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

我们以前已经证明，严格的自主增长 白细胞介素-3（IL-3）依赖性髓样32 D细胞需要激活 Myc和Raf-pathway两条途径的结合 虽然强制执行 Myc的表达在缺乏IL-3的情况下促进细胞周期进程， 它也对细胞存活有害并加速细胞凋亡。 致癌Raf积极抑制细胞凋亡的发生，从而提供 这些细胞的生存因素。 v-raf在细胞凋亡中协同作用 用弱转化癌基因bcl-2抑制， 早期显示抑制多种细胞类型的凋亡。 Bcl-2 似乎在与Raf平行的途径中起作用，因为Raf-1激酶不 影响BCL-2蛋白的水平或磷酸化状态。 的 在32 D细胞系统中用Myc和Raf获得的数据和在 具有分化能力的系统表明v-raf是相容的 与或诱导分化，而myc本身是无效的， 分化受阻。 这些发现使我们假设， 由某种受体诱导的Raf与Myc途径活性的比率将 根据细胞命运确定刺激的结果 （增殖、分化或凋亡）。 该模型支持 我们在PC 12细胞系统中的发现。 (i)分离的Myc- 在PC 12细胞中，Raf和Raf-通路显示， 诱导分化，而Myc显示毒性作用。 (ii)的 分化因子“神经生长因子”诱导持久 Raf-1激酶的激活，与观察到的瞬时激活相反， 表皮生长因子 (iii)最后，用一种 显性负性myc突变体将EGF转化为分化 因子

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.