Sane S, Abdullah A, Boudreau D A, Autenried R K, Gupta B K, Wang X, Wang H, Schlenker E H, Zhang D, Telleria C, Huang L, Chauhan S C, Rezvani K
Division of Basic Biomedical Sciences, Sanford School of Medicine, The University of South Dakota, 414 E. Clark Street, Lee Medical Building, Vermillion, SD, USA.
Department of Pharmaceutical Sciences, Cancer Research Center, University of Tennessee Health Science Center, 19S Manassas Avenue, Memphis, TN, USA.
Cell Death Dis. 2014 Mar 13;5(3):e1118. doi: 10.1038/cddis.2014.100.
Mortalin (mot-2) induces inactivation of the tumor suppressor p53's transcriptional and apoptotic functions by cytoplasmic sequestration of p53 in select cancers. The mot-2-dependent cytoprotective function enables cancer cells to support malignant transformation. Abrogating the p53-mot-2 interaction can control or slow down the growth of cancer cells. In this study, we report the discovery of a ubiquitin-like (UBX)-domain-containing protein, UBXN2A, which binds to mot-2 and consequently inhibits the binding between mot-2 and p53. Genetic analysis showed that UBXN2A binds to mot-2's substrate binding domain, and it partly overlaps p53's binding site indicating UBXN2A and p53 likely bind to mot-2 competitively. By binding to mot-2, UBXN2A releases p53 from cytosolic sequestration, rescuing the tumor suppressor functions of p53. Biochemical analysis and functional assays showed that the overexpression of UBXN2A and the functional consequences of unsequestered p53 trigger p53-dependent apoptosis. Cells expressing shRNA against UBXN2A showed the opposite effect of that seen with UBXN2A overexpression. The expression of UBXN2A and its apoptotic effects were not observed in normal colonic epithelial cells and p53-/- colon cancer cells. Finally, significant reduction in tumor volume in a xenograft mouse model in response to UBXN2A expression was verified in vivo. Our results introduce UBXN2A as a home defense response protein, which can reconstitute inactive p53-dependent apoptotic pathways. Inhibition of mot-2-p53 interaction by UBXN2A is an attractive therapeutic strategy in mot-2-elevated tumors.
在某些癌症中，mortalin（mot-2）通过将p53隔离在细胞质中，诱导肿瘤抑制因子p53的转录和凋亡功能失活。mot-2依赖的细胞保护功能使癌细胞能够支持恶性转化。消除p53与mot-2的相互作用可以控制或减缓癌细胞的生长。在本研究中，我们报告发现了一种含泛素样（UBX）结构域的蛋白质UBXN2A，它与mot-2结合，从而抑制mot-2与p53之间的结合。基因分析表明，UBXN2A与mot-2的底物结合结构域结合，且部分与p53的结合位点重叠，这表明UBXN2A和p53可能竞争性地与mot-2结合。通过与mot-2结合，UBXN2A将p53从胞质隔离中释放出来，挽救了p53的肿瘤抑制功能。生化分析和功能试验表明，UBXN2A的过表达以及p53未被隔离的功能后果触发了p53依赖的凋亡。表达针对UBXN2A的短发夹RNA（shRNA）的细胞表现出与UBXN2A过表达相反的效果。在正常结肠上皮细胞和p53基因敲除的结肠癌细胞中未观察到UBXN2A的表达及其凋亡效应。最后，在体内验证了异种移植小鼠模型中，响应UBXN2A表达，肿瘤体积显著减小。我们的研究结果表明UBXN2A是一种宿主防御反应蛋白，它可以重建失活的p53依赖的凋亡途径。在mot-2水平升高的肿瘤中，通过UBXN2A抑制mot-2与p53的相互作用是一种有吸引力的治疗策略。
