MMP13 and breast cancer: In conclusion, the present study showed that Osx promotes bone metastasis of breast cancers by: (1) upregulating MMP9, a molecule associated with invasion; (2) upregulating VEGF, a regulator for angiogenesis; and (3) upregulating IL-8, PTHrP, and MMP13, inducers of osteoclast activity (Fig. 5f).