Critical role of PPARγ in myeloid-derived suppressor cell-stimulated cancer cell proliferation and metastasis
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Ting Zhao1, Hong Du1,2, Janice S. Blum3, Cong Yan1,2
1Department of Pathology and Laboratory Medicine, Indiana University School of Medicine, Indianapolis, IN 46202, USA
2IU Simon Cancer Center, Indiana University School of Medicine, Indianapolis, IN 46202, USA
3Department of Microbiology and Immunology, Indiana University School of Medicine, Indianapolis, IN 46202, USA
Cong Yan, e-mail: firstname.lastname@example.org
Hong Du, e-mail: email@example.com
Keywords: lysosomal acid lipase, lipid metabolic signaling, myeloid-derived suppressor cells, peroxisome proliferator-activated receptor-γ, tumor growth and metastasis
Received: August 19, 2015 Accepted: November 17, 2015 Published: November 27, 2015
Lysosomal acid lipase (LAL) is a key enzyme controlling neutral lipid metabolic signaling in myeloid-derived suppressor cells (MDSCs). MDSCs from LAL-deficient (lal−/−) mice directly stimulate cancer cell proliferation. PPARγ ligand treatment inhibited lal−/− MDSCs stimulation of tumor cell growth and metastasis in vivo, and tumor cell proliferation and migration in vitro. In addition, PPARγ ligand treatment impaired lal−/− MDSCs transendothelial migration, and differentiation from lineage-negative cells. The corrective effects of PPARγ ligand on lal−/− MDSCs functions were mediated by regulating the mammalian target of rapamycin (mTOR) pathway, and subsequently blocking MDSCs ROS overproduction. Furthermore, in the myeloid-specific dominant-negative PPARγ (dnPPARγ) overexpression bitransgenic mouse model, tumor growth and metastasis were enhanced, and MDSCs from these mice stimulated tumor cell proliferation and migration. MDSCs with dnPPARγ overexpression showed increased transendothelial migration, overactivation of the mTOR pathway, and ROS overproduction. These results indicate that PPARγ plays a critical role in neutral lipid metabolic signaling controlled by LAL, which provides a mechanistic basis for clinically targeting MDSCs to reduce the risk of cancer proliferation, growth and metastasis.
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