| Ataxia telangiectasia (A-T) is a rare disorder with hallmark phenotypes such as cancer predisposition and extreme sensitivity to ionizing radiation. The Ataxia telangiectasia mutated (ATM) gene product is a serine/threonine protein kinase that is involved in DNA double strand break repair, apoptosis, and cell cycle arrest. ATM signals to a host of targets including p53, Chk2, NBS1, and BRCA1. Previous work has shown that A-T cells are deficient in the Insulin-like Growth Factor-I Receptor (IGF-IR), which may account for a portion of the observed radiosensitivity in such cells. The first part of this thesis we describe a novel interaction between ATM and the transcription factor, Sp1. ATM physically interacts with Sp1, a transcription factor that promotes IGF-IR expression. This interaction appears to affect the DNA binding activity of Sp1, as a kinase-dead form of ATM reduces the ability of Sp1 to bind to a consensus oligonucleotide. These data suggest that ATM may affect IGF-IR expression via interaction with Sp1. The second part of this thesis involves hypoxia-induced signaling to the checkpoint kinase, Chk2. ATM was found to mediate Chk2 phosphorylation on threonine 68 in response to hypoxia. Similarly, NBS1 and MLH1 were also found to contribute to Chk2 phosphorylation. Chk2 phosphorylation under these conditions appears to activate Chk2 kinase activity and, in fact, hypoxia stimulates p53 phosphorylation in a Chk2-dependent manner. Overall, this thesis examines two novel roles for ATM; one affecting basal transcription machinery and the other involving hypoxia-induced signaling to Chk2. |
