Itoh Takashi, Fujita Naonobu, Kanno Eiko, Yamamoto Akitsugu, Yoshimori Tamotsu, Fukuda Mitsunori
Department of Developmental Biology and Neurosciences, Graduate School of Life Sciences, Tohoku University, Sendai, Miyagi 980-8578, Japan.
Mol Biol Cell. 2008 Jul;19(7):2916-25. doi: 10.1091/mbc.e07-12-1231. Epub 2008 Apr 30.
Macroautophagy is a mechanism of degradation of cytoplasmic components in all eukaryotic cells. In macroautophagy, cytoplasmic components are wrapped by double-membrane structures called autophagosomes, whose formation involves unique membrane dynamics, i.e., de novo formation of a double-membrane sac called the isolation membrane and its elongation. However, the precise regulatory mechanism of isolation membrane formation and elongation remains unknown. In this study, we showed that Golgi-resident small GTPase Rab33B (and Rab33A) specifically interacts with Atg16L, an essential factor in isolation membrane formation, in a guanosine triphosphate-dependent manner. Expression of a GTPase-deficient mutant Rab33B (Rab33B-Q92L) induced the lipidation of LC3, which is an essential process in autophagosome formation, even under nutrient-rich conditions, and attenuated macroautophagy, as judged by the degradation of p62/sequestosome 1. In addition, overexpression of the Rab33B binding domain of Atg16L suppressed autophagosome formation. Our findings suggest that Rab33 modulates autophagosome formation through interaction with Atg16L.
巨自噬是所有真核细胞中细胞质成分的一种降解机制。在巨自噬过程中，细胞质成分被称为自噬体的双膜结构包裹，自噬体的形成涉及独特的膜动力学，即称为隔离膜的双膜囊泡的从头形成及其延伸。然而，隔离膜形成和延伸的确切调控机制仍不清楚。在本研究中，我们发现高尔基体驻留小GTP酶Rab33B（以及Rab33A）以鸟苷三磷酸依赖的方式与隔离膜形成中的关键因子Atg16L特异性相互作用。即使在营养丰富的条件下，GTP酶缺陷型突变体Rab33B（Rab33B-Q92L）的表达也会诱导LC3的脂化，这是自噬体形成中的一个关键过程，并通过p62/聚集体小体1的降解判断减弱了巨自噬。此外，Atg16L的Rab33B结合结构域的过表达抑制了自噬体的形成。我们的研究结果表明，Rab33通过与Atg16L相互作用来调节自噬体的形成。
