Prognostic value of phosphorylated Raf kinase inhibitory protein at serine 153 and its predictive effect on the clinical response to radiotherapy in nasopharyngeal carcinoma

Li et al. Radiation Oncology (2016) 11:121 DOI 10.1186/s13014-016-0696-5 RESEARCH Open Access Prognostic value of phosphorylated Raf kinase inhibitory protein at serine 153 and its predictive effect on the clinical response to radiotherapy in nasopharyngeal carcinoma Siwei Li1†, Taowen Liu2†, Wenfa Mo3, Qiaoyan Hou3, Yingqiong Zhou3, Meilian Liu4, Zhoukai He4, Zhengchun Liu4, Qiuqiu Chen4, Hua Wang5, Xiang Guo5,6, Weixiong Xia5,6, Musheng Zeng6 and Haiyun Zhao7* Abstract Background: Radiation is an effective treatment against nasopharyngeal carcinoma (NPC). However, radioresistance-induced locoregional recurrence remains as a major cause of treatment failure. Therefore, radiosensitivity indicators prior to treatment should be developed to screen radioresistant patients. Previous studies revealed that RKIP (Raf kinase inhibitor protein) is associated with NPC prognosis and radiosensitivity. However, the relationship of p-Ser153 RKIP (RKIP in a phosphorylated form at residue serine153) expression with the effect of radiation and prognosis of NPC patients is not elucidated. Thus, these clinical implication of the phosphorylated RKIP in NPC has yet to be described. Methods: The effect of p-Ser153 RKIP on locoregional relapse-free survival (LRRFS) was first analyzed in a retrospective cohort of NPC patients without distant metastasis at initial diagnosis. They received radical intensity-modulated radiotherapy alone. Of 180 patients were enrolled in the ongoing matched pair study. The patients were re-classified into radioresistant group or radiosensitive group on the basis of the specified criteria. Patients in the two groups were matched in terms of radiosensitivity-related factors. p-Ser153 RKIP was examined by immunohistochemical staining on a NPC tissue microarray before radiotherapy. The relationship between the expression of p-Ser153 RKIP and the effect of radiotherapy was also analyzed. Results: In this study, a retrospective cohort with 733 cases who received radical radiotherapy alone was established. Using the cohort, we validated that the p-Ser153 RKIP expression observed through immunohistochemical staining in a pretreatment NPC tissue microarray was an independent prognostic factor of LRRFS and OS; we also confirmed that endemic patients with a positive p-Ser153 RKIP expression benefited from irradiation alone in terms of locoregional relapse-free survival. A total of 180 patients were enrolled in a matched pair study. Both groups were well matched in terms of radiosensitivity-related factors. On the basis of the p-Ser153 RKIP expression, we predicted the following data: 80.0 % sensitivity, 73.3 % specificity, 76.7 % accuracy, 75.0 % positive predictive value, and 78.6 % negative predictive value. (Continued on next page) * Correspondence: † Equal contributors 7 Department of Otorhinolaryngology, Head and Neck Surgery, Nanxishan Hospital of Guangxi Zhuang Autonomous Region, No.46 Chongxin Road, Guilin 541004, Guangxi Zhuang Autonomous Region, People’s Republic of China Full list of author information is available at the end of the article © 2016 The Author(s). Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Li et al. Radiation Oncology (2016) 11:121 Page 2 of 11 (Continued from previous page) Conclusions: Our results revealed for the first time that positive p-Ser153 RKIP expression was a favorable prognostic factor. It was also positively correlated with the radiosensitivity of NPC. p-Ser153 RKIP could also be used as a biomolecular marker with good availability and authenticity to preliminarily screen NPC-related clinical radiosensitivity. Keywords: Phosphorylated Raf kinase inhibitor protein (pRKIP), Nasopharyngeal carcinoma, Radiotherapy, Sensitivity, Prediction, Prognosis Introduction Radical radiation is an effective treatment against NPC; however, locoregional recurrence remains as a major cause of the failure of treatments for locoregionally advanced NPC [1]. As such, local control should be enhanced to improve survival and prognosis [1]. Therefore, radiosensitivity indicators prior to treatment should be developed on the basis of simple, reliable, and effective methods to screen radioresistant patients. These indicators provide a reasonable basis of specific NPC radiotherapy. RKIP, a well-established metastasis suppressor gene, has been identified as a negative regulator of survival signals induced by the activation of MAPK and NF-kB pathways. The overexpression of RKIP reverses tumor cell resistance to apoptosis by various factors, such as irradiation [2, 3], chemotherapeutic drugs [4, 5], and TRAIL [6]. RKIP is also considered as a prognostic marker of several nonhead–neck cancers [7–11]. Furthermore, the RKIP protein is associated with the metastasis, progression, and prognosis of NPC [12]. The functional activities of RKIP are regulated by its phosphorylation status on serine 153 [13]. In contrast to the unphosphorylated form, p-Ser153 RKIP (RKIP in a phosphorylated form at residue S153) antagonizes the actions of the unphosphorylated RKIP, which inhibits survival signals and promotes apoptosis. It is because p-Ser153 RKIP fails to effectively bind to Raf-1, p-Ser153 RKIP does not inhibit the MAPK signaling pathway [14]. Limited data are available to explore the clinical implication of p-Ser153 RKIP in tumors. For example, the loss or reduction of p-Ser153 RKIP expression in breast cancer [15] is associated with poor disease-free survival; furthermore, the complete loss of p-Ser153 RKIP is an independent prognostic factor. In patients with early-stage lung cancer or in elderly individuals, the normal expression of phospho-RKIP is a predictive indicator of a more favorable survival than the reduced expression of phosphoRKIP [16]. In contrast to these tumors, other tumors, such as multiple myeloma (MM) and stage II colon cancer, exhibit p-Ser153 RKIP that may positively contribute to the overall cell survival and drug resistance of MM through the constitutive activation of survival pathways and the downstream transcription of anti-apoptotic genes [17, 18]. Considering the varied results in different tumors, we should investigate the clinical implication of the phosphorylated RKIP in NPC. However, studies have yet to describe the relationship of p-Ser153 RKIP expression with the prognosis of NPC patients and the effect of radiation on NPC. In this study, the effect of pre-RT p-Ser153 RKIP expression in a NPC (...truncated)