Effect of HPV-16 E5 expression on the proliferation, cell viability and on cell specific metabolic activity of M14 and FRM melanoma cells. Cell proliferation (upper row) was slightly decreased in E5 expressing cells (empty symbols) as compared with control cells (full symbols). The cell viability of E5 expressing cells and control cells is shown in the middle row. The cell specific activity of E5 expressing cells (lower row) was higher than that of control cells. This effect, sharply evident in FRM cells appeared slighter in M14 and indicates an increased oxidative metabolism in E5 expressing cells. Values are the mean ± S.D. of eight independent replicas and are derived from a representative experiment in a set of four. Statistical comparison of E5 expressing cells was made using either parametric (Student's t-test) or non paramentric (Mann – Whitney test) according to the results of the Shapiro – Wilk assay. (* = p < 0.05; ** = p < 0.005). The specific metabolic activities are calculated as the simple cell viability/cell proliferation ratio (MTT/CV ratio) and are expressed in arbitrary units as the mean of four different experiments ± SD.