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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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 6

VPS33B regulates the release of growth factor–containing exosomes to maintain mouse and human HSC functions.

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VPS33B regulates the release of growth factor–containing exosomes to mai...
(A) Representative flow cytometric analyses for the binding activity of ANGPTL2-containing exosomes (ANGPTL2-Exo) and control exosomes (Ctrl-Exo) to LILRB2-transfected 293T cells. ANGPTL2-conditioned medium (ANGPTL2-CM) and control conditioned medium (Ctrl-CM) served as the positive and negative controls, respectively (n = 3). (B) Representative images of LT-HSCs from VPS33B+/+ and VPS33B–/– mice cultured in basic medium (SCF+TPO; Ctrl), ANGPTL2-conditioned medium (A2), and ANGPTL3-conditioned medium (A3); in medium containing purified control exosomes (CExo), ANGPTL2-containing exosomes (A2Exo), and ANGPTL3-containing exosomes (A3Exo) from conditioned medium; and in human plasma–derived exosomes (hExo) for 6 days (n = 4). (C) Multilineage contribution of CD34+ cells from human umbilical cord blood upon VPS33B knockdown. Representative flow cytometric profiles from 1 transplanted NOD-SCID mouse of each group. The IgG isotype served as a negative control. The middle set of profiles shows results for myeloid cells, and the right set of profiles shows results for lymphoid (CD19+/CD20+) and HSCs/progenitor cells (CD19–/CD20–CD34+). (D) Repopulation of human CD45+/CD71+ in the BM of NOD-SCID mice as shown in C at 2 months after transplantation (n = 7; ***P < 0.001 using Student’s t test). (E) Summary of the multilineage contributions as described in C (n = 7; **P < 0.01, ***P < 0.001 using Student’s t test). Experiments were conducted 3 times for validation.