Findley H W, Gu L, Yeager A M, Zhou M
Division of Pediatric Hematology/Oncology/Bone Marrow Transplantation, Emory University School of Medicine, Atlanta, GA 30322, USA.
Blood. 1997 Apr 15;89(8):2986-93.
Bcl-2 and its homologue, Bcl-x1, encode membrane-associated proteins that protect neoplastic cells from DNA damage-induced apoptosis, whereas Bax is a Bcl-2 antagonist that promotes cell death. In the present study, we examined the expression and regulation of these genes at both the mRNA and protein level in 22 pediatric acute lymphoblastic leukemia (ALL) cell lines, as well as their sensitivity to apoptosis after exposure to ionizing radiation (IR). Eleven of 22 lines expressed wild-type (wt) p53, 4 expressed mutant p53, and 7 did not express p53 (p53-null). Nine of 22 (41%) lines expressed Bcl-2; of these, 8 were wt-p53+ and 1 expressed mutant p53. Bcl-2 was not expressed in any p53-null lines. In contrast, all 22 lines were positive for Bcl-x1 and Bax, although expression level varied. Treatment with IR (10 Gy) induced both downregulation of Bcl-2 and upregulation of Bax at 2 to 5 hours post-IR in 5 of 8 (63%) wt-p53+ lines, leading to apoptosis. Conversely, lines that failed to both downregulate Bcl-2 and upregulate Bax after IR were resistant to apoptosis. Although levels of Bcl-x1 expression varied among the 22 lines, high levels of Bcl-x1 were observed in 5 of 7 (71%) p53- lines. There were no obvious changes in the expression of Bcl-x1 in these lines after IR. However, among the p53-null lines, resistance to IR was observed only in those expressing high levels of Bcl-x1. These results suggest that expression of Bcl-2 but not Bcl-x1 is p53-dependent and that IR-induced downregulation of Bcl-2 and upregulation of Bax occur in most wt-p53+ lines and are associated with radiosensitivity. Furthermore, high-level expression of Bcl-x1 occurs predominantly in p53-null lines and is associated with resistance to IR-induced apoptosis in these lines, indicating differential expression and regulation of Bcl-2 and Bcl-x1 in pediatric ALL.
Bcl-2及其同源物Bcl-x1编码与膜相关的蛋白质，可保护肿瘤细胞免受DNA损伤诱导的凋亡，而Bax是一种促进细胞死亡的Bcl-2拮抗剂。在本研究中，我们检测了22种小儿急性淋巴细胞白血病（ALL）细胞系中这些基因在mRNA和蛋白质水平的表达及调控情况，以及它们在暴露于电离辐射（IR）后对凋亡的敏感性。22个细胞系中有11个表达野生型（wt）p53，4个表达突变型p53，7个不表达p53（p53缺失）。22个细胞系中有9个（41%）表达Bcl-2；其中，8个是wt-p53阳性，1个表达突变型p53。在任何p53缺失的细胞系中均未检测到Bcl-2表达。相反，所有22个细胞系的Bcl-x1和Bax均呈阳性，尽管表达水平有所不同。用IR（10 Gy）处理后，在8个wt-p53阳性细胞系中的5个（63%）中，于IR后2至5小时诱导了Bcl-2的下调和Bax的上调，从而导致凋亡。相反，IR后未能下调Bcl-2和上调Bax的细胞系对凋亡具有抗性。尽管22个细胞系中Bcl-x1的表达水平各不相同，但在7个p53缺失细胞系中的5个（71%）中观察到了高水平的Bcl-x1。IR后这些细胞系中Bcl-x1的表达没有明显变化。然而，在p53缺失的细胞系中，仅在那些表达高水平Bcl-x1的细胞系中观察到对IR的抗性。这些结果表明，Bcl-2而非Bcl-x1的表达是p53依赖性的，并且IR诱导的Bcl-2下调和Bax上调发生在大多数wt-p53阳性细胞系中，且与放射敏感性相关。此外，Bcl-x1的高水平表达主要发生在p53缺失的细胞系中，并与这些细胞系对IR诱导的凋亡的抗性相关，这表明小儿ALL中Bcl-2和Bcl-x1的表达及调控存在差异。
