Abi Enhances Abl-mediated Cdc2 Phosphorylation and Inactivation for DNA Damage G2-M Checkpoint

• Main Authors: Tzu-Yang Lin, 林子暘
• Other Authors: Wen-Gang Chou
• Format: Others
• Language: en_US
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/gp5cv4

博士 === 國立清華大學 === 生命科學系 === 92 === Abl is a non-receptor tyrosine kinase, which is frequently coupled by adaptor proteins to interact with its substrates for the regulation of cytoskeleton rearrangement, cell growth, and apoptosis in response to a variety of biological stimuli. The Abl-interactor (Abi) family members were first reported as Abl adaptors involved in the regulation of oncogenic Abl transforming activity. In the present study, we have used a yeast two-hybrid screen to identify Cdc2 as a novel Abi-binding protein. This finding led us to investigate the role of Abi in linking Abl and Cdc2. These three proteins formed tri-complex in Drosophila and mammalian cells. Expressing Abi in cells greatly enhanced the formation of Abl-Cdc2 complex, suggesting Abi functions as an adaptor protein facilitating the binding between Abl and Cdc2. We showed that Abi promoted Abl-mediated phosphorylation of Cdc2 at tyrosine 15 and inactivation of kinase activity of Cdc2. Coexpression of Abl and Abi in Drosophila S2 cells led to suppression of cell growth. Furthermore, we showed that Bcr-Abl-positive cells exhibited abrogated radiation-induced Cdc2-Y15 phosphorylation and G2-M arrest as Bcr-Abl kinase activity was blocked by STI571 or protein expression was suppressed by siRNA. This result is consistent with the fact that inhibitory phosphorylation at Y15 of Cdc2 triggers the G2-M arrest in response to DNA damage. Nonetheless, in Bcr-Abl-negative cells, c-Abl appears to be redundant in modulating Cdc2 for checkpoint control. Since both Abl and Abi are also involved in actin dynamics, we investigated the subcellular localization of Cdc2 and, surprisingly, found that it was recruited to the lamellipodia, colocalizing with Abl and Abi in actin-rich bundles. Together, the data suggest that inhibition of Cdc2 kinase for G2-M DNA damage checkpoint in Bcr-Abl cells and the recruitment of Cdc2 to lamellipodia for actin dynamics are associated with Abl and Abi proteins.