Overexpression of Merlin in B16F10 mouse melanoma cells reduces their metastatic activity: role of the cell surface heparan sulfate glycosaminoglycans.

Merlin, the protein product of the neurofibromatosis type 2 gene (NF2) acts as a tumor suppressor in mice and humans. In this study, melanoma B16F10 cells were engineered to overexpress the NF2 gene by establishing stable transductants. A cell line overexpressing Merlin (B16F10-M) was generated. When compared to the parental cells, the B16F10-M cells demonstrated differences in their cell surface organization. The overexpressing strain changed its ability to grow in soft agar as well as its cell motility properties. B16F10-M cells were then examined in the in vivo mouse melanoma tumor growth and tumor metastasis models. While tumor growth was marginally affected, the presence of increased Merlin severely reduced the metastastatic ability of the cells. When isolated using specific enzymes with distinct substrate specificity, the cell surface heparan sulfate glycosaminoglycans (HSGAGs) from the overexpressing B16F10-M cells, inhibited the metastatic properties of the parental B16F10 cells. The results obtained provide a causal link between the reorganization/changes to the cell surface HSGAGs by the overexpression of Merlin and the inhibition of the metastatic activity of the mouse melanoma B16F10 cells in vivo.

Genetically engineered mouse melanoma and mouse Lewis lung carcinoma models.

Melanoma B16-F10 cells and Lewis lung carcinoma LL/2 cells were engineered with a bacterial gene -- chloramphenicol acetyl transferase (CAT) -- by establishing stable transductants. Expression of CAT in both cell types did not alter the ability of these cells to grow into tumors when injected subcutaneously into mice. In addition, the measurement of CAT levels in the lung using a simple ELISA assay revealed a close correlation with direct counting of metastatic nodules. Thus, the CAT-expressing cells will likely have wide ranging applications to quantify tumor metastasis especially in situations where visual counting is difficult. The availability of genetically labeled mouse B16-F10 melanoma and Lewis lung carcinoma cell lines will facilitate future studies of the mechanism and progression of cancer and the discovery of new therapies.