title: Clinicopathological significance of KU70/KU80, a key DNA damage repair protein in breast cancer.
abstract: Although the role of BRCA1 and the homologous recombination (HR) pathway in breast cancer (BC) has been extensively studied, the alternative repair pathway for DNA double-strand breaks (DSBs), non-homologous end-joining (NHEJ) remains to be defined. Ku proteins bind to DNA DSB ends and play a key role in NHEJ. In this study we aimed to assess the expression and biological significance of the KU70/KU80 heterodimer in the different molecular classes of BC. The expression of KU70/KU80 was assessed immunohistochemically in a well-characterised and annotated series of 1302 unselected invasive BC cases with a long-term follow-up together with 25 cases with known BRCA1 mutations. The results were correlated with clinicopathological parameters, other DNA repair proteins and patient outcome. The expression of KU70/KU80 protein was further evaluated in various BC cell lines using western blotting and reverse-phase protein microarray (RPPA). Nuclear KU70/KU80 expression was correlated with features of poor prognosis including higher histological grade, lymphovascular invasion, negative oestrogen receptor expression, basal-like phenotype, P53 and CHK1 positivity. KU70/KU80 was expressed in all BRCA1-associated tumours and showed an inverse correlation with nuclear BRCA1 protein and aberrant cytoplasmic RAD51 expression. RPPA confirmed these results and showed higher expression of KU70/KU80 in BRCA1-deficient cell line compared to BRCA1-proficient cell line. KU70/KU80 expression showed an association with disease-free interval; however, it was not an independent predictor of outcome. As a conclusion, KU70/KU80 may play a role in DNA DSBs repair in HR-deficient tumours. Further study of other NHEJ markers in sporadic BC is warranted.
authors.affiliation: Department of Histopathology and School of Molecular Medical Sciences, The University of Nottingham and Nottingham University Hospitals NHS Trust, Nottingham City Hospital, Nottingham, UK. mrxaa31@nottingham.ac.uk
authors.forename: Alaa T
authors.initials: AT
authors.lastname: Alshareeda
authors.forename: Ola H
authors.initials: OH
authors.lastname: Negm
authors.forename: Nada
authors.initials: N
authors.lastname: Albarakati
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Green
authors.forename: Christopher
authors.initials: C
authors.lastname: Nolan
authors.forename: Rebeka
authors.initials: R
authors.lastname: Sultana
authors.forename: Srinivasan
authors.initials: S
authors.lastname: Madhusudan
authors.forename: Ahmed
authors.initials: A
authors.lastname: Benhasouna
authors.forename: Paddy
authors.initials: P
authors.lastname: Tighe
authors.forename: Ian O
authors.initials: IO
authors.lastname: Ellis
authors.forename: Emad A
authors.initials: EA
authors.lastname: Rakha
mesh_terms: D000328:Adult; D000368:Aged; D034961:Antigens, Nuclear / Q000235:genetics / Q000378:metabolism*; D014408:Biomarkers, Tumor / Q000378:metabolism; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism / Q000401:mortality / Q000473:pathology*; D045744:Cell Line, Tumor; D004260:DNA Repair; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D005260:Female; D015870:Gene Expression; D006801:Humans; D007150:Immunohistochemistry; D000072200:Ku Autoantigen; D008875:Middle Aged; D009361:Neoplasm Invasiveness; D009367:Neoplasm Staging; D040081:Protein Array Analysis; D064726:Triple Negative Breast Neoplasms / Q000235:genetics / Q000378:metabolism / Q000401:mortality / Q000473:pathology
chemical_list: D034961:Antigens, Nuclear; D014408:Biomarkers, Tumor; D004268:DNA-Binding Proteins; C000606509:Xrcc6 protein, human; D000072200:Ku Autoantigen