A new compound, withangulatin A, promotes type II DNA topoisomerase-mediated DNA damage

Withangulatin A, a new compound with a known chemical structure and from the antitumor Chinese herb Physalis angulata L, was found to act on topoisomerase II to induce topoisomerase II-mediated DNA damage in vitro. It has two effective dosage ranges of approximate 0.5 and 20 microM, with about one-third the activity of 20 microM VM-26.     

Highly efficient DNA delivery mediated by pH-sensitive immunoliposomes

We have previously shown that pH-sensitive immunoliposomes can mediate a target-specific delivery of plasmid DNA to tumor cells grown in a mouse model [Wang, C.-Y., & Huang, L. (1987) Proc. Natl. Acad. Sci. U.S.A. 84, 7851-7855]. The efficiency of delivery in terms of the target cell transformation frequency has now been characterized for both short- and long-term gene expression in a tissue culture system. Herpes simplex virus thymidine kinase (TK) gene was used as a reporter gene. It was placed under the control of the promoter for the rat phosphoenolpyruvate carboxykinase gene, which contains a cAMP regulatory element. Therefore, the expression of the exogenous gene in the target cell, mouse Ltk- cells, can be regulated by cAMP drugs. The plasmid DNA was encapsulated in liposomes using a detergent dialysis method. The efficiency of gene delivery was optimized with respect to the time course and dose of liposome-associated DNA. The existence of antibody of the liposomes was essential for the maximal level of DNA delivery. Delivery was also dependent on the lipid composition of the liposome. The pH-sensitive lipid composition gave 8-fold higher efficiency than the corresponding pH-insensitive composition. The transformation efficiency of the target cell also depended on the regulation of gene expression; cells incubated with dibutyryl-cAMP and theophylline showed a much higher level of transformation frequency than cells incubated without the drugs. When all liposome and incubation parameters are optimized, the Ltk- cells showed a 47% efficiency for the short-term transformation, and 2% for the long-term transformation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Levels of protein kinase C activity in human gastrointestinal cancers

The protein kinase C (PKC) activities of tumor tissue and adjacent normal mucosa of human cancers of the esophagus (8 cases), stomach (1 case) and colon (3 cases) were measured. Considerable variations were found in the activity of PKC and in its subcellular distribution in these cancers. The PKC activities of the membrane and cytosolic fractions of the eight esophageal cancers were, however, similar to those of the adjacent normal mucosa: the average PKC activities of the tumor tissues and normal mucosa were 7.5 and 8.3 pmol/min/mg protein, respectively, in their membrane fractions and 7.9 and 7.8 pmol/min/mg protein, respectively, in their cytosolic fractions.     

Identification of thetrans-stilbene oxide-active glutathione transferase in human mononuclear leukocytes and in liver as GST1

A glutathione transferase from human mononuclear leukocytes with a high activity towardtrans-stilbene oxide (GT-tSBO) has been studied in liver and blood from fetus and adults and in blood from neonates. Using starch gel electrophoresis, different phenotypes of GST1 have been determined, GST1 0, GST1 1, and GST1 2. As judged from activity measurements and the fact that only those individuals who express the null allele of GST1, the GST1 0, which has a low activity towardtrans-stilbene oxide, it is concluded that the hepatic transferase GST1 is identical to GT-tSBO, as well as to hepatic transferase μ. In addition, it has been shown that the different genotypes of GST1 1 (GST1 1-1, GST1 1-0) and GST1 2 (GST1 2-2, GST1 2-0) can be separated by measuring the GT-tSBO activity in whole blood from the same individual. It is also demonstrated that GT-tSBO activity is much lower in fetal liver, approximately 10 times, compared with adult liver, while this activity seems to be unchanged in the blood from fetus and adults, as well as in neonates.     

Trigramin: primary structure and its inhibition of von Willebrand factor binding to glycoprotein IIb/IIIa complex on human platelets

Trigramin, a naturally occurring peptide purified from Trimeresurus gramineus (T. stejnegeri formosensis) snake venom, inhibits platelet aggregation and the binding of 125I-fibrinogen to ADP-stimulated platelets (Ki = 2 X 10(-8) M) without affecting the platelet-release reaction. 125I-trigramin binds to ADP-stimulated and to chymotrypsin-treated normal platelets but not to thrombasthenic platelets. 125I-trigramin binding to platelets is blocked by monoclonal antibodies directed against the glycoprotein IIb/IIIa complex and by Arg-Gly-Asp-Ser (RGDS) [Huang et al. (1987) J. Biol. Chem. 262, 161]. We determined the primary structure of trigramin, which is composed of a single polypeptide chain of 72 amino acid residues and six disulfide bridges. The molecular weight of trigramin calculated on the basis of amino acid sequence was 7500, and the average pI was 5.61. An RGD sequence appeared in the carboxy-terminal domain of trigramin. An amino-terminal fragment (7-33) of trigramin showed 39% homology with a region (1555-1581) of von Willebrand factor (vWF). Trigramin also showed 36% identity in a 42 amino acid overlap and 53% identity in a 15 amino acid overlap when compared with two adhesive proteins, collagen alpha 1 (I) and laminin B1, respectively. Trigramin blocked binding of human vWF to the glycoprotein IIb/IIIa complex in thrombin-activated platelets in a dose-dependent manner. Reduction of trigramin resulted in a marked decrease in its ability to block vWF binding to human platelets.(ABSTRACT TRUNCATED AT 250 WORDS)     

Immunoliposomes with different acid sensitivities as probes for the cellular endocytic pathway

By combining dioleoylphosphatidylethanolamine (DOPE) with oleic acid (OA), palmitoylhomocysteine (PHC) or dipalmitoylsuccinylglycerol (DPSG) we have prepared pH-sensitive liposomes with different acid sensitivities. DOPE/OA liposomes are the most acid sensitive, while DOPE/DPSG liposomes are the least acid sensitive. Incubation of DOPE/OA liposomes with mouse L929 cells reduces the pH-sensitivity of these liposomes by altering the lipid composition. Using diphtheria toxin fragment A as a marker for cytoplasmic delivery, we find that the delivery kinetics of pH-sensitive immunoliposomes closely correlates with the modified acid sensitivities of the liposomes. Immunoliposomes encounter pH 6-6.2 with a t1/2 of 5-15 min after internalization. By contrast, acidification of the endosomes to pH 5.0 takes longer (t1/2 approximately 25 min). We also used a whole cell null point technique (Yamishiro and Maxfield (1987) J. Cell Biol. 105, 2713-2721) to directly determine the average pH encountered by the endocytosed immunoliposomes. We find that acidification determined by the null point method proceeds less rapidly than that estimated from DTA delivery data. This is likely due to the fact that the measured DTA delivery is done by those liposomes which first arrive at the endosomes with sufficient acidity. Our data suggests that DOPE/PHC immunoliposomes deliver at the early endosome while DOPE/DPSG immunoliposomes deliver at the late endosomes. The DOPE/OA immunoliposomes, with the altered composition and acid sensitivity, deliver with a kinetics intermediate between the other two immunoliposomes. Thus, pH-sensitive liposomes represent useful probes for studying the kinetics of endosome acidification.     

Glycolipid- and glycoprotein-based blood group A antigen expression in human thrombocytes. A1/A2 difference

Total non-acid glycolipid fractions and total sodium dodecylsulphate (SDS) solubilized protein fractions were isolated from human thrombocytes obtained from single human donors having different blood group A₁/A₂ phenotypes. The blood group A glycolipid antigens were characterized by immunostaining of thin layer plates with different monoclonal anti-A antibodies. The glycoproteins carrying blood group A epitopes were identified by SDS-PAGE and Western blot analysis using a monoclonal anti-A antibody. Blood group A glycolipid antigens were found in both A₁ and A₂ thrombocytes but the A₂ individuals expressed at least ten times less A glycolipids compared to the A₁ individuals. Expression of A type 3/4 chain and small amounts of A type 1 chain glycolipids were seen in thrombocytes of both A₁ and A₂ individuals, while the type 2 chain A glycolipids appeared to be missing from the A₂ thrombocytes. Blood group A reactive glycoproteins were only found in thrombocytes of A₁ individuals and could not be detected in A₂ individuals or a blood group O individual. The major blood group A glycoprotein were found as a double band migrating in the 130 kDa region.Abbreviations SDS sodium dodecyl sulfate - PAGE polyacrylamide gel electrophoresis - HPTLC high performance thin layer chromatography - CBB Coomassie brilliant blue - GVH graft versus host Part of this work was presented at the Xth International Symposium on Glycoconjugates, Jerusalem, Israel. September, 1989.In the short hand designation for glycolipids, the letter indicate blood group determinant, the first numeral, the number of sugar residues, and the second numeral, the type of carbohydrate chain. Thus, A-6-1 means a hexaglycosylceramide with a blood group A determinant based on the type 1 carbohydrate chain.