McCubrey J A, Lee J T, Steelman L S, Blalock W L, Moye P W, Chang F, Pearce M, Shelton J G, White M K, Franklin R A, Pohnert S C
Department of Microbiology and Immunology, Brody School of Medicine at East Carolina University, Greenville, NC 27858, USA.
Cancer Detect Prev. 2001;25(4):375-93.
The PI3K/Akt and Raf/MEK/ERK signal transduction cascades are pivotal in transmitting signals from membrane receptors to downstream targets that regulate apoptosis, gene expression, and cell growth. The abilities of activated PI3K, Akt, Raf, and MEK proteins to abrogate the cytokine dependence of three different hematopoietic cell lines were determined. Activated PI3K or Akt expression by themselves did not efficiently annul cytokine dependence. Raf and MEK could abrogate the cytokine dependence of murine FDC-PI and human TF-1 cells; however, the frequency of transformation was dependent on the particular oncogene examined, as more factor-independent cells were isolated after infection with activated retroviruses encoding A-Raf or Raf-1 than were with MEK1 or B-Raf. Cytokine-independent deltaRaf-1-infected cells formed tumors on injection into immunocompromised mice, whereas cytokine-dependent cell lines did not, demonstrating the oncogenic effects of activation of the Raf/MEK/ERK pathway. Overexpression of the antiapoptotic Bcl-2 protein synergized with activation of the Raf/MEK/ERK cascade and increased the efficiency of transformation of FDC-PI and TF-1 cells. In contrast to the results observed with FDC-P1 and TF-I cells, the activated Raf genes did not relieve the cytokine dependence of murine FL5.12 cells. The abilities of the Raf and PI3K pathways to interact and annul the cytokine dependence of FL5.12 cells were determined. The combination of Raf and either PI3K or Akt expression relieved cytokine dependence of some FL5.12 cells, and the efficiency of transformation could be enhanced further by Bcl-2 or Bcl-XL overexpression. Thus, the antiapoptotic PI3K/Akt and Bcl-2/Bcl-XL proteins can interact with the growth-promoting Raf/MEK/ERK pathway and annul the cytokine dependence of certain hematopoietic cells.
PI3K/Akt和Raf/MEK/ERK信号转导级联在将信号从膜受体传递到调节细胞凋亡、基因表达和细胞生长的下游靶点方面起着关键作用。测定了活化的PI3K、Akt、Raf和MEK蛋白消除三种不同造血细胞系对细胞因子依赖性的能力。单独表达活化的PI3K或Akt并不能有效地消除细胞因子依赖性。Raf和MEK可以消除小鼠FDC-PI和人TF-1细胞对细胞因子的依赖性；然而，转化频率取决于所检测的特定癌基因，因为在用编码A-Raf或Raf-1的活化逆转录病毒感染后分离出的不依赖因子的细胞比用MEK1或B-Raf感染后更多。注射到免疫缺陷小鼠体内后，不依赖细胞因子的deltaRaf-1感染细胞形成肿瘤，而依赖细胞因子的细胞系则不会，这证明了Raf/MEK/ERK途径激活的致癌作用。抗凋亡Bcl-2蛋白的过表达与Raf/MEK/ERK级联的激活协同作用，提高了FDC-PI和TF-1细胞的转化效率。与在FDC-P1和TF-I细胞中观察到的结果相反，活化的Raf基因并不能解除小鼠FL5.12细胞对细胞因子的依赖性。测定了Raf和PI3K途径相互作用并消除FL5.12细胞对细胞因子依赖性的能力。Raf与PI3K或Akt表达的组合可解除一些FL5.12细胞对细胞因子的依赖性，并且通过Bcl-2或Bcl-XL的过表达可进一步提高转化效率。因此，抗凋亡的PI3K/Akt和Bcl-2/Bcl-XL蛋白可以与促进生长的Raf/MEK/ERK途径相互作用，消除某些造血细胞对细胞因子的依赖性。
