EFFECT OF RAF FAMILY PROTEIN KINASES ON CELL PHYSIOLOGY

我们研究了c-raf丝氨酸/苏氨酸特异蛋白的功能。 成纤维细胞和淋巴样细胞中的激酶。结构功能分析 提出了一种非刺激酶的蛋白质结构模型，其中 活性部位被埋藏在蛋白质中。可逆激活 成纤维细胞和淋巴样细胞可由多种生长因子或 细胞内有丝分裂原至少使用两条独立的途径--一条 涉及蛋白激酶C和另一种涉及直接酪氨酸 跨膜或胞内酪氨酸对c-raf的磷酸化作用 激活剂。接下来是受体介导的c-raf蛋白激酶的激活 通过将正常的胞浆酶移位到核周区域 和细胞核。募集RAF的跨膜酪氨酸激酶蛋白 依赖配体的激酶活性包括血小板受体 衍生生长因子、集落刺激因子-1、表皮生长 因子、胰岛素和成纤维细胞生长因子。因此，来自所有四个国家的成员 跨膜酪氨酸激酶受体的结构类型共享这一点 核内信号转导的耦合机制。此外，增长 使用非激酶受体的因子，如白细胞介素2、白细胞介素3、 粒细胞-巨噬细胞集落刺激因子和T细胞 受体和Thy-1也激活RAF激酶活性。有趣的是，那些 明显通过细胞内酪氨酸激酶偶联的受体 激活与高化学计量比酪氨酸磷酸化一致的RAF (比血小板衍生生长因子-R高出约10到50倍)。 活化的RAF的表达刺激PEAI的活性 C-jun基因家族。V-raf和活化形式的c-raf-I或 A-RAF刺激PEAI，提示磷酸化参与其中 激活。我们得出结论，c-raf作为一种穿梭酶连接 质膜上的有丝分裂原启动的事件到细胞核内的事件， 推测是通过转录因子的活性调节，通过 磷酸化。

We have examined the function of c-raf serine/threonine-specific protein kinase in fibroblastic and lymphoid cells. Structure-function analysis suggests a protein structure model for the unstimulated enzyme in which the active site is buried within the protein. Reversible activation in fibroblastic and lymphoid cells can be achieved by many growth factors or intracellular mitogens which use at least two independent pathways--one involving protein kinase C and another which involves direct tyrosine phosphorylation of c-raf by transmembrane or intracellular tyrosine kinases. Receptor-mediated activation of c-raf protein kinase is followed by translocation of the normally cytosolic enzyme to the perinuclear area and the nucleus. Transmembrane tyrosine kinase proteins which recruit raf kinase activity in a ligand-dependent manner include receptors for platelet derived growth factor (PDGF), colony stimulating factor-1, epidermal growth factor, insulin, and fibroblast growth factor. Thus, members from all four structural classes of transmembrane tyrosine kinase receptors share this coupling mechanism for signal transduction to the nucleus. Moreover, growth factors that use non-kinase receptors such as interleukin-2, interleukin-3, granulocyte-macrophage colony stimulating factor, as well as the T-cell receptor, and Thy-1 also activate raf kinase activity. Interestingly, those receptors that apparently couple via intracellular tyrosine kinases activate raf concordant with high-stoichiometry tyrosine phosphorylation (about 10- to 50-fold higher than platelet-derived growth factor-R). Expression of activated raf stimulates the activity of PEAI, a member of the c-jun gene family. Both v-raf and activated forms of either c-raf-I or A-raf stimulate PEAI, suggesting that phosphorylation is involved in this activation. We conclude that c-raf acts as a shuttle enzyme which connects mitogen-initiated events at the plasma membrane to events in the nucleus, presumably by activity-modulation of transcription factors via phosphorylation.