Torrejón Blanca, Cristóbal Ion, Caramés Cristina, Prieto-Potín Iván, Chamizo Cristina, Santos Andrea, Sanz-Alvarez Marta, Serna-Blasco Roberto, Luque Melania, Madoz-Gúrpide Juan, Rojo Federico, García-Foncillas Jesús
Translational Oncology Division, Oncohealth Institute, IIS-Fundación Jiménez Diaz, Autonomous University of Madrid, University Hospital "Fundación Jiménez Diaz", Avda. Reyes Católicos-2, 28040, Madrid, Spain.
Pathology Department, Autonomous University of Madrid, University Hospital "Fundación Jiménez Diaz", 28040, Madrid, Spain.
World J Surg. 2018 Nov;42(11):3771-3778. doi: 10.1007/s00268-018-4684-9.
The functional loss of the tumor suppressor protein phosphatase 2A (PP2A) occurs in a wide variety of human cancers including colorectal cancer (CRC), and SET overexpression has been reported as a key contributing mechanism to inhibit PP2A. Although SET binding protein 1 (SETBP1) overexpression and gain of function mutations have been described in several hematological malignancies as common events that increase the expression levels of the PP2A inhibitor SET, thereby leading to PP2A inactivation, the potential existence of SETBP1 alterations in CRC still remains unexplored.
We studied the expression profile of SETBP1 by Western blot in a set of CRC cell lines and patient samples. Moreover, we performed co-immunoprecipitation assays to analyze the formation of the previously reported SETBP1-SET-PP2A inhibitory complex. Furthermore, we evaluated the mutational status of SETBP1 by pyrosequencing assays in a cohort of 55 CRC patients with metastatic disease after the immunohistochemical characterization of SET and p-PP2A expression in this cohort.
We found high SETBP1 expression in several CRC lines but only in two of the patients analyzed. In addition, we demonstrated the formation of the SETBP1-SET-PP2A heterotrimeric complex in CRC cells. However, we failed to detect SETBP1 mutations in any of the CRC patient samples included in the study.
Our results suggest that SETBP1 expression is mainly similar o lower in colorectal cancer tissue compared to normal colonic mucosa. However, its overexpression is a low prevalent alteration which could contribute to inhibit PP2A in CRC through the formation of a SETBP1-SET-PP2A complex in some CRC patients. Moreover, SETBP1 mutations are, if exist, rare events in CRC patients.
肿瘤抑制蛋白磷酸酶2A（PP2A）的功能丧失在包括结直肠癌（CRC）在内的多种人类癌症中都有发生，并且已有报道称SET的过表达是抑制PP2A的关键促成机制。尽管在几种血液系统恶性肿瘤中已描述了SET结合蛋白1（SETBP1）的过表达和功能获得性突变是增加PP2A抑制剂SET表达水平从而导致PP2A失活的常见事件，但CRC中SETBP1改变的潜在存在仍未得到探索。
我们通过蛋白质免疫印迹法研究了一组CRC细胞系和患者样本中SETBP1的表达谱。此外，我们进行了免疫共沉淀实验以分析先前报道的SETBP1-SET-PP2A抑制复合物的形成。此外，在对该队列中SET和p-PP2A表达进行免疫组织化学表征后，我们通过焦磷酸测序法评估了55例转移性CRC患者队列中SETBP1的突变状态。
我们在几个CRC细胞系中发现了高SETBP1表达，但在所分析的患者中只有两例如此。此外，我们证实在CRC细胞中形成了SETBP1-SET-PP2A异源三聚体复合物。然而，我们在该研究纳入的任何CRC患者样本中均未检测到SETBP1突变。
我们的结果表明，与正常结肠黏膜相比，结直肠癌组织中SETBP1的表达主要相似或较低。然而，其过表达是一种低发生率的改变，在一些CRC患者中可能通过形成SETBP1-SET-PP2A复合物来抑制PP2A。此外，SETBP1突变（如果存在）在CRC患者中是罕见事件。
