IKKb在癌症生成角色之研究

Abstract

Nuclear factor-κB (NF-κB)是innate與adaptive immunity之主要調節分子，IκB kinase (IKK)在NF-κB之活化扮演重要角色，二者均可調控細胞之增生和存活與對抗細胞之凋亡，並維持腫瘤之生成及入侵，是連結發炎反應與腫瘤生成之重要分子。我們之前的研究顯示，TNF-α可經由PKC/c-Src途徑磷酸化IKKβ之Tyr-188與Tyr-199，活化IKKβ而誘發NF-κB之活化，本論文中，我們研究不同IKKβ之磷酸化在腫瘤生成中所扮演的角色，因此我們建立A549/Mock、A549/IKKβ (WT)、A549/IKKβ (AA)與A549/IKKβ (FF)四株stable clones，由體內與體外實驗發現，過度表現IKKβ (WT)可以促進細胞增生、血管新生、入侵與轉移，而IKKβ (AA)與IKKβ (FF)突變株則抑制這些現象，且IKKβ (FF)的抑制效果比IKKβ (AA)來得大，IKKβ (WT)可以降低抑制細胞週期之相關蛋白如p53及p27之表現，因而促進細胞增生，且增加ICAM-1、MMP-2與MMP-9之表現而促進癌細胞之入侵及轉移； IKKβ (AA)與IKKβ (FF)突變株則可增加p53與p27之合成，阻斷ICAM-1、MMP-2與MMP-9生成。這些研究顯示IKKβ的確在癌症生成中扮演非常重要的角色，而tyrosine之磷酸化可能比serine之磷酸化更重要。因此，抑制IKK和NF-κB將是研發化學預防以及化學療法之新策略。

Nuclear factor-κB (NF-κB) is a central coordinator of innate and adaptive immune responses and IκB kinase (IKK) plays an important role in NF-κB activation. Both IKK and NF-κB are critical in linking inflammation and tumorigenesis, which control cell proliferation, survival and anti-apoptosis, and facilitate tumor maintenance and invasion. Our previous studies have shown that PKC/c-Src is involved in the TNF-α-induced NF-κB activation via phosphorylating Tyr-188 and Tyr-199 of IKKβ in A549 alveolar epithelial cells. In this thesis, we attempt to investigate the role of IKKβ in carcinogenesis. Therefore, four stable clones, A549/Mock, A549/IKKβ (WT), A549/IKKβ (AA) and A549/IKKβ (FF) were established. Overexpression of IKKβ (WT) promotes in vivo and in vitro cell proliferation, angiogenesis, invasion and metastasis. However, the dominant-negative IKKβ (AA) and IKKβ (FF) mutant inhibit these effects. The inhibitory effect of IKKβ (FF) is greater than that of IKKβ (AA). IKKβ (WT) can decrease the level of cell cycle associated inhibitory proteins such as p53 and p27 to promote cell proliferation, and increase the protein level of ICAM-1, MMP-2 and MMP-9 to promote cell invasion and metastasis. However, the IKKβ (AA) and IKKβ (FF) mutants increase the synthesis of p53 and p27, and block the production of ICAM-1, MMP-2 and MMP-9. These data suggest that tyrosine is more important than serine phosphorylation, and IKKβ indeed plays an essential role in carcinogenesis. Thus, inhibition of IKK and NF-κB is an attractive target for new chemopreventive and chemotherapeutic approaches.