| 摘要: | IKK複合體為活化NF-kB的主要蛋白激酶，可調控NF-kB所媒介之細胞生長、血管新生、發炎、腫瘤轉移等相關基因表現。許多種類的腫瘤細胞中可觀察到IKK/NF-kB的過度活化，顯示 IKK活性在腫瘤細胞增生及癌症發展過程之重要性，然而IKK/NF-kB於其中所扮演之角色仍不明確。根據我們及他人的研究發現，IKK複合體中之 IKKa除了參與NF-kB活化外，更可轉位至細胞核內，經由控制染色質上蛋白修飾作用，直接調節基因表現作用。在許多癌症細胞中可偵測到細胞核內 IKKa的表現，目前亦發現一些受IKKa磷酸化之細胞核內蛋白，可參與癌細胞生長與轉移之調節。這些證據顯示，IKKa於細胞核內的功能與角色值得進一步作深入探討。在台灣的主要死因之中，乳癌長年為婦女常見癌症之一，除了在乳癌細胞中可發現IKK/NF-kB的異常活化之外，IKKa亦被證明為乳癌細胞自我增生的重要蛋白。因此，本研究計畫將以乳癌細胞為主，探討細胞核內IKKa是否參與癌細胞的發展，並進一步研究其詳細的作用機制。此外，我們初步的研究結果意外發現在腦轉移的乳癌細胞株中，其細胞核內產生IKKa的截短型變異蛋白(truncated variant)，與未轉移的原細胞株相較之下有明顯增加，顯示此IKKa截短型可能參與乳癌細胞的腦轉移作用，此推論將於本計畫第二部分進行探討，並於第三部分進一步研究其作用的分子機制。除了核內IKKa的功能與角色未明之外，IKKa如何穿梭細胞核與細胞質之間仍未知，因此，本計畫第四部分將探討 IKKa核易位之分子機制，亦有助於釐清其在核內的功能與作用。根據上述四部分的研究成果，本計畫最後將找出可抑制細胞核內IKKa功能之方式，包括利用 adenoviral type 5 E1A gene ，小分子化合物及peptide進行測試，期望可發展成抗癌新方式。
The IkB kinase (IKK) signalsome controls the activation of nuclear factor kappa B (NF-kB), which is a critical regulator of genes involved in cell survival, proliferation, angiogenesis, inflammation, invasion, and metastasis. Aberrant or constitutive IKK/NF-kB activation has also been implicated in the tumor progression for various cancer types. However, the precise roles of IKK/NF-kB in regulating cancer-associated gene expressions remain ambiguous. In spite of the known function in activating NF-kB, accumulating evidence showed that IKKa but not IKKb translocates to the nucleus and regulates gene expressions through chromatin modification. Expression of nuclear IKKa was detected in several kinds of human cancer. Our recent study further identified CBP, a transcriptional integrator of multiple signal transduction pathways, as a novel target of nuclear IKKa. Phosphorylation by IKKa switches CBP binding preference from p53 to NF-kB and contributes to tumor cell growth. These findings reveal nuclear-specific role of IKKa as a potential field to further pursue the precise mechanisms of IKK in controlling NF-kB activation and tumor development. Among the main causes of death in Taiwan, breast cancer has ranked one of the most common cancers affecting Taiwanese women for years. Besides the aberrant IKK/NFkB activation in breast cancer, recent work also demonstrated that IKKa activity is important for self-renewal of ErbB2/Her2-transformed mammary tumor-initiating cells. Therefore, the goal of this proposal is to further verify the involvement of nuclear IKKa in tumor progression, especially in breast cancer cells, and to address the detailed molecular mechanisms by using unbiased methods (Aim-1 and Aim-3). Moreover, our preliminary data unexpectedly found that there is an increased expression of nuclear IKKa truncated variant in brain metastatic breast cancer cells (MDA-231BR) compared to their parental cells. It suggests the existence of an unidentified IKKa variant and its contribution on the brain metastasis of breast cancer. In the Aim-2 of this proposal, the nuclear IKKa truncated variant will be identified and its roles in brain metastasis of breast cancer will be characterized. In addition to the roles of nuclear IKK in tumor development, how IKKa transfer from cytoplasm to nucleus remains unclear. Thus, the molecular mechanisms for IKKa nucleocytoplasmic shuttling will also be addressed in the fourth part of this proposal, and would significantly contribute to unravel the roles of nuclear IKKa in tumor progression and metastasis. Based on the understandings obtained from these studies as proposed above, targeting nuclear IKKa might be developed as a novel strategy for anti-cancer therapy. In the final aim of this proposal, the adenoviral type 5 E1A gene therapy, small molecules, and peptides will be employed to examine their inhibitory effects on the nuclear IKKa-mediated tumor growth and metastasis. Success of these specific aims will help us not only to understand the IKK/NF-kB-mediated tumor progression but also might provide a potential opportunity to develop novel anti-cancer therapies. |
