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    Myc stimulates cell cycle progression through the activation of Cdk1 and phosphorylation of p27. García-Gutiérrez Lucía,Bretones Gabriel,Molina Ester,Arechaga Ignacio,Symonds Catherine,Acosta Juan C,Blanco Rosa,Fernández Adrián,Alonso Leticia,Sicinski Piotr,Barbacid Mariano,Santamaría David,León Javier Scientific reports Cell cycle stimulation is a major transforming mechanism of Myc oncoprotein. This is achieved through at least three concomitant mechanisms: upregulation of cyclins and Cdks, downregulation of the Cdk inhibitors p15 and p21 and the degradation of p27. The Myc-p27 antagonism has been shown to be relevant in human cancer. To be degraded, p27 must be phosphorylated at Thr-187 to be recognized by Skp2, a component of the ubiquitination complex. We previously described that Myc induces Skp2 expression. Here we show that not only Cdk2 but Cdk1 phosphorylates p27 at the Thr-187. Moreover, Myc induced p27 degradation in murine fibroblasts through Cdk1 activation, which was achieved by Myc-dependent cyclin A and B induction. In the absence of Cdk2, p27 phosphorylation at Thr-187 was mainly carried out by cyclin A2-Cdk1 and cyclin B1-Cdk1. We also show that Cdk1 inhibition was enough for the synthetic lethal interaction with Myc. This result is relevant because Cdk1 is the only Cdk strictly required for cell cycle and the reported synthetic lethal interaction between Cdk1 and Myc. 10.1038/s41598-019-54917-1
    Novel potent and selective inhibitors of p90 ribosomal S6 kinase reveal the heterogeneity of RSK function in MAPK-driven cancers. Aronchik Ida,Appleton Brent A,Basham Stephen E,Crawford Kenneth,Del Rosario Mercedita,Doyle Laura V,Estacio William F,Lan Jiong,Lindvall Mika K,Luu Catherine A,Ornelas Elizabeth,Venetsanakos Eleni,Shafer Cynthia M,Jefferson Anne B Molecular cancer research : MCR UNLABELLED:The p90 ribosomal S6 kinase (RSK) family of serine/threonine kinases is expressed in a variety of cancers and its substrate phosphorylation has been implicated in direct regulation of cell survival, proliferation, and cell polarity. This study characterizes and presents the most selective and potent RSK inhibitors known to date, LJH685 and LJI308. Structural analysis confirms binding of LJH685 to the RSK2 N-terminal kinase ATP-binding site and reveals that the inhibitor adopts an unusual nonplanar conformation that explains its excellent selectivity for RSK family kinases. LJH685 and LJI308 efficiently inhibit RSK activity in vitro and in cells. Furthermore, cellular inhibition of RSK and its phosphorylation of YB1 on Ser102 correlate closely with inhibition of cell growth, but only in an anchorage-independent growth setting, and in a subset of examined cell lines. Thus, RSK inhibition reveals dynamic functional responses among the inhibitor-sensitive cell lines, underscoring the heterogeneous nature of RSK dependence in cancer. IMPLICATIONS:Two novel potent and selective RSK inhibitors will now allow a full assessment of the potential of RSK as a therapeutic target for oncology. 10.1158/1541-7786.MCR-13-0595
    Selective Targeting of RSK Isoforms in Cancer. Casalvieri Kimberly A,Matheson Christopher J,Backos Donald S,Reigan Philip Trends in cancer The p90 ribosomal S6 kinase family (RSK1-4) is a group of highly conserved Ser/Thr kinases that act as downstream effectors of the Ras/Raf/MEK/ERK signaling pathway. The RSKs phosphorylate a range of substrates involved in transcription, translation, cell cycle regulation, and cell survival. Although the RSKs have a high degree of sequence homology, their functional differences in cancer are of great interest. Current RSK inhibitors target more than one RSK isoform, and this may limit their efficacy as anticancer agents. Here, we review the structure and function of the RSK kinases, their role in cancer growth and survival, and their potential as modulators of chemoresistance. In addition, we summarize the development of current RSK inhibitors and their limitations. 10.1016/j.trecan.2017.03.004
    [Auricular electroacupuncture improves depression possibly by promoting hippocampal Raf/ERK/RSK/CREB signaling in chronic unpredictable mild stress induced depression rats]. Li Shao-Yuan,Rong Pei-Jing,Gao Guo-Jian,Zhang Yue,Wang Jun-Ying,Wang Yu,Li Liang,Zhang Jin-Ling,Guo Xiao Zhen ci yan jiu = Acupuncture research OBJECTIVE:To observe the effect of auricular electroacupuncture (EA) on intracellular Raf/ extracellular signal-regulated kinase (ERK)/ ribosomal S6 kinase (RSK)/ cAMP response element-binding protein (CREB) signal pathway in the hippocampus of depression model rats, so as to explore its anti-depressive mechanism. METHODS:A total of 60 male SD rats were randomly divided into control, model, auricular EA, PD98059(ERK inhibitor), DMSO (Dimethylsulfoxide), PD98059+EA groups (=10 in each group). The rats in the control group were fed with normal diet without any treatment. The depression model was induced by chronic unpredictable mild stress (CUMS) for consecutive 21 days. EA (20 Hz, 2 mA) was applied to bilateral auricular "Xin"(Heart) and "Shenmen" for 30 min, once daily for 28 days. Rats of the PD98059, DMSO and PD98059+EA groups received intracerebroventricular injection of PD98059(100 µmol/L), DMSO and PD98059 (dissolved by DMSO) solutions (5 µL/d), respectively, once daily for 28 days. Sucrose preference test (sucrose consumption) was conducted at the baseline, before and after the intervention. The expression of hippocampal Raf, phosphorylated (p)-Raf, ERK, p-ERK, RSK, CREB and p-CREB proteins were detected by Western blot after EA intervention. RESULTS:Following modeling, the sucrose consumption volume, and the expression levels of hippocampal Raf, p-Raf, ERK, p-ERK, RSK, CREB, p-CREB proteins were significantly lower in the model group than those in the control group (<0.01). Following the treatment, the sucrose consumption and the expression levels of Raf, p-Raf, ERK, p-ERK, RSK, CREB, p-CREB in the auricular EA group and those of p-Raf, ERK and CREB in the PD98059+EA group were obviously increased in comparison with the model group (<0.05, <0.01), the expression level of p-ERK in the PD98059 group was obviously decreased in comparison with the model group (<0.05), suggesting an improvement of depression after auricular EA. Compared with auricular EA group, the expression level of p-ERK, p-CREB and RSK in the PD98059+EA group were significantly decreased (<0.05). CONCLUSION:EA of auricular "Xin" and "Shenmen" is able to improve depression in depression rats, which is probably related to its effect in promoting activities of hippocampal Raf/ERK/RSK/CREB signaling. 10.13702/j.1000-0607.190292
    RSK inhibitor BI-D1870 inhibits acute myeloid leukemia cell proliferation by targeting mitotic exit. Chae Hee-Don,Dutta Ritika,Tiu Bruce,Hoff Fieke W,Accordi Benedetta,Serafin Valentina,Youn Minyoung,Huang Min,Sumarsono Nathan,Davis Kara L,Lacayo Norman J,Pigazzi Martina,Horton Terzah M,Kornblau Steven M,Sakamoto Kathleen M Oncotarget The 90 kDa Ribosomal S6 Kinase (RSK) drives cell proliferation and survival in cancers, although its oncogenic mechanism has not been well characterized. Phosphorylated level of RSK (T573) was increased in acute myeloid leukemia (AML) patients and associated with poor survival. To examine the role of RSK in AML, we analyzed apoptosis and the cell cycle profile following treatment with BI-D1870, a potent inhibitor of RSK. BI-D1870 treatment increased the G2/M population and induced apoptosis in AML cell lines and patient AML cells. Characterization of mitotic phases showed that the metaphase/anaphase transition was significantly inhibited by BI-D1870. BI-D1870 treatment impeded the association of activator CDC20 with APC/C, but increased binding of inhibitor MAD2 to CDC20, preventing mitotic exit. Moreover, the inactivation of spindle assembly checkpoint or MAD2 knockdown released cells from BI-D1870-induced metaphase arrest. Therefore, we investigated whether BI-D1870 potentiates the anti-leukemic activity of vincristine by targeting mitotic exit. Combination treatment of BI-D1870 and vincristine synergistically increased mitotic arrest and apoptosis in acute leukemia cells. These data show that BI-D1870 induces apoptosis of AML cells alone and in combination with vincristine through blocking mitotic exit, providing a novel approach to overcoming vincristine resistance in AML cells. 10.18632/oncotarget.27630
    Simultaneous Targeting of RSK and AKT Efficiently Inhibits YB-1-Mediated Repair of Ionizing Radiation-Induced DNA Double-Strand Breaks in Breast Cancer Cells. Lettau Konstanze,Zips Daniel,Toulany Mahmoud International journal of radiation oncology, biology, physics PURPOSE:Y-box binding protein 1 (YB-1) overexpression is associated with chemotherapy- and radiation therapy resistance. Ionizing radiation (IR), receptor tyrosine kinase ligands, and mutation in KRAS gene stimulate activation of YB-1. YB-1 accelerates the repair of IR-induced DNA double-strand breaks (DSBs). Ribosomal S6 kinase (RSK) is the main kinase inducing YB-1 phosphorylation. We investigated the impact of RSK targeting on DSB repair and radiosensitivity. MATERIALS AND METHODS:The triple negative breast cancer (TNBC) cell lines MDA-MB-231, MDA-MB-468, and Hs 578T, in addition to non-TNBC cell lines MCF7, HBL-100, and SKBR3, were used. MCF-10A cells were included as normal breast epithelial cells. The RSK inhibitor LJI308 was used to investigate the role of RSK activity in S102 phosphorylation of YB-1 and YB-1-associated signaling pathways. The activation status of the underlying pathways was investigated by Western blotting after treatment with pharmacologic inhibitors or transfection with siRNA. The impact of LJI308 on DSB repair and postirradiation cell survival was tested by the γH2AX foci and the standard clonogenic assays, respectively. RESULTS:LJI308 inhibited the phosphorylation of RSK (T359/S363) and YB-1 (S102) after irradiation, treatment with EGF, and in cells expressing a KRAS mutation. LJI308 treatment slightly inhibited DSB repair only in some of the cell lines tested. This was shown to be due to PI3K-dependent stimulation of AKT or constitutive AKT activity mainly in cancer cells but not in normal breast epithelial MCF-10A cells. Simultaneous targeting of AKT and RSK strongly blocked DSB repair in all cancer cell lines, independent of TNBC status or KRAS mutation, with a minor effect in MCF-10A cells. Cotargeting of RSK- and AKT-induced radiation sensitivity in TNBC MDA-MB-231 and non-TNBC MCF7 cells but not in MCF-10A cells. CONCLUSIONS:Simultaneous targeting of RSK and AKT might be an efficient approach to block the repair of DSBs after irradiation and to induce radiosensitization of breast cancer cells. 10.1016/j.ijrobp.2020.09.005
    The p90 ribosomal S6 kinase (RSK) inhibitor BI-D1870 prevents gamma irradiation-induced apoptosis and mediates senescence via RSK- and p53-independent accumulation of p21WAF1/CIP1. Neise D,Sohn D,Stefanski A,Goto H,Inagaki M,Wesselborg S,Budach W,Stühler K,Jänicke R U Cell death & disease The p90 ribosomal S6 kinase (RSK) family is a group of highly conserved Ser/Thr kinases that promote cell proliferation, growth, motility and survival. As they are almost exclusively activated downstream of extracellular signal-regulated kinases 1 and 2 (ERK1/2), therapeutic intervention by RSK inhibition is less likely to produce such severe side effects as those observed following inhibition of the upstream master regulators Raf, MEK and ERK1/2. Here, we report that BI-D1870, a potent small molecule inhibitor of RSKs, induces apoptosis, although preferentially, in a p21-deficient background. On the other hand, BI-D1870 also induces a strong transcription- and p53-independent accumulation of p21 protein and protects cells from gamma irradiation (γIR)-induced apoptosis, driving them into senescence even in the absence of γIR. Although we identified p21 in in vitro kinase assays as a novel RSK substrate that specifically becomes phosphorylated by RSK1-3 at Ser116 and Ser146, RNA-interference, overexpression and co-immunoprecipitation studies as well as the use of SL0101, another specific RSK inhibitor, revealed that BI-D1870 mediates p21 accumulation via a yet unknown pathway that, besides its off-site targets polo-like kinase-1 and AuroraB, also does also not involve RSKs. Thus, this novel off-target effect of BI-D1870 should be taken into serious consideration in future studies investigating the role of RSKs in cellular signaling and tumorigenesis. 10.1038/cddis.2013.386