Ken Takai

HTLV-1 bZIP Factor Induces T-Cell Lymphoma and Systemic Inflammation In Vivo

Human T-cell leukemia virus type 1 (HTLV-1) is the causal agent of a neoplastic disease of CD4+ T cells, adult T-cell leukemia (ATL), and inflammatory diseases including HTLV-1 associated myelopathy/tropical spastic paraparesis, dermatitis, and inflammatory lung diseases. ATL cells, which constitutively express CD25, resemble CD25+CD4+ regulatory T cells (Treg). Approximately 60% of ATL cases indeed harbor leukemic cells that express FoxP3, a key transcription factor for Treg cells. HTLV-1 encodes an antisense transcript, HTLV-1 bZIP factor (HBZ), which is expressed in all ATL cases. In this study, we show that transgenic expression of HBZ in CD4+ T cells induced T-cell lymphomas and systemic inflammation in mice, resembling diseases observed in HTLV-1 infected individuals. In HBZ-transgenic mice, CD4+Foxp3+ Treg cells and effector/memory CD4+ T cells increased in vivo. As a mechanism of increased Treg cells, HBZ expression directly induced Foxp3 gene transcription in T cells. The increased CD4+Foxp3+ Treg cells in HBZ transgenic mice were functionally impaired while their proliferation was enhanced. HBZ could physically interact with Foxp3 and NFAT, thereby impairing the suppressive function of Treg cells. Thus, the expression of HBZ in CD4+ T cells is a key mechanism of HTLV-1-induced neoplastic and inflammatory diseases.

HTLV-1 bZIP Factor Suppresses Apoptosis by Attenuating the Function of FoxO3a and Altering Its Localization

As the infectious agent causing human adult T-cell leukemia (ATL), the human T-cell leukemia virus type 1 (HTLV-1) virus spreads in vivo primarily by cell-to-cell transmission. However, the factors that determine its transmission efficiency are not fully understood. The viral genome encodes the HTLV-1 bZIP factor (HBZ), which is expressed in all ATL cases and is known to promote T-cell proliferation. In this study, we investigated the hypothesis that HBZ also influences the survival of T cells. Through analyzing the transcriptional profile of HBZ-expressing cells, we learned that HBZ suppressed transcription of the proapoptotic gene Bim (Bcl2l11) and that HBZ-expressing cells were resistant to activation-induced apoptosis. Mechanistic investigations into how HBZ suppresses Bim expression revealed that HBZ perturbs the localization and function of FoxO3a, a critical transcriptional activator of the genes encoding Bim and also Fas ligand (FasL). By interacting with FoxO3a, HBZ not only attenuated DNA binding by FoxO3a but also sequestered the inactive form of FoxO3a in the nucleus. In a similar manner, HBZ also inhibited FasL transcription induced by T-cell activation. Further study of ATL cells identified other Bim perturbations by HBZ, including at the level of epigenetic alteration, histone modification in the promoter region of the Bim gene. Collectively, our results indicated that HBZ impairs transcription of the Bim and FasL genes by disrupting FoxO3a function, broadening understanding of how HBZ acts to promote proliferation of HTLV-1-infected T cells by blocking their apoptosis.

Purification and characterization of phosphoenolpyruvate carboxylase from the hyperthermophilic archaeon Methanothermus sociabilis

Phosphoenolpyruvate carboxylase (PEPC) was purified for the first time from hyperthermophilic archaeon Methanothermus sociabilis, growing autotrophically with an optimum at 88°C. The optimum temperature for enzyme activity was similar to that for growth and was 85°C. The native enzyme was a homotetramer of 240 kDa molecular mass and the subunit displayed an apparent molecular mass of 60 kDa. The archaeal PEPC was insensitive to various metabolites which are known as allosteric effectors for most bacterial and eucaryal counterparts. The enzyme showed extreme thermostability such that there remained 80% of the enzyme activity after incubation for 2 h at 80°C. These results implied that archaeal PEPC was significantly different from bacterial and eucaryal entities.

A potential link between alternative splicing of the NBS1 gene and DNA damage/environmental stress.

Abstract Takai, K., Sakamoto, S., Sakai, T., Yasunaga, J., Komatsu, K. and Matsuoka, M. A Potential Link between Alternative Splicing of the NBS1 Gene and DNA Damage/Environmental Stress. Radiat. Res. 170, 33–40 (2008). NBS1 forms a multimetric complex with MRE11/RAD50, which acts as the sensor of DNA double-strand breaks (DSBs). The mechanisms controlling the expression of NBS1 remain largely unknown. Here we show that NBS1 is transcribed as both a wild-type and an alternatively spliced form exhibiting a premature stop codon in an alternative 50-bp exon in intron 2. Although the wild-type transcript predominates in most tissues, the spliced transcript is abundant in resting peripheral blood mononuclear cells (PBMCs). Levels of the spliced form of NBS1 decreased rapidly after irradiation as levels of the wild-type NBS1 transcript increased, resulting in increased levels of NBS1 protein. Both mitogenic stimulation and methyl methanesulfonate treatment also altered the splicing pattern of NBS1. Resting PBMCs, which predominantly express spliced NBS1, were more susceptible to radiation than mitogen-stimulated cells, which showed predominant expression of the wild-type transcript. Since the alternatively spliced NBS1 gene likely did not produce protein, this alternative splicing seems to be associated with the control of NBS1 protein. Thus alternative splicing of the NBS1 gene may be associated with the regulation of NBS1 in response to DSBs, DNA alkylation damage, and mitogenic response.

Extrinsic thermostabilization factors and thermodenaturation mechanisms for phosphoenolpyruvate carboxylase (PEPC) from an extremely thermophilic bacterium Rhodothermus obamensis

The thermodenaturation of phosphoenolpyruvate carboxylase (PEPC) from an extremely thermophilic bacterium Rhodothermus obamensis, capable of growth at temperature up to 85°C, was probed at different denaturation temperatures by UV-visible absorption, fluorescence emission and 1-anilinonaphthalene-8-sulfonate (ANS) binding and renaturation was assessed from different states of denaturation. Under severe denaturation conditions at 100°C, the enzyme was rapidly inactivated and its global structure immediately reached the irreversibly aggregated state by passing through the dissociated and the putative scrambled states as observed by UV-visible absorption spectroscopy. However, under milder conditions of denaturation at 93°C, the enzyme was gradually inactivated, and its global structure shifted sequentially from the dissociated state to the scrambled state. At 80°C, about 50% of the activity was left and no apparent change in the global structure occured even after 30 h. In addition, ANS binding to the enzyme was greatly increased in accordance with the change in global structure. This implies that the hydrophobic regions of the enzyme tend to be exposed to solvent due to thermal dissociation and unfolding. The extrinsic thermostabilization factors that enhance the thermostability of the enzyme successfully suppress the thermodenaturation of the enzyme, especially the dissociation of its tetrameric form. Of these factors, the substrate for the enzyme, phosphoenolpyruvate (PEP), causes the reassociation of the dissociated inactive form of the enzyme to the active form. These results suggest that the global thermodenaturation of the enzyme results from the temperature-dependent shift of three different states and that the extrinsic thermostabilization factors act to a large extent to maintain quaternary structure.

Additional file 1: of Hydrogen and carbon isotope systematics in hydrogenotrophic methanogenesis under H2-limited and H2-enriched conditions: implications for the origin of methane and its isotopic diagnosis

Compilation of hydrogen and carbon isotope systematics from incubation and observation. Description of data: Type of ecosystem, name of ecosystem, temperature of methanogen growth (Celsius), approximate timescale for growth, fractionation factors of the carbon isotope ratio between CH4 and CO2 ( α C C H 4 – C O 2

A molecular view of archaeal diversity in marine and terrestrial hot water environments

{\upalpha^{\mathrm{C}}}_{{\mathrm{C}\mathrm{H}}_4\hbox{--} {\mathrm{C}\mathrm{O}}_2}

Biochemical relationship of phosphoenolpyruvate carboxylases (PEPCs) from thermophilic archaea

), fractionation factors of the hydrogen isotope ratio between CH4 and H2O ( α H C H 4 – H 2 O