Requirement of matrix metalloproteinase-9 for the transformation of human mammary epithelial cells by Stat3-C

Persistently activated Stat3 is found in many different cancers, including ≈60% of breast tumors. Here, we demonstrate that a constitutively activated Stat3 transforms immortalized human mammary epithelial cells and that this oncogenic event requires the activity of matrix metalloproteinase-9 (MMP-9). By immunohistochemical analysis, we observe a positive correlation between strong MMP-9 expression and tyrosine phosphorylated Stat3 in primary breast cancer specimens. These results demonstrate a relationship between activated Stat3 and MMP-9 in breast oncogenesis.