hPTTG1-induced SASP promotes the metastasis of MCF-7 cells. (A) Migration and invasion assays in the representative cell mixtures. Images show the migrating and invading fluorescent MCF-7 cells (MCF-7ZsGreen) in polycarbonate membrane filters (left panel). Original magnification, ×200. Scale bars, 100 μm. Right panels: Quantitative results of the migrating and invading cells. The results are presented as mean ± SEM (n = 3). **P < 0.01. (B) Tumor weights were measured 14 weeks after orthotopic implantation of representative cell mixtures. The representative tumors are shown in the left upper panel (a, b). The tumor sections were observed with fluorescence microscopy (c, d). Original magnification, ×200. Scale bars, 100 μm. Right panel: Quantitative results of the tumor weight (n = 6). The results are presented as the mean ± SEM. **P < 0.001. (C) Left upper panel: Images of murine lungs 14 weeks after orthotopic implantation of representative cell mixtures (a-c). Left middle panel: Lung nodules observed with fluorescence microscopy (d-f). Original magnification, ×200. Scale bars, 100 μm. Left lower panel: H&E stain of lungs from mice bearing the indicated tumors; arrows indicate metastatic foci. Original magnification, ×400. Scale bars, 25 μm. Right panel: Quantitative results of the lung metastasis of representative cells (n = 6 per group). Data are presented as the mean ± SEM. (D) Representative tumors were embedded in paraffin and sectioned for IHC analysis of representative proteins. (E) Schematic representation of the role of the hPTTG1/CXCR2 axis in breast cancer development.