title: Ribosomal S6 kinase 2 is a key regulator in tumor promoter induced cell transformation.
abstract: The ribosomal S6 kinase 2 (RSK2), a member of the p90(RSK) (RSK) family of proteins, is a widely expressed serine/threonine kinase that is activated by extracellular signal-regulated kinase 1/2 and phosphoinositide-dependent kinase 1 in response to many growth factors and peptide hormones. Its activation signaling enhances cell survival. However, the roles of RSK2 in cell transformation have not yet been elucidated. Here, we found that RSK2 is a critical serine/threonine kinase for the regulation of cell transformation. When cells were stimulated with tumor promoters, such as epidermal growth factor (EGF) or 12-O-tetradecanoylphorbol-13-acetate (TPA), phosphorylation of RSK was increased within 5 min. Cell proliferation was suppressed in RSK2(-/-) mouse embryonic fibroblasts (MEFs) compared with RSK2(+/+) MEFs. Moreover, RSK2(-/-) MEFs accumulated at the G(1) phase of the cell cycle under normal cell culture conditions as well as after stimulation with EGF or TPA. In the anchorage-independent cell transformation assay (soft agar), stable expression of RSK2 in JB6 cells significantly enhanced colony formation in either the presence or absence of tumor promoters. Furthermore, knockdown of RSK2 with small interfering RNA-RSK2 suppressed constitutively active Ras (Ras(G12V))-induced foci formation in NIH3T3 cells. In addition, kaempferol, an inhibitor of RSK2, suppressed EGF-induced colony formation of JB6 Cl41 cells in soft agar, which was associated with inhibition of histone H3 phosphorylation (Ser(10)). These results showed that RSK2 is a key regulator for cell transformation induced by tumor promoters such as EGF and TPA.
authors.affiliation: Hormel Institute, University of Minnesota, Austin, MN 55912, USA.
authors.forename: Yong-Yeon
authors.initials: YY
authors.lastname: Cho
authors.forename: Ke
authors.initials: K
authors.lastname: Yao
authors.forename: Hong-Gyum
authors.initials: HG
authors.lastname: Kim
authors.forename: Bong Seok
authors.initials: BS
authors.lastname: Kang
authors.forename: Duo
authors.initials: D
authors.lastname: Zheng
authors.forename: Ann M
authors.initials: AM
authors.lastname: Bode
authors.forename: Zigang
authors.initials: Z
authors.lastname: Dong
mesh_terms: D000818:Animals; D001483:Base Sequence; D002273:Carcinogens / Q000494:pharmacology*; D002448:Cell Adhesion / Q000235:genetics; D049109:Cell Proliferation; D002471:Cell Transformation, Neoplastic / Q000187:drug effects* / Q000235:genetics*; D002478:Cells, Cultured; D004815:Epidermal Growth Factor / Q000494:pharmacology; D016193:G1 Phase / Q000235:genetics; D051379:Mice; D008969:Molecular Sequence Data; D041681:NIH 3T3 Cells; D038744:Ribosomal Protein S6 Kinases, 90-kDa / Q000235:genetics / Q000502:physiology*; D012689:Sequence Homology, Nucleic Acid; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014162:Transfection