Aurora A是一種受細胞週期調控的serine/threonine kinase，對於細胞內中心體(centrosome)的功能扮演重要的角色。當細胞週期進行到M-phase時，中心體的正常複製與分離將影響到成對染色體平均分配至子細胞的過程，若細胞中的Aurora A蛋白有不正常的表現，則可能會造成中心體的增殖(centrosome amplification)以及非成對套數染色體(aneuploidy)的產生。過去有文獻指出，在某些癌細胞，Aurora A有過度表現情形，而這通常來自三方面的貢獻，即Aurora A基因的增幅(gene amplification)，轉錄的活化(transcriptional activation)及蛋白質穩定性的增加(protein stabilization)所造成。目前認為Aurora A的不正常表現與癌細胞的形成有關。在本研究中，我們發現在大腸直腸癌細胞株中，EGF的刺激可以造成Aurora A的表現量增加，為了更進一步研究其調控機轉，我們作了reporter assay及real-time RT-PCR，兩者的結果皆顯示EGF並不會影響Aurora A的轉錄。但是透過核糖體蛋白S6的免疫沉澱法(Ribosomal protein S6 immunoprecipitation)，我們發現EGF可以造成更多的核糖體(ribosome)結合至Aurora A的mRNA上，證實EGFR可以透過轉譯(translation)的調控使Aurora A protein的表現量增加。這是首次有證據顯示Aurora A可以經由轉譯來被調控。接著我們藉由不同化學抑制劑的處理，確認EGFR同時經由MEK/ERK以及PI3k/Akt/mTOR的路徑來調控Aurora A的轉譯。最後我們利用蛋白質降解實驗，發現EGF同時也能造成Aurora A蛋白穩定性的延長。我們的研究結果除了首次聯結在大腸直腸癌細胞中EGFR與Aurora A過量表現的關聯性，並首次提出Aurora A可以透過轉譯調控來增加其表現，相信這樣的機轉可以去解釋在大腸直腸癌細胞中Aurora A過量表現的原因。

Aurora-A is a cell-cycle regulated serine/threonine kinase and plays an important role in centrosome’s function. During mitosis, the correct replication and separation of centrosomes are important for the accurate segregation of duplicated chromosomes. Aurora-A kinase overexpression may results in centrosomes amplification and chromosome aneuploidy. Previously studies indicated that Aurora-A are overexpressed in many cancer cells, and the increased level of Aurora-A is through the DNA amplification, protein stabilization and transcriptional up-regulation. According the documents previously reported, the Aurora-A gene is a potential oncogene. In this study, we found that EGF can enhance the Aurora-A expression in human colorectal cancer cell lines. In order to study the molecular mechanism which involved in the EGF-enhanced Aurora-A expression, we performed the reporter assay and real-time RT-PCR. Both results indicated that the EGF-enhanced Aurora-A expression was not through the transcriptional activation. By ribosomal protein S6 immunoprecipitation assay, however, the result showed that EGF-enhanced Aurora-A expression may through the translational up-regulation. This is the first time to demonstrate that the translational activation maybe involved in the regulation of Aurora-A overexpression in cancer cells. The signalling pathway involved in the translational regulation was further investigated by using chemical inhibitors. The results indicated that the EGF-enhanced Aurora-A overexpression is both through the MEK/ERK and PI3K/Akt/mTOR pathway. Finally, we found that the prolonged protein stability doses coincide with the translational up-regulation of Aurora-A by the EGF stimulation. Our study not only linked the relationship between EGFR and Aurora-A, but also found out a novel mechanism about the translational regulation of Aurora-A. We believe that this discovery may make more elucidation about the cause of the Aurora-A overexpression in human colorectal cancer.

Abd El-Rehim, D. M., Pinder, S. E., Paish, C. E., Bell, J. A., Rampaul, R. S., Blamey, R. W., Robertson, J. F., Nicholson, R. I., and Ellis, I. O. (2004). Expression and co-expression of the members of the epidermal growth factor receptor (EGFR) family in invasive breast carcinoma. Br J Cancer 91, 1532-1542.

Anand, S., Penrhyn-Lowe, S., and Venkitaraman, A. R. (2003). AURORA-A amplification overrides the mitotic spindle assembly checkpoint, inducing resistance to Taxol. Cancer Cell 3, 51-62.

Atalay, G., Cardoso, F., Awada, A., and Piccart, M. J. (2003). Novel therapeutic strategies targeting the epidermal growth factor receptor (EGFR) family and its downstream effectors in breast cancer. Ann Oncol 14, 1346-1363.

Bischoff, J. R., Anderson, L., Zhu, Y., Mossie, K., Ng, L., Souza, B., Schryver, B., Flanagan, P., Clairvoyant, F., Ginther, C., et al. (1998). A homologue of Drosophila aurora kinase is oncogenic and amplified in human colorectal cancers. Embo J 17, 3052-3065.

Briassouli, P., Chan, F., and Linardopoulos, S. (2006). The N-terminal domain of the Aurora-A Phe-31 variant encodes an E3 ubiquitin ligase and mediates ubiquitination of IkappaBalpha. Hum Mol Genet 15, 3343-3350.

Briassouli, P., Chan, F., Savage, K., Reis-Filho, J. S., and Linardopoulos, S. (2007). Aurora-A regulation of nuclear factor-kappaB signaling by phosphorylation of IkappaBalpha. Cancer Res 67, 1689-1695.

Chan, C. S., and Botstein, D. (1993). Isolation and characterization of chromosome-gain and increase-in-ploidy mutants in yeast. Genetics 135, 677-691.

Chen, S. S., Chang, P. C., Cheng, Y. W., Tang, F. M., and Lin, Y. S. (2002). Suppression of the STK15 oncogenic activity requires a transactivation-independent p53 function. Embo J 21, 4491-4499.

Danielsen, A. J., and Maihle, N. J. (2002). The EGF/ErbB receptor family and apoptosis. Growth Factors 20, 1-15.

Ducat, D., and Zheng, Y. (2004). Aurora kinases in spindle assembly and chromosome segregation. Exp Cell Res 301, 60-67.

Dutertre, S., Descamps, S., and Prigent, C. (2002). On the role of aurora-A in centrosome function. Oncogene 21, 6175-6183.

Fischer, O. M., Hart, S., Gschwind, A., and Ullrich, A. (2003). EGFR signal transactivation in cancer cells. Biochem Soc Trans 31, 1203-1208.

Furukawa, T., Kanai, N., Shiwaku, H. O., Soga, N., Uehara, A., and Horii, A. (2006). AURKA is one of the downstream targets of MAPK1/ERK2 in pancreatic cancer. Oncogene 25, 4831-4839.

Glover, D. M., Leibowitz, M. H., McLean, D. A., and Parry, H. (1995). Mutations in aurora prevent centrosome separation leading to the formation of monopolar spindles. Cell 81, 95-105.

Gritsko, T. M., Coppola, D., Paciga, J. E., Yang, L., Sun, M., Shelley, S. A., Fiorica, J. V., Nicosia, S. V., and Cheng, J. Q. (2003). Activation and overexpression of centrosome kinase BTAK/Aurora-A in human ovarian cancer. Clin Cancer Res 9, 1420-1426.

Harrington, E. A., Bebbington, D., Moore, J., Rasmussen, R. K., Ajose-Adeogun, A. O., Nakayama, T., Graham, J. A., Demur, C., Hercend, T., Diu-Hercend, A., et al. (2004). VX-680, a potent and selective small-molecule inhibitor of the Aurora kinases, suppresses tumor growth in vivo. Nat Med 10, 262-267.

Helton, E. S., and Chen, X. (2007). p53 modulation of the DNA damage response. J Cell Biochem 100, 883-896.

Honda, K., Mihara, H., Kato, Y., Yamaguchi, A., Tanaka, H., Yasuda, H., Furukawa, K., and Urano, T. (2000). Degradation of human Aurora2 protein kinase by the anaphase-promoting complex-ubiquitin-proteasome pathway. Oncogene 19, 2812-2819.

Hontz, A. E., Li, S. A., Lingle, W. L., Negron, V., Bruzek, A., Salisbury, J. L., and Li, J. J. (2007). Aurora a and B overexpression and centrosome amplification in early estrogen-induced tumor foci in the Syrian hamster kidney: implications for chromosomal instability, aneuploidy, and neoplasia. Cancer Res 67, 2957-2963.

Horn, V., Thelu, J., Garcia, A., Albiges-Rizo, C., Block, M. R., and Viallet, J. (2007). Functional interaction of Aurora-A and PP2A during mitosis. Mol Biol Cell 18, 1233-1241.

Jeng, Y. M., Peng, S. Y., Lin, C. Y., and Hsu, H. C. (2004). Overexpression and amplification of Aurora-A in hepatocellular carcinoma. Clin Cancer Res 10, 2065-2071.

Li, D., Zhu, J., Firozi, P. F., Abbruzzese, J. L., Evans, D. B., Cleary, K., Friess, H., and Sen, S. (2003). Overexpression of oncogenic STK15/BTAK/Aurora A kinase in human pancreatic cancer. Clin Cancer Res 9, 991-997.

Littlepage, L. E., and Ruderman, J. V. (2002). Identification of a new APC/C recognition domain, the A box, which is required for the Cdh1-dependent destruction of the kinase Aurora-A during mitotic exit. Genes Dev 16, 2274-2285.

Liu, Q., Kaneko, S., Yang, L., Feldman, R. I., Nicosia, S. V., Chen, J., and Cheng, J. Q. (2004). Aurora-A abrogation of p53 DNA binding and transactivation activity by phosphorylation of serine 215. J Biol Chem 279, 52175-52182.

Marumoto, T., Zhang, D., and Saya, H. (2005). Aurora-A - a guardian of poles. Nat Rev Cancer 5, 42-50.

Mayer, A., Takimoto, M., Fritz, E., Schellander, G., Kofler, K., and Ludwig, H. (1993). The prognostic significance of proliferating cell nuclear antigen, epidermal growth factor receptor, and mdr gene expression in colorectal cancer. Cancer 71, 2454-2460.

Meraldi, P., Honda, R., and Nigg, E. A. (2002). Aurora-A overexpression reveals tetraploidization as a major route to centrosome amplification in p53-/- cells. Embo J 21, 483-492.

Nigg, E. A. (2001). Mitotic kinases as regulators of cell division and its checkpoints. Nat Rev Mol Cell Biol 2, 21-32.

Normanno, N., Bianco, C., De Luca, A., Maiello, M. R., and Salomon, D. S. (2003). Target-based agents against ErbB receptors and their ligands: a novel approach to cancer treatment. Endocr Relat Cancer 10, 1-21.

Normanno, N., De Luca, A., Bianco, C., Strizzi, L., Mancino, M., Maiello, M. R., Carotenuto, A., De Feo, G., Caponigro, F., and Salomon, D. S. (2006). Epidermal growth factor receptor (EGFR) signaling in cancer. Gene 366, 2-16.

Ono, M., and Kuwano, M. (2006). Molecular mechanisms of epidermal growth factor receptor (EGFR) activation and response to gefitinib and other EGFR-targeting drugs. Clin Cancer Res 12, 7242-7251.

Parsa, A. T., and Holland, E. C. (2004). Cooperative translational control of gene expression by Ras and Akt in cancer. Trends Mol Med 10, 607-613.

Pawson, T., Gish, G. D., and Nash, P. (2001). SH2 domains, interaction modules and cellular wiring. Trends Cell Biol 11, 504-511.

Proud, C. G. (2007). Signalling to translation: how signal transduction pathways control the protein synthetic machinery. Biochem J 403, 217-234.

Reiter, R., Gais, P., Jutting, U., Steuer-Vogt, M. K., Pickhard, A., Bink, K., Rauser, S., Lassmann, S., Hofler, H., Werner, M., and Walch, A. (2006). Aurora kinase a messenger RNA overexpression is correlated with tumor progression and shortened survival in head and neck squamous cell carcinoma. Clin Cancer Res 12, 5136-5141.

Schlessinger, J. (2002). Ligand-induced, receptor-mediated dimerization and activation of EGF receptor. Cell 110, 669-672.

Speake, G., Holloway, B., and Costello, G. (2005). Recent developments related to the EGFR as a target for cancer chemotherapy. Curr Opin Pharmacol 5, 343-349.

Sporn, M. B., and Roberts, A. B. (1985). Autocrine growth factors and cancer. Nature 313, 745-747.

Taguchi, S., Honda, K., Sugiura, K., Yamaguchi, A., Furukawa, K., and Urano, T. (2002). Degradation of human Aurora-A protein kinase is mediated by hCdh1. FEBS Lett 519, 59-65.

Tanaka, M., Ueda, A., Kanamori, H., Ideguchi, H., Yang, J., Kitajima, S., and Ishigatsubo, Y. (2002). Cell-cycle-dependent regulation of human aurora A transcription is mediated by periodic repression of E4TF1. J Biol Chem 277, 10719-10726.

Tanaka, T., Kimura, M., Matsunaga, K., Fukada, D., Mori, H., and Okano, Y. (1999). Centrosomal kinase AIK1 is overexpressed in invasive ductal carcinoma of the breast. Cancer Res 59, 2041-2044.

Tanner, M. M., Tirkkonen, M., Kallioniemi, A., Collins, C., Stokke, T., Karhu, R., Kowbel, D., Shadravan, F., Hintz, M., Kuo, W. L., and et al. (1994). Increased copy number at 20q13 in breast cancer: defining the critical region and exclusion of candidate genes. Cancer Res 54, 4257-4260.

Tanner, M. M., Tirkkonen, M., Kallioniemi, A., Holli, K., Collins, C., Kowbel, D., Gray, J. W., Kallioniemi, O. P., and Isola, J. (1995). Amplification of chromosomal region 20q13 in invasive breast cancer: prognostic implications. Clin Cancer Res 1, 1455-1461.

Udayakumar, T. S., Belakavadi, M., Choi, K. H., Pandey, P. K., and Fondell, J. D. (2006). Regulation of Aurora-A kinase gene expression via GABP recruitment of TRAP220/MED1. J Biol Chem 281, 14691-14699.

Warner, S. L., Bearss, D. J., Han, H., and Von Hoff, D. D. (2003). Targeting Aurora-2 kinase in cancer. Mol Cancer Ther 2, 589-595.

Wells, A. (1999). EGF receptor. Int J Biochem Cell Biol 31, 637-643.

Yarden, Y. (2001). The EGFR family and its ligands in human cancer. signalling mechanisms and therapeutic opportunities. Eur J Cancer 37 Suppl 4, S3-8.

Yu, X., Minter-Dykhouse, K., Malureanu, L., Zhao, W. M., Zhang, D., Merkle, C. J., Ward, I. M., Saya, H., Fang, G., van Deursen, J., and Chen, J. (2005). Chfr is required for tumor suppression and Aurora A regulation. Nat Genet 37, 401-406.

Zhou, H., Kuang, J., Zhong, L., Kuo, W. L., Gray, J. W., Sahin, A., Brinkley, B. R., and Sen, S. (1998). Tumour amplified kinase STK15/BTAK induces centrosome amplification, aneuploidy and transformation. Nat Genet 20, 189-193.