ABSTRACT
Malignant pleural mesothelioma (MPM) is a rare and highly aggressive neoplasm that arises from the pleural, pericardial, or peritoneal lining. Although surgery, chemotherapy, radiotherapy, and combinations of these therapies are used to treat MPM, the median survival of such patients is dismal. Therefore, there is a compelling need to develop novel therapeutics with different modes of action. Ganglioside GM2 is a glycolipid that has been shown to be overexpressed in various types of cancer. However, there are no published reports regarding the use of GM2 as a potential therapeutic target in cases of MPM. In this study, we evaluated the efficacy of the anti-GM2 antibody BIW-8962 as an anti-MPM therapeutic using in vitro and in vivo assays. Consequently, the GM2 expression in the MPM cell lines was confirmed using flow cytometry. In addition, eight of 11 cell lines were GM2-positive (73%), although the GM2 expression was variable. BIW-8962 showed a significant antibody-dependent cellular cytotoxicity activity against the GM2-expressing MPM cell line MSTO-211H, the effect of which depended on the antibody concentration and effector/target ratio. In an in vivo orthotropic mouse model using MSTO-211H cells, BIW-8962 significantly decreased the incidence and size of tumors. Additionally, the GM2 expression was confirmed in the MPM clinical specimens. Fifty-eight percent of the MPM tumors were positive for GM2, with individual variation in the intensity and frequency of staining. These data suggest that anti-GM2 antibodies may become a therapeutic option for MPM patients.
Subject(s)
Antibodies, Monoclonal, Humanized/pharmacology , Antineoplastic Agents/pharmacology , G(M2) Ganglioside/immunology , Lung Neoplasms/drug therapy , Mesothelioma/drug therapy , Pleural Neoplasms/drug therapy , Aged , Aged, 80 and over , Animals , Antibodies, Monoclonal, Humanized/therapeutic use , Antibody-Dependent Cell Cytotoxicity , Antineoplastic Agents/therapeutic use , Cell Line, Tumor , Female , G(M2) Ganglioside/metabolism , Humans , Male , Mesothelioma, Malignant , Mice, SCID , Middle Aged , Protein Engineering , Xenograft Model Antitumor AssaysABSTRACT
The mechanism of monoglucosyldiacylglycerol (MGlcDG) increase following heat shock in Synechocystis sp. PCC 6803 was examined by measuring MGlcDG synthase (Sll1377) activity. Temperature-dependent activation of Sll1377 was observed in the membrane fraction of Synechocystis sp. PCC 6803, whereas the Sll1377 protein level remained unchanged, suggesting that the activity is post-translationally regulated without covalent modification of Sll1377 by soluble enzymes. Four individual mutations introduced into recombinant Sll1377 (D147, D200, R329, and R331) significantly reduced the activity and blocked temperature-dependent activation, suggesting that these amino acid residues are essential for Sll1377 activity at both normal growth temperature and the higher temperature.
Subject(s)
Bacterial Proteins , Enzyme Activation , Gene Expression Regulation, Bacterial , Gene Expression Regulation, Enzymologic , Glucosyltransferases , Protein Processing, Post-Translational , Synechocystis , Bacterial Proteins/genetics , Bacterial Proteins/metabolism , Cell Membrane/enzymology , Glucosyltransferases/genetics , Glucosyltransferases/metabolism , Glycolipids/metabolism , Hot Temperature , Mutation , Synechocystis/enzymology , Synechocystis/geneticsABSTRACT
Plastidic phosphatidic acid phosphatase (PAP) dephosphorylates phosphatidic acid to yield diacylglycerol, which is a precursor for galactolipids, a primary and indispensable component of photosynthetic membranes. Despite its functional importance, the molecular characteristics and phylogenetic origin of plastidic PAP were unknown because no potential homologs have been found. Here, we report the isolation and characterization of plastidic PAPs in Arabidopsis that belong to a distinct lipid phosphate phosphatase (LPP) subfamily with prokaryotic origin. Because no homolog of mammalian LPP was found in cyanobacteria, we sought an LPP ortholog in a more primitive organism, Chlorobium tepidum, and its homologs in cyanobacteria. Arabidopsis had five homologs of cyanobacterial LPP, three of which (LPP gamma, LPP epsilon 1, and LPP epsilon 2) localized to chloroplasts. Complementation of yeast Delta dpp1 Delta lpp1 Delta pah1 by plastidic LPPs rescued the relevant phenotype in vitro and in vivo, suggesting that they function as PAPs. Of the three LPPs, LPP gamma activity best resembled the native activity. The three plastidic LPPs were differentially expressed both in green and nongreen tissues, with LPP gamma expressed the highest in shoots. A knock-out mutant for LPP gamma could not be obtained, although a lpp epsilon 1 lpp epsilon 2 double knock-out showed no significant changes in lipid composition. However, lpp gamma homozygous mutant was isolated only under ectopic overexpression of LPP gamma, suggesting that loss of LPP gamma may cause lethal effect on plant viability. Thus, in Arabidopsis, there are three isoforms of plastidic PAP that belong to a distinct subfamily of LPP, and LPP gamma may be the primary plastidic PAP.