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

项目总结/摘要 尽管在治疗和筛查方面取得了进展，但结直肠癌（CRC）仍然是第三大常见癌症 也是全球第四大癌症相关死亡原因。虽然硒在癌症中的作用 仍然存在争议，一些流行病学研究揭示了CRC风险与 硒营养水平。其他分子研究表明，硒缺乏会导致炎症- 驱动结肠炎相关癌症（CAC），并刺激Wnt信号通路，这是不适当的 在绝大多数CRC中激活。硒是硒蛋白（SEPs）中的一种必需微量元素 以硒代半胱氨酸（SEC）计。SEPP 1是SEP中表达量最高的一种，也是唯一一种具有多个SEC的SEP， 被假设为向各种组织提供硒，以产生基因组中的其他24种SEP。除了 SEPP 1具有硒转运能力，通过其氧化还原结构域具有抗氧化活性。等集体方式 功能声称SEPP 1的癌症预防作用。事实上，SEPP 1 mRNA表达在细胞中下调， CRC。此外，在CAC动物中，SEPP 1的整体减少促进了肿瘤发生并激活了Wnt信号传导 模型SEPP 1主要在肝脏中合成，并通过血浆递送到远处组织。 令人惊讶的是，我们观察到肝脏特异性Sepp 1缺失不影响结肠炎的严重程度，也不影响随后的结肠炎。 在小鼠CAC模型中的肿瘤发生。这些结果表明，当地产生的SEPP 1的保护作用。 有趣的是，肠上皮特异性Sepp 1缺失表型模拟了SEPP 1的整体减少， 在相同的CAC模型中降低肿瘤发生。此外，膳食硒补充减弱了 肿瘤发生和促进Sepp 1缺陷小鼠的生存。虽然这些结果意味着Se和SEPP 1 尽管SEPP 1基因修饰炎症驱动的CAC，但关于上皮SEPP 1在非炎症驱动的CAC中的作用知之甚少。 (and更普遍）散发性CRC，重要的是，如果饮食硒可以补偿遗传SEP， 缺乏以防止肿瘤发生。 为了确定SEPP 1如何调节非炎症驱动的散发性CRC，我将研究以下因素的影响： SEPP 1对初始肿瘤形成以及对已建立的结直肠肿瘤生长的影响。具体来说，我将分析 肠上皮SEPP 1缺失对肿瘤发生和Wnt信号传导的影响， 超营养硒水平。此外，我将描述肿瘤和宿主来源的SEPP 1对肿瘤细胞的作用。 结直肠肿瘤生长。最后，我将研究SEPP 1表达对细胞凋亡的影响， 使用离体3D类器官的DNA损伤、体内生长、氧化应激、增殖和Wnt活化 人原发性CRC的培养物。总之，这些实验将有助于阐明Se和SEPP 1在 散发性结直肠癌

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.