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Articles by Xiaoyu Pan
Total Records ( 3 ) for Xiaoyu Pan
  Gang Long , Xiaoyu Pan and Just M. Vlak
  The heptad repeat (HR), a conserved structural motif of class I viral fusion proteins, is responsible for the formation of a six-helix bundle structure during the envelope fusion process. The insect baculovirus F protein is a newly found budded virus envelope fusion protein which possesses common features to class I fusion proteins, such as proteolytic cleavage and the presence of an N-terminal open fusion peptide and multiple HR domains on the transmembrane subunit F1. Similar to many vertebrate viral fusion proteins, a conserved leucine zipper motif is predicted in this HR region proximal to the fusion peptide in baculovirus F proteins. To facilitate our understanding of the functional role of this leucine zipper-like HR1 domain in baculovirus F protein synthesis, processing, and viral infectivity, key leucine residues (Leu209, Leu216, and Leu223) were replaced by alanine (A) or arginine (R), respectively. By using Autographa californica multicapsid nucleopolyhedrovirus (AcMNPV) as a pseudotype expression system, we demonstrated that all mutant F proteins incorporated into budded virus, indicating that leucine substitutions did not affect intercellular trafficking of F. Furin-like protease cleavage was not affected by any of the leucine substitutions; however, the disulfide bridging and N-linked glycosylation patterns were partly altered. Single substitutions in HR1 showed that the three leucine residues were critical for F fusogenicity and the rescue of AcMNPV infectivity. Our results support the view that the leucine zipper-like HR1 domain is important to safeguard the proper folding, glycosylation, and fusogenicity of baculovirus F proteins.
  Guogen Mao , Xiaoyu Pan and Liya Gu
  Defects in DNA mismatch repair (MMR) are the molecular basisof certain cancers, including hematological malignancies. Thedefects are often caused by mutations in coding regions of MMRgenes or promoter methylation of the genes. However, in manycases, despite that a hypermutable phenotype is detected ina patient, no mutations/hypermethylations of MMR genes can bedetected. We report here a novel mechanism that a mutation inthe MLH1 3’-untranslated region (3’-UTR) leads to MMR deficiency.A relapsed leukemia patient displayed microsatellite instability,but no genetic and epigenetic alterations in key MMR genes wereidentifiable. Instead, a 3-nucleotide (TTC) deletion in the MLH1 3’-UTR was found in the patient’s blood sample. The mutant MLH1 3’-UTR was found to significantly reduce the expressionsof both a firefly luciferase reporter gene and an ectopic MLH1gene in model cell lines. Consistent with these observations,a significant reduction in the steady-state level of MLH1 mRNAwas observed in white blood cells of the patient. These findingssuggest that the mutant MLH1 3’-UTR can cause a severely reduced/defectiveMMR activity conferring leukemia relapse, likely by down-regulating MLH1 expression at the mRNA level. Although the exact mechanismby which the mutant 3’-UTR down-regulates the MLH1 mRNA is notknown, our findings provide a novel marker for cancers withMMR defects.

  Lili Zhang , Zeljka Smit-McBride , Xiaoyu Pan , Jeanette Rheinhardt and John W. B. Hershey
  Dysregulation of protein synthesis has been implicated in oncogenesis through a mechanism whereby "weak" mRNAs encoding proteins involved in cell proliferation are strongly translated when the protein synthesis apparatus is activated. Previous work has determined that many cancer cells contain high levels of eIF3h, a protein subunit of translation initiation factor eIF3, and overexpression of eIF3h malignantly transforms immortal NIH-3T3 cells. This is a general feature of eIF3h, as high levels also affect translation, proliferation, and a number of malignant phenotypes of CHO-K1 and HeLa cells and, most significantly, of a primary prostate cell line. Furthermore, overexpressed eIF3h inhibits Myc-dependent induction of apoptosis of primary prostate cells. eIF3h appears to function through translation, as the initial appearance of overexpressed eIF3h in rapidly induced NIH-3T3 cells correlates tightly with the stimulation of protein synthesis and the generation of malignant phenotypes. This oncogenic potential of eIF3h is enhanced by phosphorylation at Ser183. Finally, reduction of eIF3h levels in breast and prostate cancer cell lines by short interfering RNA methods reduces their rates of proliferation and anchorage-independent growth in soft agar. The results provide compelling evidence that high eIF3h levels directly stimulate protein synthesis, resulting in the establishment and maintenance of the malignant state in cells.
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