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Articles by X Gu
Total Records ( 7 ) for X Gu
  X Gu and K. S. Masters

Much remains to be discovered about the etiology of heart valve disease and the molecular level mechanisms that drive it. The MAPK/ERK pathway influences calcification in many cell types and has been linked to the expression of a contractile phenotype in valvular interstitial cells (VICs). However, a direct correlation between MAPK/ERK pathway activity and VIC calcification has not been previously described. Thus the role of the MAPK pathway in the calcification of VIC cultures was investigated by measuring ERK activation in both calcifying and noncalcifying VIC environments and then, conversely, analyzing the effects of ERK pathway inhibition on VIC calcification and phenotype. Prolonged elevation of phosphorylated ERK-1/2 was found in calcifying VIC cultures, whereas directly blocking phosphorylation of ERK-1/2 resulted in a dramatic decrease in nodule number, nodule size, and total calcified area. Application of the ERK pathway inhibitor was also associated with a dramatic decrease in apoptosis, which may have contributed to the decreased nodule formation obtained via ERK inhibition. Real-time PCR analysis revealed that calcified samples exhibited significantly elevated expression of several myofibroblastic and osteoblastic markers, while ERK inhibition substantially reduced the expression of these markers, often to levels comparable to the noncalcifying control. These data suggest that the MAPK pathway plays an important role in regulating the phenotype and calcification of VICs, wherein sustained pathway activation is associated with increased VIC calcification. These findings may be used to further elucidate the mechanisms of valvular disease and identify potential treatment targets.

  H Kadara , L Lacroix , C Behrens , L Solis , X Gu , J. J Lee , E Tahara , D Lotan , W. K Hong , I. I Wistuba and R. Lotan

Lung cancer continues to be a major deadly malignancy. The mortality of this disease could be reduced by improving the ability to predict cancer patients' survival. We hypothesized that genes differentially expressed among cells constituting an in vitro human lung carcinogenesis model consisting of normal, immortalized, transformed, and tumorigenic bronchial epithelial cells are relevant to the clinical outcome of non–small cell lung cancer (NSCLC). Multidimensional scaling, microarray, and functional pathways analyses of the transcriptomes of the above cells were done and combined with integrative genomics to incorporate the microarray data with published NSCLC data sets. Up-regulated (n = 301) and down-regulated genes (n = 358) displayed expression level variation across the in vitro model with progressive changes in cancer-related molecular functions. A subset of these genes (n = 584) separated lung adenocarcinoma clinical samples (n = 361) into two clusters with significant survival differences. Six genes, UBE2C, TPX2, MCM2, MCM6, FEN1, and SFN, selected by functional array analysis, were also effective in prognosis. The mRNA and protein levels of one these genes—UBE2C—were significantly up-regulated in NSCLC tissue relative to normal lung and increased progressively in lung lesions. Moreover, stage I NSCLC patients with positive UBE2C expression exhibited significantly poorer overall and progression-free survival than patients with negative expression. Our studies with this in vitro model have lead to the identification of a robust six-gene signature, which may be valuable for predicting the survival of lung adenocarcinoma patients. Moreover, one of those genes, UBE2C, seems to be a powerful biomarker for NSCLC survival prediction.

  Y Kong , G Zhou , U Avci , X Gu , C Jones , Y Yin , Y Xu and M. G. Hahn

Several genes in Arabidopsis, including PARVUS/AtGATL1, have been implicated in xylan synthesis. However, the biosynthesis of xylan in woody plants, where this polysaccharide is a major component of wood, is poorly understood. Here, we characterize two Populus genes, PdGATL1.1 and PdGATL1.2, the closest orthologs to the Arabidopsis PARVUS/GATL1 gene, with respect to their gene expression in poplar, their sub-cellular localization, and their ability to complement the parvus mutation in Arabidopsis. Overexpression of the two poplar genes in the parvus mutant rescued most of the defects caused by the parvus mutation, including morphological changes, collapsed xylem, and altered cell wall monosaccharide composition. Quantitative RT–PCR showed that PdGATL1.1 is expressed most strongly in developing xylem of poplar. In contrast, PdGATL1.2 is expressed much more uniformly in leaf, shoot tip, cortex, phloem, and xylem, and the transcript level of PdGATL1.2 is much lower than that of PdGATL1.1 in all tissues examined. Sub-cellular localization experiments showed that these two proteins are localized to both ER and Golgi in comparison with marker proteins resident to these sub-cellular compartments. Our data indicate that PdGATL1.1 and PdGATL1.2 are functional orthologs of PARVUS/GATL1 and can play a role in xylan synthesis, but may also have role(s) in the synthesis of other wall polymers.

  X Gu , C. J Wages , K. E Davis , P. J Guyett and M. Bar Peled

UDP--d-galacturonic acid (UDP-GalA) is a key precursor for the synthesis of various bacterial and plant polysaccharides. UDP-glucuronic acid 4-epimerase (UGlcAE) catalyses the reversible conversion of UDP--d-glucuronic acid to UDP-GalA. UGlcAEs isolated from bacterial species have different biochemical properties when compared with the isoenzymes from the plant dicot species, Arabidopsis. However, little is known about the specificity of UGlcAE in Poaceae species. Therefore, we cloned and expressed in Escherichia coli several maize and rice UGlcAE genes, and compared their enzymatic properties with dicot homologs from Arabidopsis. Our data show that UGlcAE isoforms in different plant species have different enzymatic properties. For example, the Poaceae UGlcAE enzymes from rice and maize have significantly lower Ki for UDP-xylose when compared with the Arabidopsis enzymes. The epimerases from different plant species are very specific and unlike their bacterial homolog in Klebsiella pneumoniae, can only use UDP-GlcA or UDP-GalA as their substrate. This study demonstrates that although members of the plant UGlcAE isoforms are highly conserved, the in vitro enzymatic activity of specific Poaceae isoform(s) may be regulated differently by specific nucleotide or nucleotide sugar.

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