Oncogenic MLK3-Pak1 Signaling in ER Negative Breast Cancer

描述(申请人提供)：混合谱系激酶3(MLK3)是一种应激激活的MAP激酶成员，其生物学功能尚不清楚。在解剖MLK3介导的信号通路时，我们观察到酵母Ste20成员的哺乳动物同源物p21激活的激酶(PAC1)与MLK3之间存在很强的相互作用。最初，我们推测Ak1可能与其酵母对应物一样调节MLK3激酶的活性。然而，观察到的结果与我们的推测相反，MLK3直接磷酸化并激活了PK1，从而导致了核因子-βB的激活。这些结果非常耐人寻味，因为pak1的激活与乳腺增生有关，最近被确认为乳腺癌的主要癌基因。我们的初步研究表明，在乳腺癌细胞系中，Ak1的活性是以MLK3依赖的方式直接调节的。我们还观察到，在原发的人乳腺肿瘤中，MLK3的活性与Ak1和NF-β的激活直接相关，仅在ER和PR阴性的乳腺肿瘤中有表达，而在ER-PR-乳腺肿瘤中有高表达。如果这些结果属实，那么可用的MLKs抑制剂CEP-1347/CEP-11004应该诱导ER-乳腺癌细胞死亡？事实上，用CEP-1347处理ER-，而不是ER+的乳腺癌细胞系会导致细胞死亡。根据我们的观察，我们假设在ER-乳腺癌细胞中，MLK3激活了Ak1及其下游的NF-βB，导致了ER-肿瘤的发生。因此，靶向MLK3或其他MLK可以消除ER-乳腺肿瘤。为了实现我们的目标，我们将确定：(1)MLK3激活Pak1诱导ER-乳腺细胞肿瘤的发生；(2)阻断MLK3-Pak1信号级联抑制ER-乳腺细胞的发生；(3)MLK3、Pak1和核因子-βB激活在ER-乳腺细胞肿瘤发生中的作用机制。通过明确MLK3在Ak1和NF-β激活和肿瘤发生中的作用，我们可能通过使用这一途径的有效抑制剂来控制/治疗ER乳腺癌。有趣的是，MLK3家族的特异性抑制剂CEP-1347已经用于治疗神经退行性疾病的临床试验。也有人建议MLKs抑制剂可能用于特定类型的癌症的治疗，强调了我们关于MLK3在ER乳腺癌中的作用的意想不到的新结果。综上所述，本研究将导致确定新的预后因素和针对难治性疾病的特定靶向治疗。 呃--乳腺癌。

DESCRIPTION (provided by applicant): Mixed Lineage Kinase 3 (MLK3) is a stress-activated MAP Kinase Kinase Kinase member, whose biological function is still elusive. While dissecting the signaling pathway mediated via MLK3, we observed a strong interaction between mammalian homolog of yeast Ste20 member, p21 activated kinase (Pak1) and MLK3. Initially, we speculated that Pak1 might regulate MLK3 kinase activities similar to its yeast counterparts. However, the observed results were counterintuitive to our speculation, and instead MLK3 directly phosphorylated and activated Pak1, which subsequently lead to NF-?B activation. These results were quite intriguing because Pak1 activation has been implicated in mammary gland hyperplasia, and recently it has been identified as a major oncogene in breast cancer. Our preliminary investigation revealed that Pak1 activity was directly regulated in a MLK3-dependent manner in breast cancer cell lines. We also observed that in primary human breast tumors, the MLK3 activities directly correlated with Pak1 and NF-?B activations, exclusively in ER and PR negative breast tumors and Pak1 was overexpressed in ER- PR- breast tumors. If these results are true then the available MLKs inhibitor, CEP-1347/CEP-11004 should induce cell death in ER- breast cancer cells? Indeed, treatment of ER-, but not ER+ breast cancer cell lines with CEP-1347 caused cell death. Based on our observations, we hypothesize that in ER- breast cancer cells, MLK3 activates Pak1 and its downstream NF-?B, leading to ER- tumorigenesis. Therefore targeting MLK3 or other MLKs could abrogate ER- breast tumors. To achieve our goals, we will determine that: (1) activation of Pak1 by MLK3 induces ER- breast cell tumorigenesis, (2) disruption of MLK3-Pak1 signaling cascade attenuates ER- breast cell tumorigenesis; and (3) the mechanism of MLK3, Pak1 and NF-?B activation in ER- breast cell tumorigenesis. It is expected that by defining the role of MLK3 in Pak1 and NF-?B activation and tumorigenesis, we might control/treat ER- breast cancers by using available inhibitors of this pathway. Interestingly, the specific inhibitor of MLK3 family, CEP-1347 has been used in clinical trials for treating neurodegenerative diseases. It has also been suggested that MLKs inhibitors might serve as a treatment for specific type of cancer, underscoring our unexpected novel results related to MLK3 role in ER- breast cancer. Taken together, the present study will lead to the identification of new prognostic factors and specific targeted therapies for difficult to treat ER- breast cancer.