ROLE OF RAF- AND MYC-PATHWAYS IN CELL FATE DETERMINATION

我们以前已经证明过，严格意义上的 白介素3(IL-3)依赖的髓系32D细胞需要激活 至少有两条途径，一条Myc途径和一条Raf途径。在强制执行时 在缺乏IL-3的情况下，Myc的表达促进细胞周期进展， 它也不利于细胞存活，加速细胞凋亡。 致癌的Raf主动抑制细胞凋亡的开始，从而提供 这些细胞的生存因素。V-RAF在细胞凋亡中的协同作用 弱转化癌基因bcl2的抑制作用 早些时候显示了抑制多种细胞类型的细胞凋亡。BCL-2 似乎在与Raf平行的途径中发挥作用，因为Raf-1激酶不是 影响bcl2蛋白的水平或磷酸化状态。这个 在32D CELL系统中使用Myc和Raf获得的数据以及在 具有分化能力的系统表明v-raf是相容的。 具有或诱导分化，而myc本身无效或 阻碍了分化。这些发现使我们假设 特定受体诱导的Raf/Myc途径活性比率将 根据细胞命运来决定刺激的结果 (增殖、分化或凋亡)。支持此模型 通过我们在PC12细胞系统中的发现。(I)分析孤立的Myc- PC12细胞中的Raf通路表明有效地激活了Raf 诱导分化，而Myc表现出毒性作用。(Ii) 分化因子“神经生长因子”诱导的长效作用 Raf-1激酶的激活，与所见的瞬时激活相反 含有表皮生长因子。(3)最后，对c-myc的抑制作用 显性负myc突变体将EGF转化为分化 因素。

We have shown previously that the autonomous growth of the strictly interleukin-3 (IL-3)-dependent myeloid 32D cells requires the activation of two pathways minimally, a Myc- and a Raf-pathway. While enforced expression of Myc promotes cell cycle progression in the absence of IL-3, it is also deleterious to cell survival and accelerates apoptosis. Oncogenic Raf actively suppresses the onset of apoptosis and thus provides a survival factor to these cells. v-raf synergizes in apoptosis suppression with a weakly transforming oncogene, bcl-2, which has been shown earlier to suppress apoptosis in a variety of cell types. BCL-2 seems to function in a pathway parallel to Raf, since Raf-1 kinase did not affect the levels or the phosphorylation status of BCL-2 protein. The data obtained with Myc and Raf in the 32D cell system and data obtained in systems with the ability to differentiate showed that v-raf was compatible with or induced differentiation, whereas myc by itself was ineffective or blocked differentiation. These findings led us to postulate that the ratio of Raf- to Myc-pathway activity induced by a certain receptor will determine the outcome of the stimulation in terms of cell fate (proliferation, differentiation, or apoptosis). This model is supported by our findings in the PC12 cell system. (i) Analysis of isolated Myc- and Raf-pathways in PC12 cells showed that activated Raf efficiently induced differentiation, whereas Myc showed toxic effects. (ii) The differentiation factor "nerve growth factor" induced long-lasting activation of Raf-1 kinase, in contrast to the transient activation seen with epidermal growth factor. (iii) Finally, inhibition of c-myc by a dominant negative myc mutant converted the EGF into a differentiation factor.