Mechanisms of chromium(VI)-induced carcinogenesis: The involvement of reactive oxygen species and signal transduction pathway.

Although Cr(VI)-containing compounds have been widely recognized as carcinogens for over 100 years, the mechanisms of their actions are not fully understood. The overall objective of this study is to investigate the role of reactive oxygen species (ROS) in Cr(VI)-induced carcinogenesis, focusing on tumor suppressor protein p53 and regulatory signal transduction pathways. In the present study, the role of ROS in p53 activation was investigated and the following conclusions were obtained: (a) Cr(VI) is able to activate p53 protein; (b) ROS, especially ·OH radical, are responsible for the p53 activation induced by Cr(VI). In addition, we presented a mechanism of cellular ROS generation induced by Cr(VI). After entering the cell, Cr(VI) can be reduced to Cr(V). During the reduction process, molecular oxygen is reduced to O2 ·− radical, which generates H2O2 via dismutation. Cr(V) reacts with H2O2 to generate ·OH radicals via a Fenton-like reaction. For the molecular mechanism of p53 activation induced by Cr(VI), post-translational modifications, including Ser 15 phosphorylation, Lys 382 acetylation, and mdm2 dissociation were found to play a crucial role. Erk, but not p38 kinase, is responsible for the phosphorylation of Ser 15 induced by Cr(VI). The present study also investigated the interaction of NF-κB and p53 protein in Cr(VI)-induced apoptosis. NF-κB activation is capable of diminishing Cr(VI)-induced p53 activation, and protecting cells from apoptosis. These studies on Ras overexpressed cells presented a new scheme for ROS generation from Cr(VI)-induced cells different from the one described above. O2·− radical, which is produced by overexpressed Ras protein, reacts with Cr(VI) to generate Cr(V). The Cr(V) further reacts with H2O2, which is produced by O 2·− radical dismutation, to produce ·OH radical. These results implicate Cr(VI) and O2·− radical into the signal transduction pathways mediated by Ras protein. Since Ras signaling pathway is important in regulating cell proliferation, the involvements of Cr(VI) in Ras signal transduction pathway may be one of the mechanisms for Cr(VI)-induced carcinogenesis. This study provides a molecular basis for the understanding of the mechanisms of Cr(VI)-induced cellular responses, and contributes to a better understanding for the carcinogenic process induced by this metal. These new findings also have the impact on other carcinogens and chemical particles that have a ROS generation machinery similar to Cr(VI)

Essays on incentive contracts, M&As, and firm risk

The three essays collected in this PhD dissertation concern agency costs, incentive contracts, mergers and acquisitions, and firm risk. The first essay demonstrates that manager sentiment, a managerial trait proxy for managerial optimism, can incur agency costs. The second and third essays state incentive contracts as an effective way to suppress agency problems and reduce agency costs. Specifically, the second essay demonstrates that firms using relative performance evaluation exhibit lower stock price crash risk and the third essay finds that relative performance evaluation increases long-term acquisition performance

A Comparative Study On the U.S. and Chinese Transportation Policies and Practices for the Transportation-Disadvantaged Populations

Even though China has entered the aging society almost 20 years ago and passed elderly and disability-related laws, its transportation-related facilities and services for the elderly and disabled remain insufficient, which has seriously impacted its Transportation-Disadvantaged Populations’ travel and quality of life. Thus, it is necessary to examine other advanced countries’ best planning practices in specialized transportation services to assess their applicability to China. This paper first reviews the U.S. and Chinese laws, regulations, implementation measures and studies related to the elderly and disabled transportation. Afterwards, it conducts an analysis on the differences between the U.S. and China and assesses the transferability and applicability of the American transportation policies and practices for the transportation-disadvantaged populations to China. Through this comparative analysis, it is concluded that China may learn from the U.S. in establishing a sound legal framework, enhancing institutional coordination, providing financial subsidy, and conducting comprehensive elderly and disabled transportation planning, design, construction and operation. In the meantime, China’s institutional well-organization, implementation efficiency and social mobilization capability can also offer many useful lessons to the U.S

Comparing Mediated Effects of Motivational Beliefs in Learning Science of Adolescents in America and Singapore: A Structural Equation Modeling Approach

M.Ed. University of Hawaii at Manoa 2016.Includes bibliographical references.American adolescents have been criticized to lack competency in science, technology, engineering, and mathematics compared to Asian countries, causing grave concerns in the country. To gain insights from psychological perspective in education, the present study examined the mediated effects of American adolescents’ motivational beliefs on science career aspiration as compared to their peers in Singapore. A structural equation modeling analysis was conducted for both countries using TIMSS data in 2011 to investigate the relationships among several key psychological constructs in learning science such as science self-efficacy, science self-concept, instrumental motivation and career aspirations. Findings revealed that (1) American adolescents’ science self-efficacy significantly predicted their career aspirations in science while Singaporean eighth graders’ science self-concept was a significant predictor for career aspirations; (2) adolescents’ instrumental motivation was more influenced by science self- efficacy rather than by science self-concept in two nations; (3) instrumental motivation positively mediated the relationships between science self-efficacy and career aspirations. Specifically, with introduction of instrumental motivation, American students’ science self-efficacy had both direct and indirect effects on career aspirations whereas Singaporean students’ science self-efficacy had only indirect effects on the outcome. Implications based on findings were discussed

Geology, geochronology and isotopic geochemistry of the Xiaoliugou W-Mo ore field in the Qilian Orogen, NW China : case study of a skarn system formed during continental collision

This study is financially supported by the National Natural Science Foundation of China (41502068).The Xiaoliugou W-Mo ore field lies within the mid-Paleozoic North Qilian Orogen, NW China, and hosts a W resource of 48.8 Mt @ 0.4% and 412.6 Mt of Mo @ 0.075%. It contains five deposits, including Xiaoliugou, Qiqing, Guishan, Qibao and Shiji. The main mineralization styles at Xiaoliugou are skarn and veins in which the mineral sequence is scheelite > molybdenite > chalcopyrite and occurs in the endo- and exo-contact zones of granite intrusions. The scheelite-dominated orebodies are overprinted by molybdenite-dominated quartz veins. Two molybdenite samples yielded Silurian Re-Os model ages of 427.4 ± 6.0 Ma and 428.2 ± 6.0 Ma. Three muscovite samples coexisting with molybdenite yielded Middle Devonian Ar-Ar ages of 392.0 ± 2.7 Ma, 391.1 ± 2.7 Ma and 391.4 ± 2.8 Ma. The Re-Os and Ar-Ar ages indicate that the W-Mo mineralization and alteration occurred at ca. 428–391 Ma, which corresponds with regional continental collision within the Qilian Orogen. δ34S for the sulfides molybdenite and pyrite are 7.70–11.67 ‰ and 4.98–13.17 ‰, respectively. The 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb of the sulfides are 17.98–21.73, 15.34–18.81, and 37.18–38.63, respectively. The granites yield similar corrected (206Pb/204Pb)i, (207Pb/204Pb)i and (208Pb/204Pb)i, ranging 16.14–19.35, 15.44–15.63, and 37.41–38.31, respectively. Calculated δ18O of the fluid inclusions in quartz range from -3.38–2.34 ‰, whereas the δD of the hydrothermal fluids ranges from -94 to -47 ‰. The S-, Pb-, O- and D-isotopic data imply that the metals originated from the granite intrusion with a minor component sourced from the host sediments, and that the ore-forming fluids were dominated by magmatic-hydrothermal fluids mixed with minor meteoric water.PostprintPeer reviewe

Temperature and composition insensitivity of thermoelectric properties of high-entropy half-heusler compounds

Composition modification by doping and solid solution is a well-studied strategy in thermoelectric (TE) materials to optimize their properties. Recently, the concept of entropy stabilization has offered the possibility of forming random solid solutions that have properties that go beyond the rule of mixture. In this study, we prepared a series of high-entropy half-Heusler solid solutions (HEHHs) with varying valence electron counts (VEC), (Ti0.33Zr0.33Hf0.33)1-x(V0.33Nb0.33Ta0.33)xCoSb (x = 0.5 to 0.75). Compared to their medium- and low-entropy counterparts, the TE properties of HEHHs are less sensitive to temperature and composition variation (charge carrier concentration efficiency of ∼10 %). An ultra-low lattice thermal conductivity for half-Heusler of 1.19 W·m−1·K−1 was achieved.Peer reviewe

The miR169b/NFYA1 module from the halophyte Halostachys caspica endows salt and drought tolerance in Arabidopsis through multi-pathways

Salt and drought are the major abiotic stress factors plaguing plant growth, development and crop yields. Certain abiotic-stress tolerant plants have developed special mechanisms for adapting to adverse environments in the long process of evolution. Elucidating the molecular mechanisms by which they can exert resistance to abiotic stresses is beneficial for breeding new cultivars to guide agricultural production. Halostachys caspica, a perennial halophyte belonging to Halostachys in Amaranthaceae, is extremely tolerant to harsh environments, which is commonly grown in the saline-alkali arid desert area of Northwest, China. However, the molecular mechanism of stress tolerance is unclear. Nuclear Factor Y-A (NFYA) is a transcription factor that regulates the expression of downstream genes in plant response to adverse environments. It has also been reported that some members of the NFYA family are the main targets of miR169 in plants. In this study, we mainly focused on exploring the functions and preliminary mechanism of the miR169b/NFYA1 module from H. caspica to abiotic stress. The main results showed that RLM-RACE technology validated that HcNFYA1 was targeted by HcmiR169b, qRT-PCR revealed that HcmiR169b was repressed and HcNFYA1 was induced in the H. caspica branches under various abiotic stress as well ABA treatment and Arabidopsis stable transformation platform with molecular methods was applied to elucidate that the HcmiR169b/HcNFYA1 module conferred the salt and drought tolerance to plants by enhancing ABA synthesis and ABA signal transduction pathways, maintaining ROS homeostasis and the stability of cell membrane. HcNFYA1 is expected to be a candidate gene to improve plant resistance to salt and drought stresses

Genome-wide analysis and characterization of Dendrocalamus farinosus SUT gene family reveal DfSUT4 involvement in sucrose transportation in plants

Sucrose is the main transported form of photosynthetic products. Sucrose transporter (SUT) participates in the translocation of sucrose from source to sink, which is important for the growth and development of plants. Dendrocalamus farinosus is an important economic crop in southwestern China because of its high growth rate, high fiber content, and dual usage for food and timber, but the mechanism of sucrose transportation in D. farinosus is unclear. In this study, a total of 12 SUT transporter genes were determined in D. farinosus by whole-genome identification. DfSUT2, DfSUT7, and DfSUT11 were homologs of rice OsSUT2, while DfSUT4 was a homolog of OsSUT4, and these four DfSUT genes were expressed in the leaf, internode, node, and bamboo shoots of D. farinosus. In addition, DfSUT family genes were involved in photosynthetic product distribution, ABA/MeJA responses, and drought resistance, especially DfSUT4. The function of DfSUT4 was then verified in Nicotiana tabacum. DfSUT4 was localized mainly in the leaf mesophyll and stem phloem of pDfSUT4::GUS transgenic plant. The overexpression of DfSUT4 gene in transgenic plant showed increases of photosynthetic rate, above-ground biomass, thousand grain weight, and cellulose content. Our findings altogether indicate that DfSUT4 can be a candidate gene that can be involved in phloem sucrose transportation from the source leaves to the sink organs, phytohormone responses, abiotic stress, and fiber formation in plants, which is very important in the genetic improvement of D. farinosus and other crops