Chi S, Kitanaka C, Noguchi K, Mochizuki T, Nagashima Y, Shirouzu M, Fujita H, Yoshida M, Chen W, Asai A, Himeno M, Yokoyama S, Kuchino Y
Biophysics Division, National Cancer Center Research Institute, Tokyo, Japan.
Oncogene. 1999 Apr 1;18(13):2281-90. doi: 10.1038/sj.onc.1202538.
To prevent neoplasia, cells of multicellular organisms activate cellular disposal programs such as apoptosis in response to deregulated oncogene expression, making the suppression of such programs an essential step for potentially neoplastic cells to become established as clinically relevant tumors. Since the mutation of ras proto-oncogenes, the most frequently mutated proto-oncogenes in human tumors, is very rare in some tumor types such as glioblastomas and gastric cancers, we hypothesized that mutated ras genes might activate a cell death program that cannot be overcome by these tumor types. Here we show that the expression of oncogenically mutated ras gene induces cellular degeneration accompanied by cytoplasmic vacuoles in human glioma and gastric cancer cell lines. Cells dying as a result of oncogenic Ras expression had relatively well-preserved nuclei that were negative for TUNEL staining. An immunocytochemical analysis demonstrated that the cytoplasmic vacuoles are derived mainly from lysosomes. This oncogenic Ras-induced cell death occurred in the absence of caspase activation, and was not inhibited by the overexpression of anti-apoptotic Bcl-2 protein. These observations suggested that oncogenic Ras-induced cell death is most consistent with a type of programmed cell death designated 'type 2 physiological cell death' or 'autophagic degeneration', and that this cell death is regulated by a molecular mechanism distinct from that of apoptosis. Our findings suggest a possible role for this non-apoptotic cell death in the prevention of neoplasia, and the activation of the non-apoptotic cell death program may become a potential cancer therapy complementing apoptosis-based therapies. In addition, the approach used in this study may be a valuable way to find genetically-regulated cell suicide programs that cannot be overcome by particular tumor types.
为预防肿瘤形成，多细胞生物的细胞会响应失调的癌基因表达激活细胞清除程序，如凋亡，因此抑制这些程序是潜在的肿瘤细胞发展成为临床相关肿瘤的关键步骤。由于ras原癌基因（人类肿瘤中最常发生突变的原癌基因）的突变在某些肿瘤类型（如胶质母细胞瘤和胃癌）中非常罕见，我们推测突变的ras基因可能激活了一种这些肿瘤类型无法克服的细胞死亡程序。在此我们表明，致癌性突变的ras基因的表达会诱导人胶质瘤和胃癌细胞系发生伴有细胞质空泡的细胞变性。因致癌性Ras表达而死亡的细胞其细胞核相对保存完好，TUNEL染色呈阴性。免疫细胞化学分析表明，细胞质空泡主要来源于溶酶体。这种致癌性Ras诱导的细胞死亡在没有半胱天冬酶激活的情况下发生，并且不受抗凋亡Bcl-2蛋白过表达的抑制。这些观察结果表明，致癌性Ras诱导的细胞死亡最符合一种被称为“2型生理性细胞死亡”或“自噬性变性”的程序性细胞死亡类型，并且这种细胞死亡受一种不同于凋亡的分子机制调控。我们的研究结果表明这种非凋亡性细胞死亡在预防肿瘤形成中可能发挥作用，并且激活非凋亡性细胞死亡程序可能成为一种补充基于凋亡的治疗方法的潜在癌症治疗手段。此外，本研究中使用的方法可能是找到特定肿瘤类型无法克服的基因调控细胞自杀程序的一种有价值的途径。
