Estrogen receptor, p38 MAPKs and topo IIa in breast cancer

描述(由申请人提供)： 雌激素受体(ER)介导雌激素信号转导，促进乳腺癌生长，是雌激素阳性乳腺癌激素治疗的靶点。另一方面，DNA拓扑异构酶II1(Topo II1)维持适当的DNA拓扑结构，并作为ER+和ER-乳腺癌的治疗靶点。尽管内在Topo II1蛋白的水平与其抑制剂的敏感性有关，但这种蛋白经常被其毒素耗尽，而且关于Topo II1在治疗应激期间是如何维持的信息缺失。P38MAPK由1、2、3和4种蛋白组成，它们是通过调节基因表达来决定细胞对上游信号的反应的主要激酶级联信号。在过去的资助期间，我们证明了ER通过c-jun结合来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 II1表达的刺激而特异性地抑制Topo II药物诱导的生长抑制。我们认为，p38MAPK的激活维持了被ER信号拮抗的Topo II1的表达，导致了ER乳腺癌中Topo II药物毒性的增加。这一假说基于我们的初步研究，发现1)topo II抑制剂，但不是紫杉醇，比p383(而不是topo II1)蛋白的表达增加更有效地抑制ER-乳腺癌的生长；2)在ER+细胞中，p381的磷酸化水平也与topo II1蛋白的抗药性有关，表明topo II1保持了p381和p383的活性，而这一活性可被ER信号拮抗；3)p383通过结合/磷酸化ER在S118上拮抗ER；4)p381和p383在ER-而不是ER+的乳腺癌中反式激活topo II1，但5)p381只与topo II1蛋白结合。这些结果表明，p38MAPK维持了被ER信号抑制的Topo II1的表达，导致了Topo II1蛋白的持续表达，并增加了ER乳腺癌中Topo II的药物毒性。第二个资助期的实验将证明，如果1)p381和p383通过它们在ER+中的过度表达和ER-乳腺癌中的缺失来协同维持topo II1蛋白的表达，2)ER通过直接结合p383蛋白和间接抑制p381磷酸化来拮抗p381/p383对topo II1蛋白表达的刺激；3)p38MAPK活性决定了topo II药物在体外和小鼠体内对Topo II药物的生长抑制效果。含有TOPO II抑制剂的化疗因其对ER-乳腺癌的较高治疗活性而闻名数十年，但这种选择性的机制仍不清楚。这一提议将检验这样的假设，即乳腺癌中p38 MAPK的激活在治疗应激期间维持Topo II1蛋白的表达，而ER信号导致ER-乳腺癌中Topo II药物活性增加而被拮抗。这些研究将揭示p38应激MAPKs通过与ER信号的相互作用调节Topo II1表达的新功能，所获得的结果将对乳腺癌的治疗具有重要意义。

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.