PDF file - 252K, S1. miR-155 expression in spleen of WT and miR-155-/- chimeric mice. S2. Effects on bone marrow miR-155 deficiency on bone marrow cell mobilization in tumor-bearing mice. S3. The effects of bone marrow miR-155 deficiency on the leukocyte subpopulations in spleen of tumor-bearing mice. S4. The effects on bone marrow miR-155 deficiency on the expression of tumor-derived factors. S5. A, Expression level of miR-155 in LLC and B16-F10 cells. Quantitative real-time PCR was performed to measure the expression of miR-155 in the lung tissue of WT mice, and cultured LLC and B16-F10 cells. Data are presented as the mean plus-minus SEM of three replicates. **, p<0.001 by Student's t test. B. Quantitative real-time PCR analysis of miR-155 levels in WT macrophages incubated with serum-free medium (SFM), LLC cell conditioned medium (LLC-CM) and B16-F10 cell conditioned medium (B16-CM) for 24 h. Data are presented as the mean plus-minus SEM of three replicates. S6. miR-155 deficiency MΦ promoted migration of B16-F10 cells.
ARTICLE ABSTRACT
Infiltration of immune cells in primary tumors and metastatic sites is known to influence tumor progression and metastasis. Macrophages represent the most abundant immune cells in the tumor microenvironment, and evidence has shown that macrophages promote seeding, extravasation, and persistent growth of tumor cells at metastatic sites. miR-155 plays an essential role in immune cell development/function, and its aberrant expression is associated with lymphomas and several solid tumor types. However, it is unknown how miR-155 expression in immune cells affects solid tumor growth and metastasis. To this end, bone marrow transplantation was performed using miR-155–deficient mice as bone marrow donors and wild-type (WT) mice as recipients, and the chimeric mice were inoculated with tumor cells. We demonstrate that bone marrow lacking miR-155 significantly enhanced lung metastasis without a substantial effect on primary tumor growth. Relative to mice with WT bone marrow, miR-155–deficient bone marrow accumulated more macrophages in the spleen and lungs. Further analysis revealed that miR-155–deficient macrophages in metastatic sites exhibited a tumor-promoting M2 phenotype. In vitro study suggested that miR-155–null macrophages were prone to M2 polarization upon incubation with tumor cell–conditioned medium, due to elevated expression of C/EBPβ, an identified miR-155 target. These data, for the first time, demonstrate that miR-155 in host immune cells plays a vital role in modulating solid tumor metastasis by affecting the recruitment and polarization of bone marrow–derived macrophages.Implications: Targeted inhibition of miR-155 delays tumor development but inhibition in host immune cells may encourage metastasis. Mol Cancer Res; 11(8); 923–36. ©2013 AACR.
