Regulation of the oncogenic potential of signalling through the Ras/ERK pathway by dual-specificity phosphatase 5

RAS/ERK信号通路的异常激活在疾病的发生和发展中起着致病作用，大约三分之一的人类癌症表现出已知的导致RAS/ERK介导的癌症形成的突变。此外，许多此类癌症，如胰腺癌、肺癌和恶性黑色素瘤，治疗选择很少，预后也很差，使这一途径成为抗癌药物开发的重点。我们对ERK通路成分的激活突变，如RAS或其下游靶点BRAF如何导致ERK信号在肿瘤中不可控地“开启”，以及这些突变可以决定肿瘤对抑制RAS/ERK通路的抗癌药物的敏感性有很多了解。相比之下，我们对RAS/ERK信号的负调控因子如何影响肿瘤发生或药物敏感性知之甚少。我们最近证明，DUSP5是一种可诱导的蛋白磷酸酶，可以抑制核Ras/ERK活性和基因表达，并且DUSP5的缺失显著增加了突变的RAS诱导的小鼠皮肤肿瘤负担，表明DUSP5是一种肿瘤抑制因子。因此，我们假设DUSP5限制了突变的RAS肿瘤在其他组织和人类肿瘤中的进展。相反，我们最近使用培养细胞进行的研究表明，在存在BRAF突变的情况下，DUSP5实际上促进了细胞生长，而它的缺失阻止了细胞的增殖。因此，我们假设，就像它们对某些抗癌药物的影响一样，RAS或BRAF癌基因的存在可以决定DUSP5是促进还是抑制癌细胞生长。这个研究项目的总体目标有两个：1)我们将确定DUSP5缺失对临床相关突变Kras诱发的癌症小鼠模型的影响，即胰腺癌和肺癌的发生。这些模型与人类疾病非常相似，将使我们能够评估DUSP5在调节肿瘤发生和发展中的作用。此外，还将详细分析与细胞增殖、衰老、存活、迁移和细胞死亡相关的ERK依赖基因表达和信号终点的变化。后者将使我们能够确定促进肿瘤发展的ERK信号转导机制(S)和关键靶点。最后，我们将筛选胰腺癌患者的正常和肿瘤组织样本，以评估DUSP5和其他关键ERK信号靶点的水平，并探索与人类疾病临床终点的相关性。2)我们将确定DUSP5在调节RAS/ERK信号的致癌效应中的作用是否取决于该通路的激活方式。这将通过监测在存在RAS或BRAF突变的情况下DUSP5对ERK信号转导和细胞命运的影响来研究。这对预测RAS/ERK通路抑制剂在癌症治疗中的有效性具有重要意义。因此，我们将研究这种功能差异的分子机制，并将这些研究扩展到RAS或BRAF突变的癌细胞系，并确定DUSP5的表达是否会影响临床上急性或慢性暴露于RAS/ERK抑制剂的敏感性。总之，这项工作将使我们了解DUSP5在调节RAS/ERK信号通路中的功能，因为它与癌症的发生和发展有关，将揭示Ras/ERK通路及其靶点在突变Kras驱动的癌症中的相对重要性，并使我们能够探索它们的临床相关性。最后，DUSP5在调节ERK中的作用在存在激活的癌基因的情况下可能变得更加重要的想法，在细胞对途径抑制剂的反应方面代表了一个未知的领域，并可能为调节或预测针对癌症中RAS/ERK信号转导的药物的患者反应开辟新的方法。

Abnormal activation of the Ras/ERK signalling pathway plays a causative role in disease initiation and progression and approximately one third of all human cancers exhibit mutations known to cause Ras/ERK mediated cancer formation. Furthermore, many of these cancers, such as pancreatic cancer, lung cancer and malignant melanoma have few treatment options and a poor prognosis, making this pathway an intense focus of anticancer drug development. We understand a lot about how activating mutations in ERK pathway components, such as Ras or its downstream target, Braf, cause ERK signalling to be uncontrollably "switched on" in tumours, and that such mutations can determine tumour sensitivity to anticancer drugs that inhibit the Ras/ERK pathway. In contrast, we know little about how the negative regulators of Ras/ERK signalling influence oncogenesis or drug sensitivity.We recently demonstrated that DUSP5, an inducible protein phosphatase, inhibits nuclear Ras/ERK activity and gene expression, and that deletion of DUSP5 dramatically increases mutant Ras-induced skin tumour burdens in mice, demonstrating that DUSP5 is a tumour suppressor. We therefore hypothesise that DUSP5 limits the progression of mutant Ras tumours in other tissues and in human tumours. In contrast, our more recent studies using cultured cells indicate that in the presence of Braf mutations, DUSP5 actually promotes cell growth and its deletion halts cell proliferation. We therefore hypothesise that, much like their effect on some anticancer drugs, the presence of Ras or Braf oncogenes can determine whether DUSP5 promotes or suppresses cancer cell growth. The overall objectives of this research project are two-fold:1) We will determine the effects of DUSP5 loss in clinically relevant mouse models of mutant Kras-induced cancer, namely pancreatic and lung carcinogenesis. These models closely resemble the human disease and will enable us to assess the role of DUSP5 in modulating the initiation and progression of tumours. This will be coupled with a detailed analysis of changes in ERK-dependent gene expression and signalling endpoints associated with cell proliferation, senescence, survival, migration and cell death. The latter will allow us to identify mechanism(s) and also key targets of ERK signalling involved in promoting tumour development. Finally, we will screen normal and tumour tissue samples from pancreatic cancer patients in order to assess the levels of DUSP5 and other key ERK signalling targets and to explore correlations with clinical endpoints in human disease.2) We will determine whether the role of DUSP5 in modulating the oncogenic effects of Ras/ERK signalling depends on the way in which the pathway is activated. This will be studied by monitoring the influence of DUSP5 on ERK signalling and cell fate in the presence of either Ras or Braf mutations. This has important implications for predicting how effective Ras/ERK pathway inhibitors may be in the treatment of cancer. We will therefore study the molecular mechanisms which underpin this functional difference and extend these studies to cancer cell lines in which Ras or Braf are mutant and determine if DUSP5 expression affects sensitivity either acute or chronic exposure to Ras/ERK inhibitors in clinical use. Overall, this work will inform us about DUSP5 function in the regulation of Ras/ERK signalling as it relates to cancer initiation and development, will shed light on the relative importance of the Ras/ERK pathway and its targets in cancers driven by mutant Kras and allow us to explore their clinical relevance. Finally, the idea that the role of DUSP5 in regulating ERK may become more important in the presence of activating oncogenes represents an unexplored area in terms of cellular responses to pathway inhibitors and may open new approaches to modulating or predicting patient responses to drugs which target Ras/ERK signalling in cancer.