Abstract. Matrix metalloproteinases (MMPs) have been well characterized for their ability to degrade extracellular matrix proteins and, thus, they have been studied to elucidate their involvement in both tumor development and progression. In the present study, attention was focused on MMP-15 and MMP-19, two less known members of the MMP family. The expression profile of MMP-15 and -19 was assayed in samples of normal colorectal mucosa, microadenomas and cancer using confocal analysis, western blotting and quantitative reverse transcription polymerase chain reaction (qRT-PCR). Both qRT-PCR and western blotting showed that MMP-15 and MMP-19 appeared to be upregulated during colorectal tumorigenesis, with different expression patterns: MMP-15 expression level increases from normal mucosa to microadenomas, with a reduced level in cancer with respect to microadenomas; the semiquantitative immunofluorescence analysis showed a stromal localization of this protein in the early phases of neoplastic transformation. Increasing amount of MMP-19 mRNA and protein levels were observed in the progression of colonic lesions; MMP-19 staining increased in the normal mucosa-microadenoma-carcinoma sequence. Such different expression patterns, are probably due to the different roles played in colorectal tumorigenesis by these two molecules. Conflicting data on the role of these proteins in tumor progression have been reported, thus, an improved understanding of the biological roles of MMPs, in particular the lesser known members such as MMP-15 and 19, in colorectal cancer may lead to a re-evaluation of the use of MMP inhibitors and suggests the need of integrated translational studies on MMP expression patterns.
IntroductionMatrix metalloproteinases (MMPs) play a sophisticated role in cancer development due to their abilities to degrade various substrates. MMPs are generally classified as pro-angiogenic factors, since they can degrade the extracellular matrix molecules to facilitate tumor cell migration and invasion (1,2). This concept of the role of MMPs in tumor invasion and metastasis is currently undergoing a major reappraisal most notably as a result of the apparent failure of several 'high-profile' clinical trials of MMP inhibitors in cancer (3).MMP-15 is a recently discovered membrane-type MMP which was originally isolated from a human lung cDNA library, and it consists of a 76-kDa product with 73.9% overall similarity to MMP-14 (4,5). Despite the high degree of structural similarity of these two MMPs, differences in substrate specificity (6,7), as well as tissue or cellular localization, have been demonstrated (8). Although MMP-15 is reported to play a similar role to MMP-14 in cell invasion (9), its implication remains to be elucidated; the importance and role of MMP-14 in promoting tumor growth have been extensively investigated (10), in contrast to the role and function of MMP-15 which is just beginning to be addressed. It has been reported involved in the progression of various kinds of cancers, such as breast, cervical, ...