title: Mutation of the BRCA1 SQ-cluster results in aberrant mitosis, reduced homologous recombination, and a compensatory increase in non-homologous end joining.
abstract: Mutations in the breast cancer susceptibility 1 (BRCA1) gene are catalysts for breast and ovarian cancers. Most mutations are associated with the BRCA1 N- and C-terminal domains linked to DNA double-strand break (DSB) repair. However, little is known about the role of the intervening serine-glutamine (SQ) - cluster in the DNA damage response beyond its importance in regulating cell cycle checkpoints. We show that serine-to-alanine alterations at critical residues within the SQ-cluster known to be phosphorylated by ATM and ATR result in reduced homologous recombination repair (HRR) and aberrant mitosis. While a S1387A BRCA1 mutant - previously shown to abrogate S-phase arrest in response to radiation - resulted in only a modest decrease in HRR, S1387A together with an additional alteration, S1423A (BRCA12P), reduced HRR to vector control levels and similar to a quadruple mutant also including S1457A and S1524A (BRCA14P). These effects appeared to be independent of PALB2. Furthermore, we found that BRCA14P promoted a prolonged and struggling HRR late in the cell cycle and shifted DSB repair from HRR to non-homologous end joining which, in the face of irreparable chromosomal damage, resulted in mitotic catastrophe. Altogether, SQ-cluster phosphorylation is critical for allowing adequate time for completing normal HRR prior to mitosis and preventing cells from entering G1 prematurely resulting in gross chromosomal aberrations.
authors: Department of Radiation Oncology, Virginia Commonwealth University, Richmond, VA 23298, USA.|Department of Biochemistry and Molecular Biology, Virginia Commonwealth University, Richmond, VA 23298, USA.
authors: Jason M
authors: JM
authors: Beckta
authors: Department of Radiation Oncology, Virginia Commonwealth University, Richmond, VA 23298, USA.|Department of Biochemistry and Molecular Biology, Virginia Commonwealth University, Richmond, VA 23298, USA.
authors: Seth M
authors: SM
authors: Dever
authors: Department of Radiation Oncology, Virginia Commonwealth University, Richmond, VA 23298, USA.
authors: Nisha
authors: N
authors: Gnawali
authors: Department of Radiation Oncology, Virginia Commonwealth University, Richmond, VA 23298, USA.
authors: Ashraf
authors: A
authors: Khalil
authors: Department of Radiation Oncology, Virginia Commonwealth University, Richmond, VA 23298, USA.|Department of Biochemistry and Molecular Biology, Virginia Commonwealth University, Richmond, VA 23298, USA.
authors: Amrita
authors: A
authors: Sule
authors: Department of Radiation Oncology, Virginia Commonwealth University, Richmond, VA 23298, USA.
authors: Sarah E
authors: SE
authors: Golding
authors: Department of Radiation Oncology, Virginia Commonwealth University, Richmond, VA 23298, USA.
authors: Elizabeth
authors: E
authors: Rosenberg
authors: National Center for Biodefense and Infectious Diseases, George Mason University, Manassas, VA 20110, USA.
authors: Aarthi
authors: A
authors: Narayanan
authors: National Center for Biodefense and Infectious Diseases, George Mason University, Manassas, VA 20110, USA.
authors: Kylene
authors: K
authors: Kehn-Hall
authors: Cancer Research Department, Southern Research Institute, Birmingham, AL 35205, USA.
authors: Bo
authors: B
authors: Xu
authors: Department of Pharmacology and Toxicology, Virginia Commonwealth University, Richmond, VA 23298, USA.
authors: Lawrence F
authors: LF
authors: Povirk
authors: Department of Radiation Oncology, Virginia Commonwealth University, Richmond, VA 23298, USA.|Department of Biochemistry and Molecular Biology, Virginia Commonwealth University, Richmond, VA 23298, USA.|Massey Cancer Center, Virginia Commonwealth University, Richmond, VA 23298, USA.
authors: Kristoffer
authors: K
authors: Valerie
mesh_terms: D000409:Alanine / Q000737:chemistry; D064007:Ataxia Telangiectasia Mutated Proteins / Q000378:metabolism; D019313:BRCA1 Protein / Q000235:genetics*; D018797:Cell Cycle Proteins / Q000378:metabolism; D016923:Cell Death; D045744:Cell Line, Tumor; D002470:Cell Survival; D002869:Chromosome Aberrations; D053903:DNA Breaks, Double-Stranded; D004249:DNA Damage; D059766:DNA End-Joining Repair; D004260:DNA Repair; D005973:Glutamine / Q000737:chemistry*; D059765:Homologous Recombination; D006801:Humans; D007150:Immunohistochemistry; D016685:Mitomycin / Q000737:chemistry; D008938:Mitosis; D009154:Mutation; D010766:Phosphorylation; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000235:genetics; D016196:S Phase; D012694:Serine / Q000737:chemistry*
chemical_list: D019313:BRCA1 Protein; C492913:BRCA1 protein, human; D018797:Cell Cycle Proteins; D011994:Recombinant Proteins; D005973:Glutamine; D012694:Serine; D016685:Mitomycin; C576324:ATM protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; D000409:Alanine
keywords: DNA damage; DNA repair; cell cycle; phosphorylation; radiation