Regulation of Ras-Dependent Signal Transduction Pathways

Ras 依赖性信号转导途径的调节

• 批准号: 8552667
• 负责人: Deborah Morrison
• 金额: $ 64.31万
• 依托单位: DIVISION OF BASIC SCIENCES - NCI
• 依托单位国家: 美国
• 资助国家: 美国
• 起止时间: 至
• 项目状态: 未结题
• 来源: https://reporter.nih.gov/project-details/8552667
• 关键词: Alleles; Area; Attenuated; Binding; Binding Proteins; Biochemical; Cell membrane; Cell physiology; Colorectal; Colorectal Cancer; Defect; Dimerization; Disease; Event; Family; Feedback; Germ-Line Mutation; Goals; Growth Factor; Human; LEOPARD Syndrome; Link; Lung; Lung Adenocarcinoma; MEKs; Malignant Neoplasms; Malignant neoplasm of ovary; Malignant neoplasm of pancreas; Mediating; Mission; Mutation; Noonan Syndrome; Normal Cell; Oncogenic; Ovarian; Papillary thyroid carcinoma; Pathway interactions; Patients; Pharmaceutical Preparations; Phosphorylation; Phosphorylation Site; Phosphotransferases; Play; Process; Protein Kinase; Protein-Serine-Threonine Kinases; Proteins; Proto-Oncogene Proteins B-raf; Ras Signaling Pathway; Receptor Protein-Tyrosine Kinases; Regulation; Research; Role; Signal Pathway; Signal Transduction; Signal Transduction Pathway; Somatic Mutation; Therapeutic; Thyroid carcinoma; Work; anticancer research; cardiofaciocutaneous syndrome; design; dimer; human disease; inhibitor/antagonist; melanoma; member; mutant; prevent; raf Kinases; ras Proteins; response; scaffold; senescence; therapeutic target; tumor; tumorigenesis

Cancer often arises when the control of normal cell function goes awry due to defects in critical signal transduction pathways. The signaling pathway regulated by the RasGTPase is one such pathway and it functions to modulate vital cellular processes, including proliferation, differentiation, survival, and senescence. Members of the Raf serine/threonine kinase family are key intermediates in the Ras pathway, serving to relay signals from activated Ras to the downstream protein kinases, MEK and ERK. There are three mammalian Raf proteins, A-Raf, B-Raf, and C-Raf (also known as Raf-1). As might be expected for proteins so centrally involved in cell signaling, the Raf kinases can directly contribute to oncogenic transformation and other human disease states. For example, mutation or amplification of upstream regulators of Raf, such as receptor tyrosine kinases and Ras, frequently results in constitutive signaling through the Raf/MEK/ERK cascade in tumors harboring these alleles. In addition, mutations in the Raf proteins themselves can function as disease drivers. Germline-mutations in C-Raf are causative for Noonan and LEOPARD syndromes, whereas B-Raf mutations are found in Noonan, LEOPARD, and cardiofaciocutaneous (CFC) syndromes, with B-Raf mutations occurring in 75% of CFC patients. Moreover, somatic mutations in B-Raf are observed in 70% of malignant melanomas as well as in many colorectal, ovarian, lung and papillary thyroid carcinomas. During this past fiscal year, our research has elucidated several important mechanisms contributing to the regulation of both normal and mutant Raf signaling. Our studies have revealed that the KSR1 scaffold plays a critical role in modulating the intensity and duration of Raf signaling emanating from the plasma membrane in response to growth factor treatment. In addition, we have found that the KSR expression levels can alter the effects of Raf inhibitors on oncogenic Ras to ERK signaling. Specifically, KSR1 competes with C-Raf for inhibitor-induced binding to B-Raf and in doing so attenuates the paradoxical activating effect of these drugs on ERK signaling. Our studies have also shown that the oncogenic potential of the B-Raf kinase can be altered by specific phosphorylation events (e. g., phosphorylation on inhibitory feedback sites and the phosphorylation of residues that mediate 14-3-3 binding) and protein interactions (e.g., 14-3-3 binding and Raf dimerization). Moreover, we have found that Raf dimerization is critical for upregulated signaling induced by human disease-associated Raf mutants with moderate, low or impaired kinase activity, or in cases where the pathway is induced by activated RTK or Ras proteins. Our work has further revealed that somatic mutations which modulate Raf dimerization have the potential to alter the progression and treatment of human disease states with elevated Ras pathway signaling. Finally, our work has provided the first 'proof of principle' that inhibiting Raf dimerization can suppress Raf signaling under conditions where dimerization is required. Taken together, these findings have important implications for the treatment of human disease states with elevated Ras pathway signaling and identify the Raf dimer interface as a therapeutic target.

当正常细胞功能的控制由于关键信号转导通路的缺陷而出错时，癌症通常会出现。 由RasGT 3调节的信号传导途径是这样的途径之一，并且其功能是调节重要的细胞过程，包括增殖、分化、存活和衰老。 Raf丝氨酸/苏氨酸激酶家族的成员是Ras途径中的关键中间体，用于将信号从活化的Ras传递到下游蛋白激酶MEK和ERK。 存在三种哺乳动物Raf蛋白，A-Raf、B-Raf和C-Raf（也称为Raf-1）。 正如可以预期的那样，Raf激酶可以直接导致致癌转化和其他人类疾病状态。 例如，Raf的上游调节因子（如受体酪氨酸激酶和Ras）的突变或扩增经常导致通过携带这些等位基因的肿瘤中的Raf/MEK/ERK级联的组成型信号传导。 此外，Raf蛋白本身的突变可以作为疾病驱动因素。C-Raf的种系突变是努南综合征和LEOPARD综合征的病因，而B-Raf突变见于努南综合征、LEOPARD综合征和心面皮肤（CFC）综合征，75%的CFC患者发生B-Raf突变。 此外，在70%的恶性黑色素瘤以及许多结直肠癌、卵巢癌、肺癌和乳头状甲状腺癌中观察到B-Raf的体细胞突变。在过去的一个财政年度，我们的研究阐明了几个重要的机制，有助于调节正常和突变的Raf信号。 我们的研究表明，KSR 1支架在调节响应于生长因子处理而从质膜发出的Raf信号的强度和持续时间中起着关键作用。此外，我们还发现KSR的表达水平可以改变Raf抑制剂对致癌Ras至ERK信号通路的影响。 具体而言，KSR 1与C-Raf竞争与B-Raf的结合，从而减弱这些药物对ERK信号传导的矛盾激活作用。我们的研究还表明，B-Raf激酶的致癌潜力可以通过特定的磷酸化事件（例如，例如，在一个实施例中，抑制性反馈位点上的磷酸化和介导14-3-3结合的残基的磷酸化）和蛋白质相互作用（例如，14-3-3结合和Raf二聚化）。 此外，我们已经发现Raf二聚化对于由具有中等、低或受损激酶活性的人类疾病相关Raf突变体诱导的上调信号传导，或在其中途径由活化的RTK或Ras蛋白诱导的情况下是关键的。我们的工作进一步揭示了调节Raf二聚化的体细胞突变具有改变具有升高的Ras通路信号传导的人类疾病状态的进展和治疗的潜力。 最后，我们的工作提供了第一个“原则证明”，即抑制Raf二聚化可以抑制Raf信号的条件下，需要二聚化。总之，这些发现对于治疗具有升高的Ras通路信号传导的人类疾病状态具有重要意义，并将Raf二聚体界面鉴定为治疗靶点。