Abstract
BackgroundTumor-associated macrophages (TAM) play an important role in tumor microenvironment. Particularly, M2 macrophages contribute to tumor progression, depending on the expression of NF-κB. Tumor-derived exosomes can modulate tumor microenvironment by transferring miRNAs to immune cells. Epigallocatechin gallate (EGCG) has well known anti-tumor effects; however, no data are available on the influence of EGCG on communication with cancer cells and TAM.MethodsMurine breast cancer cell lines, 4T1, was used for in vivo and ex vivo studies. Exosome was extracted from EGCG-treated 4T1 cells, and the change of miRNAs was screened using microarray. Tumor cells or TAM isolated from murine tumor graft were incubated with exosomes derived from EGCG-treated and/or miR-16 inhibitor-transfected 4T1 cells. Chemokines for monocytes (CSF-1 and CCL-2), cytokines both with high (IL-6 and TGF-β) and low (TNF-α) expression in M2 macrophages, and molecules in NF-κB pathway (IKKα and Iκ-B) were evaluated by RT-qPCR or western blot.ResultsEGCG suppressed tumor growth in murine breast cancer model, which was associated with decreased TAM and M2 macrophage infiltration. Expression of chemokine for monocytes (CSF-1 and CCL-2) were low in tumor cells from EGCG-treated mice, and cytokines of TAM was skewed from M2- into M1-like phenotype by EGCG as evidenced by decreased IL-6 and TGF-β and increased TNF-α. Ex vivo incubation of isolated tumor cells with EGCG inhibited the CSF-1 and CCL-2 expression. Ex vivo incubation of TAM with exosomes from EGCG-treated 4T1 cells led to IKKα suppression and concomitant I-κB accumulation; increase of IL-6 and TGF-β; and, decrease of TNF-α. EGCG up-regulated miR-16 in 4T1 cells and in the exosomes. Treatment of tumor cells or TAM with exosomes derived from EGCG-treated and miR-16-knock-downed 4T1 cells restored the above effects on chemokines, cytokines, and NF-κB pathway elicited by EGCG-treated exosomes.ConclusionsOur data demonstrate that EGCG up-regulates miR-16 in tumor cells, which can be transferred to TAM via exosomes and inhibits TAM infiltration and M2 polarization. We suggest a novel mechanism by which EGCG exerts anti-tumor activity via regulation of TAM in tumor microenvironment.
Highlights
Tumor-associated macrophages (TAM) play an important role in tumor microenvironment
We measured the levels of colony-stimulating factor1 (CSF-1) and CCL-2, major chemokines involved in the monocyte recruitment into tumor microenvironment [29], in tumor cells isolated from mice by RT-qPCR
TAM from tumors treated with Epigallocatechin gallate (EGCG) showed significant decrease of IL-6 and TGF-β level, and higher expression of TNF-α compared with those TAMs from control group (Figure 1E)
Summary
Tumor-associated macrophages (TAM) play an important role in tumor microenvironment. Tumor-derived exosomes can modulate tumor microenvironment by transferring miRNAs to immune cells. Epigallocatechin gallate (EGCG) has well known anti-tumor effects; no data are available on the influence of EGCG on communication with cancer cells and TAM. Epidemiological studies of Asian and Chinese women have reported an inverse association between the consumption of green tea and the risk of breast cancer. An increasing body of evidence indicates that exosomes play a pivotal role in cell-to-cell communication [16], and in particular, tumor cells are found to release large quantities of exosomes [17,18,19]. Exosomes may help tumor cells escape the immune surveillance [18] and carry out pro-angiogenic signals that increase tumor vascularization [20]. Exosomes may transfer genetic information, such as microRNAs (miRNAs) from tumor cells to neighboring cells [21]
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