DNA Repair In Cancer And Senescence

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Summary of work: Werner's syndrome (WS) is a homozygous recessive disease characterized by early onset of many characteristics of normal aging, such as wrinkling of the skin, graying of the hair, cataracts, diabetes, and osteoporosis. The symptoms of WS begin to appear around the age of puberty, and most patients die before age 50. Because of the acceleration of aging in WS, the study of this disease will hopefully shed light on the degenerative processes that occur in normal aging. Cells from WS patients grow more slowly and senescence at an earlier population doubling than age-matched normal cells, possibly because these cells appear to lose the telomeric ends of their chromosomes at an accelerated rate. In general, WS cells have a high level of genomic instability, with increased amounts of DNA deletions, insertions, and rearrangements. These effects could potentially be the result of defects in DNA repair, replication, and/or recombination, although the actual biochemical defect remains unknown. The gene that is defective in WS, the WRN gene, has been identified and characterized. We have made purified WRN protein for use in a number of basic and complex biochemical assays. We are pursuing several avenues to identify and characterize the biochemical defect in WS cells. WRN protein has helicase activity and will unwind small and large DNA duplex constructs. It will also unwind unusual DNA structures such as triple helices and DNA forks. We are comparing the Werner helicase activity to that of another helicase, BLM, which is mutated in Bloom syndrome. WRNp has another enzymatic activity, a 3-5' exonuclease function. We are searching for pathways in which WRN participates and have discovered a number of new functional and physical protein interactions with Werner protein. Our data strongly suggest that WRN is involved in two of the major DNA repair pathways: base excision repair and recombination. This conclusion is supported by biochemical studies of protein functional interaction and increasingly also by cell biological data. Further, our observations and results from other work suggest that a major function of WRN is at the telomere end. WRN interacts with a number of key telomeric proteins such as TRF1 and 2 and POT1. These observations of functional protein interactions corroborated by cell biological observations suggest that WRN protein is involved in DNA repair processes and maintenance at the telomere end.