title: Regulated over-expression of DNA polymerase beta mediates early onset cataract in mice.
abstract: Base excision repair (BER) is a tightly coordinated mechanism for repair of DNA base damage (via alkylation and oxidation) and base loss. From E. coli to yeast to human cells, subtle alterations in expression of BER proteins lead to mutagenic or genome instability phenotypes. DNA polymerase beta (beta-pol), the major BER polymerase, has been found to be over-expressed in human tumor tissues and more recently it has been shown that over-expression of beta-pol results in a mutator and genome instability phenotype. These previous reports imply that beta-pol over-expression is deleterious and suggests that such an imbalance may cause an overall functional deficiency in the BER pathway. In the present study, we have developed a bicistronic tetracycline-responsive transgenic system to over-express beta-pol in mice. We find that over-expression of beta-pol in the lens epithelium results in the early onset of severe cortical cataract, with cataractogenesis beginning within 4 days after birth. In utero and post-natal suppression of transgenic Flag-beta-pol expression by doxycycline administration completely prevents cataract formation through adulthood, yet cataract is subsequently observed following removal of doxycycline and re-expression of the transgene. Cataract development accompanies increased expression of cyclooxygenase-2 in the lenticular fibers of the lens, implicating oxidative stress in the development of this cataractous phenotype. Although the mechanism for the transgene mediated cataractogenesis is not clear at this time, it is nevertheless intriguing that increased expression of beta-pol leads to such a phenotype. These results suggest that either a beta-pol expression imbalance negatively affects overall fidelity and/or BER capacity or that beta-pol has a role in lens epithelial cell differentiation.
authors.affiliation: Laboratory of Structural Biology, National Institute of Environmental Health Sciences, Research Triangle Park, NC 27709, USA. rws9@pitt.edu
authors.forename: Robert W
authors.initials: RW
authors.lastname: Sobol
authors.forename: Julie F
authors.initials: JF
authors.lastname: Foley
authors.forename: Abraham
authors.initials: A
authors.lastname: Nyska
authors.forename: Michael G
authors.initials: MG
authors.lastname: Davidson
authors.forename: Samuel H
authors.initials: SH
authors.lastname: Wilson
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D020137:Base Pair Mismatch; D002386:Cataract / Q000378:metabolism*; D002454:Cell Differentiation; D051546:Cyclooxygenase 2; D019951:DNA Polymerase beta / Q000096:biosynthesis* / Q000235:genetics*; D004260:DNA Repair; D004318:Doxycycline / Q000494:pharmacology; D004847:Epithelial Cells / Q000166:cytology; D004926:Escherichia coli / Q000378:metabolism; D007150:Immunohistochemistry; D007527:Isoenzymes / Q000096:biosynthesis; D051379:Mice; D008822:Mice, Transgenic; D008954:Models, Biological; D008958:Models, Molecular; D018384:Oxidative Stress; D010641:Phenotype; D011451:Prostaglandin-Endoperoxide Synthases / Q000096:biosynthesis; D013997:Time Factors; D019076:Transgenes
chemical_list: D000900:Anti-Bacterial Agents; D007527:Isoenzymes; D051546:Cyclooxygenase 2; D011451:Prostaglandin-Endoperoxide Synthases; D019951:DNA Polymerase beta; D004318:Doxycycline