痘病毒蛋白 CP77 抑制 NF-kB 訊息傳遞之機制

腫瘤壞死因子a型可藉由 NF-kB的活化來調控發炎等免疫反應。 NF-kB可以調節基因的表現，對於細胞而言是個相當重要的轉錄因子。尤其在先天免疫與發炎反應上扮演著重要角色。在病毒的複製過程中，為了拮抗由腫瘤壞死因子所引發的免疫反應，病毒勢必製造某些病毒蛋白質以抑制細胞的反應。目前已知許多的病毒蛋白質可阻斷由腫瘤壞死因子a型與介白素一號所引發之 NF-kB之活化。在本篇報告中，我們主要研究一個痘病毒蛋白 CP77 ，其可以抑制NF-kB 進到細胞核內，因而使得 NF-kB 所調控的基因無法表現。進一步研究結果顯示 CP77 不會影響 IkBa 的磷酸化，表示其上游活化路徑仍然完整。然而我們預測 CP77 會去影響磷酸化後的 IkBa被 SCF E3 ubiquitin ligase 進行泛素化而降解。透過 GST-pull down 的分析發現 CP77 可利用其 N 端與 NF-kB 作用，而且其C 端的十三個胺基酸包含一段 F box-like domain，對抑制 NF-kB 之活化扮演很重要的角色。總結來說，我們的結果顯示 CP77 利用其 C 端的序列與 SCF complex 中的 skp1 蛋白質之作用；另一方面，CP77 可再藉由其 N 端的序列與 NF-kB 結合，以阻斷 NF-kB自由釋放，使其無法進入細胞核中。這可使其下游的基因無法表現，藉以達到抑制細胞的先天性免疫反應之目的。

關鍵字

痘病毒；腫瘤壞死因子；泛素

並列摘要

Tumor necrosis factor a (TNF-a) stimulates inflammation via activation of the nuclear factor-kB (NF-kB) transcriptional regulator. The NF-kB transcription factor family regulates expression of many genes that are important factors of innate immune response and inflammations in the hosts. To antagonize the host responses, many viruses are known to produce proteins to block NF-kB activation. In this report, we described a poxviral protein, CP77, which blocked NF-kB activation by TNF-a?{. We showed that CP77 inhibited NF-kB translocation into nucleus in HeLa cells treated with TNF-a??. Although CP77 did not block IkBa phosphorylation, further degradation of phosphorylated IkBa?nby the ubiquitin ligase SCF complex was inhibited when CP77 was expressed. Deletion analyses showed that the C-terminal region of CP77 containing a F box-like sequence was critical for binding to SCF complex and that the N-terminal region of CP77 binds to NF-kB. In summary, we showed that poxviral CP77 suppressed NF-kB activation by acting as a scaffold protein with the C-terminus of CP77 binding to SCF complex and the N-terminal region to NF-kB. This way, CP77 prevents NF-kB from being released from the SCF complex upon TFN-a activation in cells, leading to attenuation of the downstream innate immune signaling in cells.

並列關鍵字

CP77 ； NF-kB ； SCF E3 complex ； TNF-a

參考文獻

1. Baeuerle, P. A., and T. Henkel. 1994. Function and activation of NF-kappa B in the immune system. Annu Rev Immunol 12:141-79.

4. Broyles, S. S. 2003. Vaccinia virus transcription. J Gen Virol 84:2293-303.

5. Cardozo, T., and M. Pagano. 2004. The SCF ubiquitin ligase: insights into a molecular machine. Nat Rev Mol Cell Biol 5:739-51.

7. Cenciarelli, C., D. S. Chiaur, D. Guardavaccaro, W. Parks, M. Vidal, and M. Pagano. 1999. Identification of a family of human F-box proteins. Curr Biol 9:1177-9.

8. Chen, F. E., D. B. Huang, Y. Q. Chen, and G. Ghosh. 1998. Crystal structure of p50/p65 heterodimer of transcription factor NF-kappaB bound to DNA. Nature 391:410-3.

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痘病毒蛋白 CP77 抑制 NF-kB 訊息傳遞之機制

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