The LIN28B-Let7 axis in intestinal epithelial biology

描述(申请人提供)：RNA结合蛋白Lin28b与多种癌症有关，其表达与侵袭性表型、转移增加和预后不良有关。当表达到小鼠的肠上皮时，我们发现Lin28b会导致肠道肥大、Paneth细胞丢失、隐窝分裂和肠腺癌的形成。Lin28b特别针对并抑制了let-7家族的miRNAs。Lin28b通过隔离核仁中的pri-miRNAs来抑制let-7 microRNA(MiRNA)的成熟，而这是微处理器机器无法达到的。通过用可诱导的let-7a转基因小鼠模型挽救let-7水平，我们确定上述Lin28b表型是由于Lin28b对let-7的依赖作用。此外，我们发现Lin28b介导的let-7下调导致了IGF mRNA结合蛋白-1(IMP1)的上调，因此，我们将研究Lin28b和IMP-1在肠道内稳态和肿瘤中的相互作用。自从LIN28b功能的let-7独立机制被报道以来，我们通过核糖核蛋白交联、免疫沉淀和高通量测序(RNP CLIP-Seq)来鉴定LIN28B直接靶向的mRNAs和miRNAs。这表明Lin28b与参与代谢过程、剪接和肌动蛋白细胞骨架调控的mRNAs结合。因此，我们发现了一条Lin28b-Let7-IMP1在结肠癌发生中的新途径，这不仅增加了我们对潜在分子机制的了解，而且通过使用Lin28b作为疾病进展的生物标记物，并在治疗上靶向这一途径，为翻译机会提供了一个平台。

DESCRIPTION (provided by applicant): The RNA-binding protein LIN28B has been implicated in a variety of cancers, with their expression correlating with an aggressive phenotype, enhanced metastasis and poor prognosis. When expression is directed to the mouse intestinal epithelium we find that LIN28B causes intestinal hypertrophy, loss of Paneth cells, crypt fission and intestinal adenocarcinoma formation. LIN28B specifically targets and repress the Let-7 family of miRNAs. LIN28B inhibits Let-7 microRNA (miRNA) maturation through sequestration of pri-miRNAs n the nucleolus, which is inaccessible to microprocessor machinery. By rescuing Let-7 levels with an inducible Let- 7a transgenic mouse model, we determined that the LIN28B phenotypes noted above are due to Let-7 dependent actions of LIN28B. Furthermore, we find that LIN28B mediated downregulation of Let-7 results in the upregulation of Igf mRNA binding protein-1 (IMP1), and thus, we will investigate the role of the interplay between LIN28B and IMP-1 in intestinal homeostasis and cancer. Since Let-7-independent mechanisms of LIN28B function have been reported, we have pursued ribonucleoprotein cross-linking, immunoprecipitation, and high-throughput sequencing (RNP CLIP-Seq) to identify mRNAs and miRNAs that are targeted directly by LIN28B.This reveals that LIN28B binds to mRNAs involved in metabolic processes, splicing, and regulation of the actin cytoskeleton. Thus, we identify a new pathway of LIN28B-Let7-IMP1 in colon carcinogenesis that adds to our knowledge of underlying molecular mechanisms, but also provides a platform in translational opportunities by using LIN28B as a biomarker for disease progression, and targeting this pathway therapeutically.