269 - Nitric Oxide Activates the PI3Kinase-Akt Pathway in Human Melanoma Cells

Abstract

Melanoma is the most deadly form of skin cancer in the US, where the incidence rate is increasing faster than any other cancer. Growing evidence suggests that activation of the phosphatidylinositol 3-kinase (PI3K)-Akt pathway plays a significant role in melanoma tumorigenesis and progression. Our previous report presented the protein expression of nitric oxide synthase (NOS), particularly the isoform of iNOS, in proximately 60% of advanced melanoma patients’ tumor cells, and its presence significantly associated with poor prognosis. In this present study, we investigated the role of nitric oxide (NO) in PI3K-Akt pathway activation in human melanoma cells, using both conditions of extracellular NO donor exposure as well as intracellular iNOS expression. Three consistent assay results showed that multiple concentrations and time points of NO exposure activates the PI3K-Akt pathway as determined by Akt Ser 473 phosphorylation, Akt kinase activity, and Akt signaling network targets in a phosphorylation-array scan. Concurrently, biotin-switch assay was employed to test for NO-dependent post-translational modifications, and revealed that the tumor suppressor and major PI3K negative regulator, PTEN, was S-nitrosated. Post-translational modification of PTEN attenuates its phosphatase activity and is likely to contribute to the unregulated Akt pathway activation. Our findings have provided one mechanistic insight into the multifaceted role of NO supporting the growth and survival of human melanoma.