Stromelysin-1 (MMP-3) is a target and a regulator of Wnt1-induced epithelial-mesenchymal transition (EMT).

Matrix metalloproteinases (MMPs) play a well-defined role in later stages of tumor progression. However, there has been evidence that they also contribute to earlier stages of malignant transformation. The Wnt signaling transduction pathway plays a critical role in development and in the pathogenesis of many epithelial cancers. Here we have used Wnt1-induced epithelial-mesenchymal transition (EMT) in C57MG murine mammary epithelial cells to study the role of MMPs in this early step of malignant progression. Overexpression of Wnt1 in C57MG cells promoted EMT, the translocation of ß-catenin from the cell membrane to the nucleus and its transcriptional activity, cell proliferation and cell motility. Simultaneously, we observed an increased expression of stromelysin-1 (MMP-3) and a 5.5-fold increase in MMP-3 promoter activity in C57MG cells expressing Wnt1 compared with C57MG cells. Treatment of Wnt-overexpressing cells with MMP inhibitor AG3340 decreased MMP-3 expression. We also found evidence that MMP-3 and Wnt3a cooperate in enhancing the transcriptional activity of ß-catenin in C57MG cells. Consistently, the effects of Wnt1 on EMT, proliferation and migration were inhibited by MMP inhibitors, or upon downregulation of MMP-3 by siRNA. These results suggest that MMP-3 is both a direct transcriptional target and a necessary contributor of the Wnt/ß-catenin signaling pathway.

Matrix metalloproteinases play an active role in Wnt1-induced mammary tumorigenesis.

The Wnt signaling transduction pathway plays a critical role in the pathogenesis of several murine and human epithelial cancers. Here, we have used mouse mammary tumor virus (MMTV)-Wnt1 transgenic mice, which develop spontaneous mammary adenocarcinoma, to examine whether matrix metalloproteinases (MMPs)--a family of extracellular proteases implicated in multiple steps of cancer progression--contributed to Wnt1-induced tumorigenesis. An analysis of the expression of several MMPs by RT-PCR and in situ hybridization revealed an increase in the expression of MMP-2, MMP-3, MMP-9, MMP-13, and MT1-MMP (MMP-14) in hyperplastic glands and in mammary tumors of MMTV-Wnt1 transgenic mice. Interestingly, whereas MMP-2, MMP-3, and MMP-9 were exclusively expressed by stromal cells in mammary tumors, MMP-13 and MT1-MMP were expressed by transformed epithelial cells in addition to the tumor stroma. To determine whether these MMPs contributed to tumorigenesis, MMTV-Wnt1 mice were crossed with transgenic mice overexpressing tissue inhibitor of metalloproteinase-2-a natural MMP inhibitor-in the mammary gland. In the double MMTV-Wnt1/tissue inhibitor of metalloproteinases-2 transgenic mice, we observed an increase in tumor latency and a 26.3% reduction in tumor formation. Furthermore, these tumors grew at a slower rate, exhibited an 18% decrease in proliferative rate, and a 12.2% increase in apoptotic rate of the tumor cells in association with a deficit in angiogenesis when compared with tumors from MMTV-Wnt1 mice. Thus, for the first time, the data provides evidence for the active role of MMPs in Wnt1-induced mammary tumorigenesis.