A functional SRC1 SNP in bone biology

描述（由申请人提供）：雌激素受体ER1和ER2的活性通过与辅助因子的相互作用来调节，其中包括类固醇受体辅激活因子1 （SRC1）。SRC1已被证明是雌激素反应的关键调节因子。特别是在骨骼方面，SRC1-/-小鼠出现骨质减少，雌激素无法恢复卵巢切除术引起的骨质流失。也有证据表明SRC1可能在选择性雌激素受体调节剂（SERMs）如抗雌激素药物他莫昔芬的应答中发挥作用。抗雌激素具有组织特异性的混合激动剂/拮抗剂活性，在某些组织中，SRC1过表达可导致激动剂活性增加，拮抗剂活性降低。雌激素水平低与骨密度（BMD）降低有关，可能导致骨质疏松症。众所周知，骨质疏松症具有主要的遗传成分，并且已经确定了潜在的致病基因。在我们的研究中，我们旨在研究遗传变异在抗雌激素反应中的作用，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ER的共激活减少，并且半衰期较短。在接受他莫昔芬治疗12个月的乳腺癌患者中，与野生型等位基因相比，SNP携带者的骨密度显著降低，这可能反映了他莫昔芬在骨骼中的激动剂活性的丧失。我们假设SRC1 P1272S SNP导致骨细胞内质网活性降低，这是蛋白质周转增加的结果。我们还假设携带SNP的小鼠会出现骨质减少，骨骼对激素的反应降低。为了验证我们的假设，我们将i)表征SRC1 SNP对骨细胞内质网活性的影响，ii)破译P1272S变体共激活活性降低的机制，iii)生成SRC1P1278S/P1278S敲入小鼠模型，并表征骨表型。目标的成功完成将提供支持临床观察的功能数据，并将为随后的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，这可以用于“个性化医疗”，并在这种特殊情况下，确定将受益于骨骼强化药物或其他干预措施的人。1

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.