Acute myeloblastic leukemia in a patient with hereditary protein C deficiency.
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The patient had been diagnosed with hereditary protein C deficiency. She recently developed acute myeloblastic leukemia (AML). Chemotherapy for AML by cytosine arabinoside, aclarubicin followed by granulocyte colony-stimulating factor (CAG) was started. Disseminated intravascular coagulation (DIC) was observed, however thromboembolic complication was not observed during the hospital course. Hematological remission was not obtained, and the patient died of pseudomembranous pancolitis. Whether the development of these rare disorders of hereditary protein C and AML are coincidental, or involve a causal relationship remains unknown. (+info)
Stat5 constitutive activation rescues defects in spinal muscular atrophy.
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Proximal spinal muscular atrophy (SMA) is a motor neuron degeneration disorder for which there is currently no effective treatment. Here, we report three compounds (sodium vanadate, trichostatin A and aclarubicin) that effectively enhance SMN2 expression by inducing Stat5 activation in SMA-like mouse embryonic fibroblasts and human SMN2-transfected NSC34 cells. We found that Stat5 activation enhanced SMN2 promoter activity with increase in both full-length and deletion exon 7 SMN transcripts in SMN2-NSC34 cells. Knockdown of Stat5 expression disrupted the effects of sodium vanadate on SMN2 activation but did not influence SMN2 splicing, suggesting that Stat5 signaling is involved in SMN2 transcriptional regulation. In addition, constitutive activation of Stat5 mutant (Stat5A1*6) profoundly increased the number of nuclear gems in SMA-patient lymphocytes and reduced SMA-like motor neuron axon outgrowth defects. These results demonstrate that Stat5 signaling could be a possible pharmacological target for treating SMA. (+info)
Aclacinomycin oxidoreductase (AknOx) from the biosynthetic pathway of the antibiotic aclacinomycin is an unusual flavoenzyme with a dual active site.
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Aclacinomycin (Acl) oxidoreductase (AknOx) catalyzes the last two steps in the biosynthesis of polyketide antibiotics of the Acl group, the oxidation of the terminal sugar moiety rhodinose to l-aculose. We present the crystal structure of AknOx with bound FAD and the product AclY, refined to 1.65-A resolution. The overall fold of AknOx identifies the enzyme as a member of the p-cresol methylhydroxylase superfamily. The cofactor is bicovalently attached to His-70 and Cys-130 as 8alpha-Ndelta1-histidyl, 6-S-cysteinyl FAD. The polyketide ligand is bound in a deep cleft in the substrate-binding domain, with the tetracyclic ring system close to the enzyme surface and the three-sugar chain extending into the protein interior. The terminal sugar residue packs against the isoalloxazine ring of FAD and positions the carbon atoms that are oxidized close to the N5 atom of FAD. The structure and site-directed mutagenesis data presented here are consistent with a mechanism where the two different reactions of AknOx are catalyzed in the same active site but by different active site residues. Tyr-450 is responsible for proton removal from the C-4 hydroxyl group in the first reaction, the oxidation of rhodinose to cinerulose A. Tyr-378 acts as a catalytic base involved in proton abstraction from C3 of cinerulose A in the second reaction, for formation L-aculose. Replacement of this residue, however, does not impair the conversion of rhodinose to cinerulose A. (+info)
BRCA1- and BRCA2-deficient cells are sensitive to etoposide-induced DNA double-strand breaks via topoisomerase II.
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The function of BRCA1 and BRCA2 in DNA repair could affect the sensitivity of cells to cytotoxic agents, and would therefore be an important component of planning therapy for breast and ovarian cancers. Previously, both BRCA1- and BRCA2-deficient tumors were shown to be sensitive to mitomycin C, and the mechanism was presumed to be a defect in the repair of interstrand crosslinks by homologous recombination. Here, we show that both BRCA1 and BRCA2 determine the sensitivity to the cytotoxic drug, etoposide, using genetic complementation of BRCA-deficient cells. Etoposide is known to bind to topoisomerase II and prevent the resolution of the "cleavable complex," in which one DNA duplex is passed through a second duplex. The specificity of this BRCA-dependent sensitivity was confirmed by the use of aclarubicin, which is a catalytic inhibitor of topoisomerase II and prevents the formation of the cleavable complex. In the presence of aclarubicin, the differential sensitivity of BRCA-proficient and BRCA-deficient cells was lost. Thus, etoposide requires the presence of topoisomerase II to show specific sensitization in the absence of the function of BRCA1 or BRCA2. We conclude that homologous recombination is used in the repair of DNA damage caused by topoisomerase II poisons. Overall, these results suggest that etoposide is a potentially useful drug in the treatment of BRCA-deficient human cancers. (+info)
Characterization of rhodosaminyl transfer by the AknS/AknT glycosylation complex and its use in reconstituting the biosynthetic pathway of aclacinomycin A.
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The tetracyclic core of anthracycline natural products with antitumor activity such as aclacinomycin A are tailored during biosynthesis by regioselective glycosylation. We report the first synthesis of TDP-L-rhodosamine and demonstrate that the glycosyltransferase AknS transfers L-rhodosamine to the aglycone to initiate construction of the side-chain trisaccharide. The partner protein AknT accelerates AknS turnover rate for L-rhodosamine transfer by 200-fold. AknT does not affect the Km but rather affects the kcat. Using these data, we propose that AknT causes a conformational change in AknS that stabilizes the transition state and ultimately enhances transfer. When the subsequent glycosyltransferase AknK and its substrate TDP-L-fucose are also added to the aglycone, the disaccharide and low levels of a fully reconstituted trisaccharide form of aclacinomycin are observed. (+info)
DDB2 decides cell fate following DNA damage.
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Comparison of the cytotoxic effects of the high- and low-molecular-weight anticancer agents on multidrug-resistant Chinese hamster ovary cells in vitro.
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Neocarzinostatin (NCS), styrene-maleic acid copolymer-conjugated neocarzinostatin (SMANCS), and ricin exhibited cytotoxicity against two different types of Chinese hamster ovary cells, parental AUXB1 cells and the multidrug-resistant (MDR) subline CHRC5 cells at the nanomolar range. These doses were much lower than those of the other anticancer drugs tested (micromolar range), even after a short incubation. MDR CHRC5 cells were 20 to 900 times more resistant to Adriamycin, aclacinomycin, vinblastine, and mitomycin C than were AUXB1 cells. However, the resistance of CHRC5 cells to NCS, SMANCS, or ricin was relatively low: the 50% colony inhibitory concentration was only 5 to 10 times higher than that for parental AUXB1 cells. CHRC5 cells were not resistant to 5-fluorouracil and cis-diamminedichloroplatinum(II), but the effective doses of these agents to them were 10(3)-10(6) times higher, and longer incubation times were required to produce the same cytotoxicity as NCS and SMANCS. Furthermore, cell-bound NCS, SMANCS, and ricin were not released from AUXB1 or CHRC5 cells during a 120-min incubation, although Adriamycin was excreted very rapidly from CHRC5 cells after binding and internalization. These results strongly suggest that NCS, SMANCS, and ricin, which are internalized into cells by endocytosis, were not excreted from the cells by active efflux and exhibited a pronounced anticancer effect against MDR cells. (+info)