POU5F1 and melanoma: By real-time PCR analysis, we observed a tendence of stem-related genes, that were found up-regulated in acid-adapted melanoma cells, to come back near to the control level, in particular SOX2 and Nanog in both A375M6 and M21 cells, OCT4 in only M21 cell line; on the contrary, KFL4 was not only maintained at high level as acid-adapted cells but was even increased in both pH 7.4R cell lines (Fig. 3b).