Plasticity of BRCA2 Function in Homologous Recombination: Genetic Interactions of the PALB2 and DNA Binding Domains

The breast cancer suppressor BRCA2 is essential for the maintenance of genomic integrity in mammalian cells through its role in DNA repair by homologous recombination (HR). Human BRCA2 is 3,418 amino acids and is comprised of multiple domains that interact with the RAD51 recombinase and other proteins as well as with DNA. To gain insight into the cellular function of BRCA2 in HR, we created fusions consisting of various BRCA2 domains and also introduced mutations into these domains to disrupt specific protein and DNA interactions. We find that a BRCA2 fusion peptide deleted for the DNA binding domain and active in HR is completely dependent on interaction with the PALB2 tumor suppressor for activity. Conversely, a BRCA2 fusion peptide deleted for the PALB2 binding domain is dependent on an intact DNA binding domain, providing a role for this conserved domain in vivo; mutagenesis suggests that both single-stranded and double-stranded DNA binding activities in the DNA binding domain are required for its activity. Given that PALB2 itself binds DNA, these results suggest alternative mechanisms to deliver RAD51 to DNA. In addition, the BRCA2 C terminus contains both RAD51-dependent and -independent activities which are essential to HR in some contexts. Finally, binding the small peptide DSS1 is essential for activity when its binding domain is present, but not when it is absent. Our results reveal functional redundancy within the BRCA2 protein and emphasize the plasticity of this large protein built for optimal HR function in mammalian cells. The occurrence of disease-causing mutations throughout BRCA2 suggests sub-optimal HR from a variety of domain modulations

Significance of Error-avoiding Mechanisms for Oxidative DNA Damage in Carcinogenesis

Oxygen radicals are produced through normal cellular metabolism, and formation of such radicals is further enhanced by ionizing radiation and by various chemicals. Among various classes of oxidative DNA damage, 8-oxo-7,8-dihydroguanine (8-oxoG) is the most abundant, and appears to play important roles in mutagenesis and carcinogenesis. We have focused on following the two enzymes. MTH1 protein hydrolyzes 8-oxo-dGTP to monophosphate in the nucleotide pool, thereby preventing occurrence of transversion mutations. On the other hand, MUTYH protein, having adenine/2-hydroxyadenine DNA glycosylase activity, is expected to prevent G:C to T:A transversions, by excising adenine from G:A mismatches induced by 8-oxoG and 2-OH-A. To analyze the function of the mammalian MTH1 and MUTYH proteins in vivo, we established gene-knockout mice for these two enzymes, and investigated spontaneous tumorigenesis as well as mutagenesis

Sarcopenia discriminates poor prognosis in elderly patients following emergency surgery for perforation panperitonitis

Abstract Aim Sarcopenia has been reported as a prognostic predictor in various conditions; however, it has not been examined in patients with perforation panperitonitis. Methods A total of 103 consecutive patients with perforation panperitonitis who underwent emergency surgery from 2008 to 2016 were retrospectively evaluated. Skeletal muscle index (SMI) was measured as the cross‐sectional area (cm2) of skeletal muscle in the L3 region on computed tomography images normalized for height (cm2/m2). Sarcopenia was defined as an SMI of ≤43.75 and ≤41.10 cm2/m2 in men and women, respectively. The impact of sarcopenia on postoperative outcomes was investigated. Results Sarcopenia was present in 50 (48.5%) patients. Severe complications (Clavien‐Dindo grade ≥IIIb) and in‐hospital mortality were more frequently observed in patients with than without sarcopenia (28.0% vs 9.4%, P = .015) (20.0% vs 5.7%, P = .029) respectively. Multivariate analysis showed that age, sarcopenia, and renal dysfunction were independent risk factors for severe complications and in‐hospital mortality. The optimal cut‐off levels of age and SMI for predicting these were ≥79 years and SMI <38 cm2/m2, respectively. Among the patients aged ≥79 years, those with SMI <38 cm2/m2 had a severe complication rate of 71% and an in‐hospital mortality rate of 57%, whereas the rate of those with SMI ≥38 cm2/m2 was 22% (P = .011) and 11% (P = .008), respectively. Conclusion Sarcopenia is a predictive factor of severe complications and in‐hospital mortality following emergency surgery for perforation panperitonitis, especially in elderly patients. Estimation of sarcopenia may identify patients eligible or not eligible for emergency surgery among elderly patients

Neuroendocrine carcinoma of the esophagus: Clinicopathological and immunohistochemical features of 14 cases.

BACKGROUND:Neuroendocrine carcinoma (NEC) of the esophagus is a rare and highly aggressive disease but the biological features are poorly understood. The objective of this study was to analyze the clinicopathological and immunohistochemical features of NEC of the esophagus. METHODS:Fourteen patients diagnosed with NEC of the esophagus from 1998 to 2013 were included in this study. Clinicopathologic features, therapeutic outcomes and immunohistochemical results were analyzed. RESULTS:Eleven out of 14 cases showed protruding or localized type with or without ulceration. Only three patients were negative for both lymph node and organ metastasis and seven cases were positive for metastases to distant organs and/or distant lymph nodes. Of the six patients with limited disease (LD), three patients were treated by surgery. Three patients with LD and seven patients with extensive disease (ED) were initially treated with chemotherapy, except for one who underwent concurrent chemo-radiotherapy due to passage disturbance. The median survival of patients with LD was 8.5 months, whereas that of patients with LD was 17 months. Among the 14 cases, 12 cases (83.3%), 13 cases (91.7%) and 12 cases (83.3%) showed positive immunostaining for choromogranin A, synaptophysin and CD56, respectively. Nine of 14 cases (64.2%) presented positive staining for c-kit and most (8/9, 88%) simultaneously showed p53 protein abnormality. Two cases were negative for c-kit and p53, and positive for CK20. CONCLUSION:Consistent with previous reports, the prognosis of NEC of esophagus is dismal. From the results of immunohistochemical study, NEC of esophagus might be divided into two categories due to the staining positivity of c-kit and p53. This study provides new insight into the biology of NEC of the esophagus