The Function of Mrn (mre11-rad50- Nbs1) Complex during Wrn (werner) Facilitated Atm (ataxia- Telangiectasia Mutated) Activation

Title of Document: THE FUNCTION OF MRN (MRE11-RAD50NBS1) COMPLEX DURING WRN (WERNER) FACILITATED ATM (ATAXIATELANGIECTASIA MUTATED) ACTIVATION Junhao Ma, Master of Science, 2009 Directed By: Assistant Professor, Dr. Wen-Hsing Cheng, Department of Nutrition and Food Science WRN (Werner) protein is a member of the RecQ family showing helicase and exonuclease activity. WRN protein may lose function upon mutation and causes Werner syndrome (WS) which is an autosomal recessive, cancer-prone and premature aging disease. ATM (Ataxia-Telangiectasia mutated) protein initiates a signaling pathway in response to DNA double strand breaks (DSBs). Genomic disorder ataxiatelangiectasia (A-T) is associated with defective ATM. WRN protein is involved in ATM pathway activation when cells are exposed to DSBs associated with replication fork collapse. Because the Mre11-Rad50-Nbs1 (MRN) complex, a sensor of DSBs, is known to interact with WRN and ATM, we investigated whether the MRN complex mediates the WRN-dependent ATM pathway activation. In this study, we employed short-hairpin RNA to generate WRNand Nbs1-deficient U-2 OS (osteosarcoma) cells. Cells were treated with clastogens which induce collapsed replication forks, thus provided proof for whether WRN facilitates ATM activation via MRN complex. This study serves as a basis for future investigation on the correlation between ATM, MRN complex and WRN, which will ultimately help understand the mechanism of aging and cancer.