Mapping of Three Genetic Determinants of Susceptibility to Estrogen-Induced Mammary Cancer within the Emca8 Locus on Rat Chromosome 5

We are using the ACI rat model of 17beta-estradiol induced mammary cancer to define the mechanisms through which estrogens contribute to breast cancer development; identify and functionally characterize the genetic variants that determine susceptibility; and define the hormone-gene-environment interactions that influence development of mammary cancer in this physiologically relevant rat model. Female ACI rats are uniquely susceptible to development of mammary cancer when treated continuously with physiologic levels of 17beta-estradiol. Induction of mammary cancer in female ACI rats occurs through a mechanism that is largely dependent upon estrogen receptor-alpha. Interval mapping analyses of progeny generated in intercrosses between susceptible ACI rats and resistant Brown Norway (BN) rats revealed seven quantitative trait loci (QTL), designated Emca3 (Estrogen-induced mammary cancer) through Emca9, each of which harbors one or more genetic determinants of mammary cancer susceptibility. Genes that reside within Emca8 on RNO5 and were differentially expressed between 17beta-estradiol treated ACI and ACI.BN-Emca8 congenic rats were identified as Emca8 candidates. Two groups of 17beta-estradiol treated female rats were compared. Five ACI and five BN.ACI-Emca8 rats were treated with 17beta-estradiol for 12 weeks. Total RNA was isolated from the mammary glands of these animals, labeled, and hybridized to Affymetrix Rat Genome 230 2.0 Arrays (Affymetrix Inc.). Significantly differentially expressed genes were found between these groups.

本研究采用17β-雌二醇（17beta-estradiol）诱导的ACI大鼠乳腺癌模型，旨在阐明雌激素促乳腺癌发生的分子机制、鉴定并功能解析决定肿瘤易感性的遗传变异，以及在该生理相关大鼠模型中明确影响乳腺癌发生的激素-基因-环境互作调控机制。持续给予生理剂量17β-雌二醇时，雌性ACI大鼠会特异性罹患乳腺癌，其乳腺癌诱导过程主要依赖于雌激素受体α（estrogen receptor-alpha）。通过将易感ACI大鼠与抗性褐挪威（Brown Norway, BN）大鼠互交所获得的后代进行数量性状位点区间定位分析，共鉴定出7个数量性状位点（quantitative trait loci, QTL），分别命名为Emca3（雌激素诱导型乳腺癌，Estrogen-induced mammary cancer）至Emca9，每个位点均含有一个或多个乳腺癌易感性遗传决定因子。定位于大鼠5号染色体（RNO5）上Emca8位点内，且在17β-雌二醇处理的ACI大鼠与ACI.BN-Emca8同类系大鼠中存在表达差异的基因，被鉴定为Emca8的候选基因。本研究设置两组经17β-雌二醇处理的雌性大鼠开展对比实验：分别对5只ACI大鼠与5只BN.ACI-Emca8大鼠持续给予17β-雌二醇处理12周；提取上述大鼠的乳腺组织总RNA，经标记后与Affymetrix大鼠基因组230 2.0芯片（Affymetrix公司）进行杂交，最终鉴定得到两组间存在显著差异表达的基因。