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Activation of Hematopoietic Stem/Progenitor Cells Promotes Immunosuppression Within the Pre-metastatic Niche.

ABSTRACT: Metastatic tumors have been shown to establish microenvironments in distant tissues that are permissive to disseminated tumor cells. Hematopoietic cells contribute to this microenvironment, yet the precise initiating events responsible for establishing the pre-metastatic niche remain unclear. Here, we tracked the developmental fate of hematopoietic stem and progenitor cells (HSPC) in tumor-bearing mice. We show that a distant primary tumor drives the expansion of HSPCs within the bone marrow and their mobilization to the bloodstream. Treatment of purified HSPCs cultured ex vivo with tumor-conditioned media induced their proliferation as well as their differentiation into immunosuppressive myeloid cells. We furthered tracked purified HSPCs in vivo and found they differentiated into myeloid-derived suppressor cells in early metastatic sites of tumor-bearing mice. The number of CD11b(+)Ly6g(+) cells in metastatic sites was significantly increased by HSPC mobilization and decreased if tumor-mediated mobilization was inhibited. Moreover, pharmacologic mobilization of HSPCs increased metastasis, whereas depletion of Gr1(+) cells abrogated the metastasis-promoting effects of HSPC mobilization. Finally, we detected elevated levels of HSPCs in the circulation of newly diagnosed cancer patients, which correlated with increased risk for metastatic progression. Taken together, our results highlight bone marrow activation as one of the earliest steps of the metastatic process and identify circulating HSPCs as potential clinical indicators of metastatic niche formation.

SUBMITTER: Giles AJ

PROVIDER: S-EPMC4794356 | biostudies-literature | 2016 Mar

REPOSITORIES: biostudies-literature

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Project description:The pre-metastatic niche has been shown to play a critical role in tumor metastasis, and its formation is closely related to the tumor microenvironment. However, the underlying molecular mechanisms remain unclear. In the present study, we successfully established a mouse model of lung metastasis using luciferase-expressing MDA-MB-435s cells. In this model, recruitment of vascular endothelial growth factor receptor-1 (VEGFR1)+CD133+ hematopoietic progenitor cells (HPCs) was gradually increased in lung but gradually decreased after the formation of tumor colonies in lung. We also established a highly metastatic MDA-MB-435s (MDA-MB-435s-HM) cell line from the mouse model. Changes in protein profiles in different culture conditions were investigated by protein microarray analysis. The levels of CXC chemokine ligand 16, interleukin (IL)-2R?, IL-2R?, matrix metalloproteinase (MMP)-1, MMP-9, platelet-derived growth factor receptor (PDGFR)-?, stromal cell-derived factor (SDF)-1?, transforming growth factor (TGF)-?, platelet endothelial cell adhesion molecule (PECAM)-1 and vascular endothelial (VE)-cadherin were significantly greater (>?fivefold) in the culture medium from MDA-MB-435s-HM cells than in that from MDA-MB-435s cells. Moreover, the levels of MMP-9, PDGFR-?, and PECAM-1 were significantly greater in the co-culture medium of MDA-MB-435s-HM cells and CD133+ HPCs than in that from MDA-MB-435s-HM cells. Differentially expressed proteins were validated by enzyme-linked immunosorbent assay, and expression of their transcripts was confirmed by quantitative real-time polymerase chain reaction. Moreover, inhibition of MMP-9, PDGFR-?, and PECAM-1 by their specific inhibitors or antibodies significantly decreased cell migration, delayed lung metastasis, and decreased recruitment of VEGFR1+CD133+ HPCs into lung. Intra-hepatic growth of HPCs enhanced the invasive growth of MDA-MB-435s-HM cells in the liver. Our data indicate that VEGFR1+CD133+ HPCs contribute to lung metastasis.

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Activation of Hematopoietic Stem/Progenitor Cells Promotes Immunosuppression Within the Pre-metastatic Niche.

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