Abstract
520
High mobility group A2 protein (HMGA2) is a non-histone architectural transcription factor. HMGA2 is expressed during embryogenesis and becomes undetectable in terminally differentiated tissues. There is a strong correlation between ectopic HMGA2 expression and malignant tumor phenotypes, such that HMGA2 over-expression in cancer cells is associated with poor prognosis and high tumor grades. Recently, we and two other groups, have independently reported that HMGA (HMGA1 and HMGA2) over-expression conveys chemosensitization and subsequent apoptosis of cells towards agents that cause DNA double-strand break (DSBs), such as doxorubicin (Dox), cisplatin, and X-ray irradiation. In addition, this chemosensitization is associated with impaired DNA repair. Despite these evidence, the precise molecular mechanisms underlying HMGA2-mediated apoptosis remain to be elucidated. Here, we demonstrated that over-expression of HMGA2 induces a sustained basal level of DNA damage than HMGA2 under-expressing cells using Comet assays. Intriguingly, Western and immunofluorescent microscopy analyses revealed that HMGA2-expressing cells exhibited a more intense and persistent DNA-PKcs phosphorylation at Thr-2609 and Ser-2056 and were accompanied with a delayed ATM phosphorylation at Ser-1981 than that of the HMGA2 under-expressing cells upon Dox-treatment. In addition, we showed that HMGA2-mediated chemosensitization is not associated with p53 genotype and function, and that Ku70(-/-) and DNA-PKcs(-/-) cells are more sensitive towards Dox-treatment than their wild-type counterparts. Lastly, by using co-immunoprecipitation, we demonstrated that HMGA2 interacts with Ku70/80 heterodimer, implicating that HMGA2 interferes with DNA-PK signaling upon Dox-treatment. This HMGA2-dependent modulation of DNA-PK could be crucial for regulating chemoresponsiveness of cancer cells towards DSBs. (This is supported in part by R01-DE 10742, DE14183, CA72767)
[Proc Amer Assoc Cancer Res, Volume 47, 2006]
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