Article

RSK promotes G2 DNA damage checkpoint silencing and participates in melanoma chemoresistance.

Institute for Research in Immunology and Cancer (IRIC), Université de Montréal, Montreal, Quebec, Canada.
Oncogene (Impact Factor: 8.56). 10/2012; DOI: 10.1038/onc.2012.472
Source: PubMed

ABSTRACT The incidence of malignant melanoma is growing rapidly worldwide and there is still no effective therapy for metastatic disease. This type of cancer is highly resistant to conventional DNA-damaging chemotherapeutics, and intense research has been dedicated for understanding the molecular pathways underlying chemoresistance. The Ras/mitogen-activated protein kinase (MAPK) signalling pathway is often deregulated in melanoma, which frequently harbours activating mutations in NRAS or BRAF. Herein, we demonstrate that the MAPK-activated protein kinase RSK (p90 ribosomal S6 kinase) contributes to melanoma chemoresistance by altering their response to chemotherapeutic agents. We find that RSK phosphorylates checkpoint kinase 1 (Chk1) at an inhibitory site, Ser280, both in vitro and in vivo. Our results indicate that RSK is the predominant protein kinase operating downstream of mitogens and oncogenes of the Ras/MAPK pathway, and consistent with this, we find that RSK constitutively phosphorylates Chk1 in melanoma. We show that RSK inhibition increases Chk1 activity in response to DNA-damaging agents, suggesting that the Ras/MAPK pathway modulates Chk1 function and the response to DNA damage. Accordingly, we demonstrate that RSK promotes G2 DNA damage checkpoint silencing in a Chk1-dependent manner, and find that RSK inhibitors sensitize melanoma cells to DNA-damaging agents. Together, our results identify a novel link between the Ras/MAPK pathway and the DNA damage response, and suggest that RSK inhibitors may be used to modulate chemosensitivity, which is one of the major obstacles to melanoma treatment.Oncogene advance online publication, 29 October 2012; doi:10.1038/onc.2012.472.

0 Bookmarks
 · 
69 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: Mutant RAS-driven tumorigenesis was thought for decades to arise independently of wild-type RAS isoforms, but recent evidence indicates wild-type isoforms are involved. In this issue of Cancer Cell, Grabocka and colleagues report how the loss of wild-type RAS alters oncogenic signaling and dampens the DNA-damage response, thereby affecting tumor progression and chemosensitivity.
    Cancer cell 02/2014; 25(2):137-8. · 25.29 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Constitutively-activated tyrosine kinase mutants, such as BCR/ABL, FLT3-ITD, and Jak2-V617F, play important roles in pathogenesis of hematopoietic malignancies and in acquisition of therapy resistance. We previously found that hematopoietic cytokines enhance activation of the checkpoint kinase Chk1 in DNA-damaged hematopoietic cells by inactivating GSK3 through the PI3K/Akt signaling pathway to inhibit apoptosis. Here we examine the possibility that the kinase mutants may also protect DNA-damaged cells by enhancing Chk1 activation. In cells expressing BCR/ABL, FLT3-ITD, or Jak2-V617F, etoposide induced a sustained activation of Chk1, thus leading to the G2/M arrest of cells. Inhibition of these kinases by their inhibitors, imatinib, sorafenib, or JakI-1, significantly abbreviated Chk1 activation, and drastically enhanced apoptosis induced by etoposide. The PI3K inhibitor GD-0941 or the Akt inhibitor MK-2206 showed similar effects with imatinib on etoposide-treated BCR/ABL-expressing cells, including those expressing the imatinib-resistant T315I mutant, while expression of the constitutively activated Akt1-myr mutant conferred resistance to the combined treatment of etoposide and imatinib. GSK3 inhibitors, including LiCl and SB216763, restored the sustained Chk1 activation and mitigated apoptosis in cells treated with etoposide and the inhibitors for aberrant kinases, PI3K, or Akt. These observations raise a possilibity that the aberrant kinases BCR/ABL, FLT3-ITD, and Jak2-V617F may prevent apoptosis induced by DNA-damaging chemotherapeutics, at least partly through enhancement of the Chk1-mediated G2/M checkpoint activation, by inactivating GSK3 through the PI3K/Akt signaling pathway. These results shed light on the molecular mechanisms for chemoresistance of hematological malignancies and provide a rationale for the combined treatment with chemotherapy and the tyrosine kinase or PI3K/Akt pathway inhibitors against these diseases.
    PLoS ONE 11/2013; 8(11):e79478. · 3.53 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Ataxia telangiectasia mutant (ATM) is an S/T-Q-directed kinase that is critical for the cellular response to double-stranded breaks (DSBs) in DNA. Following DNA damage, ATM is activated and recruited by the MRN protein complex [meiotic recombination 11 (Mre11)/DNA repair protein Rad50/Nijmegen breakage syndrome 1 proteins] to sites of DNA damage where ATM phosphorylates multiple substrates to trigger cell-cycle arrest. In cancer cells, this regulation may be faulty, and cell division may proceed even in the presence of damaged DNA. We show here that the ribosomal s6 kinase (Rsk), often elevated in cancers, can suppress DSB-induced ATM activation in both Xenopus egg extracts and human tumor cell lines. In analyzing each step in ATM activation, we have found that Rsk targets loading of MRN complex components onto DNA at DSB sites. Rsk can phosphorylate the Mre11 protein directly at S676 both in vitro and in intact cells and thereby can inhibit the binding of Mre11 to DNA with DSBs. Accordingly, mutation of S676 to Ala can reverse inhibition of the response to DSBs by Rsk. Collectively, these data point to Mre11 as an important locus of Rsk-mediated checkpoint inhibition acting upstream of ATM activation.
    Proceedings of the National Academy of Sciences 12/2013; · 9.81 Impact Factor

Full-text

Download
32 Downloads
Available from
Jun 1, 2014