MLK3 function in neurofibromatosis tumor cells

描述（由申请人提供）：1型和2型神经纤维瘤病（分别为NF 1和NF 2）患者对良性和恶性神经鞘、骨髓细胞和其他癌症的易感性是这些疾病发病率和死亡率的主要原因。这些肿瘤的有效治疗代表了一个主要的未满足的医疗需求。NF 1和NF 2是遗传性功能丧失疾病，其中同源基因NF 1和NF 2经历一系列失活突变或截短。鉴于这种遗传异质性，再加上功能表型的丧失，靶向或利用神经纤维蛋白（NF 1的产物）或merlin（NF 2的产物）作为治疗方法是不切实际的。相比之下，神经纤维蛋白是Ras失活剂，并且正在进行的工作表明，钝化Ras信号传导可能有益于NF 1肿瘤的治疗，只要抑制Ras本身，或抑制Ras效应物，例如细胞外信号调节激酶（ERK）组的促分裂原活化蛋白激酶（MAPK）可以显著钝化NF 1细胞增殖。在某种程度上类似的静脉中，merlin通过未知的机制抑制Jun-N-末端激酶（JNK）的信号传导，并且可能抑制ERK MAPK。然而，merlin介导的JNK抑制的生物学后果尚不清楚;总的来说，我们对NF 1和NF 2肿瘤细胞生物学中MAPK通路调控和功能的认识是不完整的。显然，需要进一步的研究来确定新治疗方法的合适靶点。我们的初步工作确定了丝氨酸/苏氨酸激酶混合谱系激酶-3（MLK 3）作为NF 1和NF 2患者恶性神经鞘瘤细胞系增殖以及鼠NF 2-/-细胞增殖所需的组分。我们发现MLK 3也是NF 1/2细胞MAPK的有丝分裂原激活所必需的。令人惊讶的是，MLK 3通过一种未知的间接机制招募B-Raf激活ERK。本项目将探讨MLK 3在丝裂原处理的NF肿瘤细胞中的生化功能，以及merlin和neurofibromin调节MLK的分子基础。因此，在目的1中，我们将使用生物化学、药理学、RNAi、吗啉代反义RNA和可诱导细胞系来探索（i）NF 2细胞增殖是否是ERK和/或JNK依赖性的，（ii）merlin或NF 1 GTP酶激活蛋白相关结构域（GRD）的诱导是否抑制MLK 3及其效应物，以及这种抑制是否在与疾病相关的NF 2或NF 1突变体中丧失，和（iii）MLK 3如何调节Raf家族的ERK特异性MAP 3 Ks。在目标2中，我们将使用RNAi、吗啉代反义RNA和诱导型细胞系来评估NF 1或NF 2的消融或诱导对内源性MLK 3活性、其效应子和下游功能的影响程度。最后，我们发现，内源性和重组的梅林和MLK 3在体内有丝分裂原可逆的方式。Merlin是JNK活性的负调节剂，并且具有可与MLK 3的SH 3结构域结合的富含脯氨酸的区段。另外，merlin可抑制Rho家族GTP酶对MLK 3的募集。在目标3中，我们将使用生物化学和分子生物学方法来探索这些可能性。

DESCRIPTION (provided by applicant): The predisposition of type 1 and 2 neurofibromatosis (NF1 and NF2, respectively) patients to both benign and malignant nerve sheath, myeloid cell and other cancers represents for these diseases the principal cause of morbidity and mortality. The effective treatment of these tumors represents a major unmet medical need. NF1 and NF2 are genetic loss of function diseases in which the cognate genes, NF1 and NF2 are subject to a broad suite of inactivating mutations or truncations. Given this genetic heterogeneity, coupled with the loss of function phenotype, targeting or exploiting neurofibromin (the product of NF1) or merlin (the product of NF2) as a therapeutic approach is impractical. By contrast, neurofibromin is a Ras inactivator, and ongoing work indicates that blunting Ras signaling could be beneficial to the treatment of NF1 tumors insofar as inhibition of Ras itself, or inhibition of Ras effectors such as the extracellular signal-regulated kinase (ERK) group of mitogen-activated protein kinases (MAPKs) can significantly blunt NF1 cell proliferation. In a somewhat similar vein, merlin, by an unknown mechanism, suppresses signaling by the Jun-N-terminal kinase (JNK), and possibly the ERK MAPKs. However, the biological consequences of merlin-mediated inhibition of JNK is unclear; and overall, our knowledge of MAPK pathway regulation and function in NF1 and NF2 tumor cell biology is incomplete. Clearly, further studies are needed to identify suitable targets for new treatment approaches. Our preliminary work identifies the Ser/Thr kinase mixed lineage kinase-3 (MLK3) as a required component for the proliferation of malignant schwannoma cell lines from NF1 and NF2 patients, and for murine NF2-/- cells. We find that MLK3 is also required for mitogen activation of NF1/2 cell MAPKs. Surprisingly, MLK3, by an as yet unknown, indirect mechanism, recruits B-Raf to activate ERK. This project will explore the biochemical function(s) that MLK3 performs in mitogen-treated NF tumor cells and the molecular basis by which merlin and neurofibromin regulate MLK.3. Accordingly, in Aim 1 we will use biochemical, pharmacologic, RNAi, morpholino antisense RNA and inducible cell lines to explore (i) if NF2 cell proliferation is ERK and/or JNK-dependent, (ii) if induction of merlin or the NF1 GTPase activating protein-related domain (GRD) inhibits MLK3 and its effectors and if this inhibition is lost in NF2 or NF1 mutants associated with disease, and (iii) how MLK3 regulates ERK-specific MAP3Ks of the Raf family. In Aim 2, we will use RNAi, morpholino antisense RNA and inducible cell lines to assess the degree to which ablation or induction of NF1 or NF2 affects the activity of endogenous MLK3, its effectors and downstream functions. Finally, we find that endogenous and recombinant merlin and MLK3 associate in vivo in a mitogen-reversible manner. Merlin is a negative regulator of JNK activity, and possesses a proline-rich segment which could bind to the SH3 domain of MLK3. Alternatively, merlin could repress the recruitment of MLK3 by Rho family GTPases. In Aim 3, we will use biochemical and molecular biological methods to explore these possibilities.