Isolation of a sodium dodecyl sulfate-insoluble transglutaminase substrate from liver plasma membranes

Proteomic analysis of differentially expressed proteins inPenaeus vannameihemocytes upon Taura syndrome virus infection

To understand molecular responses of crustacean hemocytes to virus infection, we applied 2-DE proteomics approach to investigate altered proteins in hemocytes of Penaeus vannamei during Taura syndrome virus (TSV) infection. At 24 h postinfection, quantitative intensity analysis and nano-LC-ESI-MS/MS revealed 11 forms of 8 proteins that were significantly up-regulated, whereas 9 forms of 5 proteins were significantly down-regulated in the infected shrimps. These altered proteins play important roles in host defense (hemocyanin, catalase, carboxylesterase, transglutaminase, and glutathione transferase), signal transduction (14-3-3 zeta), carbohydrate metabolism (acetylglucosamine pyrophosphorylase), cellular structure and integrity (beta-tubulin, beta-actin, tropomyosin, and myosin), and ER-stress response (protein disulfide isomerase). Semiquantitative RT-PCR and Western blot analysis confirmed the upregulation of 14-3-3 at both mRNA and protein levels. Interestingly, several altered protein spots were identified as fragments of hemocyanin. Mass spectrometric analysis showed that the hemocyanin spots at acidic and basic regions represented the C- and N-terminal hemocyanin fragments, respectively. As three-quarters of C-terminal fragments were up-regulated, whereas two-thirds of N-terminal hemocyanin fragments were down-regulated, we therefore hypothesize that C- and N-terminal hemocyanin fragments may have differential roles in hemocytes. Further investigation of these data may lead to better understanding of the molecular responses of crustacean hemocytes to TSV infection.

Enhanced susceptibility to transglutaminase reaction of alpha-lactalbumin in the molten globule state

The susceptibility of alpha-lactalbumin to transglutaminase reactions was studied using an enzyme from Streptoverticillium which can catalyze the reactions irrespective of the presence or absence of Ca2+. Transglutaminase-catalyzed polymerization of alpha-lactalbumin in the native state occurred to a very limited extent. Transformation from the native state to the molten globule state brought about by Ca(2+)-removal from holo-alpha-lactalbumin enhanced the polymerization of the protein catalyzed by transglutaminase. The incorporation of Carbobenzoxy-Gln-Gly into alpha-lactalbumin through the enzyme reaction was investigated to determine the amounts of lysine residues which are present at molecular surface and available to the enzyme. There was no significant difference in the amount of available lysine residues between the native and the molten globule molecule. However, the amount of surface glutamine residues incorporated with monodansylcadaverine by transglutaminase was remarkably higher in the molten globule state than that in the native state. The monodansylcadaverine-incorporated site of alpha-lactalbumin in the molten globule state was identified as Gln-54 by amino-acid sequence analysis of fluorescence-labeled peptides separated from chymotryptic digests of the protein. Possible reason for selective labeling of Gln-54 in molten globule alpha-lactalbumin was proposed.

Transglutaminase covalently incorporates amines into human immunodeficiency virus envelope glycoprotein gp120 in vitro

Human immunodeficiency virus envelope glycoprotein gp120, but not its precursor gp160, covalently incorporates both spermidine and glycine ethyl ester in the presence of Ca2+ and transglutaminase purified from guinea pig liver. The examined ability to act as enzyme substrate of various glutamine-containing gp120 fragments, including the principal neutralizing determinant, the CD4 binding domain, and the sequence 254-274, suggested to be involved in post-binding events and in virus entry in the host cell, indicated the glutamine-265 as possible reactive acyl donor site of the protein.

Human-immunodeficiency-virus transmembrane glycoprotein gp41 is an amino acceptor and donor substrate for transglutaminase in vitro

Recombinant gp41, the transmembrane glycoprotein of the human-immunodeficiency-virus (HIV) envelope, is an amino acceptor and donor substrate for transglutaminase in vitro. Gln51, Gln52, Gln66 and Lys77 residues were suggested as reactive sites, recognized by the enzyme, for possible cross-linking reactions with gp120, CD4 or other receptor(s) occurring on the surface of HIV-target cells. Soluble CD4, even though unable to function as an amino-acceptor transglutaminase substrate, becomes active in the presence of gp41, negatively influencing the enzyme-catalyzed incorporation of the polyamine spermidine into the transmembrane protein. These results suggest a possible role for transglutaminase in virus entry into host cells, via receptor-mediated endocytosis, and/or in HIV-induced CD4+ T-cell depletion via apoptosis.

In vivo and in vitro induction of 'tissue' transglutaminase in rat hepatocytes by retinoic acid

Tissue transglutaminase (tTG) expression was found to be induced in rat liver following in vivo retinoic acid (RA) treatment (Piacentini et al. (1988) Biochem. J. 253, 33-38). Here we show that the increased enzyme expression in rat liver is at least partially the result of the action of RA in parenchymal cells. In fact, (a) when hepatocytes are isolated from RA-treated animals their transglutaminase protein content is much higher than in similarly isolated control cells; (b) higher tTG protein level is also found by immunoelectronmicroscopy in the hepatocytes of the RA-treated rats as compared with the very low amount detected in the controls; (c) RA induces tTG in hepatocytes under culture conditions as well. One of the functions of tTG is to form a protein polymer in dying apoptotic cells by epsilon(gamma-glutamyl)lysine and, specifically gamma-glutamylpolyamine cross-links (Fesus et al. (1989) FEBS Lett. 245, 150-154). Noteworthy, after in vivo and in vitro RA-treatment we could not determine any increase (there was even a slight decrease) in the number of the cross-linked apoptotic envelopes. In keeping with this is the significant reduction of protein bound gamma-glutamylpolyamine detected in hepatocytes exposed to RA in culture. These findings suggest that the RA-induced tTG in parenchimal cells is an inactive form.

Demonstration of cross-linked cytokeratin polypeptides in transplantable rat hepatoma cells

Covalently cross-linked multimers of cytokeratins were shown to be present in transplantable Morris hepatoma 7777 cells. These high molecular weight antigens were not detectable in normal rat liver cells. However, identical high molecular weight antigens were also demonstrated in rat liver cells when the cells were homogenized in solutions containing Ca2+. The cross-linking reaction was suggested to be mediated by the action of tissue transglutaminases.

Transglutaminase stabilizes melanoma adhesion under laminar flow

To resist substantial wall shear stress (WSS) exerted by flowing blood, metastatic melanoma cells can form adhesive contacts with subendothelial extracellular matrix proteins, such as fibronectin (FN). Such contacts may be stabilized by transglutaminase catalyzed-cross-linkage of cell focal adhesion proteins. We analyzed human melanoma cell adhesion under flow by decreasing the flow (WSS) of melanoma cell suspensions and allowing them to adhere to immobilized wheat germ agglutinin or FN. At the wall shear adhesion threshold (WSAT), cell adherence was rapid with no rolling. Following cell adherence, we increased the flow and determined the wall shear detachment threshold (WSDeT). Cells spread and remained adherent on immobilized FN at high WSDeTs (greater than or equal to 32.5 dynes/cm2). The high resistance of adherent cells to shear forces suggested that transglutaminase-mediated crosslinking might be involved. Transglutaminase inhibitors monodansylcadaverine and INO-3178 decreased WSAT, and at low concentrations completely inhibited tumor cell spreading and promoted detachment at low WSDeTs (0.67 dynes/cm2). In static adhesion assays, transglutaminase inhibitors decreased cell adhesion to immobilized-FN in a dose-dependent manner and prevented the formation of crosslinked 125I-FN complex that failed to enter a SDS-polyacrylamide gradient gel. The data suggest that transglutaminase-catalyzed crosslinking, particularly in the presence of WSS, may be important in stabilizing cellular adhesive contacts during adhesion to immobilized-FN.

Characterisation of the cellular substrates for transglutaminase in normal liver and hepatocellular carcinoma

The transglutaminase-mediated incorporation of [14C]methylamine into tissue slices obtained from normal rat liver and diethylnitrosamine-induced hepatocellular carcinomas was used as a means of characterising the endogenous substrates of the transglutaminase enzymes present in these tissues. The amount of radiolabel incorporated was found to be similar in both tissues with the major radiolabelled protein identified as a high molecular weight polymer unable to traverse a 3.0% (w/v) acrylamide gel and with a molecular weight of at least 5 x 10(6) Da. Measurement of the crosslink, epsilon-(gamma-glutamyl)lysine, in the hepatocellular carcinoma and in normal liver indicated a 3-fold reduction in the levels found in tumour tissue when compared to normal liver. In contrast, the levels of covalently bound polyamines present in the hepatocellular carcinoma were found to be comparable or greater than those found in normal liver. Considering that there is a selective reduction (approx. 5-fold) in the activity of the cytosolic transglutaminase present in hepatocellular carcinomas with no change in the activity of the particulate enzyme (Hand et al. (1988) Biochim. Biophys. Acta 970, 137-145) these results suggests that the two enzymes may be differentially activated and that they may act on different substrates within the cell.

Cross-linking of lipocortin I and enhancement of its Ca2+ sensitivity by tissue transglutaminase

The stimulation of human epidermoid carcinoma A431 cells with the calcium ionophore A23187 resulted in the formation of high-molecular-weight lipocortins I, having apparent molecular weights of 75 kDa and 160 kDa as detected with specific anti-lipocortin I antibody. These immunoreactive proteins were identified to be covalently cross-linked multimers of lipocortin I, since essentially the same cross-linked multimers were observed when purified lipocortin I was incubated with tissue transglutaminase (TGase) in vitro. Classical amine substrates for TGase, such as dansylcadaverine and putrescine, were also incorporated stoichiometrically into lipocortin I. Cross-linking or amine incorporation was not observed with lipocortin II. Des 1-26 lipocortin I did not serve as a substrate for TGase, indicating that the N-terminal region of lipocortin I plays an important role in the formation of lipocortin I multimers. The cross-linking of lipocortin I by TGase resulted in a remarkable enhancement of calcium sensitivity for phospholipid binding; i.e., the free calcium concentration required for the cross-linked lipocortin I to attain 50% maximal binding to phosphatidylserine vesicles was as little as 3 microM, while that required for intact monomeric lipocortin I was 20 microM.