Mechanisms of estrogen action on bone marrow-derived stem stromal cells

描述(由申请人提供)：人们普遍认为，怀孕后患乳腺癌的风险增加是由于雌激素能够促进启动的目标细胞群体的进一步增殖。然而，由于大多数在此期间发生的乳腺癌缺乏明显的雌激素(ER)或孕激素受体(PR)的表达，这表明如果激素变化在促进乳腺癌方面发挥了作用，它们可能不是通过直接与乳腺上皮细胞表达的激素受体分子结合来实现的。此外，众所周知，卵巢切除可以预防女性ER阳性和ER阴性乳腺癌的形成，这进一步强调了雌激素在ER阴性癌症发展中的重要性。为了调和这一概念冲突，我们调查了雌激素通过影响不同于乳腺上皮本身的宿主细胞类型而促进ER阴性癌症生长的假设。我们利用了一种新的异种移植小鼠模型，在该模型中，出现的肿瘤缺乏核激素受体的表达，概括了上述临床情况。尽管缺乏ER表达，但我们发现在该模型中发展的肿瘤需要循环雌激素才能形成。此外，我们证明，增加循环雌激素水平足以通过增加血管生成来促进ER阴性癌症的形成和进展。值得注意的是，伴随着新生血管生成的系统性增强，骨髓来源细胞在生长的肿瘤块中的募集显著增加，包括内皮细胞和基质细胞。基于我们的证据，我们现在建议确定雌激素影响骨髓细胞募集、血管生成和肿瘤促进的机制。为此，我们的目标是确定宿主的ER表达是否是雌激素介导的基质效应所必需的，以及这些作用是通过ER信号的基因组作用还是非基因组作用发生的。此外，我们还旨在确定骨髓间充质干细胞是否是雌激素介导的血管生成和肿瘤促进的靶点。这将通过使用ERKO小鼠模型、骨髓细胞分离以及体内和体外雌激素信号的功能分析来进行研究。最近，针对雌激素合成、周转以及受体的基因组和非基因组活性的更好和更特异的内分泌治疗已经被开发出来，然而，由于缺乏证据表明这些化合物对ER阴性的肿瘤有效，它们仅用于治疗ER阳性的乳腺癌。因此，了解雌激素促进骨髓细胞募集、血管生成和肿瘤生长的机制将对ER阴性癌症具有重要的和高度相关的科学和临床影响。

DESCRIPTION (provided by applicant): It is widely presumed that the increased risk of developing breast cancer following pregnancy is due to the ability of estrogen to promote the further proliferation of an initiated target cell population. However, since the majority of breast cancers that do develop during this time lack appreciable expression of either the estrogen (ER) or progesterone receptors (PR), this suggests that if hormonal changes play a part in promoting breast cancer, they may not be doing so through direct binding to hormone receptor molecules expressed by breast epithelial cells. Moreover, it is well established that ovariectomy prevents the formation of both ER-positive as well as ER-negative breast cancers in women, further highlighting the importance of estrogens in the development of ER-negative cancers. To reconcile this conceptual conflict, we investigated the hypothesis that estrogen promotes the outgrowth of ER-negative cancers by influencing host cell types distinct from the breast epithelium itself. We utilized a novel xenograft mouse model in which the tumors that arise lack the expression of nuclear hormone receptors, recapitulating the clinical situation described above. Despite lacking ER expression, we showed that the tumors that develop in this model require circulating estrogens for their formation. Moreover, we demonstrated that increasing the levels of circulating estrogens is sufficient to promote the formation and progression of ER-negative cancers via a systemic increase in angiogenesis. Remarkably, the systemic enhancement of neo-angiogenesis was accompanied by a striking increase in the recruitment of bone marrow derived cells into the growing tumor mass, including endothelial and stromal cells. Based on our evidence, we now propose to determine the mechanism by which estrogen effects bone marrow cell recruitment, angiogenesis and tumor promotion. To this end, we aim to determine whether ER expression by the host is necessary for the stromal effects mediated by estrogens, and whether these actions occur through the genomic or non-genomic actions of ER signaling. In addition, we also aim to determine if bone marrow mesenchymal stem cells are the targets of estrogen-mediated angiogenesis and tumor promotion. This will be investigated through the use of ERKO mouse models, bone marrow cell fractionation, and in vivo and in vitro functional assays to estrogen signaling. Most recently, superior and more specific endocrine therapies targeting estrogen synthesis, turnover, as well as genomic and non-genomic activities of the receptor have been developed, however, they are only utilized for the treatment of ER-positive breast cancers due to the lack of evidence these compounds would work in ER-negative tumors. Thus, understanding the mechanism by which estrogen can promote bone marrow cell recruitment, angiogenesis, and tumor growth would have significant and highly relevant scientific and clinical impact for ER-negative cancers.