TCTP在乳腺癌干细胞辐射抵抗中的作用及机制研究

Cancer stem cells (CSCs) have been postulated recently as responsible for recurrent tumours after radiotherapy. While the specific mechanism underlying radiation resistance of CSCs has not been fully elucidated, early data suggest differences in DNA repair, reactive oxygen species and survival signaling. Current studies indicate that the higher capability to repair DNA lesions is one of the major reasons for the resistance of Breast Cancer Stem Cells (BCSCs) to radiotherapy. However, the unique mechanisms of DNA repair pathways of BCSCs are unknown. .The Translationally Controlled Tumor Protein (TCTP) is essential for survival by yet incompletely defined mechanisms. In general, it is thought that TCTP promotes cell viability through an anti-apoptotic role. Our study (PNAS, in press) have identified that TCTP supports the survival and genomic integrity of irradiated cells through a critical role in the DNA damage response (DDR). Upon exposure of normal human cells/tumor cells to low/mild dose γ rays, the TCTP protein level was greatly increased, with a significant enrichment in nuclei. TCTP up-regulation occurred in a manner dependent on ATM- and the DNA-dependent protein kinase (DNA-PK), and was associated with protective effects against DNA damage. Conversyly, high dose exposure led to decreased levels of TCTP, which may facilitate the apoptotic process induced by p53. Surprisingly, in our preliminary study, persistent up-regulation of TCTP occurred in BCSCs exposed to 8Gy γ-Rays, instead of TCTP reduction shown in normal human cells/tumor cells. We therefore hypothesize that the abnormal regulation of DDR related with TCTP, especially in the pathway of DNA repair or survival signaling, is invovled in the radioresistance of BCSCs..There are three specific aims: Aim 1, to detect and confirm the association of TCTP with radioresistance of BCSCs by laboratory and clinical studies; Aim 2, to test the specific pathway, including DNA repair, apoptosis/senensence and G1/G2 phases, et al. , in which TCTP is involved contribute to the radioresistance of BCSCs by in vitro and in vivo analysis through overexpression/ knock-down of TCTP; and Aim 3, to examine the regulation of ATM-TCTP/HIPK2-p53 pathway in radioresistant BCSCs and its mechanism, also, by using the TCTP inhibitors in animal experiments, to test a potential strategy of TCTP depletion combined with radiotrerapy sensitizing BCSCs to radiation..Modulation of DNA damage response network to minimize repair function of BCSCs can potentially sensitize these cells to chemotherapy drugs and radiation. The abnormal function and feature of TCTP in the radioresistance of BCSCs, if identified, will provide novel insights of DDR mechanism in cancer stem cells and thus promise a new target in therapeutic interventions for the effective treatment of breast cancer.

肿瘤干细胞（CSCs）是放疗后肿瘤复发的根源，有别于正常/肿瘤细胞的异常DNA损伤反应（DDR）是导致CSCs放疗逃逸的主要原因，机制不祥。研究发现，TCTP可能与乳腺癌干细胞（BCSCs）的异常生物学行为密切相关。我们首次研究证实，TCTP作为正常/肿瘤细胞DDR体系的关键分子直接参与DNA损伤修复，随着损伤程度加重，TCTP还通过自身表达量的"先增后降"与p53协同调节细胞凋亡反应。然而，高剂量辐照后，BCSCs内TCTP表达却持续增高，提示其相关DDR调控可能发生异常。本课题首次以BCSCs为对象，从细胞-动物-临床标本多个层面阐明TCTP与BCSCs辐射抵抗的相关性，利用基因转染、Co-IP等技术手段全面揭示TCTP在BCSCs辐射抵抗中的效应通路，并围绕ATM-TCTP-p53调控深入开展相关分子机理研究。项目实施对于揭示CSCs异常辐射抗性机制，寻找新的放疗靶点具有重要意义。

研究表明，放射治疗后肿瘤的复发与转移与肿瘤干细胞密切相关，肿瘤干细胞的存在给临床放疗带来巨大挑战。我室近年来研究发现肿瘤翻译控制蛋白TCTP在DNA损伤修复中具有关键作用且TCTP与胶质瘤的临床病理分级和预后密切相关，但关于TCTP与胶质瘤放疗抵抗的关系，尚无研究。重编程是已分化细胞通过去分化向干细胞转化的过程，近年来被证实是肿瘤干细胞的重要来源，多能转录因子在重编程中发挥重要作用。本课题以放化疗抗性肿瘤细胞为研究对象，从形态学-肿瘤放射生物学-分子生物学等多个层面探讨TCTP在肿瘤细胞治疗抗性和干性重获中的作用；在证实TCTP与肿瘤恶性表型相关的基础上明确了TCTP通过调控转录因子影响辐射诱导的重编程的重要机制。研究发现，TCTP通过直接作用于多能转录因子影响辐射诱导的肿瘤细胞重编程的进程，参与肿瘤细胞化疗耐药特性和辐射诱导的胶质瘤细胞干性重获的维持，抑制TCTP可以显著抑制肿瘤细胞的恶性表型和放化疗抗性。项目成果对于阐明了TCTP在药物或辐射诱导肿瘤细胞向肿瘤干细胞转化的重要作用和机制，为临床肿瘤治疗提供了新的靶点。