Mechanism of chemoresistance mediated by TGF-beta

描述（由申请人提供）：许多化疗药物通过对DNA造成损伤来对抗癌细胞。对化疗的耐药性是癌症治疗中的主要临床障碍。癌症患者的化疗耐药机制尚未完全了解，导致迫切需要确定控制药物反应的因素并开发新的治疗方法以提高治疗效果。转化生长因子（TGF）是正常细胞中的肿瘤抑制因子，它的信号传导在癌症中被劫持以促进疾病进展。在乳腺癌中，TGF-β与不良的临床结果和化疗耐药性有关，其机制在很大程度上仍然未知。我们以前的研究表明，在乳腺癌细胞中，TGF-β诱导靶向DNA损伤传感器ATM和MSH 2的microRNA（miR-21和miR-181），因此可能调节癌症对遗传毒性化疗的反应。本研究的目的是剖析TGF-2介导的化疗耐药的分子机制，并探索潜在的治疗方法，以提高药物疗效。在目标1中，TGF-β将使用已建立的分子和细胞生物学测定，在具有不同p53状态的乳腺癌细胞中测定对各种DNA损伤处理和对聚（ADP-核糖）聚合酶（PARP）抑制的细胞应答的作用。TGF-β调节的miRNA和ATM/MSH 2通路的作用将通过基因敲低和过表达策略来确定。在目标2中，将检验增强SMAD 2/3与其RNA靶点的结合介导TGF-β在癌细胞中向诱导miRNA调节和化学抗性的功能转变的假设。乳腺癌细胞表达各种水平的SMAD 2/3辅因子（即，SMAD 4、Drosha和p68）对SMAD 2/3功能和TGF-2作用的动态调节。在目标3中，将在动物肿瘤模型中评估TGF-β对化疗反应的影响和前两个目标中确定的机制。将探索治疗性抑制这种TGF-β功能并提高治疗效果的新策略。这项研究将有助于更好地理解耐药性和TGF-β信号作为癌症治疗的标志物和靶点。虽然本文确定的机制可能具有理解癌症和定义治疗的一般应用，但我们的研究对临床侵袭性，难以治疗的基底样（主要是三阴性）乳腺癌具有重要意义，这些乳腺癌经常经历活跃的TGF-β信号传导。这项研究将通过SMAD 2/3介导的miRNA加工为TGF-β在癌症中的功能开关提供新的见解。了解TGF-2介导的化疗耐药性可能会揭示新的治疗靶点和策略，这将提高缺乏全身治疗靶点的癌症的化疗疗效。我们的长期目标是在原发性癌症中验证这种机制，并建立标准方法来识别适合靶向TGF-β耐药效应的治疗的患者，并了解TGF-β介导的miRNA失调在人类癌症中的整体效应。

DESCRIPTION (provided by applicant): Many chemotherapy drugs act against cancer cells by causing damage to the DNA. Resistance to chemotherapy is a major clinical obstacle in cancer treatment. The mechanisms of chemoresistance in cancer patients are not fully understood, leading to urgent needs for determining factors that control drug response and developing novel therapies to enhance the treatment efficacy. Signaling from transforming growth factor (TGF) ¿, a tumor suppressor in normal cells, is hijacked in cancer to promote disease progression. In breast cancer, TGF- ¿ is linked to poor clinical outcomes and chemoresistance through mechanisms that remain largely unknown. Our previous studies indicate that in breast cancer cells, TGF- ¿ induces microRNAs (miR-21 and miR-181) that target the DNA damage sensors ATM and MSH2, and may therefore regulate cancer response to genotoxic chemotherapy. The goals of this study are to dissect the molecular mechanism of TGF-2-mediated chemoresistance, and to explore potential therapies to enhance drug efficacy. In Aim 1, TGF- ¿ action on cell response to various DNA-damaging treatments and to inhibition of poly(ADP-ribose) polymerase (PARP) will be determined in breast cancer cells with different p53 status using established molecular and cellular biology assays. The role of the TGF- ¿ -regulated miRNAs and the ATM/MSH2 pathways will be determined using gene knockdown and overexpression strategies. In Aim 2, the hypothesis that enhanced SMAD2/3 binding to their RNA targets mediates TGF- ¿ 's functional shift in cancer cells towards inducing miRNA regulation and chemoresistance will be examined. Breast cancer cells expressing various levels of the SMAD2/3 cofactors (i.e., SMAD4, Drosha and p68) will be examined for their dynamic regulation of SMAD2/3 function and TGF-2 effect. In Aim 3, the effect of TGF- ¿ on chemotherapy response and the mechanism identified in the first two aims will be evaluated in animal tumor models. Novel strategies to therapeutically suppress this TGF- ¿ function and enhance the treatment efficacy will be explored. This study will enable better understandings of drug resistance and of TGF- ¿ signaling as both a marker and a target in cancer treatment. Although the mechanism identified herein may have a general application to understanding cancer and defining treatments, our study has added significance for clinically aggressive, hard-to-treat basal- like (mainly triple-negative) breast cancer that often experience active TGF- ¿ signaling. This study will provide novel insight into the functional switch of TGF- ¿ in cancer via SMAD2/3-mediated miRNA processing. Understanding TGF-2-mediated chemoresistance may reveal novel therapeutic targets and strategies that will enhance the chemotherapy efficacy for cancers that lack targets for systemic treatments. Our long-term objectives are to validate this mechanism in primary cancers and establish standard approaches to identify patients suitable for therapies targeting TGF- ¿ 's drug resistant effect, and to understand the global effect of TGF- ¿ -mediated miRNA dysregulation in human cancer.