Mutations of RAS, RAF, and PTEN, all important members of the RAS/MAPK and PI3K/AKT cascades, are reported in a variety of human tumors, including melanomas and endometrial cancer. In endometrial cancer, mutually exclusive mutations of PTEN and KRAS have been reported. On the other hand, mutation of BRAF is highly frequent, and mutually exclusive mutations of BRAF and NRAS have also been reported in melanomas. In this study, we elucidated the involvement of the up-regulation of RAS/MAPK and PI3K/AKT cascades in the pathogenesis of endometrial cancer and melanoma by analyzing the genes and molecules in these cascades. Twelve cell lines, six melanoma and six endometrial cancer, were analyzed; 4 (67%) of the 6 melanomas had gene mutations in the RAS/MAPK cascade, and a decrease or loss of PTEN expression was also observed. These results suggested that simultaneous up-regulations in these two cascades play important roles in carcinogenesis of melanocytes. However, no activation of AKT by phosphorylation was observed. On the other hand, 4 (67%) of the 6 endometrial cancer cell lines had mutually exclusive up-regulations in these cascades. However, two cell lines with up-regulation of the PI3K/AKT cascade also had up-regulation in the RAS/MAPK cascade induced by inactivation of DUSP6. These results suggest that simultaneous up-regulation of RAS/MAPK and PI3K/AKT cascades are crucial events in the pathogenesis of melanocytes, whereas up-regulation of either the RAS/MAPK or PI3K/AKT cascade is crucial for the majority of endometrial cancers.

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