ROLE OF TAK1 IN RANKL SIGNALING PATHWAY

描述(申请人提供)：通过破骨细胞的骨吸收和成骨细胞的骨形成的协调作用来维持骨的完整性。核因子-kappaB受体激活剂(核因子-kappaB)配体是破骨细胞分化和激活的关键因子。慢性炎症和骨转移主要通过增加RANKL的产生来诱导过度的骨吸收。RANKL与其受体RANK(核因子-kappaB受体激活剂)结合，通过募集细胞间适配器TRAF6(肿瘤坏死因子受体相关因子6)启动细胞间信号转导。RANKL/RANK/TRAF6介导的信号转导导致转录因子NF-kappaB的激活，丝裂原激活的激酶JNK和p38，癌基因产物c-Src和转录因子c-Fos的表达，这些在破骨细胞的形成中起重要作用。然而，RANK/TRAF6和下游效应器之间的联系尚未确定。我们先前已经证明，TAK1(转化生长因子β激活的激酶)是MAPKKK(丝裂原激活的激酶)的成员，在促炎信号和细胞分化中起着重要的作用。最近，我们发现RANKL可以诱导TAK1和TAB2(TAK1结合蛋白2)与RANK/TRAF6内源性结合。因此，我们推测TAK1和TAB2也在RANKL信号通路中发挥重要作用。在这一探索性/发展性方案中，我们将确定TAK1/TAB2在RANKL依赖的信号通路中的作用，并获得数据以发展体内模型，进一步验证TAK1/TAB2在破骨细胞形成中的具体作用。我们的具体目标是：1)确定TAK1/TAB2在RANKL诱导的NF-kappaB、JNK、p38和c-Src激活、c-Fos诱导和破骨细胞形成中的作用：2)设计和创造突变的TAK1和TAB2蛋白，它们缺乏传递RANKL依赖的信号的能力，但在介导其他信号通路方面是完整的。我们计划在未来的研究中利用这些突变体来展示RANK/TRAF6/TAB2/TAK1信号在破骨细胞形成中的功能作用。这些研究将促进对破骨细胞生成的分子机制的了解，并可能为过度破骨细胞生成引起的骨病提供新的治疗靶点。

DESCRIPTION (provided by applicant): Bone integrity is maintained through the coordinated action of bone resorption by osteoclasts and bone formation by osteoblasts. RANKL (receptor activator of nuclear factor kappaB (NF-kappaB) ligand) is a key factor for differentiation and activation of osteoclasts. Chronic inflammation and cancer metastasis to bone induce excessive bone resorption primarily by enhancing production of RANKL. RANKL binds to its receptor RANK (receptor activator of NF-kappaB) and initiates intercellular signaling by recruiting intercellular adaptor TRAF6 (tumor necrosis factor receptor-associated factor 6). RANKL/RANK/TRAF6-mediated signaling leads to activation of transcription factor NF-kappaB, mitogen-activated kinases JNK and p38, oncogene product c-Src and transcription factor c-Fos expression, which are important for osteoclastogenesis. However, the link between RANK/TRAF6 and the downstream effectors has not been identified. We have previously demonstrated that TAK1 (transforming growth factor beta activated kinase), a member of MAPKKK (mitogen-activated kinase kinase kinase), plays essential roles in proinflammatory signaling and cell differentiation. Recently, we have found that RANKL induces endogenous association of TAK1 and TAB2 (TAK1 binding protein 2) with RANK/TRAF6. Therefore, we hypothesize that TAK1 and TAB2 also play essential roles in RANKL signaling pathway. In this exploratory/developmental proposal, we will determine the roles of TAK1/TAB2 in RANKL-dependent signaling pathways and obtain data to develop in vivo model to further verify the specific roles of TAK1/TAB2 in osteoclastogenesis. Our specific Aims are: 1) To determine the roles of TAK1/TAB2 in RANKL-induced NF-kappaB, JNK, p38 and c-Src activation, c-Fos induction and osteoclastogenesis: 2) To design and create mutant TAK1 and TAB2 proteins that lack the ability to transmit the RANKL-dependent signaling but are intact in mediating other signaling pathways. We will plan to use those mutants to demonstrate functional roles of the RANK/TRAF6/TAB2/TAK1 signaling in osteoclastogenesis in the future study. These studies will advance the understanding of the molecular mechanisms underlying the osteoclastogenesis and may offer novel therapeutic targets for bone diseases caused by excessive osteoclastogenesis.