Defining the role of intestinal epithelial selenoprotein P (SEPP1) in sporadic colorectal carcinogenesis

项目摘要/摘要 尽管在治疗和筛查方面取得了进展，但结直肠癌(CRC)仍是第三大常见癌症 全球癌症相关死亡的第四大常见原因。尽管硒在癌症中的作用 仍然存在争议，几项流行病学研究显示，结直肠癌风险与 硒的营养水平。更多的分子研究表明，缺硒会加重炎症-- 导致结肠炎相关癌症(CAC)并刺激Wnt信号通路，这是不适当的 在绝大多数社区合作伙伴中都处于激活状态。硒是硒蛋白(SEPs)所必需的微量元素 作为硒半胱氨酸(SEC)。作为表达最高的SEP和唯一具有多个SEC的SEP，SEPP1 假设是为了向各种组织供应Se，以生产基因组中的其他24个SEP。除了……之外 SEPP1具有Se转运能力，通过其氧化还原结构域具有抗氧化活性。总而言之，这样 SEPP1的功能声称具有预防癌症的作用。事实上，SEPP1的mRNA表达在 CRC。此外，SEPP1的全局减少促进了CAC动物的肿瘤发生并激活了Wnt信号 模特。SEPP1主要在肝脏中合成，并通过血浆输送到远处的组织。 令人惊讶的是，我们观察到肝脏特异的Sepp1缺失并没有影响结肠炎的严重程度或随后的 小鼠CAC模型中的肿瘤发生。这些结果表明，当地生产的SEPP1具有保护作用。 有趣的是，SEP1特异性地从肠上皮中缺失会导致SEPP1的整体减少和 在相同的CAC模型中降低了肿瘤的形成。此外，日粮中补充硒的效果有所减弱。 Sepp1基因缺陷小鼠的肿瘤发生和促进存活。虽然这些结果表明Se和SEPP1 修饰炎症驱动的CAC，对上皮SEPP1在非炎症驱动中的作用知之甚少 (而且更为普遍)散发性结直肠癌，更重要的是，饮食中的硒是否能补偿遗传性SEP 预防肿瘤发生的缺陷。 为了确定SEPP1如何调节非炎症驱动的散发性结直肠癌，我将研究 SEPP1对初始肿瘤形成以及对已建立的结直肠肿瘤生长的影响。具体地说，我将分析 肠上皮细胞SEPP1缺失对肿瘤发生和Wnt信号转导的影响 超营养硒水平。此外，我将描述肿瘤和宿主来源的SEPP1对 确定结直肠肿瘤的生长。最后，我将研究SEPP1表达对细胞凋亡的影响， 使用体外3D-有机化合物的DNA损伤、体内生长、氧化应激、增殖和Wnt激活 人原发结直肠癌的培养。总之，这些实验将有助于阐明Se和SEPP1在 散发性结直肠癌的发生。

Project Summary/Abstract Despite advances in treatment and screening, colorectal cancer (CRC) remains the third most common cancer and fourth most common cause of cancer-related death worldwide. Although the role of selenium (Se) in cancer remains controversial, several epidemiological studies have revealed inverse correlations between CRC risk and Se nutritional levels. Additional molecular studies have demonstrated that Se deficiency worsens inflammatory- driven colitis-associated cancer (CAC) and stimulates the Wnt signaling pathway, which is inappropriately activated in the vast majority of CRCs. Se is an essential trace element incorporated into selenoproteins (SEPs) as selenocysteine (SEC). As both the most highly expressed SEP and the only SEP with multiple SECs, SEPP1 is hypothesized to supply Se to various tissues for production of the other 24 SEPs in the genome. In addition to its Se transport capability, SEPP1 possesses antioxidant activity via its redox domain. Collectively, such functions purport a cancer-preventive role for SEPP1. In fact, SEPP1 mRNA expression is downregulated in CRCs. Moreover, global SEPP1 reduction promoted tumorigenesis and activated Wnt signaling in a CAC animal model. SEPP1 is primarily synthesized in the liver and delivered to distant tissues through the plasma. Surprisingly, we observed that liver-specific Sepp1 deletion did not impact colitis severity nor subsequent tumorigenesis in a murine CAC model. These results suggest a protective role for locally-produced SEPP1. Interestingly, Sepp1 deletion specifically from the intestinal epithelium phenocopied global SEPP1 reduction and decreased tumorigenesis in the same CAC model. Moreover, dietary Se supplementation attenuated tumorigenesis and promoted survival in Sepp1-deficient mice. While these results imply that Se and SEPP1 modify inflammatory-driven CAC, little is known about the role of epithelial SEPP1 in non-inflammatory-driven (and much more prevalent) sporadic CRC and, importantly, if dietary Se can compensate for genetic SEP deficiencies to protect against tumorigenesis. To determine how SEPP1 modulates non-inflammatory-driven sporadic CRC, I will investigate the impact of SEPP1 on initial tumor formation as well as on established colorectal tumor growth. Specifically, I will analyze the effects of intestinal epithelial SEPP1 loss on tumorigenesis and Wnt signaling under deficient, sufficient, and supranutritional Se levels. Additionally, I will delineate the contributions of tumor- and host-derived SEPP1 to established colorectal tumor growth. Lastly, I will examine the consequences of SEPP1 expression on apoptosis, DNA damage, in vivo growth, oxidative stress, proliferation, and Wnt activation using ex vivo 3D-organoid cultures of human primary CRC. Together, these experiments will help elucidate the roles of Se and SEPP1 in sporadic colorectal carcinogenesis.