Estrogen receptor, p38 MAPKs and topo IIa in breast cancer

描述（由申请人提供）： 雌激素受体（ER）介导雌激素信号传导以促进乳腺癌生长，从而作为ER+乳腺癌中激素治疗的靶点。另一方面，DNA拓扑异构酶II 1（topo II 1）保持适当的DNA拓扑结构，并作为ER+和ER-乳腺癌的治疗靶点。虽然内在拓扑II 1蛋白的水平与其抑制剂的敏感性相关，但这种蛋白质经常被其毒素耗尽，并且关于拓扑II 1在治疗应激期间如何维持的信息缺失。p38 MAPK由1、2、3和4个蛋白组成，它们是通过调节基因表达来确定细胞对上游信号的应答的主要激酶级联。我们在过去的资助期间表明，ER通过c-Jun结合抑制应激诱导的细胞死亡，我们最近的工作进一步表明，ER通过减弱p38对topo II 1表达的刺激，特异性抑制topo II药物诱导的生长抑制。 本文提出，p38 MAPK激活维持被ER信号传导拮抗的topo II 1表达，导致ER-乳腺癌中topo II-药物毒性增加。该假设基于我们的初步研究，显示1）拓扑蛋白II抑制剂，而不是紫杉醇，在抑制ER-乳腺癌生长方面更有效，其与增加的内在p383蛋白表达而不是拓扑蛋白II 1蛋白表达相结合; 2）与ER+细胞相比，在ER-中也存在与topo II 1蛋白对topo药物诱导的消耗的抗性相关的增加的p381磷酸化，表明topo II 1维持p381和p383两者的活性，其被ER信号传导拮抗; 3）p383通过在S118处结合/磷酸化ER拮抗ER; 4）p381和p383在ER-乳腺癌中反式激活topo II 1，但在ER+乳腺癌中不激活topo II 1，但5）仅p381与topo II 1蛋白结合。这些结果共同表明，p38 MAPK维持被ER信号传导抑制的topo II 1表达，导致持续的topo II 1蛋白表达和ER-乳腺癌中topo II药物毒性增加。 在第二个资助期的实验将证明：1）p381和p383通过它们在ER+乳腺癌中的过表达和在ER-乳腺癌中的缺失而合作维持topo II 1蛋白表达，2）ER通过直接结合p383蛋白并间接减弱p381磷酸化来拮抗p381/p383对topo II 1表达的刺激; 3）p38 MAPK活性决定topo II药物在体外和小鼠中对人乳腺癌的生长抑制效力。几十年来，已知含有Topo II受体的化疗对ER-乳腺癌具有较高的治疗活性，但这种选择性的机制仍不清楚。该提议将检验乳腺癌中的p38 MAPK活化在治疗应激期间起到维持topo II 1蛋白表达的作用的假设，所述治疗应激被ER信号传导拮抗，导致ER-乳腺癌中topo II药物活性增加。这些研究将揭示p38应激MAPKs通过与ER信号交叉作用调节topo II 1表达的新功能，所获得的结果将显著有助于乳腺癌治疗。

DESCRIPTION (provided by applicant): Estrogen receptor (ER) mediates estrogen signaling to promote breast cancer growth and thereby serves as a target for hormone therapy in ER+ breast cancer. DNA topoisomerase II1 (topo II1), on the other hand, maintains proper DNA topology and acts as a therapeutic target for both ER+ and ER- breast cancer. Although levels of intrinsic topo II1 protein correlate with sensitivity to its inhibitors, this protein is frequently depleted by its toxins and information about how topo II1 is maintained during the therapeutic stress is missing. p38 MAPKs consist of 1, 2, 3, and 4 proteins that are major kinase cascades to determine cellular response to upstream signals through regulating gene expressions. We showed during the past funding period that ER inhibits stress-induced cell death via c-Jun binding and our recent work further showed that ER specifically suppresses topo II drug-induced growth inhibition by attenuating p38 stimulations of topo II1 expression. It is proposed here that p38 MAPK activations maintain topo II1 expression that is antagonized by ER signaling, leading to increased topo II-drug toxicity in ER- breast cancer. This hypothesis is based on our preliminary studies showing 1) topo II inhibitors, but not taxol, are more potent in inhibiting ER- breast cancer growth that couples with increased intrinsic p383 but not topo II1 protein expression; 2) there are also increased p381 phosphorylations linked to resistance of topo II1 proteins to topo drug-induced depletion in ER- over ER+ cells, indicating a topo II1 maintaining activity of both p381 and p383 that is antagonized by ER signaling; 3) p383 antagonizes ER through binding / phosphorylating ER at S118; 4) p381 and p383 trans- activate topo II1 in ER- but not ER+ breast cancer but 5) only p381 binds to topo II1 protein. These results together suggest that p38 MAPKs maintain topo II1 expression that is suppressed by ER signaling leading to a sustained topo II1 protein expression and increased topo II drug toxicity in ER- breast cancer. Experiments in this second funding period will demonstrate if 1) p381 and p383 cooperate to maintain topo II1 protein expression through their over-expression in ER+ and depletion in ER- breast cancer, 2) ER antagonizes p381/p383 stimulations of topo II1 expression by directly binding p383 proteins and indirectly attenuating p381 phosphorylation; and 3) p38 MAPK activities determine the growth-inhibitory efficacy of topo II drugs against human breast cancer in vitro and in mice. Topo II inhibitor-containing chemotherapy is known for its higher therapeutic activity against ER- breast cancer for several decades and mechanism involved for this selectivity however remains unknown. This proposal will test the hypothesis that p38 MAPK activation in breast cancer acts to maintain topo II1 protein expression during therapeutic stress that is antagonized by ER signaling leading to increased topo II drug activity in ER- breast cancer. These studies will reveal a novel function of p38 stress MAPKs in regulating topo II1 expression through cross-talking with ER signaling and results obtained will contribute significantly to breast cancer therapy.