Activation and overexpression of centrosome kinase BTAK/Aurora-A in human ovarian cancer.

Previous studies have demonstrated amplification of the centrosome serine/threonine kinase BTAK/Aurora-A in 10-25% of ovarian cancers. However, alterations of BTAK/Aurora-A at kinase and protein levels and its role in ovarian cancer progression have not been well documented. In this study, we examined the kinase activity and protein levels of BTAK/Aurora-A in 92 patients with primary ovarian tumors. In vitro kinase analyses revealed elevated BTAK/Aurora-A kinase activity in 44 cases (48%). Increased BTAK/Aurora-A protein levels were detected in 52 (57%) specimens. High protein levels of BTAK/Aurora-A correlated well with elevated kinase activity. Activation and overexpression of BTAK/Aurora-A were more frequently detected in early stage/low-grade ovarian tumors, although there was no statistic significance at the kinase level between early stage/low-grade and late stage/high-grade tumors. Moreover, BTAK/Aurora-A was preferentially expressed in noninvasive tumors, as revealed by immunohistochemical staining, suggesting that alterations of BTAK/Aurora-A could be an early event in human ovarian oncogenesis. To our knowledge, this is the first demonstration of recurrent activation and overexpression of BTAK/Aurora-A in human ovarian cancer, which may play a critical role in development of this malignancy.

Inhibition of JNK by cellular stress- and tumor necrosis factor alpha-induced AKT2 through activation of the NF kappa B pathway in human epithelial Cells.

Previous studies have demonstrated that AKT1 and AKT3 are activated by heat shock and oxidative stress via both phosphatidylinositol 3-kinase-dependent and -independent pathways. However, the activation and role of AKT2 in the stress response have not been fully elucidated. In this study, we show that AKT2 in epithelial cells is activated by UV-C irradiation, heat shock, and hyperosmolarity as well as by tumor necrosis factor alpha (TNFalpha) through a phosphatidylinositol 3-kinase-dependent pathway. The activation of AKT2 inhibits UV- and TNF alpha-induced c-Jun N-terminal kinase (JNK) and p38 activities that have been shown to be required for stress- and TNF alpha-induced programmed cell death. Moreover, AKT2 interacts with and phosphorylates I kappa B kinase alpha. The phosphorylation of I kappa B kinase alpha and activation of NF kappa B mediates AKT2 inhibition of JNK but not p38. Furthermore, phosphatidylinositol 3-kinase inhibitor or dominant negative AKT2 significantly enhances UV- and TNF alpha-induced apoptosis, whereas expression of constitutively active AKT2 inhibits programmed cell death in response to UV and TNFalpha -induced apoptosis by inhibition of stress kinases and provide the first evidence that AKT inhibits stress kinase JNK through activation of the NF kappa B pathway.

Positive feedback regulation between Akt2 and MyoD during muscle differentiation. Cloning of Akt2 promoter.

Akt2 is a member of the Akt/PKB family, which is involved in a variety of cellular events including cell survival, proliferation, and differentiation. During skeletal muscle differentiation, the Akt2 but not Akt1 expression was significantly increased. Microinjection of anti-Akt2 but not anti-Akt1 antibody efficiently abrogated myogenesis, indicating that Akt2 plays a specific role in muscle differentiation. It has been well documented that ectopic expression of MyoD is sufficient to induce muscle differentiation in myoblasts. However, the mechanism of induction of Akt2 during muscle differentiation and the significance of Akt2 protein in MyoD-induced myogenesis are largely unknown. In this study, we provide direct evidence that Akt2 is transcriptionally regulated by MyoD and activates MyoD-myocyte enhancer binding factor-2 (MEF2) transactivation activity. The Akt2 promoter was isolated and found to contain nine putative E-boxes (CANNTG), which are putative MyoD binding sites. Electrophoretic mobility shift analyses revealed that MyoD bound to eight of the sites. The expression of MyoD significantly enhanced Akt2 promoter activity and up-regulated Akt2 mRNA and protein levels. Moreover, Akt2 but not Akt1 was activated during differentiation. The expression of Akt2 activated MyoD-MEF2 transcriptional activity and induced myogenin expression. These data indicate that there is a positive feedback regulation loop between Akt2 and MyoD-MEF2 during muscle differentiation, which is essential for MyoD-induced myogenesis.