title: An overlapping reading frame in the PRNP gene encodes a novel polypeptide distinct from the prion protein.
abstract: The prion protein gene PRNP directs the synthesis of one of the most intensively studied mammalian proteins, the prion protein (PrP). Yet the physiological function of PrP has remained elusive and has created controversies in the literature. We found a downstream alternative translation initiation AUG codon surrounded by an optimal Kozak sequence in the +3 reading frame of PRNP. The corresponding alternative open reading frame encodes a polypeptide termed alternative prion protein (AltPrP) with a completely different amino acid sequence from PrP. We introduced a hemagglutinin (HA) tag in frame with AltPrP in PrP cDNAs from different species to test the expression of this novel polypeptide using anti-HA antibodies. AltPrP is constitutively coexpressed with human, bovine, sheep, and deer PrP. AltPrP is localized at the mitochondria and is up-regulated by endoplasmic reticulum stress and proteasomal inhibition. Generation of anti-AltPrP antibodies allowed us to test for endogenous expression of AltPrP in wild-type human cells expressing PrP. By transfecting cells with siRNA against PrP mRNA, we repressed expression of both PrP and AltPrP, confirming endogenous expression of AltPrP from PRNP. AltPrP was also detected in human brain homogenate, primary neurons, and peripheral blood mononuclear cells. These results demonstrate an unexpected function for PRNP, which, in addition to plasma membrane-anchored PrP, also encodes a second polypeptide termed AltPrP.
authors.affiliation: Department of Biochemistry, Faculty of Medicine, University of Sherbrooke, 3001 12ème Avenue Nord, Sherbrooke, QC, J1H 5N4, Canada.
authors.forename: Benoît
authors.initials: B
authors.lastname: Vanderperre
authors.forename: Antanas B
authors.initials: AB
authors.lastname: Staskevicius
authors.forename: Guillaume
authors.initials: G
authors.lastname: Tremblay
authors.forename: Marie
authors.initials: M
authors.lastname: McCoy
authors.forename: Megan A
authors.initials: MA
authors.lastname: O'Neill
authors.forename: Neil R
authors.initials: NR
authors.lastname: Cashman
authors.forename: Xavier
authors.initials: X
authors.lastname: Roucou
mesh_terms: D000818:Animals; D001483:Base Sequence; D045744:Cell Line, Tumor; D002478:Cells, Cultured; D018076:DNA, Complementary / Q000235:genetics; D004721:Endoplasmic Reticulum / Q000378:metabolism; D015870:Gene Expression; D005807:Genes, Overlapping / Q000235:genetics*; D057809:HEK293 Cells; D006801:Humans; D015151:Immunoblotting; D007963:Leukocytes, Mononuclear / Q000166:cytology / Q000378:metabolism; D007976:Leupeptins / Q000494:pharmacology; D018613:Microscopy, Confocal; D024101:Mitochondrial Proteins / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D009474:Neurons / Q000166:cytology / Q000378:metabolism; D016366:Open Reading Frames / Q000235:genetics*; D010455:Peptides / Q000235:genetics* / Q000378:metabolism; D000072002:Prion Proteins; D011328:Prions / Q000235:genetics* / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D061988:Proteasome Inhibitors; D034622:RNA Interference; D012689:Sequence Homology, Nucleic Acid
chemical_list: D018076:DNA, Complementary; D007976:Leupeptins; D024101:Mitochondrial Proteins; C512656:PRNP protein, human; D010455:Peptides; D000072002:Prion Proteins; D011328:Prions; D061988:Proteasome Inhibitors; D046988:Proteasome Endopeptidase Complex; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde