CCL2 and Interleukin-6 Promote Survival of Human CD11b+ Peripheral Blood Mononuclear Cells and Induce M2-type Macrophage Polarization

Hernan Roca,Zachary S Varsos,Sudha Sud,Matthew J Craig,Chi Ying,Kenneth J Pienta

doi:10.1074/jbc.m109.042671

Abstract

CCL2 and interleukin (IL)-6 are among the most prevalent cytokines in the tumor microenvironment, with expression generally correlating with tumor progression and metastasis. CCL2 and IL-6 induced expression of each other in CD11b(+) cells isolated from human peripheral blood. It was demonstrated that both cytokines induce up-regulation of the antiapoptotic proteins cFLIP(L) (cellular caspase-8 (FLICE)-like inhibitory protein), Bcl-2, and Bcl-X(L) and inhibit the cleavage of caspase-8 and subsequent activation of the caspase-cascade, thus protecting cells from apoptosis under serum deprivation stress. Furthermore, both cytokines induced hyperactivation of autophagy in these cells. Upon CCL2 or IL-6 stimulation, CD11b(+) cells demonstrated a significant increase in the mannose receptor (CD206) and the CD14(+)/CD206(+) double-positive cells, suggesting a polarization of macrophages toward the CD206(+) M2-type phenotype. Caspase-8 inhibitors mimicked the cytokine-induced up-regulation of autophagy and M2 polarization. Furthermore, E64D and leupeptin, which are able to function as inhibitors of autophagic degradation, reversed the effect of caspase-8 inhibitors in the M2-macrophage polarization, indicating a role of autophagy in this mechanism. Additionally, in patients with advanced castrate-resistant prostate cancer, metastatic lesions exhibited an increased CD14(+)/CD206(+) double-positive cell population compared with normal tissues. Altogether, these findings suggest a role for CCL2 and IL-6 in the survival of myeloid monocytes recruited to the tumor microenvironment and their differentiation toward tumor-promoting M2-type macrophages via inhibition of caspase-8 cleavage and enhanced autophagy.

Highlights

Cells, which are released from the bone marrow and circulate in the blood stream until signaled to differentiate within target tissues, typically through interactions with cytokines and colony-stimulating factors [1, 3]
CCL2 and IL-6 Induce Each Other in Human CD11bϩ Cells— Tumor cells produce numerous chemokines that attract inflammatory cells, which are capable of producing an assorted array of cytokines, angiogenic growth factors, and proteases, all of which dictate the fate of a developing tumor
Because CD14 is a surface marker expressed in macrophages, and CD206 is a marker of M2 polarized macrophages, these results suggest that CCL2 and IL-6 induce the differentiation of CD11bϩ monocytes into M2-type macrophages

Summary

Introduction

Cells, which are released from the bone marrow and circulate in the blood stream until signaled to differentiate within target tissues, typically through interactions with cytokines and colony-stimulating factors [1, 3]. These results correlate with the previous observation that CCL2 and IL-6 promote CD11bϩ cell survival (Fig. 2, A–C) and suggest that the extrinsic apoptotic pathway, mediated by death receptor and caspase-8, is the predominant death mechanism activated in these cells.

Results

Conclusion