MECHANISMS OF RAF ACTIVATION

Raf-1蛋白丝氨酸/苏氨酸激酶（PSK）作为一种关键的蛋白质， 连接生长因子受体的刺激和 蛋白激酶C（PKC）在细胞膜上，激活早期生长 细胞核中的反应基因。 最近我们发现另一个成员 Raf家族的B-Raf在神经生长后在PC 12细胞中被激活 因素刺激。 Raf-1和B-Raf激活的受体偶联是 p21 Ras的作用。 细胞的生长因子刺激导致 Raf-1的磷酸化和伴随的激酶活化增加， 拉夫 除了调节磷酸化，磷酸化的作用， 脂质衍生的产物在Raf-1的活化中的作用已经由 半胱氨酸指基序在Raf的N-末端一半中的存在， 1蛋白，其在其他Raf PSK家族成员中是保守的， 与蛋白激酶C的相似结构 我们现在已经扩展了对Raf-1的研究 和B-Raf到A-Raf，并且能够显示（i）A-Raf的激酶激活， Raf在相同的条件下发生，并具有与 以前在Raf-1中观察到，（ii）PKC-α磷酸化并激活 Raf-1，（iii）磷脂酰胆碱水解产物 激活Raf-1，和（iv）我们已经确定了PSK癌基因mos和cot 作为潜在的Raf激酶。

Raf-1 protein serine/threonine kinase (PSK) functions as a critical shuttle enzyme that connects stimulation of growth factor receptors and protein kinase C (PKC) at the membrane with activation of early growth response genes in the nucleus. Recently we have shown that another member of the Raf family, B-Raf, is activated in PC12 cells after nerve growth factor stimulation. Receptor coupling of Raf-1 and B-Raf activation is controlled by p21Ras. Growth factor stimulation of cells results in the increased phosphorylation and concomitant kinase activation of Raf-1 and B-Raf. In addition to regulatory phosphorylations, a role for phospho- lipid-derived products in the activation of Raf-1 has been suggested by the presence of a cysteine finger motif in the N-terminal half of the Raf- 1 protein, which is conserved in other Raf PSK family members and related to a similar structure in PKC. We have now extended our studies on Raf-1 and B-Raf to A-Raf, and were able to show that (i) kinase activation of A- Raf occurs under identical conditions and with similar kinetics as previously seen with Raf-1, (ii) PKC-alpha phosphorylates and activates Raf-1, (iii) products derived from the hydrolysis of phosphatidylcholine activate Raf-1, and (iv) we have identified the PSK oncogenes mos and cot as potential Raf kinase kinases.