title: Yeast Npi3/Bro1 is involved in ubiquitin-dependent control of permease trafficking.
abstract: The membrane traffic and stability of the general amino acid permease Gap1 of Saccharomyces cerevisiae are under nitrogen control. Addition of a preferential nitrogen source such as ammonium to cells growing on a poor nitrogen source induces internalization of the permease and its subsequent degradation in the vacuole. This down-regulation requires ubiquitination of Gap1 through a process involving ubiquitin ligase Npi1/Rsp5, ubiquitin hydrolase Npi2/Doa4, and Bul1/2, two Npi1/Rsp5 interacting proteins. Here we report that yet another protein, Npi3, is involved in the regulation of Gap1 trafficking. We show that Npi3 is required for NH4+-induced down-regulation of Gap1, and particularly for efficient ubiquitination of the permease. Npi3 plays a pleiotropic role in permease down-regulation, since it is also involved in ubiquitination and stress-induced down-regulation of the uracil permease Fur4 and in glucose-induced degradation of hexose transporters Hxt6/7. We further provide evidence that Npi3 is required for direct vacuolar sorting of neosynthesized Gap1 permease as it occurs in npr1 mutant cells. NPI3 is identical to BRO1, a gene encoding a protein of unknown biochemical function and recently proposed to be involved in protein turnover. Npi3/Bro1 homologues include fungal proteins required for proteolytic cleavage of zinc finger proteins and the mouse Aip1 protein involved in apoptosis. We propose that proteins of the Npi3/Bro1 family, including homologues from higher species, may play a conserved role in ubiquitin-dependent control of membrane protein trafficking.
authors.affiliation: Laboratoire de Physiologie Cellulaire, Institut de Biologie et de Médecine Moléculaires, Université Libre de Bruxelles, Gosselies, Belgium.
authors.forename: Jean Yves
authors.initials: JY
authors.lastname: Springael
authors.forename: Elina
authors.initials: E
authors.lastname: Nikko
authors.forename: Bruno
authors.initials: B
authors.lastname: André
authors.forename: Anne Marie
authors.initials: AM
authors.lastname: Marini
mesh_terms: D000818:Animals; D001692:Biological Transport; D003001:Cloning, Molecular; D017124:Conserved Sequence / Q000235:genetics; D015536:Down-Regulation; D011992:Endosomes / Q000378:metabolism; D005057:Eukaryotic Cells / Q000378:metabolism; D005656:Fungal Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D026901:Membrane Transport Proteins / Q000378:metabolism*; D009004:Monosaccharide Transport Proteins / Q000378:metabolism; D033704:Nucleotide Transport Proteins; D017434:Protein Structure, Tertiary; D021381:Protein Transport / Q000502:physiology; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism; D025801:Ubiquitin / Q000378:metabolism*; D014617:Vacuoles / Q000378:metabolism; D015003:Yeasts / Q000378:metabolism*; D028901:alpha Karyopherins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: C035528:FUR4 protein, S cerevisiae; D005656:Fungal Proteins; C095258:HXT7 protein, S cerevisiae; D026901:Membrane Transport Proteins; D009004:Monosaccharide Transport Proteins; D033704:Nucleotide Transport Proteins; C104643:PALA protein, Emericella nidulans; D029701:Saccharomyces cerevisiae Proteins; D025801:Ubiquitin; D028901:alpha Karyopherins; C087978:karyopherin alpha 2