Nuclear mRNA retention and aberrant doppel protein expression in human astrocytic tumor cells

Sergio Comincini, Laurent R. Chiarelli, Paola Zelini, Igor Del Vecchio, Alberto Azzalin, Agustina Arias, Valentina Ferrara, Paola Rognoni, Antonella Dipoto, Rosanna Nano, Giovanna Valentini, Luca Ferretti

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Abstract

Doppel (Dpl) is a paralogue of the mammalian Prion (PrP) protein. It is abundant in testis and, unlike PrP, it is expressed at low levels in the adult central nervous system (CNS). Besides, Dpl overexpression correlates with some prion-disease pathological features, such as ataxia and death of cerebellar neurons. Recently, ectopic expression of doppel was found in two different tumor types, specifically in glial and haematological cancers. In this study the doppel gene ( PRND ) mRNA and protein expression in PRT-HU2 and IPDDC-A2 astrocytoma-derived cell lines was investigated. Northern blot analysis revealed two equally abundant PRND mRNA isoforms, while real-time PCR, on nuclear and cytoplasmic RNA fractions, and cRNA in situ hybridization, on astrocytoma cells and bioptical specimens, showed a nuclear retention of PRND transcripts. Western blot analysis showed that the amount of protein expressed is low compared to the level of mRNA. Moreover deglycosylation studies indicated that Dpl undergoes unusual glycosylation processes. Immunohistochemistry experiments demonstrated that Dpl was mainly localised in the cytoplasm of the astrocytic tumor cells, and that it failed to be GPI-anchored to the cell membrane. This unusual cellular localization was also confirmed through EGFP-Dpl expression in astrocytomas; on the contrary, HeLa cells exhibited the expected Dpl membrane localization. Our findings suggest an aberrant doppel gene expression pattern, characterized by a substantial nuclear retention of the transcript, an altered post-translational modification of the protein and an unusual cytoplasmic localization.

Original languageEnglish
Pages (from-to)1325-1332
Number of pages8
JournalOncology Reports
Volume16
Issue number6
Publication statusPublished - Dec 2006

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Keywords

  • Astrocytoma cell lines
  • Dpl
  • Glial tumor
  • Glycosylation
  • Nucleus
  • PRND

ASJC Scopus subject areas

  • Cancer Research
  • Oncology

Cite this

Comincini, S., Chiarelli, L. R., Zelini, P., Del Vecchio, I., Azzalin, A., Arias, A., Ferrara, V., Rognoni, P., Dipoto, A., Nano, R., Valentini, G., & Ferretti, L. (2006). Nuclear mRNA retention and aberrant doppel protein expression in human astrocytic tumor cells. Oncology Reports, 16(6), 1325-1332.