gms | German Medical Science

Objective: Glioblastomas are the most common malignant brain tumors in adults. Despite multidisciplinary treatment including surgery, radiation and chemotherapy, the mean survival time of the patients is very low. This limited prognosis is the result of the very aggressive local growth pattern and the marked degree of invasiveness displayed by these tumors. Tumor invasiveness is facilitated by increased activity of proteolytic enzymes like e.g. matrix metalloproteinases (MMPs), which are involved in destruction of the extracellular matrix of the surrounding normal brain tissue. Several MMPs have been identified to be overexpressed by astrocytic tumors. However, for some MMPs, like MMP1, MMP11 and MMP19, such reports are based on very limited data or data are contradictory. Therefore, we decided to analyse expression patterns of these MMPs in glioblastomas in order to define their role during brain tumor development.

Methods: Expression analysis of MMPs in normal brain and tumor brain samples were performed by semiquantitative RT-PCR, Western-blotting and immunostaining. Total RNA and proteins were isolated from 3 normal brain, 15 low-grade astrocytoma and 15 glioblastoma biopsies. Primers were designed in flanking exons, specific for each transcript. cDNAs were normalized to an equal level of GAPDH. Protein-lysates were used for PAGE, followed by Western-blotting. Immunostaining was carried out using the Histostain Plus Kit (Zytomed, Berlin, Germany) with tissue-tek embedded tumor samples. Primary antibodies recognized both, the pro- and active forms, of MMPs.

Results: By semiquantitative RT-PCR we found increased levels of mRNAs encoding for MMP1, MMP11 and MMP19 in glioblastomas as compared with low-grade astrocytomas and normal brain. Expression of these genes showed high level of diversity between the individual tumor samples. We further examined expression of these genes on protein level by Western-blots and immunohistochemical analysis. These experiments confirmed the above mentioned data.

Conclusions: In the literature, expression of MMP1 in glioblastomas is controversly discussed and for MMP11 and MMP19 there are only limited data available. Our results suggest a role for these three MMPs during brain tumor development, since all three show increased expression on both, mRNA and protein level. Therefore, these three MMPs may be additional targets for therapy.