Hypovitaminosis D promotes MED12-associated genomic instability in uterine fibroids

项目总结/摘要 子宫肌瘤（UFs;平滑肌瘤）是最重要的良性肿瘤威胁妇女的健康 世界各地，但不成比例地影响有色人种妇女，特别是非洲裔美国人（AA）妇女，她们有一个 UFs的发生率和相对风险是白人（CC）女性的三倍。虽然底层 这种风险差异的原因尚不完全清楚，最近的研究表明维生素D缺乏症是一种主要的 贡献者。因此，AA女性与CC女性相比，维生素D缺乏的风险增加了10倍， 正如我们首次报道的，UF风险与血清25-羟基维生素D水平呈负相关。尽管如此， 目前尚不清楚是否以及如何驱动UF形成和确定相对风险的过程是遗传的， 或者是生物化学上的联系在这方面，我们和其他人已经确定了转录水平上的体细胞突变。 介体亚基MED 12是UF的主要驱动因素，占肿瘤的约70%。值得注意的是，MED 12- 突变型UF的特征是显著的染色体丢失和重排，这表明基因组 不稳定性作为肿瘤进展的驱动力。在此，我们阐明了突变MED 12的分子基础- 驱动的基因组不稳定性，并进一步确定维生素D3受体信号传导作为这一可能的抑制剂， 过程我们发现MED 12突变的UF干细胞（SC）积累了高水平的未修复DNA双链， 链断裂（DSB）通过下调关键的DNA损伤反应（DDR）和修复基因。值得注意的是， 我们发现维生素D3/受体轴是MED 12调节的DDR基因表达的可变调节剂。 因此，我们表明，减少维生素D3/受体信号抑制，而升高的信号激活， DDR基因在MED 12突变UF SC中下调。基于这些发现，我们假设， 维生素D缺乏症加剧了MED 12突变体DNA损伤积累和基因组不稳定性 UF，导致肿瘤进展和负荷增强。因此，我们建议维生素D3，通过 受损DDR的修复将在MED 12突变肿瘤中提供治疗益处。测试这些 假设，我们将（1）阐明MED 12突变型UF基因组不稳定性的分子基础。我们将 确定MED 12突变UF SC中的DSB蓄积是否源于DNA损伤诱导的缺陷， 检查点信号传导和修复和/或R环诱导的复制应激。(2)研究动脉瘤性 维生素D3和MED 12在UF基因组维持中的作用。我们会问维生素D3 信号强度调节MED 12突变UF SC中的DDR缺陷，将该活性与患者种族相关， 血清维生素D水平，并阐明维生素D3/受体轴和MED 12 在基因组和表观基因组水平上协调控制DDR网络;（3）检查治疗性 维生素D3在人类UFs临床前小鼠模型中的潜力。使用肾包膜小鼠模型， 人UFs，我们将评估维生素D3及其有效的非高钙类似物的治疗功效， 安全性和作用机制，包括对肿瘤DNA损伤负荷和DDR基因网络的影响。

PROJECT SUMMARY/ABSTRACT Uterine fibroids (UFs; leiomyomas) are the most important benign neoplastic threat to women's health worldwide, but disproportionately affect women of color, particularly African American (AA) women, who have a threefold higher incidence rate and relative risk of UFs than Caucasian (CC) women. While the underlying cause for this risk disparity is not fully understood, recent studies implicate hypovitaminosis D as a major contributor. Thus, AA women have a tenfold increased risk of vitamin D deficiency compared to CC women, and as we first reported, UF risk is inversely correlated with 25-hydroxy vitamin D serum levels. Nonetheless, it is not clear whether and how the processes that drive UF formation and determine relative risk are genetically or biochemically linked. In this regard, we and others have identified somatic mutations in the transcriptional Mediator subunit MED12 as the dominant drivers of UFs, accounting for ~70% of tumors. Notably, MED12- mutant UFs are characterized by significant chromosomal loss and rearrangement, suggesting genomic instability as a driving force in tumor progression. Herein, we clarify the molecular basis for mutant MED12- driven genomic instability, and further identify vitamin D3 receptor signaling as a likely suppressor of this process. We show that MED12-mutant UF stem cells (SCs) accumulate high levels of unrepaired DNA double- strand breaks (DSBs) through downregulation of key DNA damage response (DDR) and repair genes. Notably, we find the vitamin D3/receptor axis to be a variable modulator of MED12-regulated DDR gene expression. Thus, we show that reduced vitamin D3/receptor signaling suppresses, while elevated signaling activates, DDR genes downregulated in MED12-mutant UF SCs. Based on these findings, we hypothesize that hypovitaminosis D exacerbates DNA damage accumulation and genomic instability arising in MED12-mutant UFs, leading to enhanced tumor progression and burden. Accordingly, we propose that vitamin D3, through reparation of an impaired DDR will provide therapeutic benefit in MED12-mutant tumors. To test these hypotheses, we will (1) Elucidate the molecular basis of genomic instability in MED12-mutant UFs. We will determine if DSB accumulation in MED12-mutant UF SCs derives from defects in DNA damage-induced checkpoint signaling and repair and/or R-loop-induced replication stress. (2) Investigate the relationship between vitamin D3 and MED12 in UF genome maintenance. We will ask whether and how vitamin D3 signaling strength modulates the DDR defects in MED12-mutant UF SCs, relate this activity to patient race and serum vitamin D levels, and elucidate the mechanism by which the vitamin D3/receptor axis and MED12 coordinately control the DDR network at the genomic and epigenomic levels; (3) Examine the therapeutic potential of vitamin D3 in a preclinical mouse model of human UFs. Using a renal capsule mouse model of human UFs, we will evaluate vitamin D3 and its potent non-hypercalcemic analogs for therapeutic efficacy, safety, and mechanism of action, including impact on tumor DNA damage load and DDR gene networks.