'Proteolytic switching': opposite patterns of regulation of gelatinase B and its inhibitor TIMP-1 during human melanoma progression and consequences of gelatinase B overexpression

Although it is generally accepted that proteolytic degradation is an import ant mechanism used by malignant cells in the process of metastasis, compara tively little is known about the regulation of molecules responsible for pr oteolysis and how they become de-regulated during human tumour progression. Using a genetically related pair of human melanoma cell lines, derived fro m the same patient at different stages of disease, we analysed differences in the cytokine-mediated regulation of gelatinase B (MMP-9), an enzyme thou ght to play an important role in cellular invasiveness, and TIMP-1, a physi ological inhibitor of this enzyme. Whereas the advanced stage (i.e. metasta tic) partner of this pair (WM 239) could produce gelatinase B upon inductio n with interleukin (II)-1 beta or tumour necrosis factor alpha (TNF-alpha), the early stage (i.e. primary) partner (WM 115) could not. In sharp contra st, we found that TIMP-1 displayed an opposite pattern of induction in thes e cell lines. Specifically, the early stage cell line, WM 115, demonstrated a marked increase in the production of TIMP-1 when treated with IL-1 beta or TNF-alpha whereas the advanced cell line, WM 239, showed no such increas e. Treatment with the DNA demethylating agent, 2-deoxy-5-azacytidine, resul ted in a marked up-regulation of both gelatinase B and TIMP-1 in both cell lines. It was further found that constitutive overexpression of gelatinase B in WM 239 cells and an additional melanoma cell line (MeWo), derived from a metastatic lesion, was able to greatly enhance lung colonization in an e xperimental metastasis assay while we did not observe differences in tumori genicity. From these results we conclude that an altered responsiveness of gelatinase B and TIMP-1 to induction by similar agents is associated with d isease progression in human melanoma and that this altered responsiveness c an have consequences to the aggressive nature of the disease.