The assembly of RAB22A/TMEM33/RTN4 initiates a secretory ER-phagy pathway

  • Cell Discov. 2025 Apr 29;11(1):41. doi: 10.1038/s41421-025-00792-2.
Xueping Zheng  #  1 ,  Dongmei Fang  #  1 ,  Hao Shan  #  1 ,  Beibei Xiao  1 ,  Denghui Wei  1 ,  Yingyi Ouyang  1 ,  Lanqing Huo  1 ,  Zhonghan Zhang  1 ,  Yuanzhong Wu  1 ,  Ruhua Zhang  1 ,  Tiebang Kang  2 ,  Ying Gao  3
Affiliations
  • 1. Sun Yat-sen University Cancer Center, State Key Laboratory of Oncology in South China, Guangdong Provincial Clinical Research Center for Cancer, Guangzhou, Guangdong, China.
  • 2. Sun Yat-sen University Cancer Center, State Key Laboratory of Oncology in South China, Guangdong Provincial Clinical Research Center for Cancer, Guangzhou, Guangdong, China. [email protected].
  • 3. Sun Yat-sen University Cancer Center, State Key Laboratory of Oncology in South China, Guangdong Provincial Clinical Research Center for Cancer, Guangzhou, Guangdong, China. [email protected].
  • # Contributed equally.
PMID: 40301304 DOI: 10.1038/s41421-025-00792-2
Abstract

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.

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