Tumour malignancy loss and cell differentiation are associated with induction of gef gene in human melanoma cells

Summary Background Gene therapy is a new method used to induce cancer cell differentiation. Our group previously showed that transfection of the gef gene from Escherichia coli, related to cell‐killing functions, may be a novel candidate for cancer gene therapy. Its expression leads to cell cycle arrest unrelated to the triggering of apoptosis in MS‐36 melanoma cells. Objectives To determine the basis of the antiproliferative effect of the gef gene in this cell line. Methods Transmission electron microscopy, apoptosis analysis by confocal microscopy, flow cytometry and immunocytochemical analysis were used. Results Ultrastructural analysis showed a strikingly different morphology after treatment with dexamethasone and expression of the gef gene, with large accumulations of pigment throughout the cell cytoplasm and presence of melanosomes in different stages of development. High mitochondrial turnover and myeloid bodies, characteristics of neurone cells, were also observed. In addition, both immunocytochemical and indirect immunofluorescence analysis demonstrated a significant decrease in HMB‐45, Ki‐67 and CD44 antigen expression and an increase in S100 and p53 expression in gef gene‐transfected MS‐36 melanoma cells that were correlated with the duration of dexamethasone treatment. In the present work, we report that gef gene not only reduces cell proliferation in transfected melanoma MS‐36TG cell line but also induces morphological changes clearly indicative of melanoma cell differentiation and a reduction in tumour malignancy. Conclusions These findings support the hypothesis that the gef gene offers a new approach to differentiation therapy in melanoma.