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Articles by J Guo
Total Records ( 4 ) for J Guo
  W Yuan , J Guo , X Li , Z Zou , G Chen , J Sun , T Wang and D. Lu
 

It has been reported that phospholipase C-1 (PLC-1) plays an important protective role in hydrogen peroxide (H2O2)-induced pheochromocytoma (PC) 12 cells death. However, most studies have used high doses of H2O2 and the downstream targets of PLC-1 activation remain to be identified. The present study was designed to examine the roles of PLC-1 signaling pathway in the apoptosis of PC12 cells induced by low dose of H2O2, as well as the downstream factors involved in this pathway. Low-dose treatment of H2O2 resulted in PLC-1 tyrosine phosphorylation in a time-dependent manner and H2O2 killed the PC12 cells by inducing necrosis. In contrast, pretreatment of PC12 cells with U73122, a specific inhibitor of PLC, markedly increased the percentage of dead cells. The mode of cell death was converted to apoptosis as determined by Hoechst/PI nuclear staining and fluorescence microscopy. Western blot analysis demonstrated that the expression of Bcl-2 protein and the activation of pro-caspase-3 were not significantly affected by low dose of H2O2 alone. However, after pretreatment with U73122, Bcl-2 protein expression was dramatically decreased and the activation of pro-caspase-3 was significantly increased. We concluded that PLC-1 plays an important protective role in H2O2-induced PC12 cells death. Bcl-2 and caspase-3 probably participate in the signaling pathway as downstream factors.

  M Cuendet , J Guo , Y Luo , S Chen , C. P Oteham , R. C Moon , R. B van Breemen , L. E Marler and J. M. Pezzuto
 

Isoliquiritigenin (2',4',4-trihydroxychalcone; ILG), a chalcone found in licorice root and many other plants, has shown potential chemopreventive activity through induction of phase II enzymes such as quinone reductase-1 in murine hepatoma cells. In this study, the in vivo metabolism of ILG was investigated in rats. In addition, ILG glucuronides and ILG-glutathione adducts were observed in human hepatocytes and in livers from rats treated with ILG. ILG glucuronides were detected in both plasma and rat liver tissues. In addition, in a full-term cancer chemoprevention study conducted with 7,12-dimethylbenz(a)anthracene–treated female Sprague-Dawley rats, dietary administration of ILG slightly increased tumor latency but had a negative effect on the incidence of mammary tumors starting at ~65 days after 7,12-dimethylbenz(a)anthracene administration. Further, no significant induction of phase II enzymes was found in mammary glands, which is consistent with the low level of ILG observed in these tissues. However, ILG significantly induced quinone reductase-1 activity in the colon, and glutathione as well as glutathione S-transferase in the liver. Analysis of mRNA expression in tissues of rats treated with ILG supported these findings. These results suggest that ILG should be tested for chemopreventive efficacy in nonmammary models of cancer. Cancer Prev Res; 3(2); 221–32

  H Massaeli , J Guo , J Xu and S. Zhang
 

Rationale: The human ether-a-go-go–related gene (HERG) encodes the pore-forming subunits of the rapidly activating delayed rectifier potassium channel (IKr) that is important for cardiac repolarization. Dysfunction of HERG causes long QT syndrome (LQTS) which can lead to sudden cardiac death. We previously showed that a reduction in extracellular K+ concentration ([K+]o) prolongs QT intervals in intact rabbits, and decreases the cell surface density of IKr in rabbit ventricular myocytes and of the HERG channel expressed in human embryonic kidney (HEK) cells.

Objective: The goal of the present study was to gain insights into the mechanisms for low [K+]o induced reduction in HERG expression levels.

Methods and Results: Using patch clamp, Western blot and confocal imaging methods, we demonstrated that at low [K+]o, the HERG channel entered a novel nonconducting state. Furthermore, this novel functional state triggered rapid internalization and degradation of the cell surface HERG channels. Thus, our data demonstrated for the first time a direct link between a gating state and the plasma membrane stability of an ion channel, HERG. Using HERG-permeant cations and site-directed mutagenesis, we identified the sites in the channel which are involved in the K+o dependence of HERG channels.

Conclusions: Extracellular K+ is a prerequisite for HERG function and membrane stability.

  J Guo , L Cong , V. O Rybin , Z Gertsberg and S. F. Steinberg
 

Protein kinase C- (PKC) exerts important cardiac actions as a lipid-regulated kinase. There is limited evidence that PKC also might exert an additional kinase-independent action as a regulator of the subcellular compartmentalization of binding partners such as Shc (Src homologous and collagen), a family of adapter proteins that play key roles in growth regulation and oxidative stress responses. This study shows that native PKC forms complexes with endogenous Shc proteins in H2O2-treated cardiomyocytes; H2O2 treatment also leads to the accumulation of PKC and Shc in a detergent-insoluble cytoskeletal fraction and in mitochondria. H2O2-dependent recruitment of Shc isoforms to cytoskeletal and mitochondrial fractions is amplified by wild-type-PKC overexpression, consistent with the notion that PKC acts as a signal-regulated scaffold to anchor Shc in specific subcellular compartments. However, overexpression studies with kinase-dead (KD)-PKC-K376R (an ATP-binding mutant of PKC that lacks catalytic activity) are less informative, since KD-PKC-K376R aberrantly localizes as a constitutively tyrosine-phosphorylated enzyme to detergent-insoluble and mitochondrial fractions of resting cardiomyocytes; relatively little KD-PKC-K376R remains in the cytosolic fraction. The aberrant localization and tyrosine phosphorylation patterns for KD-PKC-K376R do not phenocopy the properties of native PKC, even in cells chronically treated with GF109203X to inhibit PKC activity. Hence, while KD-PKC-K376R overexpression increases Shc localization to the detergent-insoluble and mitochondrial fractions, the significance of these results is uncertain. Our studies suggest that experiments using KD-PKC-K376R overexpression as a strategy to competitively inhibit the kinase-dependent actions of native PKC or to expose the kinase-independent scaffolding functions of PKC should be interpreted with caution.

 
 
 
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