Title: Ultraviolet-induced phosphorylation of p70(S6K) at Thr(389) and Thr(421)/Ser(424) involves hydrogen peroxide and mammalian target of rapamycin but not Akt and atypical protein kinase C.
Authors: Huang, Chuanshu; Li, Jingxia; Ke, Qingdong; Leonard, Stephen S; Jiang, Bing-Hua; Zhong, Xiao-Song; Costa, Max; Castranova, Vincent; Shi, Xianglin
Published In Cancer Res, (2002 Oct 15)
Abstract: The p70 S6 kinase (p70(S6k)) is a Ser/Thr kinase that plays an important role in cell growth, transformation, and the transition of the cell cycle in mammalian cells. Because UV radiation has been reported to induce activation of p70(S6k), which is believed to play some role in the carcinogenic effects of sun exposure, the present study investigated the signaling pathways involved in this activation induced by UV radiation in mouse epidermal JB6 Cl41 cells. Exposure of cells to UV radiation led to marked increases in p70(S6k) activity and phosphorylation at Thr(389) and Thr(421)/Ser(424). UV radiation also generated reactive oxygen species as measured by electron spin resonance and by H(2)O(2) and O( minus sign, dot below )(2) fluorescence staining assays in JB6 Cl 41 cells. The scavenging of UV-generated H(2)O(2) by N-acety-L-cyteine (a general antioxidant) or catalase (a specific H(2)O(2) scavenger) inhibited p70(S6k) phosphorylation at Thr(389) and Thr(421)/Ser(424), whereas pretreatment of cells with sodium formate (an.OH radical scavenger) or superoxide dismutase (an O( minus sign, dot below )(2) radical scavenger) did not show any inhibitory effects. Importantly, UV-induced increases in p70(S6k) phosphorylation at Thr(389) and Thr(421)/Ser(424) were dramatically inhibited by pretreatment of cells with rapamycin, LY294002, or PD98059, whereas overexpression of dominant-negative mutants of PKClambda/iota and Akt1 did not inhibit p70(S6k) phosphorylation at Thr(389) and Thr(421)/Ser(424). These results demonstrated that H(2)O(2), phosphatidylinositol 3-kinase, and mammalian target of rapamycin were important players for UV-induced p70(S6k) phosphorylation at Thr(389) and Thr(421)/Ser(424), whereas Akt and atypical protein kinase C were not involved in this activation. The role of H(2)O(2) in p70(S6k) phosphorylation at Thr(389) and Thr(421)/Ser(424) was further supported by the findings that treatment of cells with H(2)O(2) also caused p70(S6k) phosphorylation at Thr(389) and Thr(421)/Ser(424).
PubMed ID: 12384526
MeSH Terms: Animals; Cells, Cultured; Electron Spin Resonance Spectroscopy; Enzyme Induction/radiation effects; Hydrogen Peroxide/metabolism*; Mice; Phosphorylation/radiation effects; Protein Kinase C/metabolism*; Protein Kinases/metabolism*; Protein-Serine-Threonine Kinases*; Proto-Oncogene Proteins c-akt; Proto-Oncogene Proteins/metabolism*; Reactive Oxygen Species/metabolism; Ribosomal Protein S6 Kinases, 70-kDa/biosynthesis; Ribosomal Protein S6 Kinases, 70-kDa/metabolism*; Serine/metabolism; Signal Transduction/radiation effects; Skin/cytology; Skin/metabolism; Skin/radiation effects; TOR Serine-Threonine Kinases; Threonine/metabolism; Ultraviolet Rays