Matrilysin (MMP-7, EC 3.4.24.23) is the smallest member o f the matrix metalloproteinase (MMP) family and has been shown to be overexpressed in various tumours including breast and colon cancers. Matrilysin has also been shown to play an important role in several aspects of tumour biology including growth, progression, invasion and metastasis. With respect to colon cancer, matrilysin is unique in that it is the only MMP expressed exclusively by the malignant epithelia o f colonic adenocarcinomas. These facts combine to make matrilysin a promising therapeutic target. However, in order to develop drugs which specifically inhibit matrilysin it is important to understand how matrilysin gene expression is controlled, something which to date remains poorly understood. We have examined a panel of human colon tumour cell lines and have shown that matrilysin expression can be upregulated by a number of cytokines including EGF, IL-6 and bFGF. Analysis of the matrilysin promoter revealed the presence of a number of potential transcription factor binding sites including three ETS sites. We have shown that EGF treatment increased matrilysin gene expression by activation of PEA3 transcription factors using artificial promoter, western blot and EMSA analysis. ‘Supershift’ EMSA analysis showed that other PEA3 subfamily members such as ERM and ER81 may also be involved which is in agreement with other studies. In addition, we have found that EGF increased cellular levels o f [3-catenin through destabilisation of the E-cadherin/catenin complex which resulted in increased binding to the T c f site within the matrilysin promoter. We also examined the expression and regulation of matrilysin in the K562 and HL-60 myeloid leukaemia cell lines. Results showed that only the K562 cell line expressed matrilysin and in vitro invasion assays showed that the K562 cells were up to 4 times more invasive than the HL- 60 cell line. Matrilysin antibody blocking experiments showed a significant decrease in invasion in the K562 cell line suggesting a role for matrilysin in leukaemia invasion. The MMP and TIMP profiles o f these cell lines were also examined. Our data suggests that EGF plays an important role in the regulation of matrilysin gene expression via a number of new mechanisms. Furthermore, we have shown that matrilysin plays an important role in leukaemia cell line invasion. These findings have identified possible new drug targets that will inhibit matrilysin expression which in turn should lead to decreased tumourigenesis and invasion and metastasis.