Regulation of the human AP-endonuclease (APE1/Ref-1) expression by the tumor suppressor p53 in response to DNA damage

The human AP-endonuclease (APE1/Ref-1), an essential multifunctional protein, plays a central role in the repair of oxidative base damage via the DNA base excision repair (BER) pathway. The mammalian AP-endonuclease (APE1) overexpression is often observed in tumor cells, and confers resistance to various anticancer drugs; its downregulation sensitizes tumor cells to those agents via induction of apoptosis. Here we show that wild type (WT) but not mutant p53 negatively regulates APE1 expression. Time-dependent decrease was observed in APE1 mRNA and protein levels in the human colorectal cancer line HCT116 p53^(+/+), but not in the isogenic p53 null mutant after treatment with camptothecin, a DNA topoisomerase I inhibitor. Furthermore, ectopic expression of WTp53 in the p53 null cells significantly reduced both endogenous APE1 and APE1 promoter-dependent luciferase expression in a dose-dependent fashion. Chromatin immunoprecipitation assays revealed that endogenous p53 is bound to the APE1 promoter region that includes a Sp1 site. We show here that WTp53 interferes with Sp1 binding to the APE1 promoter, which provides a mechanism for the downregulation of APE1. Taken together, our results demonstrate that WTp53 is a negative regulator of APE1 expression, so that repression of APE1 by p53 could provide an additional pathway for p53-dependent induction of apoptosis in response to DNA damage.     

The complexity of DNA double strand breaks is a critical factor enhancing end-resection

DNA double strand breaks (DSBs) induced by ionizing radiation (IR) are deleterious damages. Two major pathways repair DSBs in human cells, DNA non-homologous end-joining (NHEJ) and homologous recombination (HR). It has been suggested that the balance between the two repair pathways varies depending on the chromatin structure surrounding the damage site and/or the complexity of damage at the DNA break ends. Heavy ion radiation is known to induce complex-type DSBs, and the efficiency of NHEJ in repairing these DSBs was shown to be diminished. Taking advantage of the ability of high linear energy transfer (LET) radiation to produce complex DSBs effectively, we investigated how the complexity of DSB end structure influences DNA damage responses. An early step in HR is the generation of 3′-single strand DNA (SSD) via a process of DNA end resection that requires CtIP. To assess this process, we analyzed the level of phosphorylated CtIP, as well as RPA phosphorylation and focus formation, which occur on the exposed SSD. We show that complex DSBs efficiently activate DNA end resection. After heavy ion beam irradiation, resection signals appear both in the vicinity of heterochromatic areas, which is also observed after X-irradiation, and additionally in euchromatic areas. Consequently, ∼85% of complex DSBs are subjected to resection in heavy ion particle tracks. Furthermore, around 20–40% of G1 cells exhibit resection signals. Taken together, our observations reveal that the complexity of DSB ends is a critical factor regulating the choice of DSB repair pathway and drastically alters the balance toward resection-mediated rejoining. As demonstrated here, studies on DNA damage responses induced by heavy ion radiation provide an important tool to shed light on mechanisms regulating DNA end resection.     

The management of hyperthyroidism due to Graves' disease in Japan in 1988. The Japan Thyroid Association

The management of hyperthyroidism due to Graves' disease in Japan was the subject of a survey of the members of the Japan Thyroid Association (JTA), and the results were compared to those of the European Thyroid Association (ETA). In the questionnaire, in vivo and in vitro diagnostic procedures, the choice of treatment and the details of the treatment for a patient with typical, moderate and uncomplicated hyperthyroidism due to Graves' disease was at first asked, and eight variations with a single alternative were proposed to evaluate how each alternative would affect the choice of treatment. For the diagnostic procedures, thyroid uptake/scintigraphy was carried out by approximately 60% of the respondents and the isotope mainly used was 123I. The number of in vitro tests used for diagnosis averaged 8.1 +/- 1.8 tests. Measurements of basal TSH and free T4 were the most frequent tests performed to confirm the diagnosis of hyperthyroidism (94 and 80%, respectively). Determinations of microsomal, thyroglobulin and TSH-receptor autoantibodies were also employed by many respondents (96, 96 and 77%, respectively). On the other hand, the free T4 index and TRH test were less frequently employed. In the treatment of these patients, antithyroid drug treatment was the first choice, and surgery was not, in general, regarded as a primary therapy except in a patient with a large goiter. The frequency of the respondents who advocated radioiodine therapy was considerably higher for patients with recurrences and old age. No respondents proposed radioiodine therapy for young patients. Specialists tended to favor their own specialist treatment regimens. The initial dose of antithyroid drugs was reduced according to thyroid function, and withdrawal of antithyroid drug treatment was determined by some specific criteria (basal TSH in supersensitive assays, TSH-receptor autoantibodies, T3 suppression test, etc.). The aim of radioiodine therapy and surgery was to restore euthyroidism. The significant differences between the results from the JTA and those from the ETA were as follows; radionuclide used for thyroid uptake/scintigraphy was mainly 123I in Japan, but 131I in Europe, the number of diagnostic studies in Japan was more than that in Europe, and the dosage of antithyroid drugs was reduced according to thyroid function and discontinued based on certain specific criteria in Japan, but after fixed periods in Europe. These results may represent actual trends in how hyperthyroidism due to Graves' disease is managed in specialist clinics in Japan today and the differences between the JTA and the ETA.     

Staurosporine: An Effective Inhibitor for Ca2+/Calmodulin-Dependent Protein Kinase II

We investigated the effect of staurosporine on Ca2+/calmodulin-dependent protein kinase II (CaM kinase II) purified from rat brain. (a) Staurosporine (10-100 nM) inhibited the activity of CaM kinase II. The half-maximal and maximal inhibitory concentrations were 20 and 100 nM, respectively. (b) The inhibition with staurosporine was of the noncompetitive type with respect to ATP, calmodulin, and phosphate acceptor (beta-casein). (c) Staurosporine suppressed the auto-phosphorylation of alpha- and beta-subunits of CaM kinase II at concentrations similar to those at which the enzyme activity was inhibited. (d) Staurosporine also attenuated the Ca2+/calmodulin-independent activity of the autophosphorylated CaM kinase II. These results suggest that staurosporine inhibits CaM kinase II by interacting with the catalytic domain, distinct from the ATP-binding site or substrate-binding site, of the enzyme and that staurosporine is an effective inhibitor for CaM kinase II in the cell system.     

PNLDC1, mouse pre‐piRNA Trimmer,is required for meiotic and post‐meiotic male germ cell development

PIWI‐interacting RNAs (piRNAs) are germ cell‐specific small RNAs essential for retrotransposon gene silencing and male germ cell development. In piRNA biogenesis, the endonuclease MitoPLD/Zucchini cleaves long, single‐stranded RNAs to generate 5′ termini of precursor piRNAs (pre‐piRNAs) that are consecutively loaded into PIWI‐family proteins. Subsequently, these pre‐piRNAs are trimmed at their 3′‐end by an exonuclease called Trimmer. Recently, poly(A)‐specific ribonuclease‐like domain‐containing 1 (PNLDC1) was identified as the pre‐piRNA Trimmer in silkworms. However, the function of PNLDC1 in other species remains unknown. Here, we generate Pnldc1 mutant mice and analyze small RNAs in their testes. Our results demonstrate that mouse PNLDC1 functions in the trimming of both embryonic and post‐natal pre‐piRNAs. In addition, piRNA trimming defects in embryonic and post‐natal testes cause impaired DNA methylation and reduced MIWI expression, respectively. Phenotypically, both meiotic and post‐meiotic arrests are evident in the same individual Pnldc1 mutant mouse. The former and latter phenotypes are similar to those of MILI and MIWI mutant mice, respectively. Thus, PNLDC1‐mediated piRNA trimming is indispensable for the function of piRNAs throughout mouse spermatogenesis.     

Anti-androgen receptor ASC-J9 versus anti-androgens MDV3100 (Enzalutamide) or Casodex (Bicalutamide) leads to opposite effects on prostate cancer metastasis via differential modulation of macrophage infiltration and STAT3-CCL2 signaling

Despite androgen deprivation therapy (ADT) suppression of prostate cancer (PCa) growth, its overall effects on PCa metastasis remain unclear. Using human (C4-2B/THP1) and mouse (TRAMP-C1/RAW264.7) PCa cells–macrophages co-culture systems, we found currently used anti-androgens, MDV3100 (enzalutamide) or Casodex (bicalutamide), promoted macrophage migration to PCa cells that consequently led to enhanced PCa cell invasion. In contrast, the AR degradation enhancer, ASC-J9, suppressed both macrophage migration and subsequent PCa cell invasion. Mechanism dissection showed that Casodex/MDV3100 reduced the AR-mediated PIAS3 expression and enhanced the pSTAT3-CCL2 pathway. Addition of CCR2 antagonist reversed the Casodex/MDV3100-induced macrophage migration and PCa cell invasion. In contrast, ASC-J9 could regulate pSTAT3-CCL2 signaling using two pathways: an AR-dependent pathway via inhibiting PIAS3 expression and an AR-independent pathway via direct inhibition of the STAT3 phosphorylation/activation. These findings were confirmed in the in vivo mouse model with orthotopically injected TRAMP-C1 cells. Together, these results may raise the potential concern about the currently used ADT with anti-androgens that promotes PCa metastasis and may provide some new and better therapeutic strategies using ASC-J9 alone or a combinational therapy that simultaneously targets androgens/AR signaling and PIAS3-pSTAT3-CCL2 signaling to better battle PCa growth and metastasis at castration-resistant stage.     

High-resolution spatial and temporal analysis of phytoalexin production in oats

The production of oat (Avena sativa L.) phytoalexins, avenanthramides, occurs in response to elicitor treatment with oligo-N-acetylchitooligosaccharides. In this study, avenanthramides production was investigated by techniques that provide high spatial and temporal resolution in order to clarify the process of phytoalexin production at the cellular level. The amount of avenanthramides accumulation in a single mesophyll cell was quantified by a combination of laser micro-sampling and low-diffuse nanoflow liquid chromatography–electrospray ionization tandem mass spectrometry (LC–ESI-MS/MS) techniques. Avenanthramides, NAD(P)H and chlorophyll were also visualized in elicitor-treated mesophyll cells using line-scanning fluorescence microscopy. We found that elicitor-treated mesophyll cells could be categorized into three characteristic cell phases, which occurred serially over time. Phase 0 indicated the normal cell state before metabolic or morphological change in response to elicitor, in which the cells contained abundant NAD(P)H. In phase 1, rapid NAD(P)H oxidation and marked movement of chloroplasts occurred, and this phase was the early stage of avenanthramides biosynthesis. In phase 2, avenanthramides accumulation was maximized, and chloroplasts were degraded. Avenanthramides appear to be synthesized in the chloroplast, because a fluorescence signal originating from avenanthramides was localized to the chloroplasts. Moreover, our results indicated that avenanthramides biosynthesis and the hypersensitive response (HR) occurred in identical cells. Thus, the avenanthramides production may be one of sequential events programmed in HR leading to cell death. Furthermore, the phase of the defense response was different among mesophyll cells simultaneously treated with elicitor. These results suggest that individual cells may have different susceptibility to the elicitor. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Homogeneous tetracycline‐regulatable gene expression in mammalian fibroblasts

The expression of transfected genes in mammalian cells is rapidly repressed by epigenetic mechanisms such that, within a matter of weeks, only a fraction of the cells in most clonal populations still exhibit detectable expression. This problem can become prohibitive when one wants to express two ectopically introduced genes, as is necessary to establish cell lines that harbor genes regulated by the tetracycline‐controlled transactivators. We describe an approach to establish Chinese hamster ovary (CHO) cell lines that stably induce a tet‐responsive reporter gene in all cells of a transfected clonal population. Screening of more than 100 colonies resulting from a standard co‐transfection of the tetracycline transactivator (tTA) with a green fluorescent protein (GFP) reporter plasmid failed to identify a single colony that could induce GFP in more than 20% of cells. The presence of chromatin insulator sequences, previously shown to protect some transfected genes from epigenetic silencing, moderately improved stability but was not sufficient to produce homogeneous transformants. However, when cell lines were first established in which selection could be maintained either for the expression of tTA activity (co‐transfection with a tTA‐responsive selectable marker) or the presence of tTA mRNA (bicistronic message encoding a selectable marker), these cell lines could be subsequently transfected with the GFP reporter construct, and nearly 10% of the resulting colonies exhibited stable homogeneous tet‐responsive GFP expression in 100% of the expanded clonal cell population. J. Cell. Biochem. 76:280–289, 1999. © 1999 Wiley‐Liss, Inc.