This study aims to investigate the mechanisms underlying leptin-mediated crosstalk between tumor-associated macrophages (M2 macrophages) and breast cancer cells. THP1 human leukemic monocytes were induced to differentiate into M2 macrophages by PMA (100 nM) and IL-4 (20 ng/mL). Quantitative RT-PCR and Western blot revealed that leptin (100 nM) significantly increased the expression of leptin receptor (ObR) in the M2 macrophages (P < 0.01) and stimulated interleukin (IL)-8 expression in the M2 macrophages, mouse macrophage cells RAW264.7, and primary mouse peritoneal macrophages in a dose- and time-dependent manner. Leptin-induced IL-8 production was sensitive to the ERK inhibitor PD980590 (10 μmol/L), p38 MAPK inhibitor SB203580 (20 μmol/L), and anti-ObR neutralizing antibody (4 μg/mL). Leptin (100 ng/mL) substantially increased the phosphorylation of p38 and ERK1/2. Thus, leptin may induce IL-8 production in M2 macrophages by interacting with ObR to activate the p38 and ERK signaling pathways. Scratch and transwell chamber assay showed that both recombinant IL-8 and leptin-induced M2 macrophage-derived IL-8 promoted the migration and invasion of human breast cancer cells MCF7 and MDA-MB-231 (All P < 0.01). In a nude mice xenograft model of breast cancer (n = 5 per group), injection of leptin (0.1 μg/g) dramatically increased tumor volume and mass, reduced survival, exacerbated pulmonary metastasis, and elevated IL-8 and Ki67 expression in the tumor tissue (All P < 0.05) compared with PBS injection. Depletion of mouse macrophage by Clophosome®-clodronate liposome and injection of anti-mouse IL-8 neutralizing antibodies in the xenograft tumor significantly attenuated those leptin-mediated stimulations (All P < 0.05). These findings indicate that leptin may promote tumor growth and metastasis by stimulating IL-8 production in tumor-associated macrophage.
Keywords: IL-8; breast cancer; invasion; leptin; migration.