Zhonghua Zhang
Research interests
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Interestsintracellular cholesterol processing, SR-BI-mediated selective uptake, glucose metabolism, Lipid
Publications
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3.23Impact points
Differential roles of cysteine residues in the cellular trafficking, dimerization, and function of the high-density lipoprotein receptor, SR-BI.
Biochemistry. 11/2011; 50(50):10860-75.
The scavenger receptor, class B, type I (SR-BI) binds high-density lipoprotein (HDL) and mediates selective delivery of cholesteryl esters (CEs) to the liver and steroidogenic cells of the adrenal glands and gonads. Although it is clear that the large extracellular domain (ECD) of SR-BI binds HDL, t... [more] The scavenger receptor, class B, type I (SR-BI) binds high-density lipoprotein (HDL) and mediates selective delivery of cholesteryl esters (CEs) to the liver and steroidogenic cells of the adrenal glands and gonads. Although it is clear that the large extracellular domain (ECD) of SR-BI binds HDL, the role of ECD in the selective HDL-CE transport remains poorly understood. In this study, we used a combination of mutational and chemical approaches to systematically evaluate the contribution of cysteine residues, especially six cysteine residues of ECD, in SR-BI-mediated selective HDL-CE uptake, intracellular trafficking, and SR-BI dimerization. Pretreatment of SR-BI-overexpressing COS-7 cells with a disulfide (S-S) bond reducing agent, β-mercaptoethanol (100 mM) or dithiothreitol (DTT) (10 mM), modestly but significantly impaired SR-BI-mediated selective HDL-CE uptake. Treatment of SR-BI-overexpressing COS-7 cells with the optimal doses of membrane permeant alkyl methanethiosulfonate (MTS) reagents, positively charged MTSEA or neutral MMTS, that specifically react with the free sulfhydryl group of cysteine reduced the rate of SR-BI-mediated selective HDL-CE uptake, indicating that certain intracellular free cysteine residues may also be critically involved in the selective cholesterol transport process. In contrast, use of membrane impermeant MTS reagent, positively charged MTSET and negatively charged MTSES, showed no such effect. Next, the importance of eight cysteine residues in SR-BI expression, cell surface expression, dimer formation, and selective HDL-derived CE transport was evaluated. These cysteine residues were replaced either singly or in pairs with serine, and the mutant SR-BIs were expressed in either COS-7 or CHO cells. Four mutations, C280S, C321S, C323S, and C334S, of the ECD, either singly or in various pair combinations, resulted in significant decreases in SR-BI (HDL) binding activity, selective CE uptake, and trafficking to the cell surface. Surprisingly, we found that mutation of the two remaining cysteine residues, C251 and C384 of the ECD, had no effect on either SR-BI expression or function. Other cysteine mutations and substitutions were also without effect. Western blot data indicated that single and double mutations at C280, C321, C323, and C334 residues strongly favor dimer formation. However, they are rendered nonfunctional presumably because of mutation-induced formation of aberrant disulfide linkages resulting in inhibition of optimal HDL binding and, thus, selective HDL-CE uptake. These results provide novel insights into the functional role of four cysteine residues, C280, C321, C323, and C334, of the SR-BI ECD in SR-BI expression and trafficking to the cell surface, its dimerization, and associated selective CE transport function.
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7.75Impact points
p53 directly represses Id2 to inhibit the proliferation of neural progenitor cells.
Stem cells (Dayton, Ohio). 05/2011; 29(7):1090-101.
Neural progenitor cells (NPCs) have the capacity to proliferate and give rise to all major central nervous system cell types and represent a possible cell of origin in gliomagenesis. Deletion of the tumor suppressor gene Tp53 (p53) results in increased proliferation and self-renewal of NPCs and is a... [more] Neural progenitor cells (NPCs) have the capacity to proliferate and give rise to all major central nervous system cell types and represent a possible cell of origin in gliomagenesis. Deletion of the tumor suppressor gene Tp53 (p53) results in increased proliferation and self-renewal of NPCs and is a common genetic mutation found in glioma. We have identified inhibitor of DNA binding 2 (Id2) as a novel target gene directly repressed by p53 to maintain normal NPC proliferation. p53((-/-)) NPCs express elevated levels of Id2 and suppression of Id2 expression is sufficient to inhibit the increased proliferation and self-renewal which results from p53 loss. Elevated expression of Id2 in wild-type NPCs phenocopies the behavior of p53((-/-)) NPCs by enhancing NPC proliferation and self-renewal. Interestingly, p53 directly binds to a conserved site within the Id2 promoter to mediate these effects. Finally, we have identified elevated Id2 expression in glioma cell lines with mutated p53 and demonstrated that constitutive expression of Id2 plays a key role in the proliferation of glioma stem-like cells. These findings indicate that Id2 functions as a proproliferative gene that antagonizes p53-mediated cell cycle regulation in NPCs and may contribute to the malignant proliferation of glioma-derived tumor stem cells.
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4.59Impact points
Adipocytes decrease Runx2 expression in osteoblastic cells: roles of PPARγ and adiponectin.
Journal of cellular physiology. 11/2010; 225(3):837-45.
The mechanisms through which bone marrow adipocytes might influence differentiation and function of osteoblasts are not completely understood. To investigate the direct effects of bone marrow fat cells on osteoblast function, an ex vivo co-culture system was utilized comprising either primary fat ce... [more] The mechanisms through which bone marrow adipocytes might influence differentiation and function of osteoblasts are not completely understood. To investigate the direct effects of bone marrow fat cells on osteoblast function, an ex vivo co-culture system was utilized comprising either primary fat cells or differentiated 3T3-L1 adipocytes and osteoblastic cells on transwells. In co-culture, both adipocytes and osteoblastic cells were differentiated into adipocytes or osteoblasts, respectively, before culturing on transwells. Co-culture with either primary fat cells or fully differentiated 3T3-L1 adipocytes significantly decreased mRNA and protein expression of runt-related transcription factor 2 (Runx2) in osteoblastic cells. An increase in mRNA and protein expression of peroxisome proliferator-activated receptor γ (PPARγ) occurred concomitantly with the reduction of Runx2 expression. Adiponectin concentration was increased in the media by co-culture. In addition, co-culture with conditioned media from fat cells increased PPARγ promoter activity and decreased Runx2 promoter activity. Knockdown of PPARγ or adiponectin receptor 1 in osteoblastic cells by siRNA prevented the down-regulation of mRNA expression of Runx2 in osteoblastic cells cultured with fully differentiated 3T3-L1 cells. Furthermore, co-transfection with PPARγ decreased Runx2 promoter activity. A marker of osteogenesis, alkaline phosphatase activity in osteoblastic cells was significantly decreased by co-culture. Annexin V/propidium iodide staining showed that co-culture did not induce apoptosis in osteoblastic cells. Thus, we conclude that adipocytes modulate key metabolic functions of osteoblasts through the release of secretory products. PPARγ plays a key role in mediating the effects of adipocytes on osteoblasts.
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2.62Impact points
Cellular cholesterol delivery, intracellular processing and utilization for biosynthesis of steroid hormones.
Nutrition & metabolism. 01/2010; 7:47.
Steroid hormones regulate diverse physiological functions such as reproduction, blood salt balance, maintenance of secondary sexual characteristics, response to stress, neuronal function and various metabolic processes. They are synthesized from cholesterol mainly in the adrenal gland and gonads in ... [more] Steroid hormones regulate diverse physiological functions such as reproduction, blood salt balance, maintenance of secondary sexual characteristics, response to stress, neuronal function and various metabolic processes. They are synthesized from cholesterol mainly in the adrenal gland and gonads in response to tissue-specific tropic hormones. These steroidogenic tissues are unique in that they require cholesterol not only for membrane biogenesis, maintenance of membrane fluidity and cell signaling, but also as the starting material for the biosynthesis of steroid hormones. It is not surprising, then, that cells of steroidogenic tissues have evolved with multiple pathways to assure the constant supply of cholesterol needed to maintain optimum steroid synthesis. The cholesterol utilized for steroidogenesis is derived from a combination of sources: 1) de novo synthesis in the endoplasmic reticulum (ER); 2) the mobilization of cholesteryl esters (CEs) stored in lipid droplets through cholesteryl ester hydrolase; 3) plasma lipoprotein-derived CEs obtained by either LDL receptor-mediated endocytic and/or SR-BI-mediated selective uptake; and 4) in some cultured cell systems from plasma membrane-associated free cholesterol. Here, we focus on recent insights into the molecules and cellular processes that mediate the uptake of plasma lipoprotein-derived cholesterol, events connected with the intracellular cholesterol processing and the role of crucial proteins that mediate cholesterol transport to mitochondria for its utilization for steroid hormone production. In particular, we discuss the structure and function of SR-BI, the importance of the selective cholesterol transport pathway in providing cholesterol substrate for steroid biosynthesis and the role of two key proteins, StAR and PBR/TSO in facilitating cholesterol delivery to inner mitochondrial membrane sites, where P450scc (CYP11A) is localized and where the conversion of cholesterol to pregnenolone (the common steroid precursor) takes place.
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2.71Impact points
Silencing of heparanase by siRNA inhibits tumor metastasis and angiogenesis of human breast cancer in vitro and in vivo.
Cancer biology & therapy. 05/2007; 6(4):587-95.
Expression of the heparanase gene is associated with invasive, angiogenic and metastatic potential of diverse malignant tumors and cell lines. Here we used RNA interference strategies to evaluate the role of human heparanase in breast malignancy and to explore the therapeutic potential of its specif... [more] Expression of the heparanase gene is associated with invasive, angiogenic and metastatic potential of diverse malignant tumors and cell lines. Here we used RNA interference strategies to evaluate the role of human heparanase in breast malignancy and to explore the therapeutic potential of its specific targeting. The siRNA targeting human heparanase almost completely inhibited the expression of heparanase in human breast carcinoma MDA-MB-435 cells, whereas the mismatched siRNA showed no effect. Cells transfected with heparanase siRNA expressed significantly less heparanase and profoundly reduced invasion and adhesion in vitro. In MDA-MB-435 cell xenograft model, tumors treated with siRNA were less vascularized and less metastatic than those treated with saline and the mismatched controls. The association of reduced levels of heparanase and altered tumorigenic properties in cells with anti-heparanase siRNA indicates that heparanase is important in cancer progress and has potential use as a target for anticancer drug development.
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7.54Impact points
Oligomannurarate sulfate, a novel heparanase inhibitor simultaneously targeting basic fibroblast growth factor, combats tumor angiogenesis and metastasis.
Cancer research. 10/2006; 66(17):8779-87.
Inhibitors of tumor angiogenesis and metastasis are increasingly emerging as promising agents for cancer therapy. Recently, heparanase inhibitors have offered a new avenue for such work because heparanase is thought to be critically involved in the metastatic and angiogenic potentials of tumor cells... [more] Inhibitors of tumor angiogenesis and metastasis are increasingly emerging as promising agents for cancer therapy. Recently, heparanase inhibitors have offered a new avenue for such work because heparanase is thought to be critically involved in the metastatic and angiogenic potentials of tumor cells. Here, we report that oligomannurarate sulfate (JG3), a novel marine-derived oligosaccharide, acts as a heparanase inhibitor. Our results revealed that JG3 significantly inhibited tumor angiogenesis and metastasis, both in vitro and in vivo, by combating heparanase activity via binding to the KKDC and QPLK domains of the heparanase molecule. The JG3-heparanase interaction was competitively inhibited by low molecular weight heparin (4,000 Da) but not by other glycosaminoglycans. In addition, JG3 abolished heparanase-driven invasion, inhibited the release of heparan sulfate-sequestered basic fibroblast growth factor (bFGF) from the extracellular matrix, and repressed subsequent angiogenesis. Moreover, JG3 inactivated bFGF-induced bFGF receptor and extracellular signal-regulated kinase 1/2 phosphorylation and blocked bFGF-triggered angiogenic events by directly binding to bFGF. Thus, JG3 seems to inhibit both major heparanase activities by simultaneously acting as a substrate mimetic and as a competitive inhibitor of heparan sulfate. These findings suggest that JG3 should be considered as a promising candidate agent for cancer therapy.
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Orientation relationship between TiC carbides and B2 phase in as-cast and heat-treated NiTi shape memory alloys
Materials Science and Engineering: A.
In the present study, Ni50.7 at.%–Ti shape memory alloys were prepared by vacuum induction melting using graphite crucibles. During melting the carbon concentration of the alloy increased and TiC carbides formed during solidification. The microstructure of the as-cast NiTi alloys was examined using ... [more] In the present study, Ni50.7 at.%–Ti shape memory alloys were prepared by vacuum induction melting using graphite crucibles. During melting the carbon concentration of the alloy increased and TiC carbides formed during solidification. The microstructure of the as-cast NiTi alloys was examined using scanning and transmission electron microscopy (SEM, TEM). Only eutectic TiC fibers were found in a low carbon NiTi alloy. For higher carbon concentrations, primary TiC carbides were observed in addition to the fine eutectic TiC phase. TEM results suggest that there is no specific orientation relationship between primary TiC carbides and B2. For the eutectic TiC phase, however, the following orientation relationship could be identified for low and high carbon contents in the NiTi alloy: B2 [0 0 1]||TiC [0 0 1], B2 (2 0 0)||TiC (2 2 0), B2 ||TiC (2 0 0), and B2 (1 1 0)||TiC (0 2 0). It was also found that the interface between TiC and B2 is semi-coherent. During a subsequent post-cast heat treatment new carbides formed with different morphology (sizes and shapes) but with the same orientation relationship. Experimental evidence including SEM and TEM micrographs and diffraction patterns is presented to document these findings.
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On the reaction between NiTi melts and crucible graphite during vacuum induction melting of NiTi shape memory alloys
Acta Materialia.
The functional and structural properties of NiTi shape memory alloys (SMAs) which are often produced by vacuum induction melting (VIM) using electro graphite crucibles are strongly dependent on the alloy composition. It is known that NiTi melts react with electro graphite crucibles and the associate... [more] The functional and structural properties of NiTi shape memory alloys (SMAs) which are often produced by vacuum induction melting (VIM) using electro graphite crucibles are strongly dependent on the alloy composition. It is known that NiTi melts react with electro graphite crucibles and the associated carbon pick up will affect the alloy properties. So far no effort has been made to study the thermodynamics and kinetics of this reaction. In the present work the reaction between NiTi melts and electro graphite crucibles during VIM processing was investigated. The reaction results in the growth of a TiC layer and a simultaneous increase of carbon concentration in the melt. A physical view of the underlying transport processes and reactions is given and a phenomenological rate equation for the increase of carbon concentration during melting is provided.
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Melnikov method to a bacteria-immunity model with bacterial quorum sensing mechanism
Chaos, Solitons & Fractals.
A bacteria-immunity model with bacterial quorum sensing is formulated, which describes the competition between bacteria and immune cells. After periodic perturbation and a series of coordinate transformations, the model is brought into a standard form, and which is amenable to Melnikov method. By th... [more] A bacteria-immunity model with bacterial quorum sensing is formulated, which describes the competition between bacteria and immune cells. After periodic perturbation and a series of coordinate transformations, the model is brought into a standard form, and which is amenable to Melnikov method. By the method, the existences of chaotic motion and homoclinic bifurcations are proved.
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A SIRS epidemic model with infection-age dependence
Journal of Mathematical Analysis and Applications.
Based on J. Mena-Lorca and H.W. Hethcote's epidemic model, a SIRS epidemic model with infection-age-dependent infectivity and general nonlinear contact rate is formulated. Under general conditions, the unique existence of its global positive solutions is obtained. Moreover, under more general as... [more] Based on J. Mena-Lorca and H.W. Hethcote's epidemic model, a SIRS epidemic model with infection-age-dependent infectivity and general nonlinear contact rate is formulated. Under general conditions, the unique existence of its global positive solutions is obtained. Moreover, under more general assumptions than the existing, the existence and asymptotical stability of its equilibria are discussed. In the end, the condition on the stability of endemic equilibrium is verified by a special model.
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Analysis of a bacteria–immunity model with delay quorum sensing
Journal of Mathematical Analysis and Applications.
A bacteria–immunity model with bacterial quorum sensing is formulated, which describes the competition between bacteria and immune cells. A distributed delay is introduced to characterize the time in which bacteria receive signal molecules and then combat with immune cells. In this paper, we focus o... [more] A bacteria–immunity model with bacterial quorum sensing is formulated, which describes the competition between bacteria and immune cells. A distributed delay is introduced to characterize the time in which bacteria receive signal molecules and then combat with immune cells. In this paper, we focus on a subsystem of the bacteria–immunity model, analyze the stability of the equilibrium points, discuss the existence and stability of periodic solutions bifurcated from the positive equilibrium point, and finally investigate the stability of the nonhyperbolic equilibrium point by the center manifold theorem.
Following (7)
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Mark Israel
Dartmouth Medical School -
Pranam Chatterjee
Dartmouth College -
Huajun Zhao
Medical College of Wisconsin -
Mathieu Lupien
Ontario Cancer Institute, Princess Margaret Hospital, UHN -
Wen-Jun Shen
Stanford University School of Medicine
