Biosynthesis of Prion Protein Nucleocytoplasmic Isoforms by Alternative Initiation of Translation

María E. Juanes; Gema Elvira; Aranzazu García-Grande; Miguel Calero; María Gasset

doi:10.1074/jbc.M804051200

Biosynthesis of Prion Protein Nucleocytoplasmic Isoforms by Alternative Initiation of Translation*

^‡Instituto de Química-Física “Rocasolano, Consejo Superior de Investigaciones Científicas (CSIC),” Serrano 119, 28006 Madrid, the ^§Centro Nacional de Investigaciones Oncológicas, Melchor Fernández Almagro 3, 28029 Madrid, and the ^¶Centro Nacional de Microbiología, Instituto de Salud Carlos III, Carretera Pozuelo Km 2, 28220 Majadahonda, Madrid, Spain

↵1 To whom correspondence should be addressed: Insto Química-Física “Rocasolano,” CSIC, Serrano 119, 28006 Madrid, Spain; Tel: 34915619400, Fax: +34915612431, E-mail: mgasset{at}iqfr.csic.es.

Abstract

The cellular prion protein PrP^C is synthesized as a family of four distinct forms. Of these, ^CytPrP is a minor member that segregates outside of the secretory route and can generate cytotoxic forms. Using signal sequence mutants, we found that ^CytPrP is translated from a downstream AUG (coding for Met-8 in human PrP or Met-15 in Syrian hamster PrP). Shortening of the signal sequence dictated the spillage of this isoform into the cytosol, from where it accessed the nucleus or formed insoluble cytosolic aggregates if the proteasome is inhibited. The PrP isoform isolated from the nuclear fractions of cell and brain homogenates was partially SUMO-1-conjugated. Expression of HaPrP(M15) in cells caused an antiproliferative phenotype due to a cell cycle arrest at the G₀/G₁ phase. The identification of this PrP isoform and its properties provides novel insight into PrP^C physiological and pathological functions.

Footnotes

↵* This work was supported by Grants SAF2006-00418 (to M. G.) and FIS PI050912 (to M. C.) from the Ministerio de Ciencia e Innovación (to M. G.) and Grant FOOD-CT-2004 506579 (M. G.) from the European Union. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.