Natsuko Chiba

BRCA1 is the first susceptibility gene to be linked to breast and ovarian cancers. Although mounting evidence has indicated that BRCA1 participates in DNA double-strand break (DSB) repair pathways, its precise mechanism is still unclear. Here, we analyzed the in situ response of BRCA1 at DSBs produced by laser microirradiation. The amino (N)- and carboxyl (C)-terminal fragments of BRCA1 accumulated independently at DSBs with distinct kinetics. The N-terminal BRCA1 fragment accumulated immediatel

The BRCA1 protein is known to participate in multiple cellular processes. In these experiments, we resolved four distinct BRCA1-containing complexes. We found BRCA1 associated with the RNA polymerase II holoenzyme (holo-pol), a large mass complex called the fraction 5 complex, the Rad50-Mre11-Nbs1 complex, and a complex that has not been described previously. We observed this new complex after treating cells with hydroxyurea, suggesting that the hydroxyurea-induced complex (HUIC) is involved wit

Because the vitamin D receptor interacting protein (DRIP) coactivator complex shares components with the RNA polymerase II (Pol II) holoenzyme complex, we tested whether the two protein complexes associate in cellular extracts. On initial purification steps, the DRIP complex copurified with the Pol II holoenzyme. Pol II was found to bind to the vitamin D receptor in a ligand-dependent fashion when either nuclear extracts or partially purified preparations were used as sources of DRIP and Pol II

We have previously shown that endogenous BRCA1 and overexpressed epitope-tagged BRCA1 are present in the transcription complex called the RNA polymerase II holoenzyme (holo-pol). In this study, we further characterized BRCA1 association with the holo-pol by overexpressing deletion mutants of epitope-tagged BRCA1. We found that BRCA1-associated RING domain protein (BARD1) is a component of the holo-pol complex. Deletion of the BRCA1 NH(2) terminus, which is bound by BARD1 as well as other protein

BRCA1 is an important gene involved in susceptibility to breast and ovarian cancer and its product regulates the cellular response to DNA double-strand breaks. Here, we present evidence that BRCA1 also contributes to the transcription-coupled repair (TCR) of ultraviolet (UV) light-induced DNA damage. BRCA1 immediately accumulates at the sites of UV irradiation-mediated damage in cell nuclei in a manner that is fully dependent on both Cockayne syndrome B (CSB) protein and active transcription. Su

The centrosome, consisting of mother and daughter centrioles surrounded by the pericentriolar matrix (PCM), functions primarily as a microtubule organizing center (MTOC) in most animal cells. In dividing cells the centrosome duplicates once per cell cycle and its number and structure are highly regulated during each cell cycle to organize an effective bipolar spindle in the mitotic phase. Defects in the regulation of centrosome duplication lead to a variety of human diseases, including cancer, t

A case of alpha-fetoprotein (AFP)-producing hepatoid adenocarcinoma in association with Barrett's esophagus with multiple liver metastases, responding to chemotherapy, is reported. A 47-year-old man was admitted to our hospital with abdominal pain after subtotal esophagectomy for an esophageal adenocarcinoma in association with Barrett's esophagus, and was diagnosed as having multiple liver tumors. Most tumor markers were normal, but the serum AFP level was markedly elevated. Dynamic computed to

Alterations in breast cancer gene 1 (BRCA1), a tumor suppressor gene, increase the risk of breast and ovarian cancers. BRCA1 forms a heterodimer with BRCA1-associated RING domain protein 1 (BARD1) and functions in multiple cellular processes, including DNA repair and centrosome regulation. BRCA1 acts as a tumor suppressor by promoting homologous recombination (HR) repair, and alterations in BRCA1 cause HR deficiency, not only in breast and ovarian tissues but also in other tissues. The molecular

Breast cancer gene 1 (BRCA1)-associated RING domain protein 1 (BARD1) forms a heterodimer with BRCA1, a tumor suppressor associated with hereditary breast and ovarian cancer. BRCA1/BARD1 functions in multiple cellular processes including DNA repair and centrosome regulation. Centrosomes are the major microtubule-organizing centers in animal cells and are critical for the formation of a bipolar mitotic spindle. BRCA1 and BARD1 localize to the centrosome during the cell cycle, and the BRCA1/BARD1

Homologous recombination (HR)-deficient cells are sensitive to PARP inhibitors through a synthetic lethal effect. We previously developed an HR activity assay named Assay of Site-Specific HR Activity (ASHRA). Here, we evaluated the HR activity of 30 missense variants of BRCA1 by ASHRA and found that several BRCA1 variants showed intermediate HR activity, which was not clearly discerned by our previous analyses using a conventional method. HR activity measured by ASHRA was significantly correlate

The BRCA1-interacting protein Obg-like ATPase 1 (OLA1) functions in centriole duplication. In this study, we show the role of the mitotic kinase Aurora A in the reduction of centrosomal OLA1. Aurora A binds to and polyubiquitinates OLA1, targeting it for proteasomal degradation. NIMA-related kinase 2 (NEK2) phosphorylates the T124 residue of OLA1, increases binding of OLA1 to Aurora A and OLA1 polyubiquitination by Aurora A, and reduces centrosomal OLA1 in G2 phase. The kinase activity of Aurora

Breast cancer gene 1 (BRCA1) plays roles in DNA repair and centrosome regulation and is involved in DNA damage-induced centrosome amplification (DDICA). Here, the centrosomal localization of BRCA1 and the kinases involved in centrosome duplication were analyzed in each cell cycle phase after treatment with DNA crosslinker cisplatin (CDDP). CDDP treatment increased the centrosomal localization of BRCA1 in early S-G2 phase. BRCA1 contributed to the increased centrosomal localization of Aurora A in