Matrix metalloproteinase 8 reduces the invasive, tumorigenic and metastatic potential of breast cancer cells Free

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Knowledge of the molecular mechanisms involved in metastatic spread is needed to facilitate advances in prognostic evaluation for individual patients and in the design of therapeutic interventions to inhibit the process. We have previously characterized an experimental system in which the role of candidate metastasis-related genes can be screened and tested. Monoclonal cell lines M4A4 and NM2C5 are spontaneously occurring sublines of the MDA-MB-435 cell breast tumor cell line that exhibit phenotypic differences in growth, invasion, and metastatic efficiency in athymic mice. We have previously reported the overexpression of matrix metalloproteinase 8 (MMP8) in the non-metastatic cell line NM2C5 with respect to its expression in the metastatic M4A4 cell line and that the reduction of MMP8 expression by antisense methodology resulted in increased invasiveness in NM2C5 cells. In the present study the effect of overexpression of different alternatively spliced MMP8 isoforms in the metastatic M4A4 cell line was investigated. In addition to the 467 amino acid (aa) standard MMP8 isoform, at least two other variant forms are expressed in various cell lines. The first variant (444 aa) is characterized by an absence of the signal peptide as a result of the use of a different translation initiation codon. The second MMP 8 variant (368 aa) is the result of a deletion in exon 8 which introduces a frame shift and the truncation of the C-terminus hemopexin domain. The metastatic potential of M4A4 cells engineered to overexpress the standard MMP8 and these variant isoforms was found to be considerably reduced (p<0.05) when compared with the same cells transduced with the respective vector only controls after orthotopic implantation in athymic mice. In addition, the invasive and tumorigenic capabilities of these engineered M4A4 cells were reduced as a result of the expression of the MMP8 variants. Our results are in agreement with the protective role conferred by MMP8 in cancer reported by Balbin et al. in MMP8 deficient mice and open new avenues for the study of the mechanisms through which MMP8 isoforms influence the biological activities of their substrates. This study also underscores the need of specific anti-MMP therapeutic approaches in cancer.