Evaluation of phenylthiourea derivatives as inhibitors of transglutaminase-catalyzed reaction in Chinese hamster ovary cells

Transglutaminase activation in neurodegenerative diseases

The following review examines the role of calcium in promoting the in vitro and in vivo activation of transglutaminases in neurodegenerative disorders. Diseases such as Alzheimer's disease, Parkinson's disease and Huntington's disease exhibit increased transglutaminase activity and rises in intracellular calcium concentrations, which may be related. The aberrant activation of transglutaminase by calcium is thought to give rise to a variety of pathological moieties in these diseases, and the inhibition has been shown to have therapeutic benefit in animal and cellular models of neurodegeneration. Given the potential clinical relevance of transglutaminase inhibitors, we have also reviewed the recent development of such compounds.

Site-directed mutagenesis of human tissue transglutaminase: Cys-277 is essential for transglutaminase activity but not for GTPase activity

Transglutaminases (EC 2.3.2.13) catalyze an acyl-transfer reaction between peptide-bound glutamine residues and primary amines, including the epsilon-amino group of lysine residues in protein. Purified human erythrocyte transglutaminase was found to have another activity, i.e., GTP hydrolysis. Treatment of the enzyme with iodoacetamide, a cysteine-directed reagent, caused a 94% loss of TGase activity within 8 min, but no significant loss of GTPase activity. Cys-277, a known residue which is selectively modified by iodoacetamide, was replaced with Ser by site-directed mutagenesis to assess the role of the Cys-277 in the transglutaminase/GTPase activities. Wild-type cDNA, coding for human endothelial cell transglutaminase, and its C277S-mutated cDNA were cloned into a plasmid vector that contained a promoter from phage T7, and then expressed in Escherichia coli. The wild-type recombinant enzyme was indistinguishable from human erythrocyte transglutaminase in mobility on a SDS-polyacrylamide gel, immunoreactivity and catalytic activities for transglutaminase and GTPase. However, the recombinant enzyme was not blocked at the N-terminal alanine residue, as is the case in the naturally occurring erythrocyte enzyme. The C277S mutant enzyme showed no transglutaminase activity, but had Km and kcat values for GTPase activity that were comparable to those of wild-type recombinant and natural erythrocyte enzymes. These results demonstrate that Cys-277 is essential for transglutaminase activity, but not for GTPase activity, and that N-terminal blocking of tissue-type transglutaminase is not critical for either transglutaminase or GTPase activities.

Identification of transglutaminase substrates in HT29 colon cancer cells: use of 5-(biotinamido)pentylamine as a transglutaminase-specific probe

A biotinamine probe, 5-(biotinamido)pentylamine, was used for biotin-labeling of proteins in HT29 colon cancer cell extracts by endogenous transglutaminase activity. The biotin-labeled protein substrates were isolated and recovered by avidin-affinity chromatography. The proteins were separated using SDS-polyacrylamide gel electrophoresis, electroblotted onto a polyvinylidene difluoride membrane, visualized using Coomassie blue, cut out, and sequenced. Amino acid sequence data identified human fructose-1,6-bisphosphate aldolase A, an intracellular protein, as a substrate for cellular transglutaminase.

Inactivation of Placental Factor XIIIa by Acrylamide

Acrylamide rapidly and irreversibly inactivates thrombin activated Factor XIIIa, without affecting neither the intact zymogen nor its proteolytic activation. The inactivation is strictly dependent on the presence of calcium ions and is accompanied by a decrease in the number of free and total thiol residues, suggesting that cysteine residue(s), whose reactivity is modulated by calcium, is (are) probably responsible for the acrylamide-directed inactivation.

Stable expression of transfected human involucrin gene in various cell types: evidence for in situ cross-linking by type I and type II transglutaminase

Involucrin is a 68-kd precursor of the cornified envelope in keratinocytes. During terminal differentiation, involucrin becomes covalently cross-linked to other proteins by a membrane-anchored calcium-activated transglutaminase (TG) to form part of the cornified envelope. To better understand this process, we have used vector-mediated gene transfer to express human involucrin in a variety of cell types. Authentic involucrin protein was expressed in Chinese hamster ovarian (CHO) cells (fibroblasts), PtK2 rat kangaroo kidney cells (simple epithelial), and rat epidermal keratinocytes (stratifying squamous epithelial). The expression vector included an independent transcription unit encoding the aminoglycoside phosphotransferase gene (neo-r) allowing selection of stable involucrin-positive, G418-resistant clonal cell lines. In each cell type, involucrin levels were comparable to the endogenous expression observed in SCC-13 cells. Immunofluorescence localization studies revealed a uniform involucrin distribution throughout the cytoplasm in each cell type. Elevation of intracellular calcium resulted in cross-linking of involucrin in both CHO cells and rat keratinocytes, a process that was inhibited by EDTA and cystamine. In contrast, no cross-linking was observed in PtK2 cells or long-term passaged rat keratinocytes. Transglutaminase assays showed that rat keratinocytes contain predominantly a particulate (type I) form, whereas CHO cells contain only soluble TG (type II). PtK2 cells and long-term passaged keratinocytes, which were unable to cross-link involucrin, contained barely detectable TG activity. These results indicate 1) that involucrin is an efficient in situ substrate for both type I and type II transglutaminase and 2) that involucrin cross-linking is strictly TG dependent.

Formation of N epsilon-(gamma-glutamyl)-lysine isodipeptide in Chinese-hamster ovary cells

N epsilon-(gamma-Glutamyl)-lysine isodipeptide was detected in a protein-free fraction of Chinese-hamster ovary cells and their culture fluid by using radioactive lysine as a tracer. The identity of the isodipeptide was established by its separation on ion-exchange chromatography, analysis by h.p.l.c. after derivatization, recovery of lysine after acidic hydrolysis or after cleavage by a specific enzyme, namely gamma-glutamylamine cyclotransferase. The amount of isodipeptide was raised (460 pmol/10(7) cells and 61 pmol/ml of culture fluid were observed as highest values) as the cell density increased. Effects of inhibitors of intracellular protein degradation have shown that the isodipeptide derives from cross-linking N epsilon-(gamma-glutamyl)-lysine bonds formed by tissue transglutaminase. Estimated half-life values of cross-linked proteins were about 3 h. gamma-Glutamylamine cyclotransferase, which may split the isodipeptide formed during the continuous turnover of cross-linked proteins, was also found in Chinese-hamster ovary cells. Isodipeptide may have been accumulated when either its generated amount is beyond the capacity of gamma-glutamylamine cyclotransferase or it is generated in cell compartments where this enzyme is not present.

Colorimetric assay for cellular transglutaminase

A colorimetric assay for cellular transglutaminase using 5-(biotinamido)pentylamine and polyvinylidine difluoride membranes for crude cellular preparations and purified enzyme has been developed. The biotinpentylamine substrate was incorporated into N,N-dimethylcasein by transglutaminase, the biotinylated products were adsorbed onto the membrane disks and conjugated with streptavidin-beta-galactosidase, and the absorbance resulting from the formation of p-nitrophenol from hydrolysis of p-nitrophenyl-beta-D-galactopyranoside was measured at 405 nm. The validity of the assay was established by showing a good correlation, gamma = 0.922, between the colorimetric procedure and the commonly used radiometric filter paper method for the enzyme. The procedure offers a rapid, sensitive, and nonisotopic method for the estimation of cellular transglutaminase activity in as low as 20 ng of purified guinea pig liver transglutaminase and 10 micrograms of crude fibroblast cytosol protein.

GTP hydrolysis by guinea pig liver transglutaminase

Homogeneous guinea pig liver transglutaminase was purified from a commercially available enzyme preparation by affinity chromatography on GTP-agarose. The purified transglutaminase exhibited a single band of apparent Mr = 80,000 on sodium dodecyl sulfate polyacrylamide gel and Western blotting and had enzyme activity of both transglutaminase and GTPase. The guinea pig liver transglutaminase has an apparent Km value of 4.4 microM for GTPase activity. GTPase activity was inhibited by guanine nucleotides in order GTP-gamma-S greater than GDP, but not by GMP. These results demonstrate that purified guinea pig liver transglutaminase catalyzes GTP hydrolysis.