Journal
FRONTIERS IN IMMUNOLOGY
Volume 8, Issue -, Pages -Publisher
FRONTIERS MEDIA SA
DOI: 10.3389/fimmu.2017.01171
Keywords
apoptosis; phagocytosis; macrophage polarization; sphingosine-1-phosphate; lipocalin-2; tumor progression
Categories
Funding
- German Research Association [SFB815: TP08, SFB1039: TPB04, TPB06]
- Deutsche Krebshilfe [109599, 70112451]
- Else Kroner- Fresenius-Stiftung (Else Kroner-Fresenius-Graduiertenkolleg)
- LOEWE (Research Center for Translational Medicine and Pharmacology TMP)
- Else Kroner- Fresenius Foundation (EKFS)
- Research Training Group Translational Research Innovation Pharma (TRIP)
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Carcinogenesis is a multistep process. Besides somatic mutations in tumor cells, stroma-associated immunity is a major regulator of tumor growth. Tumor cells produce and secrete diverse mediators to create a local microenvironment that supports their own survival and growth. It is becoming apparent that iron acquisition, storage, and release in tumor cells is different from healthy counterparts. It is also appreciated that macrophages in the tumor microenvironment acquire a tumor-supportive, anti-inflammatory phenotype that promotes tumor cell proliferation, angiogenesis, and metastasis. Apparently, this behavior is attributed, at least in part, to the ability of macrophages to support tumor cells with iron. Polarization of macrophages by apoptotic tumor cells shifts the profile of genes involved in iron metabolism from an iron sequestering to an iron-release phenotype. Iron release from macrophages is supposed to be facilitated by ferroportin. However, lipid mediators such as sphingosine-1-phosphate, released form apoptotic tumor cells, upregulate lipocalin-2 (Lcn-2) in macrophages. This protein is known to bind siderophore-complexed iron and thus, may participate in iron transport in the tumor microenvironment. We describe how macrophages handle iron in the tumor microenvironment, discuss the relevance of an iron-release macrophage phenotype for tumor progression, and propose a new role for Lcn-2 in tumor-associated macrophages.
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