A regulatory mechanism for RSK2 NH(2)-terminal kinase activity.
Our previous findings indicated that RSK2 plays a critical role in proliferation and cell transformation induced by tumor promoters, such as epidermal growth factor or 12-O-tetradecanoylphorbol-13-acetate, and that kaempferol, a natural compound found in edible plants, selectively inhibits RSK2 activity. However, the molecular mechanism for RSK2 activation is unclear. Herein, we provide evidence showing that NH(2)-terminal kinase domain (NTD) activation of RSK2 is required for the activation of the extracellular signal-regulated kinase-mediated COOH-terminal kinase domain (CTD). We also found that the NTD plays a key role in substrate phosphorylation and that kaempferol binds with the NTD but not the CTD in both the active and inactive forms. Homology modeling of the RSK2 NH(2)-terminal domain and small-molecule docking, validated by mutagenesis experiments, clearly showed that Val(82) and Lys(100) are critical amino acids for kaempferol binding and RSK2 activity. Furthermore, immunohistofluorescence and Western blot results indicated that the RSK2 protein level is markedly higher in cancer cell lines as well as cancer tissues compared with nonmalignant cell lines or normal tissues. In addition, kaempferol inhibited proliferation of malignant human cancer cell lines, including A431, SK-MEL-5 and SK-MEL-28, and HCT-116. These results indicate that targeting RSK2 with natural compounds, such as kaempferol, might be a good strategy for chemopreventive or chemotherapeutic application.
The Hormel Institute, University of Minnesota, Austin, MN 55912, USA.
Yong-Yeon
YY
Cho
Ke
K
Yao
Angelo
A
Pugliese
Margarita L
ML
Malakhova
Ann M
AM
Bode
Zigang
Z
Dong
D001665:Binding Sites; D002455:Cell Division / Q000187:drug effects / Q000502:physiology; D045744:Cell Line, Tumor; D002471:Cell Transformation, Neoplastic; D004815:Epidermal Growth Factor / Q000494:pharmacology; D006801:Humans; D044949:Kaempferols / Q000494:pharmacology* / Q000627:therapeutic use; D007700:Kinetics; D008239:Lysine; D009369:Neoplasms / Q000201:enzymology / Q000473:pathology; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D012016:Reference Values; D038744:Ribosomal Protein S6 Kinases, 90-kDa / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D012867:Skin / Q000201:enzymology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D046888:Tissue Array Analysis; D014633:Valine
D044949:Kaempferols; D011994:Recombinant Proteins; D004815:Epidermal Growth Factor; C006552:kaempferol; D011494:Protein Kinases; C060137:carboxy-terminal domain kinase; D038744:Ribosomal Protein S6 Kinases, 90-kDa; C069330:ribosomal protein S6 kinase, 90kDa, polypeptide 3; D014633:Valine; D008239:Lysine; D013755:Tetradecanoylphorbol Acetate