Regulation of Ras-Dependent Signal Transduction Pathways

Ras 依赖性信号转导途径的调节

• 批准号: 7592665
• 负责人: DEBORAH K MORRISON
• 金额: $ 123.7万
• 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/7592665
• 关键词: Alleles; Apoptosis; Apoptotic; Area; Biochemical; C-terminal; Caspase; Cell Proliferation; Cells; Colorectal; Colorectal Cancer; Cyclic AMP; Event; Family; Family member; Goals; Hippocampus (Brain); Human; Laboratories; Link; Lung Adenocarcinoma; MEKs; Malignant Neoplasms; Malignant neoplasm of pancreas; Mammalian Cell; Membrane; Mission; Molecular; Mus; Mutation; Nervous system structure; Oncogenic; Ovarian; Papillary thyroid carcinoma; Pathway interactions; Phosphorylation; Process; Protein Kinase; Protein-Serine-Threonine Kinases; Proteins; Proto-Oncogene Proteins B-raf; Receptor Protein-Tyrosine Kinases; Regulation; Research; Role; Signal Transduction; Signal Transduction Pathway; Synaptic plasticity; Therapeutic; Therapeutic Intervention; Thyroid carcinoma; Work; anticancer research; cell transformation; classical conditioning; design; human KSR protein; insight; melanoma; member; novel; prevent; raf Kinases; scaffold; transmission process; tumor; tumorigenesis

The Ras pathway is a critical signal transduction cascade involved in regulating cellular proliferation, differentiation, and survival. Members of the Raf serine/threonine kinase family are key intermediates in this pathway, functioning to relay signals from activated Ras to the downstream protein kinases, MEK and ERK. Three Raf proteins are found in mammalian cells, Raf-1, A-Raf and B-Raf. As might be expected for proteins so centrally involved in cell signaling, the Raf kinases also contribute to oncogenic transformation and cancer. For example, mutation or amplification of upstream regulators of Raf, such as receptor tyrosine kinases and Ras, frequently induces deregulated signaling through the Raf/MEK/ERK cascade in tumors harboring these alleles. Moreover, constitutively active Raf proteins can themselves cause cell transformation. In particular, mutation of the B-Raf family member is observed in 67% of malignant melanomas as well as in many colorectal, ovarian and papillary thyroid carcinomas. During this past fiscal year, our research identified CK2 as an upstream protein kinase that contributes to Raf activation. Our studies has also revealed that the oncogenic potential of the B-Raf kinase can be altered by specific phosphorylation events and protein interactions. Together, these findings identify potential targets for therapeutic intervention in tumors with constitutive Ras- or Raf-dependent signaling. Another conserved component of the Ras pathway is KSR1, a protein that acts as a molecular scaffold to facilitate signal transmission through the ERK cascade. During the past fiscal year, our studies provided novel insight into the endogenous scaffolding role of KSR1 within the nervous system. This work demonstrated that KSR1 functions biochemically in the hippocampus to scaffold the components of the ERK cascade, specifically regulating the cascade when a membrane fraction of ERK is activated via a PKC-dependent pathway but not via a cAMP/PKA-dependent pathway. Consistent with these findings, mice lacking KSR1 were found to have deficits in associative learning and certain typses of synaptic plasticity. In this fiscal year, we also discovered that KSR1 undergoes caspase-dependent cleavage in apoptotic cells and that cleavage destroys the scaffolding function of the KSR1 and generates a stable C-terminal fragment (CTF) that can inhibit ERK activation. These findings indicate that cleavage of the KSR1 scaffold is another mechanism whereby caspases down-regulate ERK survival signaling to promote cellular apoptosis.

Ras通路是参与调节细胞增殖、分化和存活的关键信号转导级联。Raf丝氨酸/苏氨酸激酶家族的成员是该途径中的关键中间体，其功能是将信号从活化的Ras传递到下游蛋白激酶MEK和ERK。在哺乳动物细胞中发现三种Raf蛋白，Raf-1、A-Raf和B-Raf。正如所预期的那样，Raf激酶在细胞信号传导中起重要作用，也有助于致癌转化和癌症。例如，Raf的上游调节因子（如受体酪氨酸激酶和Ras）的突变或扩增经常通过携带这些等位基因的肿瘤中的Raf/MEK/ERK级联诱导失调的信号传导。此外，组成型活性Raf蛋白本身可以引起细胞转化。特别是，在67%的恶性黑色素瘤以及许多结直肠癌、卵巢癌和乳头状甲状腺癌中观察到B-Raf家族成员的突变。在过去的财政年度，我们的研究确定CK 2作为上游蛋白激酶，有助于Raf激活。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和蛋白质相互作用来改变。总之，这些发现确定了具有组成性Ras或Raf-dependent信号传导的肿瘤中治疗干预的潜在靶点。Ras通路的另一个保守组分是KSR 1，这是一种充当分子支架以促进通过ERK级联的信号传递的蛋白质。在过去的一个财政年度，我们的研究提供了新的见解KSR 1在神经系统内的内源性支架作用。这项工作表明，KSR 1在海马中的生物化学功能，以支架ERK级联的组件，特别是调节级联时，ERK的膜部分通过PKC依赖性途径激活，但不通过cAMP/PKA依赖性途径。与这些发现相一致，缺乏KSR 1的小鼠被发现在联合学习和某些类型的突触可塑性方面存在缺陷。在本财政年度，我们还发现KSR 1在凋亡细胞中经历半胱天冬酶依赖性切割，切割破坏了KSR 1的支架功能，并产生了一个稳定的C末端片段（CTF），可以抑制ERK激活。这些发现表明KSR 1支架的切割是半胱天冬酶下调ERK存活信号以促进细胞凋亡的另一种机制。