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Articles by A. Schneider
Total Records ( 2 ) for A. Schneider
  X Wang and A. Schneider
 

Despite their individual key roles in promoting head and neck squamous cell carcinoma (HNSCC) progression and treatment resistance, little is known about the impact of intratumoral hypoxia on the activity of the epidermal growth factor receptor (EGFR) signaling pathway in this cancer type. Here, we show that in highly EGFR-expressing HNSCC cells, hypoxic stress triggers the activation of the EGFR and downstream targets, including Akt and phospholipase C (PLC) 1. In support of these findings, we also demonstrate that EGFR activation takes place within hypoxic foci in a subset of human HNSCC tissues. Whereas hypoxia had no major effect on HNSCC cell proliferation, it markedly altered tumor cell shape by inducing morphological changes consistent with a more spindle-shaped, fibroblast-like morphology together with an enhanced migratory capacity. We found that hypoxia-induced EGFR activation and cell migration could be prevented by targeting EGFR signaling with the tyrosine kinase inhibitor tyrphostin, the phospholipase C inhibitor U73122, or by inhibiting the expression of the subunit of hypoxia-inducible factor 2 via RNA interference or the topoisomerase II inhibitor etoposide. Our results position hypoxia-inducible factor-2 as a novel regulator of EGFR activation under low oxygen conditions, and suggest that hypoxia-induced EGFR signaling may promote a more aggressive phenotype in a fraction of HNSCC tumors. Because EGFR continues in the forefront as a highly attractive target in clinical oncology, further studies are warranted to define the mechanistic and therapeutic implications of the hypoxic response relative to the EGFR signaling pathway in head and neck cancer.

  F Charriere , P O`Donoghue , S Helgadottir , L Marechal Drouard , M Cristodero , E. K Horn , D Soll and A. Schneider
 

The mitochondrion of the parasitic protozoon Trypanosoma brucei does not encode any tRNAs. This deficiency is compensated for by partial import of nearly all of its cytosolic tRNAs. Most trypanosomal aminoacyl-tRNA synthetases are encoded by single copy genes, suggesting the use of the same enzyme in the cytosol and in the mitochondrion. However, the T. brucei genome encodes two distinct genes for eukaryotic aspartyl-tRNA synthetase (AspRS), although the cell has a single tRNAAsp isoacceptor only. Phylogenetic analysis showed that the two T. brucei AspRSs evolved from a duplication early in kinetoplastid evolution and also revealed that eight other major duplications of AspRS occurred in the eukaryotic domain. RNA interference analysis established that both Tb-AspRS1 and Tb-AspRS2 are essential for growth and required for cytosolic and mitochondrial Asp-tRNAAsp formation, respectively. In vitro charging assays demonstrated that the mitochondrial Tb-AspRS2 aminoacylates both cytosolic and mitochondrial tRNAAsp, whereas the cytosolic Tb-AspRS1 selectively recognizes cytosolic but not mitochondrial tRNAAsp. This indicates that cytosolic and mitochondrial tRNAAsp, although derived from the same nuclear gene, are physically different, most likely due to a mitochondria-specific nucleotide modification. Mitochondrial Tb-AspRS2 defines a novel group of eukaryotic AspRSs with an expanded substrate specificity that are restricted to trypanosomatids and therefore may be exploited as a novel drug target.

 
 
 
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