Masahiko Tanabe

A histone chaperone, DEK, transcriptionally coactivates a nuclear receptor

Chromatin reorganization is essential for transcriptional control by sequence-specific transcription factors. However, the molecular link between transcriptional control and chromatin reconfiguration remains unclear. By colocalization of the nuclear ecdysone receptor (EcR) on the ecdysone-induced puff in the salivary gland, Drosophila DEK (dDEK) was genetically identified as a coactivator of EcR in both insect cells and intact flies. Biochemical purification and characterization of the complexes containing fly and human DEKs revealed that DEKs serve as histone chaperones via phosphorylation by forming complexes with casein kinase 2. Consistent with the preferential association of the DEK complex with histones enriched in active epigenetic marks, dDEK facilitated H3.3 assembly during puff formation. In some human myeloid leukemia patients, DEK was fused to CAN by chromosomal translocation. This mutation significantly reduced formation of the DEK complex, which is required for histone chaperone activity. Thus, the present study suggests that at least one histone chaperone can be categorized as a type of transcriptional coactivator for nuclear receptors.

Distinct function of 2 chromatin remodeling complexes that share a common subunit, Williams syndrome transcription factor (WSTF)

A number of nuclear complexes modify chromatin structure and operate as functional units. However, the in vivo role of each component within the complexes is not known. ATP-dependent chromatin remodeling complexes form several types of protein complexes, which reorganize chromatin structure cooperatively with histone modifiers. Williams syndrome transcription factor (WSTF) was biochemically identified as a major subunit, along with 2 distinct complexes: WINAC, a SWI/SNF-type complex, and WICH, an ISWI-type complex. Here, WSTF−/− mice were generated to investigate its function in chromatin remodeling in vivo. Loss of WSTF expression resulted in neonatal lethality, and all WSTF−/− neonates and ≈10% of WSTF+/− neonates suffered cardiovascular abnormalities resembling those found in autosomal-dominant Williams syndrome patients. Developmental analysis of WSTF−/− embryos revealed that Gja5 gene regulation is aberrant from E9.5, conceivably because of inappropriate chromatin reorganization around the promoter regions where essential cardiac transcription factors are recruited. In vitro analysis in WSTF−/− mouse embryonic fibroblast (MEF) cells also showed impaired transactivation functions of cardiac transcription activators on the Gja5 promoter, but the effects were reversed by overexpression of WINAC components. Likewise in WSTF−/− MEF cells, recruitment of Snf2h, an ISWI ATPase, to PCNA and cell survival after DNA damage were both defective, but were ameliorated by overexpression of WICH components. Thus, the present study provides evidence that WSTF is shared and is a functionally indispensable subunit of the WICH complex for DNA repair and the WINAC complex for transcriptional control.

A case of carcinosarcoma of the breast.

Carcinosarcoma is a rare malignant tumor of the breast. A 59-year-old woman was admitted to our hospital with a complaint of a right breast mass for one month. The mass grew rapidly, and modified radical mastectomy was performed. Based on the histological findings of carcinomatous and sarcomatous components entangled without a transition area, and the results of immunohistochemical staining, carcinosarcoma of the breast was diagnosed. Within 9 months of the surgery, a recurrent lesion appeared in her chest wall. As shown by local resection, this recurrent tumor had only a carcinomatous component. Such tumors are very rare, and there have been no detailed reports of recurrence patterns of carcinosarcoma. Here we report our pathological findings in detail.

Corepressive Action of CBP on Androgen Receptor Transactivation in Pericentric Heterochromatin in a Drosophila Experimental Model System

ABSTRACT Ligand-bound nuclear receptors (NR) activate transcription of the target genes. This activation is coupled with histone modifications and chromatin remodeling through the function of various coregulators. However, the nature of the dependence of a NR coregulator action on the presence of the chromatin environment at the target genes is unclear. To address this issue, we have developed a modified position effect variegation experimental model system that includes an androgen-dependent reporter transgene inserted into either a pericentric heterochromatin region or a euchromatic region of Drosophila chromosome. Human androgen receptor (AR) and its constitutively active truncation mutant (AR AF-1) were transcriptionally functional in both chromosomal regions. Predictably, the level of AR-induced transactivation was lower in the pericentric heterochromatin. In genetic screening for AR AF-1 coregulators, Drosophila CREB binding protein (dCBP) was found to corepress AR transactivation at the pericentric region whereas it led to coactivation in the euchromatic area. Mutations of Sir2 acetylation sites or deletion of the CBP acetyltransferase domain abrogated dCBP corepressive action for AR at heterochromatic areas in vivo. Such a CBP corepressor function for AR was observed in the transcriptionally silent promoter of an AR target gene in cultured mammalian cells. Thus, our findings suggest that the action of NR coregulators may depend on the state of chromatin at the target loci.

Possible use of combination chemotherapy with mitomycin C and methotrexate for metastatic breast cancer pretreated with anthracycline and taxanes

BackgroundMost patients with breast cancer need anthracycline-based chemotherapy regimens in the adjuvant setting, and an increasing number of them receive taxanes either in this setting or as first-line therapy for metastatic breast cancer (MBC). However, no standard chemotherapy has been fully established for MBC patients pretreated with anthracycline and taxanes.MethodsWe retrospectively reviewed the medical records of 48 patients with MBC who had been treated with chemotherapy combining mitomycin C and methotrexate (MMC/MTX), following treatment with anthracycline and taxanes. MMC was given at a dose of 8xa0mg/m2 on day 1, and MTX of 60xa0mg/m2 on day 1 and day 15. The cycle was repeated every 4xa0weeks.ResultsThere were 11 partial responses (24%). The median time to progression was 4.8xa0months. The response rate of liver metastasis was 31%. Thrombocytopenia (grade 3) was observed in five patients (10%). Other toxicity was mild and manageable.ConclusionsOur findings suggest that MMC/MTX could be an effective subsequent treatment for patients whose MBC has been pretreated with anthracycline and taxanes.

Drosophila arginine methyltransferase 1 (DART1) is an ecdysone receptor co-repressor.

Histone arginine methylation is an epigenetic marker that regulates gene expression by defining the chromatin state. Arginine methyltransferases, therefore, serve as transcriptional co-regulators. However, unlike other transcriptional co-regulators, the physiological roles of arginine methyltransferases are poorly understood. Drosophila arginine methyltransferase 1 (DART1), the mammalian PRMT1 homologue, methylates the arginine residue of histone H4 (H4R3me2). Disruption of DART1 in Drosophila by imprecise P-element excision resulted in low viability during metamorphosis in the pupal stages. In the pupal stage, an ecdysone hormone signal is critical for developmental progression. DART1 interacted with the nuclear ecdysone receptor (EcR) in a ligand-dependent manner, and co-repressed EcR in intact flies. These findings suggest that DART1, a histone arginine methyltransferase, is a co-repressor of EcR that is indispensable for normal pupal development in the intact fly.

Aberrant E2F activation by polyglutamine expansion of androgen receptor in SBMA neurotoxicity.

Spinal and bulbar muscular atrophy (SBMA) is a neurodegenerative disorder caused by a polyglutamine repeat (polyQ) expansion within the human androgen receptor (AR). Unlike other neurodegenerative diseases caused by abnormal polyQ expansion, the onset of SBMA depends on androgen binding to mutant human polyQ-AR proteins. This is also observed in Drosophila eyes ectopically expressing the polyQ-AR mutants. We have genetically screened mediators of androgen-induced neurodegeneration caused by polyQ-AR mutants in Drosophila eyes. We identified Rbf (Retinoblastoma-family protein), the Drosophila homologue of human Rb (Retinoblastoma protein), as a neuroprotective factor. Androgen-dependent association of Rbf or Rb with AR was remarkably potentiated by aberrant polyQ expansion. Such potentiated Rb association appeared to attenuate recruitment of histone deacetyltransferase 1 (HDAC1), a corepressor of E2F function. Either overexpression of Rbf or E2F deficiency in fly eyes reduced the neurotoxicity of the polyQ-AR mutants. Induction of E2F function by polyQ-AR-bound androgen was suppressed by Rb in human neuroblastoma cells. We conclude that abnormal expansion of polyQ may potentiate innate androgen-dependent association of AR with Rb. This appears to lead to androgen-dependent onset of SBMA through aberrant E2F transactivation caused by suppressed histone deacetylation.

Epigenetic Silencing of Core Histone Genes by HERS in Drosophila

Cell cycle-dependent expression of canonical histone proteins enables newly synthesized DNA to be integrated into chromatin in replicating cells. However, the molecular basis of cell cycle-dependency in the switching of histone gene regulation remains to be uncovered. Here, we report the identification and biochemical characterization of a molecular switcher, HERS (histone gene-specific epigenetic repressor in late S phase), for nucleosomal core histone gene inactivation in Drosophila. HERS protein is phosphorylated by a cyclin-dependent kinase (Cdk) at the end of S-phase. Phosphorylated HERS binds to histone gene regulatory regions and anchors HP1 and Su(var)3-9 to induce chromatin inactivation through histone H3 lysine 9 methylation. These findings illustrate a salient molecular switch linking epigenetic gene silencing to cell cycle-dependent histone production.

Low FOXA1 expression predicts good response to neo-adjuvant chemotherapy resulting in good outcomes for luminal HER2-negative breast cancer cases

Background:FOXA1 expression is a good prognostic marker for endocrine therapy in hormone-positive breast cancer. We retrospectively examined breast cancer patients with luminal human epidermal growth factor receptor 2 (HER2)-negative tumours, as defined by immunohistochemistry, who received neo-adjuvant chemotherapy (NAC) and investigated the relationship between treatment effects and FOXA1 expression.Methods:Biopsy specimens from 103 luminal HER2-negative tumours were immunohistochemically examined. FOXA1 effects on chemo-sensitivity were also investigated employing in vitro experiments.Results:FOXA1 and Ki67 expressions independently predicted a pathological complete response (pCR). Knockdown of FOXA1 by siRNA boosted the chemo-effect in oestrogen receptor-positive cells. The Cox hazards model revealed a pCR to be the strongest factor predicting a good patient outcome.Conclusions:Our present study showed low FOXA1 expression to be associated with a good response to NAC in luminal HER2-negative breast cancer. Improved outcomes of these patients suggest that NAC should be recommended to patients with low FOXA1 tumours.

Breast Cancer Subtype and Distant Recurrence after Ipsilateral Breast Tumor Recurrence

BackgroundThere is little information about the impact of breast cancer subtype on prognosis after ipsilateral breast tumor recurrence (IBTR).MethodsOne hundred eighty-five patients were classified according to breast cancer subtype, as approximated by estrogen receptor, human epidermal growth factor receptor 2 (HER2), and Ki-67, of IBTR, and we evaluated whether breast cancer subtype was associated with distant recurrence after IBTR.ResultsThere was a significant difference in distant disease-free survival (DDFS) after IBTR according to breast cancer subtype defined by a cutoff of the Ki-67 index of 20xa0% (pxa0=xa00.0074, log-rank test). The 5-year DDFS rates for patients with luminal A, luminal B, triple-negative, and HER2 types were 86.3, 57.1, 56.6, and 65.9xa0%, respectively. In addition, breast cancer subtype was significantly associated with distant recurrence after IBTR on adjustment for various clinicopathologic factors (pxa0=xa00.0027, Cox proportional hazards model).ConclusionsOur study suggests that breast cancer subtype based on immunohistochemical staining predicts the outcomes of patients with IBTR. Further analyses are needed (UMIN-CTR number UMIN000008136).