Mechanisms and relevance of alternative processing of miRNAs and 5'isomiRs in breast cancer

乳腺癌（BRCA）是德国和全世界女性中最常见的癌症。值得注意的是，来自乳腺组织的癌在患者之间是不一样的。治疗选择和预后是由关键受体的表达决定的，因此由由此产生的基因表达改变决定。然而，患有任何亚型BRCA的患者都有复发或转移的风险，因此更好地了解疾病机制和潜在的治疗靶点非常重要。BRCA的发展和进展与编码基因表达的基本改变有关，但也与非编码参与者（如miRNAs）的表达有关。这些小RNA分子根据其种子序列（miRNA分子的核苷酸2-8）与靶mrna结合，以降低靶蛋白的表达，从而发挥其调节功能。5 '异构体是细胞miRNA的天然衍生物，由主要miRNA转录物的替代加工产生。重要的是，与它们的规范对应物相比，它们表现出了移位的种子序列。因此，一个或两个核苷酸的变化可以在很大程度上改变它们的靶谱，从而也改变它们在BRCA和其他情况下对细胞表型的影响。尽管它们被证明与癌症相关的表型相关，尽管有关于癌症中单个mirna的异常加工的报道，但尚未对其进行全面研究，如果加工和成熟在癌症中普遍改变，以及如何在分子水平上解释这一点。因此，我们的目标是系统地表征BRCA中的miRNA加工景观，并研究5 ' isomir产生的分子机制。沿着这条路线，我们的目标是深入了解癌症中5'isomiR加工异常调节的分子机制和生物学相关性，并表征其表型后果。为此，我们将战略性地结合对患者数据集的计算分析，以产生可靠的假设，并对这些假设进行全面的体外和最终的体内验证。基于我们在第一个资助阶段获得的初步结果，我们假设在细胞周期、剪接和miRNA成熟之间存在复杂的相互作用，这种相互作用在癌变和癌症进展中一致受到干扰。因此，确定RNA加工机制中的这些改变是否也有助于癌细胞的表型优势是至关重要的，因为这可能为风险评估、患者分层以及基于个体RNA加工模式的潜在个性化治疗开辟新的视角。

Breast cancer (BRCA) is the most frequently diagnosed cancer in women in Germany and worldwide. Notably, carcinomas arising from mammary tissue are heterogeneous between patients. Therapeutic options and prognosis are determined by the expression of key receptors and consequently by the resulting gene expression alterations. Yet, patients suffering from any subtype of BRCA are at risk of relapse or metastasis making it highly important to better understand disease mechanisms and consequently potential therapeutic targets. BRCA development and progression is associated with fundamental alterations in the expression of coding genes, but also of non-coding players such as miRNAs. These small RNA molecules exert their regulatory functions by binding to target mRNAs based on their seed sequence, nucleotides 2-8 of the miRNA molecule, to reduce expression of the target proteins. 5’isomiRs are naturally occurring derivatives of cellular miRNAs arising from alternative processing of the primary miRNA transcript. Importantly, they exhibit a shifted seed sequence as compared to their canonical counterpart. Consequently, this shift by one or two nucleotides can largely alter their target spectrum and thereby also their impact on cellular phenotypes both in BRCA and other contexts. Despite their proven relevance to cancer-related phenotypes and despite reports on aberrant processing of individual miRNAs in cancer, it has not yet been studied comprehensively, if processing and maturation is altered in cancer in general and how this might be explained on a molecular level. Therefore, we aim here to systematically characterize the miRNA processing landscape in BRCA and investigate the molecular mechanisms underlying the generation of 5’isomiRs. Along this line, we aim to gain insights into the molecular mechanisms and the biological relevance of aberrant regulation of 5’isomiR processing in cancer and characterize the phenotypic consequences. For that purpose, we will strategically combine computational analyses of patient data sets to generate solid hypotheses with comprehensive in vitro and eventually in vivo validation of these hypotheses. Based on the preliminary results that we have obtained in the first funding phase, we hypothesize that there is a complex interplay between cell cycle, splicing and miRNA maturation which is coherently perturbed in carcinogenesis and cancer progression. Hence, it is of crucial importance to determine if these alterations in the RNA processing machinery also contribute to phenotypic advantages for the cancer cells as this might open new perspectives for risk assessment, patient stratification and potentially also personalized therapy based on the individual RNA processing pattern.