Elliott K, Ge K, Du W, Prendergast G C
The Wistar Institute, Philadelphia, PA, USA.
Oncogene. 2000 Sep 28;19(41):4669-84. doi: 10.1038/sj.onc.1203681.
Cell death processes are progressively inactivated during malignant development, in part by loss of tumor suppressors that can promote cell death. The Bin1 gene encodes a nucleocytosolic adaptor protein with tumor suppressor properties, initially identified through its ability to interact with and inhibit malignant transformation by c-Myc and other oncogenes. Bin1 is frequently missing or functionally inactivated in breast and prostate cancers and in melanoma. In this study, we show that Bin1 engages a caspase-independent cell death process similar to type II apoptosis, characterized by cell shrinkage, substratum detachment, vacuolated cytoplasm, and DNA degradation. Cell death induction was relieved by mutation of the BAR domain, a putative effector domain, or by a missplicing event that occurs in melanoma and inactivates suppressor activity. Cells in all phases of the cell cycle were susceptible to death and p53 and Rb were dispensable. Notably, Bin1 did not activate caspases and the broad spectrum caspase inhibitor ZVAD.fmk did not block cell death. Consistent with the lack of caspase involvement, dying cells lacked nucleosomal DNA cleavage and nuclear lamina degradation. Moreover, neither Bcl-2 or dominant inhibition of the Fas pathway had any effect. In previous work, we showed that Bin1 could not suppress cell transformation by SV40 large T antigen. Consistent with this finding, we observed that T antigen suppressed the death program engaged by Bin1. This observation was interesting in light of emerging evidence that T antigen has roles in cell immortalization and human cell transformation beyond Rb and p53 inactivation. In support of a link to c-Myc-induced death processes, AEBSF, a serine protease inhibitor that inhibits apoptosis by c-Myc, potently suppressed DNA degradation by Bin1. Our findings suggest that the tumor suppressor activity of Bin1 reflects engagement of a unique cell death program. We propose that loss of Bin1 may promote malignancy by blunting death penalties associated with oncogene activation.
在恶性肿瘤发展过程中，细胞死亡过程会逐渐失活，部分原因是能够促进细胞死亡的肿瘤抑制因子缺失。Bin1基因编码一种具有肿瘤抑制特性的核质衔接蛋白，最初是通过其与c-Myc及其他致癌基因相互作用并抑制恶性转化的能力而被鉴定出来的。Bin1在乳腺癌、前列腺癌和黑色素瘤中常常缺失或功能失活。在本研究中，我们发现Bin1参与了一种类似于II型凋亡的非半胱天冬酶依赖性细胞死亡过程，其特征为细胞萎缩、与基质脱离、细胞质空泡化以及DNA降解。BAR结构域（一种假定的效应结构域）的突变或黑色素瘤中发生的剪接错误事件（该事件会使抑制活性失活）可减轻细胞死亡诱导。细胞周期各阶段的细胞均易发生死亡，且p53和Rb并非必需。值得注意的是，Bin1不会激活半胱天冬酶，广谱半胱天冬酶抑制剂ZVAD.fmk也不会阻断细胞死亡。与不涉及半胱天冬酶一致，濒死细胞缺乏核小体DNA切割和核纤层降解。此外，Bcl-2或Fas途径的显性抑制均无任何作用。在之前的研究中，我们表明Bin1无法抑制SV40大T抗原诱导的细胞转化。与此发现一致，我们观察到T抗原抑制了Bin1引发的死亡程序。鉴于新出现的证据表明T抗原在细胞永生化和人类细胞转化中的作用不仅仅是使Rb和p53失活，这一观察结果很有意思。为支持与c-Myc诱导的死亡过程存在联系，AEBSF（一种通过抑制c-Myc诱导的凋亡的丝氨酸蛋白酶抑制剂）可有效抑制Bin1诱导的DNA降解。我们的研究结果表明，Bin1的肿瘤抑制活性反映了一种独特的细胞死亡程序的参与。我们提出，Bin1的缺失可能通过削弱与致癌基因激活相关的死亡惩罚来促进恶性肿瘤的发生。
