Rhabdomyosarcoma (RMS) is a malignant tumour of skeletal muscle origin which includes two major histological subtypes: alveolar rhabdomyosarcoma (ARMS), the more aggressive, and embryonal rhabdomyosarcoma (ERMS). In order to establish whether the higher metastatic potential of ARMS cells may depend on differential expression of specific matrix metalloproteinases (MMPs) and angiogenesis-related factors, we studied the expression of MMP-2, MT1-MMP, TIMP-2, VEGF and VEGF receptors in four ARMS (RH30, RH4, RH18, RH28), three ERMS (RD, RH36, SMS-CTR) and one undifferentiated sarcoma cell line (A204). Semi-quantitative analysis of MMP-2 revealed high levels of expression in 3 out of 4 ARMS cell lines whereas, among ERMS, only RH36 showed comparable levels of the protease. TIMP-2 and MT1-MMP showed no significant differences among cell lines. in vitro invasiveness was also evaluated. The MMP-2-overexpressing RH30 cells were more invasive than RD cells, which expressed low levels of MMP-2. Exogenous expression of the ARMS specific PAX3-FKHR chimeric protein in RD cells increased MMP-2 activity and invasiveness. Of the three main VEGF isoforms only VEGF165 and VEGF121 were detected in RMS lines: ARMS expressed both isoforms, whereas the ERMS cell line SMS-CTR and the undifferentiated sarcoma cell line A204 showed the VEGF121 isoform only. All RMS cell lines expressed VEGFR-1 at mRNA as well as at protein level. The VEGFR-2, on the contrary, was undetectable with the sole exception of the RH28 cell line. Overall, our data suggest that a high level of MMP-2 protein and VEGF/VEGFR expression may contribute to the metastatic phenotype of ARMS cells and that exogenously induced PAX3-FKHR expression increases MMP-2 secretion and invasive capability of RMS cells.

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