Matrix metalloproteinases in human melanoma cell lines and xenografts: increased expression of activated matrix metalloproteinase-2 (MMP-2) correlates with melanoma progression

Matrix metalloproteinases (MMPs) and their tissue inhibitors (TIMPs) are in volved in tumour progression and metastasis. In this study, we investigated the in vitro and in vivo expression patterns of MMP-1, MMP-2, MMP-3, NMP-9 , TIMP-1 and TIMP-2 mRNA and protein in a previously described human melano ma xenograft model. This model consists of eight human melanoma cell lines with different metastatic behaviour after subcutaneous (s.c.) injection int o nude mice. MMP-1 mRNA was detectable in all cell lines by reverse transcr iption polymerase chain reaction (RT-PCR), but the expression was too low t o be detected by Northern blot analysis. No MMP-1 protein could be found us ing Western blotting. MMP-2 mRNA and protein were present in all cell lines , with the highest expression of both latent and active MMP-2 in the highes t metastatic cell lines MV3 and BLM. MMP-3 mRNA was expressed in MV3 and BL M, and in the non-metastatic cell line 530, whereas MMP-3 protein was detec table only in MV3 and BLM. None of the melanoma cell lines expressed MMP-9. TIMP-1 and TIMP-2 mRNA and protein, finally, were present in all cell line s. A correlation between TIMP expression level and metastatic capacity of c ell lines, however, was lacking. MMP and TIMP mRNA and protein expression l evels were also studied in s.c. xenograft lesions derived from a selection of these cell lines. RT-PGR analysis revealed that MMP-1 mRNA was present i n MV3 and BLM xenografts, and to a lesser extent in 530. Positive staining for MMP-1 protein was found in xenograft lesions derived from both low and high metastatic cell lines, indicating an in vivo up-regulation of MMP-1. M MP-2 mRNA was detectable only in xenografts derived from the highly metasta tic cell lines 1F6m, MV3 and BLM. In agreement with the in vitro results, t he highest levels of both latent and activated MMP-2 protein were observed in MV3 and BLM xenografts. With the exception of MMP-9 mRNA expression in 5 30 xenografts, MMP-3, MMP-9, and TIMP-1 mRNA and protein were not detectabl e in any xenograft, indicating a down-regulated expression of MMP-3 and TIM P-1 in vivo. TIMP-2 mRNA and protein were present in all xenografts; intere stingly, the strongest immunoreactivity of tumour cells was found at the bo rder of necrotic areas. Our study demonstrates that of all tested component s of the matrix metalloproteinase system, only expression of activated MMP- 2 correlates with increased malignancy in our melanoma xenograft model, cor roborating an important role of MMP-2 in human melanoma invasion and metast asis. (C) 1999 Cancer Research Campaign.