David Orren,
Ph.D.

Associate Professor

Director of Graduate Studies

Graduate Center for Toxicology

Phone:
(859)  323-3612

Fax:
(859) 323-1059

e-mail:
dkorre2@uky.edu

Our focus of study is how endogenous processes and environmental agents contribute to genetic changes that, in turn, lead to carcinogenesis and other characteristics of human aging. We are currently using cancer-prone and premature aging diseases as model systems to examine these processes. Of particular interest to our laboratory are hereditary diseases such as Werner syndrome that are caused by deficiencies in RecQ helicase genes. Individuals with Werner syndrome have an early onset and accelerated development of many aging characteristics (including an increased frequency of cancer and atherosclerosis). Intriguingly, all of these changes appear to be the result of defects in a single protein known as WRN. WRN has the ability to unwind double-stranded DNA (helicase) and degrade one strand of a DNA duplex substrate (exonuclease), indicating an (as yet) unknown function in DNA metabolism. The lack of WRN function leads to accumulation of chromosomal abnormalities, accelerated loss of telomeric DNA sequences, and reduced cellular replicative capacity (premature senescence). The phenotypes of Werner syndrome and other RecQ helicase deficiencies solidify the connection between the accumulation of genetic changes during life and the appearance of at least some characteristics of human aging. By examining these connections, we also hope to gain insight into how the normal aging process occurs and possibly design strategies to slow the debilitating processes that occur in later life.

Research Publications/Presentations

Machwe, A., Xiao, L., Groden, J. and Orren, D.K. The Werner and Bloom syndrome proteins catalyze regression of a model replication fork.  Biochemistry 45, 13939-13946, 2006.

Machwe, A., Xiao, L., Lloyd, R.G, Bolt, E., and  Orren, D.K.  Replication fork regression in vitro by the Werner syndrome protein (WRN): Holliday junction formation, the effect of leading arm structure and a potential role for WRN  exonuclease activity.  Nucleic Acids Research (in press), 2007.

Orren, D.K.  Werner syndrome: molecular insights into the relationships between defective DNA metabolism, genomic instability, cancer and aging.  Frontiers in Bioscience 11, 2657-2671, 2006.

Machwe, A., Xiao, L., and Orren, D.K.  Length-dependent degradation of single-stranded 3’ ends by the Werner syndrome protein (WRN): implications for spatial orientation and coordinated 3’ ® 5’ movement of its ATPase/helicase and exonuclease domains.  BMC Mol. Biol. 7:6, 2006.

Machwe, A., Lozada, E.M., Xiao, L., and Orren, D.K.  Competition between the DNA unwinding and strand pairing activities of the Werner and Bloom syndrome proteins.  BMC Mol. Biol. 7:1, 2006.

Orren, D.K.  The irresistible resistance of nonsense: evolutionary adaptation of termination condons to minimize the effects of common DNA damage.  DNA Repair 4, 1208-1212,  2005.

Machwe, A. Xiao, L., Groden, J., Matson, S.W. and Orren, D.K.  RecQ family members combine strand pairing and unwinding activities to catalyze strand exchange.  J. Bio. Chem. 280, 23397-23407, 2005.

Lillard-Wetherell, K., Machwe, A., Combs, K.A., Langland, G.T., Behbehani, G.K., Turchi, J.J., Orren, D.K. and Groden, J.  Association and regulation of the BLM helicase by the telomere proteins TRF1 and TRF2.  Human Mol. Genet. 13, 1919-1932, 2004.

Machwe, A., Xiao, L., and Orren, D.K. (2004).  TRF2 recruits the Werner syndrome (WRN) exonuclease for processing of telomeric DNA.  Oncogene 23, 149-156.

Orren, D.K., Theodore, S., and Machwe, A. (2002).  The Werner syndrome protein (WRN) disrupts and degrades D-loops in vitro.  Biochemistry 41, 13483-13488.

 Machwe, A., Xiao, L., Theodore, S., and Orren, D.K. (2002).  DNase I footprinting and enhanced exonuclease function of the bipartite Werner syndrome protein (WRN) bound to partially melted duplex DNA.  J. Biol. Chem. 277, 4492-4504.

Orren, D.K., Machwe, A., Karmakar, P., Piotrowski, J., Cooper, M.P., and Bohr, V.A. (2001). The functional interaction of Ku with WRN exonuclease facilitates digestion of damaged DNA.  Nucleic Acids Res. 29, 1926-1934.

Machwe, A., Orren, D.K., and Bohr, V.A.  (2000).  Accelerated methylation of ribosomal RNA genes during the in vitro cellular senescence of Werner syndrome fibroblasts.  FASEB J. 14, 1715-1724.