CIRCULATING AND TISSUE FORMS OF MMP2 AND MMP9 IN BREAST CANCER PROGRESSION

Abstract

Tumor progression and metastasis represent the leading causes of cancer related death. One of the major features that may contribute to neoplastic cell dissemination is the progressive and local degradation of the extracellular matrix (ECM) surrounding the primary tumour. Degradation of the ECM requires the coordinated action of a number of enzymes produced locally by neoplastic cells and/or stromal cells. Five categories of proteinases have been implicated in the invasive process: serine, cysteine, aspartic, threonine proteinases and matrix metalloproteinases (MMPs), also known as matrixins, which play a key role as terminal effectors of the proteolytic cascade. At present 23 members of the matrixin family have been found in humans and classified into subsets of enzymes, according to their molecular domains and preference for the substrates. Since the classic work of Liotta and collaborators [1], much attention has been focused on MMP-2 and MMP-9 because of their ability to degrade type IV collagen, a major constituent of basement membranes. MMP-9 and MMP-2 are secreted by cells as zymogens; both enzymes are activated, by the cleavage of their amino-terminal pro-domains, through distinct pathways operating at the cell-matrix boundary [2]. Tissue detection of MMPs has suggested that augmented secretion and proteolytic activation of MMPs is often associated with tumor metastasis. Several authors have also detected incremented levels of circulating forms MMP-2 and MMP-9 in oncologic patients [3-6]. However, their clinical applications remain controversial. To confirm and extend our previous observations, in this study we analyzed the circulating forms of MMP-9 and MMP-2 in serum samples of 56 selected breast carcinoma patients, in comparison with the enzymatic activities present in tissue extracts from surgical fragments (primary tumor and its paired healthy tissues) of same patients. The activity levels of MMP-2 and MMP-9 were detected by gelatin zymography and quantified by ImageQuant TL. Two bands of activity, corresponding to the proforms of MMP-9 and MMP-2, were detected in the serum samples and tissue extracts of all oncologic patients, but with highly variable levels of intensity. In general the intensity of lytic bands was higher in serum than in the tissue extracts. In addition, most serum samples, and some of the tissue extracts, displayed additional proteolytic bands at higher Mw, corresponding likely to complexed forms of MMP-9 [5]. As previously reported for a pilot number of cases, lytic bands corresponding the activated forms of the two gelatinases were uniquely present in the tumor extracts, and absent in the paired normal tissues, thus confirming the hypothesis that activation of the enzymes is a key step during the invasive growth of the tumor. In order to assess the possible association between MMPs activities and other proteins potentially involved in tumor progression, we correlated the activity levels of both MMPs with the proteomic-based expression levels of the S100 protein members. One of the reasons of interest for this family of proteins is because there is increasing evidence that S100 proteins are often up-regulated in many cancers, including breast cancer, and this is frequently associated with tumour progression. Interestingly we have observed a correlation between the gelatinase activity levels and expression levels of some S100 proteins. In conclusion, our results, which show higher variability of MMP-9 levels suggest its usefulness as a marker evaluable both in the follow-up and in the prognosis of breast cancer patients.