T antigens inhibit Notch to promote Merkel cell carcinoma in skin stem cells

项目摘要 默克尔细胞癌(MCC)是一种高度侵袭性的皮肤神经内分泌恶性肿瘤。一个新的 发现的人类多瘤病毒，默克尔细胞多瘤病毒(MCV)，编码致癌的小T细胞和大T细胞 在80%以上的MCC中发现的抗原。MCV T抗原促进正常细胞转化 是MCC维护所必需的。但这些病毒蛋白的确切分子机制 实现这一点还有待确定。研究MCV T抗原将提供一个独特的机会 研究MCC和其他侵袭性神经内分泌癌的发病机制并发现许多 所需的治疗靶点。最近，DeCaprio实验室发现MCV小T抗原(ST) 特异性结合MYCL(L-MYC)转录因子和EP400染色质重构体复合体 激活基因表达。我们发现，与EP400和MYCL形成的复合体中的ST能激活默克尔细胞-- 特异性转录因子Atoh1，以及核心转录抑制物复合体的组成部分。 在MCC中使用化学抑制剂的核心失活导致生长停滞和Notch肿瘤增加 抑制子信号基因。在这里，我们假设通过直接激活和间接抑制 Noch信号基因通过Corest，ST增加MCC中的Atoh1，促进肿瘤的发生。我们还发现， 核心失活上调LGR6皮肤干细胞受体。在体内LGR6的表达受到限制 通常为毛囊干细胞。最近在LGR6血统追踪小鼠模型中的研究表明，LGR6+ 成体干细胞在创伤后能够重建整个卵泡间上皮，这表明 显示默克尔单元格属性的MCC可能来自这些单元格。因此，我们建议 以下具体目的是检验默克尔细胞多瘤病毒通过以下途径致癌的假设 激活Atoh1抑制毛囊干细胞中的Notch。在目标1中，我将确定ST 通过直接激活EP400-MYCL和通过COREST抑制Notch信号基因来诱导Atoh1。这就做 研究ST在MCC细胞中的占位情况及COREST对Notch信号基因表达的影响。在……里面 目的2，我将评估Atoh1转录程序和Notch信号在MCC维持中的作用。至 为此，我将研究Atoh1转录组，并探讨Notch信号激活在MCC中的作用。在AIM 3、我建议确定LGR6驱动的默克尔细胞多瘤病毒T抗原在头发中的表达 毛囊干细胞导致Atoh1+Merkel细胞样细胞在小鼠皮肤中积聚。 影响：在完成这些目标后，拟议的研究将揭示ATOH1未被认识到的作用， 巨噬细胞癌中的Corest和Notch信号通路及其调控机制 主持转录节目。这些发现将揭示MCC和其他潜在癌症的新靶点 难以治疗的神经内分泌恶性肿瘤。

Project Summary Merkel cell carcinoma (MCC) is a highly aggressive neuroendocrine malignancy in the skin. A newly discovered human polyomavirus, Merkel cell polyomavirus (MCV), encodes oncogenic small and large T antigens that are found in more than 80% of MCC. MCV T antigens promote transformation of normal cells and are required for MCC maintenance. But the precise molecular mechanism by which these viral proteins accomplish this has yet to be determined. Studying MCV T antigens will provide a unique opportunity to investigate the pathogenesis of MCC and other aggressive neuroendocrine cancers and to discover much needed therapeutic targets. Recently, the DeCaprio laboratory discovered that MCV Small T antigen (ST) specifically associates with MYCL (L-MYC) transcription factor and the EP400 chromatin remodeler complex to activate gene expression. We found that ST in a complex with EP400 and MYCL activates the Merkel cell- specific transcription factor ATOH1, as well as components of the coREST transcription repressor complex. coREST inactivation using chemical inhibitors in MCC causes a growth arrest and an increase in Notch tumor suppressor signaling genes. Here we hypothesize that through direct activation and indirect repression of Notch signaling genes via coREST, ST increases ATOH1 in MCC to promote oncogenesis. We also found that coREST inactivation upregulates the LGR6 skin stem cell receptor. In vivo LGR6 expression is restricted normally to hair follicle stem cells. Recent work in an LGR6 lineage-tracing mouse model suggests that LGR6+ adult stem cells are able to reconstitute the entire interfollicular epithelium after wounding, suggesting the possibility that MCC displaying Merkel cell properties may arise from these cells. Thus, we propose the following specific aims to test the hypothesis that Merkel cell polyomavirus causes cancer by activating ATOH1 and inhibiting Notch in hair follicle stem cells. In Aim 1, I will determine whether ST induces ATOH1 through direct activation EP400-MYCL and Notch signaling gene repression by coREST. I will investigate ST’s occupancy and the effect of coREST on Notch signaling gene expression in MCC cell lines. In Aim 2, I will assess the role of the ATOH1 transcription program and Notch signaling in MCC maintenance. To do so, I will study the ATOH1 transcriptome and probe the effect of Notch signaling activation in MCC. In Aim 3, I propose to determine whether LGR6-driven expression of Merkel cell polyomavirus T antigens in the hair follicle stem cells leads to accumulation of ATOH1+ Merkel cell-like cells in mouse skin. Impact: After completing these aims, the proposed research will uncover the unappreciated role of ATOH1, coREST and Notch signaling pathway in MCC and determine how ST contributes to MCC through modulating host transcription programs. These findings will disclose novel cancer targets for MCC and potentially other difficult to treat neuroendocrine malignancies.