MMP-9 secretion and MMP-2 activation distinguish invasive and metastatic sublines of a mouse mammary carcinoma system showing epithelial-mesenchymal transition traits

We have investigated the gelatinase profiles and invasiveness of clonal tum our sublines derived from a spontaneously arising mammary tumour in a Balb/ cfC3H mouse. The 67NR, 66cl4 and 4T1.2 sublines have low, intermediate and high metastatic potential respectively. In Boyden chamber studies, Matrigel invasion was seen to be progressively higher in the more metastatic lines 4T1.2 > 66cl4 > 67NR, consistent with MMP-2 activation potential, MMP-9 sec retion, and migration over either type I or IV collagen, which were low in both 67NR and 66cl4 cells compared to 4T1.2 cells. These attributes are con sistent with those seen in human breast cancer cell lines which appear to h ave undergone an epithelial-mesenchymal transition (EMT) as indicated by vi mentin expression. We were, however, surprised to find vimentin expression, MT1-MMP expression and stellate Matrigel outgrowth in the non-invasive, no n-metastatic 67NR cells, indicating that they had undergone an EMT despite not being invasive. We conclude that the EMT is manifested to differing deg rees in these three clonal cell lines, and that the 67NR cells have either undergone a partial EMT or have since lost certain important attributes of the EMT-derived phenotype. This model should prove useful in further charac terizing the regulation of MT1-MMP mediated MMP-2 activation and delineatin g the EMT in breast cancer progression.