title: MCL-1 localizes to sites of DNA damage and regulates DNA damage response.
abstract: MCL-1, a pro-survival member of the BCL-2 family, was previously shown to have functions in ATR-dependent Chk1 phosphorylation following DNA damage. To further delineate these functions, we explored possible differences in DNA damage response caused by lack of MCL-1 in mouse embryo fibroblasts (MEFs). As expected, Mcl-1(-/-) MEFs had delayed Chk1 phosphorylation following etoposide treatment, compared to wild type MEFs. However, their response to hydroxyurea, which causes a G(1)/S checkpoint response, was not significantly different. In addition, appearance of gamma-H2AX was delayed in the Mcl-1(-/-) MEFs treated with etoposide. We next investigated whether MCL-1 is present, together with other DNA damage response proteins, at the sites of DNA damage. Immunoprecipitation of etoposide-treated extracts with anti-MCL-1 antibody showed association of MCL-1 with gamma-H2AX as well as NBS1. Immunofluorescent staining for MCL-1 further showed increased co-staining of MCL-1 and NBS1 following DNA damage. By using a system that creates DNA double strand breaks at specific sites in the genome, we demonstrated that MCL-1 is recruited directly adjacent to the sites of damage. Finally, in a direct demonstration of the importance of MCL-1 in allowing proper repair of DNA damage, we found that treatment for two brief exposures to etoposide , followed by periods of recovery, which mimics the clinical situation of etoposide use, resulted in greater accumulation of chromosomal abnormalities in the MEFs that lacked MCL-1. Together, these data indicate an important role for MCL-1 in coordinating DNA damage mediated checkpoint response, and have broad implications for the importance of MCL-1 in maintenance of genome integrity.
authors.affiliation: Department of Medicine, University of British Columbia and Vancouver Coastal Health Research Institute, Vancouver, BC, Canada.
authors.forename: Sarwat
authors.initials: S
authors.lastname: Jamil
authors.forename: Cezar
authors.initials: C
authors.lastname: Stoica
authors.forename: Tillie-Louise
authors.initials: TL
authors.lastname: Hackett
authors.forename: Vincent
authors.initials: V
authors.lastname: Duronio
mesh_terms: D000818:Animals; D018797:Cell Cycle Proteins / Q000378:metabolism; D000071877:Checkpoint Kinase 1; D053903:DNA Breaks, Double-Stranded; D004260:DNA Repair; D005047:Etoposide / Q000494:pharmacology; D006367:HeLa Cells; D006657:Histones / Q000378:metabolism; D006801:Humans; D051379:Mice; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009687:Nuclear Proteins / Q000378:metabolism; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000032:analysis* / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000378:metabolism
chemical_list: D018797:Cell Cycle Proteins; D006657:Histones; C579094:Mcl1 protein, mouse; D064549:Myeloid Cell Leukemia Sequence 1 Protein; C112156:NBN protein, human; D009687:Nuclear Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D034741:RNA, Small Interfering; D005047:Etoposide; D011494:Protein Kinases; C000605867:CHEK1 protein, human; D000071877:Checkpoint Kinase 1; C000605869:Chek1 protein, mouse