Chemokine (C-C Motif) Ligand 2 Engages CCR2+ Stromal Cells of Monocytic Origin to Promote Breast Cancer Metastasis to Lung and Bone

Xin Lu,Yibin Kang

doi:10.1074/jbc.m109.035899

Abstract

Metastatic spread of cancer to distant vital organs, including lung and bone, is the overwhelming cause of breast cancer mortality and morbidity. Effective treatment of systemic metastasis relies on the identification and functional characterization of metastasis mediators to multiple organs. Overexpression of the chemokine (C-C motif) ligand 2 (CCL2) is frequently associated with advanced tumor stage and metastatic relapse in breast cancer. However, the functional mechanism of CCL2 in promoting organ-specific metastasis of breast cancer has not been rigorously investigated. Here, we used organ-specific metastatic sublines of the MDA-MB-231 human breast cancer cell line to demonstrate that overexpression of CCL2 promotes breast cancer metastasis to both lung and bone. Conversely, blocking CCL2 function with a neutralizing antibody reduced lung and bone metastases. The enhancement of lung and bone metastases by CCL2 was associated with increased macrophage infiltration and osteoclast differentiation, respectively. By performing functional assays with primary cells isolated from the wild type, CCL2 and CCR2 knock-out mice, we showed that tumor cell-derived CCL2 depends on its receptor CCR2 (chemokine, CC motif, receptor 2) expressed on stromal cells to exert its function in promoting macrophage recruitment and osteoclast differentiation. Overall, these data demonstrated that CCL2-expressing breast tumor cells engage CCR2(+) stromal cells of monocytic origin, including macrophages and preosteoclasts, to facilitate colonization in lung and bone. Therefore, CCL2 and CCR2 are promising therapeutic targets for simultaneously inhibiting lung and bone metastasis of breast cancer.

Highlights

Bone pain, and hypercalcemia [3,4,5], whereas lung metastasis is accompanied by cough, bloody sputum, rib cage pain, and, eventually, failure of the respiratory functions [6]
By using macrophages and bone marrow cells isolated from wild type, CCL2-deficient, and CCR2-deficient mice, we showed that CCR2 expression in stromal cells is essential for tumor-derived CCL2 to recruit macrophages and promote osteoclastogenesis
Bone marrow growth medium precondithese results suggest that tumor cell-derived CCL2 induces tioned with SCP28-Vec or SCP28-CCL2 cells for 24 h were directional migration of monocyte/macrophages in a CCR2- added to the bone marrow culture to compare their ability to dependent manner, which may be responsible for the elevated induce the formation of multinucleated TRAPϩ osteoclasts

Summary

Introduction

Bone pain, and hypercalcemia [3,4,5], whereas lung metastasis is accompanied by cough, bloody sputum, rib cage pain, and, eventually, failure of the respiratory functions [6]. We used the recently developed organ-specific metastatic sublines of the human breast cancer cell MDA-MB231 [9, 10, 33] and showed that overexpression of CCL2 promotes both lung and bone metastases.

Results

Conclusion