DNA-dependent protein kinase is not required for the p53-dependent response to DNA damage.

Damage to DNA in the cell activates the tumour-suppressor protein p53, and failure of this activation leads to genetic instability and a predisposition to cancer. It is therefore crucial to understand the signal transduction mechanisms that connect DNA damage with p53 activation. The enzyme known as DNA-dependent protein kinase (DNA-PK) has been proposed to be an essential activator of p53, but the evidence for its involvement in this pathway is controversial. We now show that the p53 response is fully functional in primary mouse embryonic fibroblasts lacking DNA-PK: irradiation-induced DNA damage in these defective fibroblasts induces a normal response of p53 accumulation, phosphorylation of a p53 serine residue at position 15, nuclear localization and binding to DNA of p53. The upregulation of p53-target genes and cell-cycle arrest also occur normally. The DNA-PK-deficient cell line SCGR11 contains a homozygous mutation in the DNA-binding domain of p53, which may explain the defective response by p53 reported in this line. Our results indicate that DNA-PK activity is not required for cells to mount a p53-dependent response to DNA damage.     

Formation of carthamin by a partially purified enzyme from safflower seedlings

Summary An enzyme responsible for synthesizing carthamin from precarthamin was partially purified and the catalytic properties were investigated.Acknowledgments. The authors wish to thank Prof. A. Komamine, University of Tokyo, for reading this paper. We are indebted to Prof. A. Saito, Tokai University, for performing emission spectrochemical analysis of the enzyme protein used in this study.     

Structure-activity relationship of the cardenolide,with special reference to the substituents and configurations at C-14 and C-15

Zusammenfassung Es wurden die kardiotonischen Wirkungen sechs neuer Derivate von 14-Deoxy-14H-digitoxigenin und 14-Deoxy-14-chloro-digitoxigenin auf das isolierte Froschherz untersucht, sowie die Beziehungen zwischen deren chemischen Strukturen und Wirkungen diskutiert.

---

---

This study was supported by a research grant (No. 78 7012) from the Ministry of Education, Japan, and by a Grant-in-Aid from Tokyo Biochemical Research Foundation.     

Effects of thyroidectomy on monoamine oxidase activities toward tyramine and serotonin in the circumventricular nuclei of the rat.

Following thyroidectomy, monoamine oxidase (MAO) activities toward tyramine decreased significantly by 20% in the nucleus periventricularis and the nucleus arcuatus among the 3 hypothalamic nuclei of the rat, while MAO activity toward serotonin decreased significantly by 10% only in the nucleus periventricularis. It is suggested that thyroidectomy induced selective changes on the multiple forms of MAO in the discrete circumventricular nuclei.     

Inhibitory effect of cytokinins on PHA-induced human lymphocyte stimulation

Summary The inhibitory effect of various purine derivatives on PHA-induced human lymphocyte blast formation was studied. Two nucleoside cytokinins, N⁶-benzyladenosine and N⁶-isopentenyladenosine, inhibited blast formation at concentrations as low as 10^–6 M. However, the other cytokinins, which lacked the ribosyl residue at N⁹ position, had to be at the higher molar concentration of 10^–4 before they could induce the same inhibitory effect.     

Hypertrophy of pulmonary arteries and arterioles with cor pulmonale in rats induced by seneciphylline,a pyrrolizidine alkaloid

Summary Seneciphylline, one of the hepatotoxic pyrolizidine alkaloids, induced, as do also monoclotaline, etc., a marked arterial and arteriolar hypertrophy of the lung of young Wistar rats a month after a single s. c. injection of 50–80 mg/kg. Cor pulmonale with leftward shift of the ventricular septum was also noted.     

Fluorometric study of interaction between ACTH fragments and bovine adrenocortical membranes

Summary Corticotropin_1–24 and [Gly¹]corticotropin_1–18 amide increased the fluorescence of 1-anilinonaphthalene-8-sulfonate which bound to the bovine adrenocortical membranes. The two ACTH fragments interacted with the protein of the membranes and increased the net positive charge of the membranes.We thank Prof. Dr.M. Kikuno for his stimulating criticism. This work was partly supported by a grant from Keio University School of Medicine.     

Cytotoxicity of new cytochalasans fromChaetomium globosum

Zusammenfassung Nachweis, dass CHCl₃-Rohextrakte aus Myzelien und Filtraten der Zuchtmedien vonChaetomium globosum Kunze ex Fries einen akuten toxischen Effect auf HeLa-Zellen in vitro, sowie auf Mäuse zeigten. Chaetoglobosine die aus Mycelium-Rohextrakt isoliert wurden und chemisch zu den Cytochalasanen gehören, induzierten in HeLa-Zellen eine Polynukleierung und multipolare Kernverteilung. Auch beim Chaetogobosin wird eine Mikrofilament-Schädigung angenommen.     

Amplification of PPM1D in human tumors abrogates p53 tumor-suppressor activity

Expression of oncogenic Ras in primary human cells activates p53, thereby protecting cells from transformation. We show that in Ras-expressing IMR-90 cells, p53 is phosphorylated at Ser33 and Ser46 by the p38 mitogen-activated protein kinase (MAPK). Activity of p38 MAPK is regulated by the p53-inducible phosphatase PPM1D, creating a potential feedback loop. Expression of oncogenic Ras suppresses PPM1D mRNA induction, leaving p53 phosphorylated at Ser33 and Ser46 and in an active state. Retrovirus-mediated overexpression of PPM1D reduced p53 phosphorylation at these sites, abrogated Ras-induced apoptosis and partially rescued cells from cell-cycle arrest. Inactivation of p38 MAPK (the product of Mapk14) in vivo by gene targeting or by PPM1D overexpression expedited tumor formation after injection of mouse embryo fibroblasts (MEFs) expressing E1A+Ras into nude mice. The gene encoding PPM1D (PPM1D, at 17q22/q23) is amplified in human breast-tumor cell lines and in approximately 11% of primary breast tumors, most of which harbor wildtype p53. These findings suggest that inactivation of the p38 MAPK through PPM1D overexpression resulting from PPM1D amplification contributes to the development of human cancers by suppressing p53 activation.