title: Replication protein A and the Mre11.Rad50.Nbs1 complex co-localize and interact at sites of stalled replication forks.
abstract: In response to replicative stress, cells relocate and activate DNA repair and cell cycle arrest proteins such as replication protein A (RPA, a three subunit protein complex required for DNA replication and DNA repair) and the MRN complex (consisting of Mre11, Rad50, and Nbs1; involved in DNA double-strand break repair). There is increasing evidence that both of these complexes play a central role in DNA damage recognition, activation of cell cycle checkpoints, and DNA repair pathways. Here we demonstrate that RPA and the MRN complex co-localize to discrete foci and interact in response to DNA replication fork blockage induced by hydroxyurea (HU) or ultraviolet light (UV). Members of both RPA and the MRN complexes become phosphorylated during S-phase and in response to replication fork blockage. Analysis of RPA and Mre11 in fractionated lysates (cytoplasmic/nucleoplasmic, chromatin-bound, and nuclear matrix fractions) showed increased hyperphosphorylated-RPA and phosphorylated-Mre11 in the chromatin-bound fractions. HU and UV treatment also led to co-localization of hyperphosphorylated RPA and Mre11 to discrete detergent-resistant nuclear foci. An interaction between RPA and Mre11 was demonstrated by co-immunoprecipitation of both protein complexes with anti-Mre11, anti-Rad50, anti-NBS1, or anti-RPA antibodies. Phosphatase treatment with calf intestinal phosphatase or lambda-phosphatase not only de-phosphorylated RPA and Mre11 but also abrogated the ability of RPA and the MRN complex to co-immunoprecipitate. Together, these data demonstrate that RPA and the MRN complex co-localize and interact after HU- or UV-induced replication stress and suggest that protein phosphorylation may play a role in this interaction.
authors.affiliation: Department of Environmental Health, University of Cincinnati College of Medicine, 3223 Eden Avenue, Cincinnati, OH 45267, USA.
authors.forename: Jacob G
authors.initials: JG
authors.lastname: Robison
authors.forename: James
authors.initials: J
authors.lastname: Elliott
authors.forename: Kathleen
authors.initials: K
authors.lastname: Dixon
authors.forename: Gregory G
authors.initials: GG
authors.lastname: Oakley
mesh_terms: D017766:Acid Anhydride Hydrolases; D015153:Blotting, Western; D002453:Cell Cycle; D018797:Cell Cycle Proteins / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism; D002843:Chromatin / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D004249:DNA Damage; D004260:DNA Repair; D045643:DNA Repair Enzymes / Q000378:metabolism*; D004261:DNA Replication; D004268:DNA-Binding Proteins / Q000378:metabolism*; D016193:G1 Phase; D006367:HeLa Cells; D006801:Humans; D006918:Hydroxyurea / Q000494:pharmacology; D000076228:MRE11 Homologue Protein; D008856:Microscopy, Fluorescence; D008954:Models, Biological; D009687:Nuclear Proteins / Q000378:metabolism*; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism; D010766:Phosphorylation; D011233:Precipitin Tests; D011485:Protein Binding; D051716:Replication Protein A; D016196:S Phase; D013347:Subcellular Fractions; D013997:Time Factors; D014466:Ultraviolet Rays
chemical_list: D018797:Cell Cycle Proteins; D002843:Chromatin; D004268:DNA-Binding Proteins; C121766:MRE11 protein, human; C112156:NBN protein, human; D009687:Nuclear Proteins; C497167:RPA1 protein, human; D051716:Replication Protein A; D000076228:MRE11 Homologue Protein; D010744:Phosphoric Monoester Hydrolases; D017766:Acid Anhydride Hydrolases; C112158:RAD50 protein, human; D045643:DNA Repair Enzymes; D006918:Hydroxyurea