Translating gene-calcium interactions to precision medicine for colorectal cancer

描述（由申请人提供）：尽管结直肠癌的发病率和死亡率都有所下降，部分原因是内窥镜检查的使用迅速增加，但结直肠癌（CRC）仍然是美国第四大常见癌症和第二大常见癌症死亡原因。因此，制定新的一级预防战略至关重要。高钙摄入与降低结直肠腺瘤和结直肠癌的风险有关；然而，结果并不一致。SLC12A1编码的NKCC2是KCNJ1编码的ROMK的直接下游效应体。NKCC2和ROMK都是Ca和Mg重吸收的驱动力。SLC12A1和KCNJ1的纯合罕见突变分别导致I型和II型高前列腺素E综合征，这两种综合征的特征都是明显的高钙尿（钙浪费）和高前列腺素E2（高水平的PGE2）。在过去的5年中，在NIH R01项目（AT004660, PI: Dai）中，我们研究了SLC12A1， KCNJ1和其他12个候选基因的单核苷酸多态性（snp），这些基因与Ca和Mg （re）的吸收和调节密切相关，与Ca摄入量，Mg或Ca/Mg比值的相互作用与结直肠腺瘤风险有关。在这项两期研究中，我们发现并复制了KCNJ1和SLC12A1中2个snp，这些snp与Ca摄入量显著相互作用，与结直肠腺瘤风险相关，特别是多发性/晚期腺瘤。在2个基因的联合分析中，我们观察到在2个基因中没有变异等位基因的患者中，最高钙摄入量与风险无关，但在携带1个和2个基因变异等位基因的患者中，最高钙摄入量与腺瘤风险分别降低39%和69%显著相关。在两种基因中都有变异等位基因的患者中，患晚期或多发性腺瘤的风险相应降低了89%。我们在第三组独立的增生性息肉病例与对照组中也发现了类似的结果。我们扩展到另外10个候选基因，鉴定并复制了SLC8A1中与Ca相互作用与腺瘤风险相关的1个SNP。38%的美国人在3个基因中的任意2个基因中至少有1个变异等位基因，其中高钙摄入量与腺瘤风险降低70%相关。这些发现新颖而有希望。然而，ca基因相互作用中的3个snp是非功能性标签。此外，我们只研究了标记snp的小等位基因频率为5%，而这些基因的罕见突变与钙稳态功能障碍疾病有因果关系。此外，尚不清楚这些相互作用是否与结直肠癌或腺瘤复发有关，或是否赋予接受内镜筛查的个体额外的结直肠癌保护。基于PLCO提供的独特资源的拟议研究将前瞻性地解决这些重要问题。我们建议对这3个基因进行靶向深度重测序，以检测功能性和罕见的snp及其与钙摄入的相互作用。此外，我们将进行分子流行病学研究，以前瞻性地了解这些钙基因相互作用的机制。

DESCRIPTION (provided by applicant): Despite a reduction in both incidence and mortality of colorectal cancer, partially due to rapidly increased use of endoscopy, colorectal cancer (CRC) still remains the 4th most common incident cancer and the 2nd most common cause of cancer death in the US. Thus, it is critical to develop new primary prevention strategies. High consumption of calcium (Ca) has been linked to reduced risks of colorectal adenoma and CRC; however, results have been inconsistent. NKCC2, encoded by SLC12A1, is the direct downstream effector of ROMK encoded by KCNJ1. Both NKCC2 and ROMK serve as driving forces for reabsorption of Ca and Mg. Homozygous rare mutations in SLC12A1 and KCNJ1 cause type I and type II hyperprostaglandin E syndrome, respectively, both of which are characterized by marked hypercalcinuria (calcium wasting) and hyperprostaglandin E2 (high levels of PGE2). Over the past 5 years, in an NIH R01 project (AT004660, PI: Dai), we have examined single nucleotide polymorphisms (SNPs) in SLC12A1,and KCNJ1 and 12 other candidate genes which are critically involved in Ca and Mg (re)absorption and regulation, for interaction with intakes of Ca, Mg or Ca/Mg ratio in relation to colorectal adenoma risk. In this two-phase study, we identified and replicated 2 SNPs in KCNJ1 and SLC12A1 that significantly interacted with Ca intake in relation to colorectal adenoma risk, particularly multiple/advanced adenoma. In joint analysis of 2 genes, we observed highest Ca intake was not associated with risk among those with no variant alleles in 2 genes, but was significantly related to 39% and 69% reduced adenoma risk, among those who carry variant allele(s) in 1 and 2 genes, respectively. The corresponding reduction in risk with advanced or multiple adenomas was 89% among those with variant alleles in both genes. We also found similar findings in a third independent set of hyperplastic polyp cases vs. controls. We expanded to 10 more candidate genes and identified and replicated 1 SNP in SLC8A1 interacting with Ca in relation to adenoma risk. 38% of the US population have at least 1 variant allele in any 2 of 3 genes, among whom high Ca intake was associated with a 70% reduced adenoma risk. These findings are novel and promising. However, 3 SNPs in the Ca-gene interactions are non-functional tags. Also, we only examined tagging SNPs with a minor allele frequencye 5%, whereas rare mutations in these genes are causally linked to diseases with Ca homeostasis dysfunction. Furthermore, it is unknown if these interactions are associated with incident CRC or adenoma recurrence or confer additional protection from CRC in individuals receiving endoscopic screenings. The proposed study based on the unique resources available from PLCO will prospectively address these important questions. We propose to conduct targeted deep resequencing in these 3 genes to examine functional and rare SNPs and their interactions with Ca intake. In addition, we will conduct a molecular epidemiologic study to prospectively understand the mechanisms underlying these Ca-gene interactions.