Sorting protein VPS33B regulates exosomal autocrine signaling to mediate hematopoiesis and leukemogenesis
Hao Gu, … , Guo-Qiang Chen, Junke Zheng
Hao Gu, … , Guo-Qiang Chen, Junke Zheng
Published October 31, 2016
Citation Information: J Clin Invest. 2016;126(12):4537-4553. https://doi.org/10.1172/JCI87105.
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Research Article Hematology

Sorting protein VPS33B regulates exosomal autocrine signaling to mediate hematopoiesis and leukemogenesis

Abstract

Certain secretory proteins are known to be critical for maintaining the stemness of stem cells through autocrine signaling. However, the processes underlying the biogenesis, maturation, and secretion of these proteins remain largely unknown. Here we demonstrate that many secretory proteins produced by hematopoietic stem cells (HSCs) undergo exosomal maturation and release that is controlled by vacuolar protein sorting protein 33b (VPS33B). Deletion of VPS33B in either mouse or human HSCs resulted in impaired exosome maturation and secretion as well as loss of stemness. Additionally, VPS33B deficiency led to a dramatic delay in leukemogenesis. Exosomes purified from either conditioned medium or human plasma could partially rescue the defects of HSCs and leukemia-initiating cells (LICs). VPS33B co-existed in exosomes with GDI2, VPS16B, FLOT1, and other known exosome markers. Mechanistically, VPS33B interacted with the GDI2/RAB11A/RAB27A pathway to regulate the trafficking of secretory proteins as exosomes. These findings reveal an essential role for VPS33B in exosome pathways in HSCs and LICs. Moreover, they shed light on the understanding of vesicle trafficking in other stem cells and on the development of improved strategies for cancer treatment.

Authors

Hao Gu, Chiqi Chen, Xiaoxin Hao, Conghui Wang, Xiaocui Zhang, Zhen Li, Hongfang Shao, Hongxiang Zeng, Zhuo Yu, Li Xie, Fangzhen Xia, Feifei Zhang, Xiaoye Liu, Yaping Zhang, Haishan Jiang, Jun Zhu, Jiangbo Wan, Chun Wang, Wei Weng, Jingjing Xie, Minfang Tao, Cheng Cheng Zhang, Junling Liu, Guo-Qiang Chen, Junke Zheng

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Figure 5

Supplement of exogenous ANGPTL2 and ANGPTL3 proteins or overexpression of GDI2 restores the impaired activities of VPS33B-null HSCs.

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Supplement of exogenous ANGPTL2 and ANGPTL3 proteins or overexpression o...
(A) Representative images of LT-HSCs from VPS33B+/+ and VPS33B–/– mice cultured in basic medium (SCF+TPO), ANGPTL2-, and ANGPT3-conditioned medium (referred as Ctrl, A2, and A3, respectively) for 8 days (n = 5). (B and C) Cell numbers and apoptosis were measured in cultured WT and VPS33B-null LT-HSCs in A (n = 5; **P < 0.01, ***P < 0.001 using Student’s t test). (D) ANGPTL2 and ANGPTL3 were overexpressed in VPS33B-null HSCs, which were subjected to competitive reconstitution analysis. Engraftment was analyzed at 4, 8, and 16 weeks after transplantation (n = 5; ***P < 0.001 using Student’s t test). (E) GDI2 was overexpressed in VPS33B-null HSCs, which were subjected to competitive reconstitution analysis. Engraftment was analyzed at 3, 8, and 16 weeks after transplantation (n = 5; ***P < 0.001 using Student’s t test). (F) GDI2 was knocked down in WT HSCs, which were subjected to competitive reconstitution analysis. Engraftment was analyzed at 3, 8, and 16 weeks after transplantation (n = 5; ***P < 0.001 using Student’s t test). Experiments were conducted 3 times for validation.