Pancreatic cancer (PC) is a leading cause of cancer related deaths in United States. The lack of early symptoms results in late-stage detection and a high mortality rate. Currently, the only potentially curative approach for PC is surgical resection, which is often unsuccessful because the invasive and metastatic nature of the tumor masses makes their complete removal difficult. Consequently, patients suffer relapses from remaining cancer stem cells or drug resistance that eventually lead to death. To improve the survival rate, the early detection of PC is critical. Current biomarker research in PC indicates that a serum carbohydrate antigen, CA 19-9, is the only available biomarker with approximately 90% specificity to PC. However, the efficacy of CA 19-9 for assessing prognosis and monitoring patients with PC remains contentious. Thus, advances in technology and the detection of new biomarkers with high specificity to PC are needed to reduce the mortality rate of pancreatic cancer.

Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing this collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden to Department of Defense, Washington Headquarters Services, Directorate for Information , 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302 Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid 0MB control number PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. REPORT DATE (DD-MM-YYYY)2 ABSTRACT: Concurrent activation of poly (ADP-ribose) polymerase (PARP) and DNA ligase was observed in cultured human epidermal keratinocytes (HEK) exposed to the DNA alkylating compound sulfur mustard (SM), suggesting that DNA ligase activation could be due to its modification by PARP. Using HEK, intracellular "H-labeled NAD÷ (H-adenine) was metabolically generated and then these cells were exposed to SM (1 mm). DNA ligase I isolated from these cells was not 3 H-labeled, indicating that DNA ligase I is not a substrate for (ADP-ribosyl)ation by PARP. In HEK, when PARP was inhibited by 3-amino benzamide (3-AB, 2 msm), SM-activated DNA ligase had a half-life that was four-fold higher than that observed in the absence of 3-AB. These results suggest that DNA repair requires PARP, and that DNA ligase remains activated until DNA damage repair is complete. The results show that in SM-exposed HEK, DNA ligase I is activated by phosphorylation catalysed by DNA-dependent protein kinase (DNA-PK). Therefore, the role of PARP in DNA repair is other than that of DNA ligase I activation. By using the DNA ligase I phosphorylation assay and decreasing PARP chemically as well as by PARP anti-sense mRNA expression in the cells, it was confirmed that PARP does not modify DNA ligase I. In conclusion, it is proposed that PARP is essential for efficient DNA repair; however, PARP participates in DNA repair by altering the chromosomal structure to make the DNA damage site(s) accessible to the repair enzymes. KEY WORDS: poly(ADP-ribose) polymerase (PARP); DNA repair; sulfur mustard-DNA ligase 1; DNA repair mechanism Introduction and apoptosis. SM produces alkyl adducts, cross-links and double-strand breaks in the chromosomal DNA Sulfur mustard (SM, bis-(2-chloroethyl) sulfide) inflicts (Papirmeister et al., 1991). Repair of this damage can debilitating injury to skin (blistering or vesication) and to restore DNA integrity and cell viability. On the other other organs exposed to it. At the molecular level, SM hand, apoptosis leads to caspase-3-mediated PARP degtargets chromosomal DNA, RNA and proteins. Following radation, DNA fragmentation and cell deat...

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Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing this collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, induding suggestions for reducing this burden to Department of Defense, Washington Headquarters Services, Directorate for Information Maryland 21010-5400, and Department of Chemistry, Lincoln University, Pennsylvania 19352-0999 Received July 28, 2005; Revised Manuscript Received January 9, 2006 ABSTRACT: DNA-dependent protein kinase (DNA-PK) phosphorylates several cellular proteins in vitro, but its cellular function and natural substrate(s) in vivo are not established. We reported activation of DNA ligase in cultured normal human epidermal keratinocytes (NHEK) on exposure to the DNA-damaging compound bis-(2-chloroethyl) sulfide. The activated enzyme was identified as DNA ligase I, and this activation was attributed to phosphorylation of the enzyme. Here, we show that the phosphorylation is mediated by DNA-PK and that DNA ligase I is one of its natural substrates in vivo. DNA ligase I phosphorylation-cum-activation is a response specific to DNA double-strand breaks. We also demonstrate that affinity-purified inactive DNA ligase I is phosphorylated and activated in vitro by HeLa Cell DNA-PK confirming the in vivo observations. The findings specify the roles of DNA-PK and DNA ligase I in mammalian DNA double-strand break repair.