title: Involvement of a novel Q-SNARE, D12, in quality control of the endomembrane system.
abstract: The cellular endomembrane system requires the proper kinetic balance of synthesis and degradation of its individual components, which is maintained in part by a specific membrane fusion apparatus. In this study, we describe the molecular properties of D12, which was identified from a mouse expression library. This C-terminal anchored membrane protein has sequence similarity to both a yeast soluble N-ethylmaleimide-sensitive factor attachment protein (SNAP) receptor (SNARE), Use1p/Slt1p, and a recently identified human syntaxin 18-binding protein, p31. D12 formed a tight complex with syntaxin 18 as well as Sec22b and bound to alpha-SNAP, indicating that D12 is a SNARE protein. Although the majority of D12 is located in the endoplasmic reticulum and endoplasmic reticulum-Golgi intermediate compartments at steady state, overexpression or knockdown of D12 had no obvious effects on membrane trafficking in the early secretory pathway. However, suppression of D12 expression caused rapid appearance of lipofuscin granules, accompanied by apoptotic cell death without the apparent activation of the unfolded protein response. The typical cause of lipofuscin formation is the impaired degradation of mitochondria by lysosomal degradative enzymes, and, consistent with this, we found that proper post-Golgi maturation of cathepsin D was impaired in D12-deficient cells. This unexpected observation was supported by evidence that D12 associates with VAMP7, a SNARE in the endosomal-lysosomal pathway. Hence, we suggest that D12 participates in the degradative function of lysosomes.
authors.affiliation: Division of Molecular and Cellular Immunology, Medical Institute of Bioregulation, Kyushu University, Higashi-ku, Fukuoka, Japan.
authors.forename: Akiko Joo
authors.initials: AJ
authors.lastname: Okumura
authors.forename: Kiyotaka
authors.initials: K
authors.lastname: Hatsuzawa
authors.forename: Taku
authors.initials: T
authors.lastname: Tamura
authors.forename: Hisao
authors.initials: H
authors.lastname: Nagaya
authors.forename: Kazuko
authors.initials: K
authors.lastname: Saeki
authors.forename: Fumihiko
authors.initials: F
authors.lastname: Okumura
authors.forename: Kenji
authors.initials: K
authors.lastname: Nagao
authors.forename: Mitsuo
authors.initials: M
authors.lastname: Nishikawa
authors.forename: Akihiko
authors.initials: A
authors.lastname: Yoshimura
authors.forename: Ikuo
authors.initials: I
authors.lastname: Wada
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D017209:Apoptosis; D011992:Endosomes / Q000502:physiology*; D008062:Lipofuscin / Q000096:biosynthesis; D008247:Lysosomes / Q000502:physiology*; D051379:Mice; D008969:Molecular Sequence Data; D041681:NIH 3T3 Cells; D050682:Q-SNARE Proteins / Q000737:chemistry / Q000502:physiology*; D050683:R-SNARE Proteins / Q000502:physiology; D034741:RNA, Small Interfering / Q000494:pharmacology
chemical_list: D008062:Lipofuscin; D050682:Q-SNARE Proteins; D050683:R-SNARE Proteins; D034741:RNA, Small Interfering; C496927:Sybl1 protein, mouse