Article

Eriodictyol inhibits RSK2-ATF1 signaling and suppresses EGF-induced neoplastic cell transformation.

Hormel Institute, University of Minnesota, Austin, Minnesota 55912, USA.
Journal of Biological Chemistry (Impact Factor: 4.6). 01/2011; 286(3):2057-66. DOI: 10.1074/jbc.M110.147306
Source: PubMed

ABSTRACT RSK2 is a widely expressed serine/threonine kinase, and its activation enhances cell proliferation. Here, we report that ATF1 is a novel substrate of RSK2 and that RSK2-ATF1 signaling plays an important role in EGF-induced neoplastic cell transformation. RSK2 phosphorylated ATF1 at Ser-63 and enhanced ATF1 transcriptional activity. Docking experiments using the crystal structure of the RSK2 N-terminal kinase domain combined with in vitro pulldown assays demonstrated that eriodictyol, a flavanone found in fruits, bound with the N-terminal kinase domain of RSK2 to inhibit RSK2 N-terminal kinase activity. In cells, eriodictyol inhibited phosphorylation of ATF1 but had no effect on the phosphorylation of RSK, MEK1/2, ERK1/2, p38 or JNKs, indicating that eriodictyol specifically suppresses RSK2 signaling. Furthermore, eriodictyol inhibited RSK2-mediated ATF1 transactivation and tumor promoter-induced transformation of JB6 Cl41 cells. Eriodictyol or knockdown of RSK2 or ATF1 also suppressed Ras-mediated focus formation. Overall, these results indicate that RSK2-ATF1 signaling plays an important role in neoplastic cell transformation and that eriodictyol is a novel natural compound for suppressing RSK2 kinase activity.

0 Followers
 · 
121 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: Solar ultraviolet (SUV) irradiation is a major factor in skin carcinogenesis, the most common form of cancer in the USA. The mitogen-activated protein (MAP) kinase cascades are activated by SUV irradiation. The 90 kDa ribosomal S6 kinase (RSK) and mitogen and stress activated protein kinase (MSK) proteins constitute a family of protein kinases that mediate signal transduction downstream of the MAP kinase cascades. In this study, phosphorylation of RSK and MSK1 was up-regulated in human squamous cell carcinoma (SCC) and solar UV-treated mouse skin. Kaempferol, a natural flavonol, found in tea, broccoli, grapes, apples and other plant sources, is known to have anticancer activity, but its mechanisms and direct target(s) in cancer chemoprevention are unclear. Kinase array results revealed that kaempferol inhibited RSK2 and MSK1. Pull-down assay results, ATP competition and in vitro kinase assay data revealed that kaempferol interacts with RSK2 and MSK1 at the ATP-binding pocket and inhibits their respective kinase activities. Mechanistic investigations showed that kaempferol suppresses RSK2 and MSK1 kinase activities to attenuate solar UV-induced phosphorylation of CREB and histone H3 in mouse skin cells. Kaempferol was a potent inhibitor of solar UV-induced mouse skin carcinogenesis. Further analysis showed that skin from the kaempferol-treated group exhibited a substantial reduction in solar UV-induced phosphorylation of cAMP response element-binding protein (CREB), c-Fos and histone H3. Overall, our results identify kaempferol as a safe and novel chemopreventive agent against solar UV-induced skin carcinogenesis that acts by targeting RSK2 and MSK1.
    Cancer Prevention Research 07/2014; 7(9). DOI:10.1158/1940-6207.CAPR-14-0126 · 5.27 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Extracellular stimulation of cells with growth factors such as epidermal growth factor (EGF) induces cell proliferation and cell transformation. Although fibroblast growth factor (FGF) is a well-known family member of growth factors and acts as a ligand of FGF receptor (FGFR), a receptor tyrosine kinase, in cytoplasmic membrane, the tumor promoter potential of FGF has not been clearly understood.
  • [Show abstract] [Hide abstract]
    ABSTRACT: Our previous studies demonstrated that RSK2 plays a key role in cell proliferation and transformation induced by tumor promoters such as epidermal growth factor (EGF) in mouse and human skin cells. However, no direct evidence has been found regarding the relationship of RSK2 and cell survival. In this study, we found that RSK2 interacted and phosphorylated GSK3β at Ser9. Notably, GSK3β phosphorylation at Ser9 was suppressed in RSK2(-/-) MEFs compared with RSK2(+/+) MEFs by stimulation of EGF and calcium ionophore A23187, a cellular calcium stressor. In proliferation, we found that RSK2 deficiency suppressed cell proliferation compared with RSK2(+/+) MEFs. In contrast, GSK3β(-/-) MEFs induced the cell proliferation compared with GSK3β(+/+) MEFs. Importantly, RSK2(-/-) MEFs were induced severe cellular morphology change by A23187 and enhanced G1/G0 and sub-G1 accumulation of the cell cycle phase compared with RSK2(+/+) MEFs. The sub-G1 induction in RSK2(-/-) MEFs by A23187 was correlated with increase of cytochrome c release, caspase-3 cleavage and apoptotic DNA fragmentation compared with RSK2(+/+) MEFs. Notably, return back of RSK2 into RSK2(-/-) MEFs restored A23187-induced morphological change, and decreased apoptosis, apoptotic DNA fragmentation and caspase-3 induction compared with RSK2(-/-)/mock MEFs. Taken together, our results demonstrated that RSK2 plays an important role in stress-tolerance and cell survival, resulting in cell proliferation and cancer development.
    Biochemical and Biophysical Research Communications 09/2013; DOI:10.1016/j.bbrc.2013.09.042 · 2.28 Impact Factor