, ranging from cell growth to apoptosis, in response to external stimuli. A conserved docking site, termed DVD, is found in the mammalian MAP kinase kinases (MAPKKs) belonging to the three major subfamilies, namely MEK1, MKK4/7, and MKK3/6. The DVD sites bind to their specific upstream MAP kinase kinase kinases (MAPKKKs), including MTK1 (MEKK4), ASK1, TAK1, TAO2, MEKK1, and Raf-1. DVD site is a stretch of about 20 amino acids immediately on the C-terminal side of the MAPKK catalytic domain. Mutations in the DVD site strongly inhibited MAPKKs from binding to, and being activated by, their specific MAPKKKs, both in vitro and in vivo. DVD site mutants could not be activated by various external stimuli in vivo. Synthetic DVD oligopeptides inhibited specific MAPKK activation, both in vitro and in vivo, demonstrating the critical importance of the DVD docking in MAPK signaling.

Amino Acid Sequence↗
PubMed2004

Regulation of the osmoregulatory HOG MAPK cascade in yeast.

The budding yeast Saccharomyces cerevisiae has at least five signal pathways containing a MAP kinase (MAPK) cascade. The high osmolarity glycerol (HOG) MAPK pathway is essential for yeast survival in high osmolarity environment. This mini-review surveys recent developments in regulation of the HOG pathway with specific emphasis on the roles of protein phosphatases and protein subcellular localization. The Hog1 MAPK in the HOG pathway is negatively regulated jointly by the protein tyrosine phosphatases Ptp2/Ptp3 and the type 2 protein phosphatases Ptc1/Ptc2/Ptc3. Specificities of these phosphatases are determined by docking interactions as well as their cellular localizations. The subcellular localizations of the osmosensors (Sln1 and Sho1), kinases (Pbs2, Hog1), and phosphatases in the HOG pathway are intricately regulated to achieve their specific functions.

Cell Nucleus↗
PubMed2003

Yeast recombination pathways triggered by topoisomerase II-mediated DNA breaks.

Topoisomerase II is a ubiquitous enzyme that removes knots and tangles from the genetic material by generating transient double-strand DNA breaks. While the enzyme cannot perform its essential cellular functions without cleaving DNA, this scission activity is inherently dangerous to chromosomal integrity. In fact, etoposide and other clinically important anticancer drugs kill cells by increasing levels of topoisomerase II-mediated DNA breaks. Cells rely heavily on recombination to repair double-strand DNA breaks, but the specific pathways used to repair topoisomerase II-generated DNA damage have not been defined. Therefore, Saccharomyces cerevisiae was used as a model system to delineate the recombination pathways that repair DNA breaks generated by topoisomerase II. Yeast cells that expressed wild-type or a drug-hypersensitive mutant topoisomerase II or overexpressed the wild-type enzyme were examined. Based on cytotoxicity and recombination induced by etoposide in different repair-deficient genetic backgrounds, double-strand DNA breaks generated by topoisomerase II appear to be repaired primarily by the single-strand invasion pathway of homologous recombination. Non-homologous end joining also was triggered by etoposide treatment, but this pathway was considerably less active than single-strand invasion and did not contribute significantly to cell survival in S.cerevisiae.

Cell Cycle↗
PubMed2003

A docking site determining specificity of Pbs2 MAPKK for Ssk2/Ssk22 MAPKKKs in the yeast HOG pathway.

Mitogen-activated protein kinase (MAPK) cascades are conserved signaling modules composed of three sequentially activated kinases (MAPKKK, MAPKK and MAPK). Because individual cells contain multiple MAPK cascades, mechanisms are required to ensure the fidelity of signal transmission. In yeast, external high osmolarity activates the HOG (high osmolarity glycerol) MAPK pathway, which consists of two upstream branches (SHO1 and SLN1) and common downstream elements including the Pbs2 MAPKK and the Hog1 MAPK. The Ssk2/Ssk22 MAPKKKs in the SLN1 branch, when activated, exclusively phosphorylate the Pbs2 MAPKK. We found that this was due to an Ssk2/Ssk22-specific docking site in the Pbs2 N-terminal region. The Pbs2 docking site constitutively bound the Ssk2/Ssk22 kinase domain. Docking site mutations drastically reduced the Pbs2-Ssk2/Ssk22 interaction and hampered Hog1 activation by the SLN1 branch. Fusion of the Pbs2 docking site to a different MAPKK, Ste7, allowed phosphorylation of Ste7 by Ssk2/Ssk22. Thus, the docking site contributes to both the efficiency and specificity of signaling. During these analyses, we also found a nuclear export signal and a possible nuclear localization signal in Pbs2.

Amino Acid Sequence↗
PubMed2002

Smad-dependent GADD45beta expression mediates delayed activation of p38 MAP kinase by TGF-beta.

Transforming growth factor-beta (TGF-beta), when bound to its specific receptor, activates the transcription factor Smad by phosphorylation. TGF-beta also activates the p38 MAPK pathway, but there seem to be disparate mechanisms for the early p38 activation and delayed p38 activation. In this report, we demonstrate that Smad-dependent expression of GADD45beta is responsible for the delayed activation of p38 by TGF-beta. The GADD45beta protein binds and activates MTK1 (= MEKK4), which is a member of the MAPKKK family kinases and an upstream activator of the p38 MAPK cascade. Both TGF-beta-induced GADD45beta expression and the delayed p38 activation require functional Smad proteins. Antisense inhibition of GADD45beta expression suppresses the TGF-beta-induced delayed p38 activation, whereas overexpression of GADD45beta activates the p38 MAPK via MTK1. Expression of the angiogenesis inhibitor thrombospondin-1 (TSP-1) is induced by TGF-beta via Smad-dependent p38 activation. Thus TGF-beta-induced p38 activation, mediated by GADD45beta expression, may play an important role in the biological effects of TGF-beta.

Animals↗
PubMed2002

Effect of the DNA topoisomerase II inhibitor VP-16 on illegitimate recombination in yeast chromosomes.

Etoposide and teniposide, derivatives of podophyllotoxin, are inhibitors of DNA topoisomerase II and are potent anticancer agents. An adverse effect linked to the use of these drugs is the development of acute myeloid leukemia, a disorder usually associated with chromosomal translocation. To examine podophyllotoxin-induced DNA rearrangement, we developed an assay system to measure illegitimate recombination in Saccharomyces cerevisiae chromosomes. This approach uses juxtaposed CAN1-CYH2 negative selection markers that are introduced into the LEU2 locus, which is located on chromosome III, in a yeast strain carrying the mutated can1 and cyh2 genes. Upon formation of a deletion over the active CAN1-CYH2 genes, a cell becomes resistant to both canavanine and cycloheximide. To introduce drugs into the cell, we used a yeast strain carrying an ISE2 mutation, thereby making the cell drug-permeable. Here we show that treatment of cells with etoposide (VP-16) increases the rate of illegitimate recombination in yeast, indicating that VP-16 stimulates DNA topoisomerase-mediated illegitimate recombination. Structural analysis of the resulting recombinants indicate that most are formed by deletion mutations on chromosome III, which take place between short homologous regions of DNA. We propose a model for illegitimate recombination, in which VP-16 facilitates formation of a cleavable complex between DNA topoisomerase II and DNA, thus promoting DNA double-strand breakage with the resulting DNA ends joined by a non-homologous mechanism.

3-Isopropylmalate Dehydrogenase↗