Mgm101: A double-duty Rad52-like protein

Mgm101 has well-characterized activity for the repair and replication of the mitochondrial genome. Recent work has demonstrated a further role for Mgm101 in nuclear DNA metabolism, contributing to an S-phase specific DNA interstrand cross-link repair pathway that acts redundantly with a pathway controlled by Pso2 exonuclease. Due to involvement of FANCM, FANCJ and FANCP homologues (Mph1, Chl1 and Slx4), this pathway has been described as a Fanconi anemia-like pathway. In this pathway, Mgm101 physically interacts with the DNA helicase Mph1 and the MutSα (Msh2/Msh6) heterodimer, but its precise role is yet to be elucidated. Data presented here suggests that Mgm101 functionally overlaps with Rad52, supporting previous suggestions that, based on protein structure and biochemical properties, Mgm101 and Rad52 belong to a family of proteins with similar function. In addition, our data shows that this overlap extends to the function of both proteins at telomeres, where Mgm101 is required for telomere elongation during chromosome replication in rad52 defective cells. We hypothesize that Mgm101 could, in Rad52-like manner, preferentially bind single-stranded DNAs (such as at stalled replication forks, broken chromosomes and natural chromosome ends), stabilize them and mediate single-strand annealing-like homologous recombination event to prevent them from converting into toxic structures

MRE11 Function in Response to Topoisomerase Poisons Is Independent of its Function in Double-Strand Break Repair in Saccharomyces cerevisiae

Camptothecin (CPT) and etoposide (ETP) trap topoisomerase-DNA covalent intermediates, resulting in formation of DNA damage that can be cytotoxic if unrepaired. CPT and ETP are prototypes for molecules widely used in chemotherapy of cancer, so defining the mechanisms for repair of damage induced by treatment with these compounds is of great interest. In S. cerevisiae, deficiency in MRE11, which encodes a highly conserved factor, greatly enhances sensitivity to treatment with CPT or ETP. This has been thought to reflect the importance of double-strand break (DSB) repair pathways in the response to these to agents. Here we report that an S. cerevisiae strain expressing the mre11-H59A allele, mutant at a conserved active site histidine, is sensitive to hydroxyurea and also to ionizing radiation, which induces DSBs, but not to CPT or ETP. We show that TDP1, which encodes a tyrosyl-DNA phosphodiesterase activity able to release both 5′- and 3′-covalent topoisomerase-DNA complexes in vitro, contributes to ETP-resistance but not CPT-resistance in the mre11-H59A background. We further show that CPT- and ETP-resistance mediated by MRE11 is independent of SAE2, and thus independent of the coordinated functions of MRE11 and SAE2 in homology-directed repair and removal of Spo11 from DNA ends in meiosis. These results identify a function for MRE11 in the response to topoisomerase poisons that is distinct from its functions in DSB repair or meiotic DNA processing. They also establish that cellular proficiency in repair of DSBs may not correlate with resistance to topoisomerase poisons, a finding with potential implications for stratification of tumors with specific DNA repair deficiencies for treatment with these compounds

Production and characterization of monoclonal antibodies against the extracellular domain of CA 125

Carcinoma antigen 125 (CA 125) is overexpressed in ovarian cancer and antibodies against it are widely employed for diagnostic purposes. The rarity of CA 125 antigenic domains and its highly glycosylated structure, however, is a problem that may prevent immunized mice from developing a diversified population of anti-CA 125 antibodies. In this study a prime-boost strategy, which potentially could augment the humoral immune responses against rare and poorly immunogenic determinants, was used for immunization of mice and monoclonal antibodies (mAbs) were produced by hybridoma technology. Reactivity of mAbs was then assessed by ELISA, western blotting, immunoprecipitation, immunohistochemistry and immunofluorescence staining of OVCAR-3 cell line. Altogether, 10 clones were produced, 3 of which had IgG isotype and the rest were IgM. Two-third of clones recognized cognate antigen in fixed and living cells and had strong immunoreactivity in IHC staining. In Western blotting, our antibodies recognized CA 125 as high molecular weight antigen mostly migrated in the 3 stacking gel. Immunoprecipitation of OVCAR-3 cell lysate by mAbs resulted in a very similar migration pattern that reconfirmed their specificities. The mAbs produced in this study are invaluable tools in diagnosis and research fields for assessment of CA 125 expression in cancerous ovarian tissues. © Informa Healthcare USA, Inc. 2010

Differential reactivity of mouse monoclonal anti-HBs antibodies with recombinant mutant HBs antigens

AIM: To investigate the reactivity of a panel of 8 mouse anti-hepatitis B surface antigen (HBsAg) monoclonal antibodies (mAbs) using a collection of 9 recombinant HBsAg mutants with a variety of amino acid substitutions mostly located within the "a" region. METHODS: The entire HBs genes previously cloned into a mammalian expression vector were transiently transfected into COS7 cells. Two standard unmutated sequences of the ayw and adw subtypes served as controls. Secreted mutant proteins were collected and measured by three commercial diagnostic immunoassays to assess transfection efficiency. Reactivity of anti-HBs mAbs with mutated HBsAgs was determined by sandwich enzyme-linked immunosorbent assay (ELISA). RESULTS: Reactivity of anti-HBs mAbs with mutated HBsAgs revealed different patterns. While three mutants reacted strongly with all mAbs, two mutants reacted weakly with only two mAbs and the remaining proteins displayed variable degrees of reactivity towards different mAbs. Accordingly, four groups of mAbs with different but overlapping reactivity patterns could be envisaged. One group consisting of two mAbs (37C5-S7 and 35C6-S11) was found to recognize stable linear epitopes conserved in all mutants. Mutations outside the "a" determinant at positions 120 (P-->>S), 123(T-->N) and 161 (M-->T) were found to affect reactivity of these mAbs. CONCLUSION: Our findings could have important implications for biophysical studies, vaccination strategies and immunotherapy of hepatitis B virus (HBV) mutants

Production and characterization of anti-Her2 monoclonal antibodies

Objective: Breast cancer is the most common cancer among women in the world. Early diagnosis of this cancer is a key element for its treatment. One of the approaches for diagnosis of breast cancer is detection of its tumour-associated markers. Hence, Her2 has been the main focus of the researches in the field. Materials and Methods: For diagnosis of Her2 overexpression, monoclonal antibodies (mAb) reacting against Her2 were produced in this study. For this purpose, two peptides from extracellular domain of Her2 were selected and the mAbs reacting against them were produced by hybrodoma technology. Reactivity of these antibodies were then evaluated in different immunological assays including ELISA, Immunoflurescence (IF), western blot (WB) and immunoprecipitation (IP). Results: Total of 5 clones were produced from two separate fusions, and antibody isotyping revealed that all clones were IgM. These mAbs showed appropriate reactivities in the following assays: ELISA, immunofluresence by staining of breast cancer cell line (SKBR3), WB and IP by detecting the 185 KD band of Her2. Conclusion: In conclusion, it seems that the mAbs are useful diagnostic tools for detection of Her2 expression in patients with breast cancer

Antiretroviral Therapy With Efavirenz Accentuates Pregnancy-Associated Reduction of Dihydroartemisinin-Piperaquine Exposure During Malaria Chemoprevention.

Dihydroartemisinin (DHA)-piperaquine is promising for malaria chemoprevention in pregnancy. We assessed the impacts of pregnancy and efavirenz-based antiretroviral therapy on exposure to DHA and piperaquine in pregnant Ugandan women. Intensive sampling was performed at 28 weeks gestation in 31 HIV-uninfected pregnant women, in 27 HIV-infected pregnant women receiving efavirenz, and in 30 HIV-uninfected nonpregnant women. DHA peak concentration and area under the concentration time curve (AUC0-8hr ) were 50% and 47% lower, respectively, and piperaquine AUC0-21d was 40% lower in pregnant women compared to nonpregnant women. DHA AUC0-8hr and piperaquine AUC0-21d were 27% and 38% lower, respectively, in pregnant women receiving efavirenz compared to HIV-uninfected pregnant women. Exposure to DHA and piperaquine were lower among pregnant women and particularly in women on efavirenz, suggesting a need for dose modifications. The study of modified dosing strategies for these populations is urgently needed