Zheng Xueping, Fang Dongmei, Shan Hao, Xiao Beibei, Wei Denghui, Ouyang Yingyi, Huo Lanqing, Zhang Zhonghan, Wu Yuanzhong, Zhang Ruhua, Kang Tiebang, Gao Ying
Sun Yat-sen University Cancer Center, State Key Laboratory of Oncology in South China, Guangdong Provincial Clinical Research Center for Cancer, Guangzhou, Guangdong, China.
Cell Discov. 2025 Apr 29;11(1):41. doi: 10.1038/s41421-025-00792-2.
Rafeesome, a newly identified multivesicular body (MVB)-like organelle, forms through the fusion of RAB22A-mediated ER-derived noncanonical autophagosomes with RAB22A-positive early endosomes. However, the mechanism underlying the formation of RAB22A-mediated noncanonical autophagosomes remains unclear. Herein, we report a secretory ER-phagy pathway in which the assembly of RAB22A/TMEM33/RTN4 induces the clustering of high-molecular-weight RTN4 oligomers, leading to ER membrane remodeling. This remodeling drives the biogenesis of ER-derived RTN4-positive noncanonical autophagosomes, which are ultimately secreted as TMEM33-marked RAB22A-induced extracellular vesicles (R-EVs) via Rafeesome. Specifically, RAB22A interacts with the tubular ER membrane protein TMEM33, which binds to the TM2 domain of the ER-shaping protein RTN4, promoting RTN4 homo-oligomerization and thereby generating RTN4-enriched microdomains. Consequently, the RTN4 microdomains may induce high curvature of the ER, facilitating the bud scission of RTN4-positive vesicles. These vesicles are transported by ATG9A and develop into isolation membranes (IMs), which are then anchored by LC3-II, a process catalyzed by the ATG12-ATG5-ATG16L1 complex, allowing them to grow into sealed RTN4 noncanonical autophagosome. While being packaged into these ER-derived intermediate compartments, ER cargoes bypass lysosomal degradation and are directed to secretory autophagy via the Rafeesome-R-EV route. Our findings reveal a secretory ER-phagy pathway initiated by the assembly of RAB22A/TMEM33/RTN4, providing new insights into the connection between ER-phagy and extracellular vesicles.
Rafeesome是一种新发现的类似多囊泡体(MVB)的细胞器,它通过RAB22A介导的内质网(ER)来源的非经典自噬体与RAB22A阳性早期内体融合形成。然而,RAB22A介导的非经典自噬体形成的潜在机制仍不清楚。在此,我们报道了一种分泌性内质网自噬途径,其中RAB22A/TMEM33/RTN4的组装诱导高分子量RTN4寡聚体的聚集,导致内质网膜重塑。这种重塑驱动内质网来源的RTN4阳性非经典自噬体的生物发生,这些自噬体最终通过Rafeesome作为TMEM33标记的RAB22A诱导的细胞外囊泡(R-EVs)分泌。具体而言,RAB22A与管状内质网蛋白TMEM33相互作用,TMEM33与内质网塑形蛋白RTN4的TM2结构域结合,促进RTN4同源寡聚化,从而产生富含RTN4的微结构域。因此,RTN4微结构域可能诱导内质网的高曲率,促进RTN4阳性囊泡的芽切离。这些囊泡由ATG9A运输并发育成隔离膜(IMs),然后由LC3-II锚定,这一过程由ATG12-ATG5-ATG16L1复合物催化,使其生长成密封的RTN4非经典自噬体。在内质网来源的这些中间隔室中被包装时,内质网货物绕过溶酶体降解,并通过Rafeesome-R-EV途径导向分泌性自噬。我们的发现揭示了一种由RAB22A/TMEM33/RTN4组装引发 的分泌性内质网自噬途径,为内质网自噬与细胞外囊泡之间的联系提供了新的见解。