Role of Phospho-Progesterone Receptors (PR) in Hormone Refractory Breast Cancer

描述（由申请人提供）：乳腺癌进展为类固醇受体（SR）阳性但激素难治性乳腺癌的机制尚不清楚。该领域的许多研究都集中在雌激素受体-？肽生长因子激活酪氨酸激酶受体介导的信号转导；这些分子是重要的临床靶点。然而，孕激素受体（PR）也可能作为早期乳腺癌进展的介质发挥关键作用。最近，我们发现了一种由膜启动磷酸化事件介导的不依赖激素的PR转录活性过度激活的新机制。有丝分裂蛋白激酶（c-Src, MAPKs, CDK2）在乳腺癌中经常升高，PR Ser294的持续磷酸化会阻断配体诱导的K388的sumo化（一种抑制性修饰）。丰富的总PR是“良好肿瘤”行为的标志。然而，我们假设去抑制磷酸化pr作用于其产物介导早期乳腺癌进展或“不良肿瘤”行为的基因。对PR过度活跃的一种检查包括通过泛素-蛋白酶体途径快速的配体依赖性降解。事实上，在激素存在的情况下，phospho-PR经历了快速的转换，通常使低丰度蛋白无法通过标准抗体结合试验（即临床使用的IHC）检测到。PR“缺失”的临床观察导致了PR转录活性在“低PR”乳腺癌中不重要的错误结论。然而，我们的研究表明，phospho-PR是转录亢进的，值得注意的是，它靶向对黄体酮或孕激素不敏感的基因；IRS-1是一个不依赖配体的磷酸pr基因的例子。此外，在高激酶活性的条件下，ser294磷酸化的pr不会被转录，因此不能转抑内质网，而是在完全没有类固醇激素的情况下，在非经典（不含pre）基因靶点与内质网合作；STC-1是er基因被phospho-PR去抑制的一个例子。值得注意的是，表达不能被同化的突变pr （K388R）的乳腺癌细胞模型的增殖对雌激素非常敏感，但对抗雌激素有抗性。同样，我们预测phospho-PR信号可以驱动一些激素难治性乳腺癌的生长，这些乳腺癌可以通过独特的PR基因标记来识别。在这里，我们将使用独特的细胞系模型来定义phospho-PR基因的特征，以诱导PR表达。PR summoylation /磷酸化“开关”在调节内源性基因的激素反应性中的作用将被定义（机制；目标1）。我们独特的phospho-PR基因标记将在tam-和AI-（芳香酶抑制剂）耐药性和人类肿瘤的体外模型中得到验证（验证；目标2）。最后，我们的创新假设将在aib1转基因小鼠（sr驱动（ER+/PR+）和耐药乳腺癌的体内模型）中进行验证（生物学；Aim 3）。对于乳腺肿瘤中PR和ER/PR的相互作用如何促进激素抵抗，我们知之甚少。我们对磷酸- PR信号的研究将为PR和ER功能的协调调节提供有价值的见解，这些通路可以很容易地靶向治疗干预。

DESCRIPTION (provided by applicant): The mechanism(s) of breast cancer progression to steroid receptor (SR)-positive but hormone refractory breast cancer remain elusive. Much of the research in this field is focused on the linkage of estrogen receptor-? (ER) to signal transduction, as mediated by peptide growth factor activation of tyrosine kinase receptors; these molecules are important clinical targets. However, progesterone receptors (PR) may also play a key role as mediators of early breast cancer progression. Recently, we uncovered a novel mechanism of hormone-independent hyperactivation of PR transcriptional activity that is mediated by membrane-initiated phosphorylation events. In response to mitogenic protein kinases (c-Src, MAPKs, CDK2) often elevated in breast cancer, persistent phosphorylation of PR Ser294 blocks ligand-induced sumoylation at K388 (a repressive modification). Abundant total PR is a marker of "good tumor" behavior. However, we hypothesize that de-repressed phospho-PR acts on genes whose products mediate early breast cancer progression or "bad tumor" behavior. One check on PR hyperactivity includes rapid ligand-dependent degradation by the ubiquitin-proteasome pathway. Indeed, in the presence of hormone, phospho-PR undergoes rapid turnover, often rendering the low abundance protein undetectable by standard antibody-binding assays (i.e. clinically used IHC). Clinical observations of PR "loss" have led to the incorrect conclusion that PR transcriptional activity is unimportant in "PR-low" breast cancers. However, our studies reveal that phospho-PR is transcriptionally hyperactive and remarkably, targets genes that are not sensitive to progesterone or progestins; IRS-1 is an example of a ligand-independent phospho-PR gene. Furthermore, under conditions of high kinase activities, Ser294-phosphorylated PRs are not sumoylated, and thus fail to transrepress ER but may instead cooperate with ER at non-classical (non-PRE containing) gene targets in the complete absence of steroid hormones; STC-1 is an example of an ER-gene that is de-repressed by phospho-PR. Notably, the proliferation of breast cancer cell models expressing mutant PRs that cannot be sumoylated (K388R) is very sensitive to estrogen, but resistant to anti-estrogen. Similarly, we predict that phospho-PR signaling drives the growth of some hormone-refractory breast cancers that can be identified by a unique PR gene signature. Herein, we will define the phospho-PR gene signature using unique cell line models engineered for inducible PR expression. The role of the PR sumoylation/phosphorylation "switch" in the regulation of hormone responsiveness at endogenous genes will be defined (Mechanisms; Aim 1). Our unique phospho-PR gene signature will be validated in in vitro models of tam- and AI- (aromatase inhibitor) resistance and in human tumors (Validation; Aim 2). Finally, our innovative hypothesis will be tested in AIB1-transgenic mice, an in vivo model of SR-driven (ER+/PR+) and tam-resistant breast cancer (Biology; Aim 3). Little is known about how PR and ER/PR interactions contribute to hormone resistance in breast tumors. Our studies on phospho- PR signaling will provide valuable insight into the coordinated regulation of PR and ER function by pathways that can be easily targeted for therapeutic intervention.