Platelet factor 4 is produced by subsets of myeloid cells in premetastatic lung and inhibits tumor metastasis
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Jiang Jian1,2,*, Yanli Pang1,3,*, H. Hannah Yan1, Yongfen Min4, Bhagelu R. Achyut1,5, M. Christine Hollander1, P. Charles Lin4, Xinhua Liang2, Li Yang1
1Laboratory of Cancer Biology and Genetics, National Cancer Institute, NIH, Bethesda, MD, USA
2Department of Oral and Maxillofacial Surgery, State Key Laboratory of Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu, Sichuan, P. R. China
3Current address: Department of Obstetrics and Gynecology, Center for Reproductive Medicine, Peking University Third Hospital, Beijing, P. R. China
4Cancer and Inflammation Program, Center for Cancer Research, National Cancer Institute, NIH, Frederick, MD, USA
5Tumor Angiogenesis Laboratory, Cancer Center, Georgia Regents University, Augusta, GA, USA
*These authors contributed equally to this work
Li Yang, email: email@example.com
Xinhua Liang, email: firstname.lastname@example.org
Keywords: PF4, metastasis, myeloid cells, premetastatic lung
Received: January 15, 2016 Accepted: May 01, 2016 Published: May 19, 2016
Bone marrow-derived myeloid cells can form a premetastatic niche and provide a tumor–promoting microenvironment. However, subsets of myeloid cells have also been reported to have anti-tumor properties. It is not clear whether there is a transition between anti- and pro- tumor function of these myeloid cells, and if so, what are the underlying molecular mechanisms. Here we report platelet factor 4 (PF4), or CXCL4, but not the other family members CXCL9, 10, and 11, was produced at higher levels in the normal lung and early stage premetastatic lungs but decreased in later stage lungs. PF4 was mostly produced by Ly6G+CD11b+ myeloid cell subset. Although the number of Ly6G+CD11b+ cells was increased in the premetastatic lungs, the expression level of PF4 in these cells was decreased during the metastatic progression. Deletion of PF4 (PF4 knockout or KO mice) led an increased metastasis suggesting an inhibitory function of PF4. There were two underlying mechanisms: decreased blood vessel integrity in the premetastatic lungs and increased production of hematopoietic stem/progenitor cells (HSCs) and myeloid derived suppressor cells (MDSCs) in tumor-bearing PF4 KO mice. In cancer patients, PF4 expression levels were negatively correlated with tumor stage and positively correlated with patient survival. Our studies suggest that PF4 is a critical anti-tumor factor in the premetastatic site. Our finding of PF4 function in the tumor host provides new insight to the mechanistic understanding of tumor metastasis.
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