A functional SRC1 SNP in bone biology

描述（由申请人提供）：雌激素受体ER 1和ER 2的活性通过与辅因子（其中包括类固醇受体辅激活因子1（SRC 1））的相互作用进行调节。SRC1已被证明是雌激素反应的关键调节剂。特别是在骨方面，SRC 1-/-小鼠表现出骨质减少，雌激素未能恢复卵巢切除术引起的骨丢失。也有证据表明SRC1可能在对选择性雌激素受体调节剂（SERM）如抗雌激素他莫昔芬的反应中发挥作用。抗雌激素具有组织特异性混合激动剂/拮抗剂活性，并且SRC1过表达可导致某些组织中激动剂活性增加和拮抗剂活性降低。 低雌激素水平与骨矿物质密度（BMD）降低相关，可能导致骨质疏松症。众所周知，骨质疏松症有一个主要的遗传成分，潜在的致病基因已经确定。在我们的研究中，旨在研究遗传变异对抗雌激素的作用，我们最近发现，并随后开始表征SRC1（P1272S）中的非同义单核苷酸多态性（SNP）。我们的初步数据显示，SRC1 P1272S变体显示出ER共激活降低，并且具有较短的半衰期。在接受他莫昔芬治疗12个月的乳腺癌患者中，SNP携带者与野生型等位基因携带者相比，BMD显著降低，这可能反映了他莫昔芬在骨中的激动剂活性丧失。我们假设SRC1 P1272S SNP导致骨细胞中ER活性降低，这是蛋白质周转增加的结果。我们还假设携带SNP的小鼠将表现出骨质减少和骨骼对激素的反应降低。为了解决我们的假设，我们将i）表征SRC1 SNP对骨细胞中ER活性的影响，ii）解释P1272S变体的共激活活性降低的潜在机制，以及iii）产生SRC1P1278S/P1278S敲入小鼠模型，并表征骨表型。 成功完成目标将提供支持临床观察的功能数据，并为后续R01提交提供强有力的数据。最终，我们希望我们的研究将导致SNP的进一步表征，可用于“个性化医疗”，并在这种特定情况下，确定谁将受益于骨骼强化药物或其他干预措施。1 公共卫生相关性：我们已经确定了核受体辅因子SRC1的功能性非同义变体，其显示出降低的共激活潜力，导致雌激素受体活性降低。总的来说，我们的初步数据表明，这种SNP可能导致骨丢失增加。在这里，我们建议提供进一步的功能支持，通过分析这种变异的骨细胞，通过研究的基本机制，最后通过生成和表征的小鼠基因敲入模型。

DESCRIPTION (provided by applicant): The activity of the estrogen receptors ER1 and ER2 are regulated via interaction with cofactors, among them the steroid receptor coactivator 1 (SRC1). SRC1 has been shown to be a critical regulator of estrogen response. With particular regard to bone, SRC1-/- mice showed osteopenia, and estrogen failed to restore ovariectomy-induced bone loss. There is also evidence that SRC1 may play a role in the response to selective estrogen receptor modulators (SERMs) such as the antiestrogen tamoxifen. Antiestrogens have tissue-specific mixed agonist/antagonist activity, and SRC1 overexpression can result in increased agonist, and decreased antagonist activity in some tissues. Low estrogen levels are associated with decreased bone mineral density (BMD) potentially resulting in osteoporosis. It is known that osteoporosis has a major genetic component, and potential causal genes have been identified. In our studies aimed at examining the role of genetic variants in response to antiestrogens, we recently identified, and subsequently started to characterize, a non-synonymous single nucleotide polymorphism (SNP) in SRC1 (P1272S). Our preliminary data show that the SRC1 P1272S variant displays decreased co-activation of ER, and that is has a shorter half life. In breast cancer patients treated with tamoxifen for 12 months, SNP carriers showed significantly decreased BMD compared to those with wildtype alleles, possibly reflecting a loss of tamoxifen's agonist activity in bone. We hypothesize that the SRC1 P1272S SNP results in decreased ER activity in bone cells, and that this is a result of increased protein turn-over. We also hypothesize that mice harboring the SNP will display osteopenia, and decreased skeletal response to hormone. To address our hypotheses we will i) characterize the effect of the SRC1 SNP on ER activity in bone cells, ii) decipher the mechanism(s) underlying the decreased co-activation activity of the P1272S variant, and iii) generate an SRC1P1278S/P1278S knock-in mouse model, and characterize bone phenotypes. Successful completion of the aims will provide functional data supporting the clinical observation, and would allow strong data for a subsequent R01 submission. Ultimately, we hope that our studies will lead to the further characterization of a SNPs which could be used to "personalize medicine", and in this specific case, to identify people who would benefit from bone-strengthening medications, or other interventions. 1 PUBLIC HEALTH RELEVANCE: We have identified a functional non-synonymous variant in the nuclear receptor cofactor SRC1 which displays decreased coactivation potential, resulting in decreased activity of the estrogen receptor. Collectively, our preliminary data suggest that this SNP could result in increased bone loss. Here we propose to provide further functional support through the analysis of this variant in bone cells, through the study of the underlying mechanism, and finally through the generation and characterization of a mouse knock-in model.