Figure 6. Suppression of TrkB expression inhibited metastasis from the mammary gland to the lung.

A, B. Tumor formation by MDA-MB-231 control-shRNA or MDA-MB-231 TrkB-shRNA cells. 1.0 × 10⁵ cells were implanted in the mammary fat pads of mice (n = 7 mice/group). A P < 0.0001 was considered to indicate significance for ANOVA. C. Lung metastasis by MDA-MB-231 control-shRNA or MDA-MB-231 TrkB-shRNA cells. The total numbers of lung metastatic nodules in each mouse in each group were counted using a dissection scope (n = 6 mice/group). A P < 0.0001 was considered to indicate significance for ANOVA. D. Representative images of lungs from mice harboring MDA-MB-231 control-shRNA or TrkB-shRNA cell mammary tumors for 30 days after implantation of tail veins of mice. E. Representative H&E staining in sections of the lungs from Figure 6D. N, Normal lung tissue; M, metastatic nodule. F, G. Western blot analysis (F) and quantitative RT-PCR (G) of TrkB, and Twist-1 in tumor cells recovered from the lungs of individual mice expressing either MDA-MB-231 control-shRNA or MDA-MB-231 TrkB-shRNA. Tubulin and 18S mRNA were used as loading controls. H. Representative immunohistochemical images of Twist-1 staining in sections of the lungs from individual mice expressing either MDA-MB-231 control-shRNA or MDA-MB-231 TrkB-shRNA (magnification: 200×). I. The expression levels of the mRNA encoding Twist-1 and Twist-2 in tumor cells recovered from the lungs of individual mice expressing either MDA-MB-231 control-shRNA or TrkB-shRNA cells.