Involvement of a novel Q-SNARE, D12, in quality control of the endomembrane system.
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.
Okumura
Akiko Joo
AJ
Division of Molecular and Cellular Immunology, Medical Institute of Bioregulation, Kyushu University, Higashi-ku, Fukuoka, Japan.
Hatsuzawa
Kiyotaka
K
Tamura
Taku
T
Nagaya
Hisao
H
Saeki
Kazuko
K
Okumura
Fumihiko
F
Nagao
Kenji
K
Nishikawa
Mitsuo
M
Yoshimura
Akihiko
A
Wada
Ikuo
I
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
D008062:Lipofuscin; D050682:Q-SNARE Proteins; D050683:R-SNARE Proteins; D034741:RNA, Small Interfering; C496927:Sybl1 protein, mouse