Developmental regulation of tissue transglutaminase during human placentation and expression in neoplastic trophoblast

Hypoxia and inflammation conditions differentially affect the expression of tissue transglutaminase spliced variants and functional properties of extravillous trophoblast cells

PROBLEM

Persistent hypoxia and inflammation beyond early pregnancy are involved in a bad outcome because of defective trophoblast invasiveness. Tissue transglutaminase (TG2) coregulates several cell functions. An aberrant expression and/or transamidation activity could contribute to placental dysfunction.

METHOD OF STUDY

The first-trimester trophoblast cell line (Swan-71) was used to study TG2 expression and cell functions in the absence or presence of inflammatory cytokines (TNF-α, IL-1β) or chemical hypoxia (CoCl₂ ). We analyzed The concentration of cytokines in the supernatant by ELISA; Cell migration by scratch assay; NF-κB activation by detection of nuclear p65 by immunofluorescence or flow cytometry using a Swan-71 NF-κB-hrGFP reporter cell line. Tissue transglutaminase expression was analyzed by immunoblot and confocal microscopy. Expression of spliced mRNA variants of tissue transglutaminase was analyzed by RT-PCR. Transamidation activity was assessed by flow cytometry using 5-(biotinamido)-pentylamine substrate.

RESULTS

Chemical hypoxia and TGase inhibition, but not inflammatory stimuli, decreased Swan-71 migration. IL-6 production was also decreased by chemical hypoxia, but increased by inflammation. Intracellular TGase activity was increased by all stimuli, but NF-κB activation was observed only in the presence of proinflammatory cytokines. TG2 expression was decreased by CoCl₂ and TNF-α. Translocation of TG2 and p65 to nuclei was observed only with TNF-α, without colocalization. Differential relative expression of spliced variants of mRNA was observed between CoCl₂ and inflammatory stimuli.

CONCLUSION

The observed decrease in total TG2 expression and relative increase in short variants under hypoxia conditions could contribute to impaired trophoblast invasion and impact on pregnancy outcome.

Inflammation, Autoimmunity, and Hypertension: The Essential Role of Tissue Transglutaminase

Inflammatory cytokines cause hypertension when introduced into animals. Additional evidence indicates that cytokines induce the production of autoantibodies that activate the AT1 angiotensin receptor (AT1R). Extensive evidence shows that these autoantibodies, termed AT1-AA, contribute to hypertension. We review here recent studies showing that cytokine-induced hypertension and AT1-AA production require the ubiquitous enzyme, tissue transglutaminase (TG2). We consider 3 mechanisms by which TG2 may contribute to hypertension. (i) One involves the posttranslational modification (PTM) of AT1Rs at a glutamine residue that is present in the epitope sequence (AFHYESQ) recognized by AT1-AA. (ii) Another mechanism by which TG2 may contribute to hypertension is by PTM of AT1Rs at glutamine 315. Modification at this glutamine prevents ubiquitination-dependent proteasome degradation and allows AT1Rs to accumulate. Increased AT1R abundance is likely to account for increased sensitivity to Ang II activation and in this way contribute to hypertension. (iii) The increased TG2 produced as a result of elevated inflammatory cytokines is likely to contribute to vascular stiffness by modification of intracellular contractile proteins or by crosslinking vascular proteins in the extracellular matrix. This process, termed inward remodeling, results in reduced vascular lumen, vascular stiffness, and increased blood pressure. Based on the literature reviewed here, we hypothesize that TG2 is an essential participant in cytokine-induced hypertension. From this perspective, selective TG2 inhibitors have the potential to be pharmacologic weapons in the fight against hypertension.

Transglutaminase 2-dependent deamidation of glyceraldehyde-3-phosphate dehydrogenase promotes trophoblastic cell fusion

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a multifunctional protein as well as a classic glycolytic enzyme, and its pleiotropic functions are achieved by various post-translational modifications and the resulting translocations to intracellular compartments. In the present study, GAPDH in the plasma membrane of BeWo choriocarcinoma cells displayed a striking acidic shift in two-dimensional electrophoresis after cell-cell fusion induction by forskolin. This post-translational modification was deamidation of multiple glutaminyl residues, as determined by molecular mass measurement and tandem mass spectrometry of acidic GAPDH isoforms. Transglutaminase (TG) inhibitors prevented this acidic shift and reduced cell fusion. Knockdown of the TG2 gene by short hairpin RNA reproduced these effects of TG inhibitors. Various GAPDH mutants with replacement of different numbers (one to seven) of Gln by Glu were expressed in BeWo cells. These deamidated mutants reversed the suppressive effect of wild-type GAPDH overexpression on cell fusion. Interestingly, the mutants accumulated in the plasma membrane, and this accumulation was increased according to the number of Gln/Glu substitutions. Considering that GAPDH binds F-actin via an electrostatic interaction and that the cytoskeleton is rearranged in trophoblastic cell fusion, TG2-dependent GAPDH deamidation was suggested to participate in actin cytoskeletal remodeling.

Tissue transglutaminase contributes to the pathogenesis of preeclampsia and stabilizes placental angiotensin receptor type 1 by ubiquitination-preventing isopeptide modification

Preeclampsia is a life-threatening pregnancy disorder that is widely thought to be triggered by impaired placental development. However, the placenta-related pathogenic factors are not fully identified, and their underlying mechanisms in disease development remain unclear. Here, we report that the protein level and enzyme activity of tissue transglutaminase (TG2 or tTG), the most ubiquitous member of a family of enzymes that conducts post-translational modification of proteins by forming ε-(γ-glutamyl)-lysine isopeptide bonds, are significantly elevated in placentas of preeclamptic women. TG2 is localized in the placental syncytiotrophoblasts of patients with preeclampsia where it catalyzes the isopeptide modification of the angiotensin receptor type 1 (AT1). To determine the role of elevated TG2 in preeclampsia, we used a mouse model of preeclampsia based on injection of AT1-agonistic autoantibody. A pathogenic role for TG2 in preeclampsia is suggested by in vivo experiments in which cystamine, a potent transglutaminase inhibitor, or small interfering RNA-mediated TG2 knockdown significantly attenuated autoantibody-induced hypertension and proteinuria in pregnant mice. Cystamine treatment also prevented isopeptide modification of placental AT1 receptors in preeclamptic mice. Mechanistically, we revealed that AT1-agonistic autoantibody stimulation enhances the interaction between AT1 receptor and TG2 and results in increased AT1 receptor stabilization via transglutaminase-mediated isopeptide modification in trophoblasts. Mutagenesis studies further demonstrated that TG2-mediated isopeptide modification of AT1 receptors prevents ubiquitination-dependent receptor degradation. Taken together, our studies not only identify a novel pathogenic involvement of TG2 in preeclampsia but also suggest a previously unrecognized role of TG2 in the regulation of G protein-coupled receptor stabilization by inhibiting ubiquitination-dependent degradation.

Effect of single post-ovulatory administration of levonorgestrel on gene expression profile during the receptive period of the human endometrium

The hypothesis that levonorgestrel (LNG) used as an emergency contraceptive interferes with endometrial receptivity remains unproven. We compared the endometrial gene expression profile during the receptive period after administering a single dose of LNG 1.5 mg or placebo on day 1 of the luteal phase. An endometrial biopsy was done on day LH+7 or LH+8 and samples were taken from seven volunteers, each one contributing with one cycle treated with placebo and another with LNG. The expression of 20 383 genes was determined using cDNA microarrays. Real-time RT-PCR was used 1) to confirm the differences found in DNA microarray analysis and 2) to determine the effect of LNG on transcript levels of C3, C4BPα, COX2, MAOA, S100A4, and SERPINB9, known to be upregulated during receptivity, and on cPLA2α, JAK1, JNK1, CTSL1, and GSTP1, known to respond to mifepristone. Additional endometrial biopsies were done during the pre-receptive (LH+3) and receptive (LH+7) period and samples were taken from eight untreated volunteers in order to determine the changes associated with acquisition of receptivity of 14 genes. Mean levels of PAEP, TGM2, CLU, IGF2, and IL6ST mRNAs increased after administering LNG while those of HGD, SAT1, EVA1, LOC90133, ANXA1, SLC25A29, CYB5A, CRIP1, and SLC39A14 decreased. Except for the level of ANXA1 transcript, all changes remained within the range observed in untreated controls, and none of the transcripts responding to mifepristone changed in response to LNG. Post-ovulatory administration of LNG caused minimal changes in gene expression profiling during the receptive period. Neither the magnitude nor the nature or direction of the changes endorses the hypothesis that LNG interferes with endometrial receptivity.

Maternal celiac disease autoantibodies bind directly to syncytiotrophoblast and inhibit placental tissue transglutaminase activity

BACKGROUND

Celiac disease (CD) occurs in as many as 1 in 80 pregnant women and is associated with poor pregnancy outcome, but it is not known if this is an effect on maternal nutrient absorption or, alternatively, if the placenta is an autoimmune target. The major autoantigen, tissue transglutaminase (tTG), has previously been shown to be present in the maternal-facing syncytiotrophoblast plasma membrane of the placenta.

METHODS

ELISA was used to demonstrate the presence of antibodies to tissue transglutaminase in a panel of CD sera. Immunohistochemistry was used to evaluate the binding of IgA autoantibodies from CD serum to term placenta. In addition, novel direct binding and activity assays were developed to mimic the in vivo exposure of the villous placenta to maternal autoantibody.

RESULTS AND DISCUSSION

CD IgA autoantibodies located to the syncytial surface of the placenta significantly more than IgA antibodies in control sera (P < 0.0001). The distribution of antigen was similar to that observed using a monoclonal antibody to tissue transglutaminase. Staining was reduced by pre-absorption of CD serum with recombinant human tissue transglutaminase. In direct binding assays, autoimmune immunoglobulin A (IgA) from the maternal compartment became associated with antigen at the syncytial surface of the placenta, as a result of which transglutaminase activity at this site was inhibited.

CONCLUSION

These data indicate that direct immune effects in untreated CD women may compromise placental function.

A role for tissue transglutaminase in stabilization of membrane-cytoskeletal particles shed from the human placenta

Tissue transglutaminase (TGM2; also known as TG2 or tTG) localizes to the syncytial microvillous membrane (MVM) of the human placenta, the primary interface between maternal and fetal tissue. To identify TGM2 substrates in the MVM, membrane vesicles were prepared and labeled with biotinylated acyl donor or acceptor probes. Biotinylated species were selected on an avidin affinity matrix and identified by mass spectrometry of tryptic peptides. The most abundant were cytoskeletal (actin, tubulin, and cytokeratin) and membrane-associated (annexins, integrins, and placental alkaline phosphatase) proteins. During pregnancy, apoptotic particulate material, the end product of the trophoblast life cycle, is shed from the MVM into maternal circulation. Shed material was isolated from primary trophoblast cultures in which syncytial-like masses develop by fusion. A substantial fraction of actin in the particles was in the form of covalent polymeric aggregates, in contrast to cellular actin, which dissociated completely into monomer in SDS-PAGE. When cells were cultured in the presence of transglutaminase inhibitors, actin in the shed particles remained exclusively in monomeric form, and a reduction in trophoblast intercellular fusion and differentiation was observed. These findings suggest that transglutaminase-mediated cross-linking stabilizes the particulate material shed from the placenta.

Tissue Transglutaminase Expression and Activity in Placenta

Tissue transglutaminase (tTG) expression, distribution and activity were examined in human placenta and derived cells. Immunochemical techniques and RT-PCR were used to demonstrate tTG protein and mRNA in stromal cells and trophoblast in first trimester and at term, with higher levels later in pregnancy. Decidual cells also produce tTG. The data were confirmed using primary cultures of trophoblast, fibroblasts and decidual stromal cells. Substrate incorporation studies indicated tTG activity in association with fibroblast extracellular matrix and the syncytial microvillous membrane (MVM), where several target polypeptides could be observed. tTG is a major autoantigen in Coeliac disease (CoD) which is associated with poor pregnancy outcome. tTG at the placental MVM is a plausible target of maternal autoantibody action.

Tissue transglutaminase at embryo-maternal interface

CONTEXT

Tissue transglutaminase (tTG) has a high affinity for fibronectin (FN) and is a coreceptor of both beta1 and beta3 integrin subunits. Considering the notion that FN and integrins have critical roles during the implantation process, this study was undertaken to elucidate the expression pattern and the potential physiological function of tTG at the embryo-maternal interface.

METHODS

The primary cultures of human placentas from 15 legal elective abortions at the first trimester of normal pregnancies and endometrial biopsies of 12 female patients in the midluteal phase as well as normal trophoblastic cell lines (CRL) were employed to address these issues using several approaches, such as scanning and transmission electron microscopies, immunostaining for light and electron microscopies, western blotting, and function assays using GRGDSP hexapeptide and an antibody against tTG.

RESULTS

The results demonstrated tTG expression on uterine pinopodes and lamellipodia of extravillous trophoblasts. The colocalization of tTG with beta1 and beta3 integrins and its interaction with alpha(v)beta3 integrin and integrin-associated proteins at focal adhesions of the extravillous trophoblasts were illustrated in the results of immunofluorescence, immunoblot, and coimmunoprecipitation studies. Furthermore, function assays revealed that tTG mediated the adhesion and spread of the placental cells on intact FN-coated and 42- and 110-kDa FN fragment-coated wells.

CONCLUSION

In conclusion, our findings demonstrated for the first time that tTG actively participates in adhesion events at the embryo-maternal interface through its interaction with FN, at least in part, by activating integrin-signaling pathways.

Honor your father and your mother

While on the one hand there is much mutual love and care in the relationship between parents and their offspring, there may, on the other hand, be also much mutual 'sound and fury', which sometimes is far from 'signifying nothing' (William Shakespeare, Macbeth). Indeed, from conception on, individuals are confronted with parent-offspring conflicts of all kinds. Initially these conflicts concern physiological matters (implantation, nutrition, weaning, etc.), but later in life the accent is on psychological ('you must this', 'you must that', 'don't do that' etc.) and social affairs, and phenomena such as child abuse, infanticide and incest may occur. It is, therefore, certainly not self-evident that children honor their parents. To reinforce their position, parents (societies) may appeal to a 'divine' commandment which helps them make their children suppress any tendency to conflict toward them (and hence to their culture), so that children conform to their parents' norms and values. When such psychological and sociological parent-offspring conflicts are not resolved satisfactorily, it can be suggested, children may (consciously or unconsciously) have aggressive feelings toward their parents: Freud's 'Oedipus complex'. This complex, it is argued, can also be seen as a parent-offspring conflict. Given their biological basis, parent-offspring conflicts can hardly be considered as abnormal. Conflicts between adults and their offspring have always existed and will always exist, simply because it is inherent in our genetic make-up: parents and offspring of sexually reproducing species--humans included--are only about 50% genetically related and hence have different interests at all levels of being. Indeed, parent-offspring conflicts are such stuff as we are made on, and our little life is rounded with its consequences (adapted from William Shakespeare, The Tempest).

Loss of tissue transglutaminase as a biomarker for prostate adenocarcinoma

BACKGROUND

Additional molecular tissue biomarkers for prostate carcinoma are needed to stratify patients with clinically suspicious findings, such as an elevated prostate specific antigen (PSA) with a negative biopsy, according to risk.

METHODS

Prostate tissues from 43 cancer cases and 47 controls with no evidence of cancer were labeled for transglutaminase by immunohistochemistry. Immunoreactivity was quantified using the Autocyte Pathology Workstation. In addition, quantitative fluorescence image analysis was used to compare transglutaminase concentrations in cells obtained by fine-needle aspiration from excised prostates. Loss of gene expression was evaluated by reverse transcriptase-polymerase chain reaction and growth with 5-azacytidine.

RESULTS

Visually, benign glands from controls generally expressed tissue transglutaminase, whereas regions with adenocarcinoma generally were negative. With quantitative immunohistochemistry, 41 of 43 adenocarcinoma of the prostate (CaP) cases expressed lower mean percentage areas positive for transglutaminase than did 30 of 30 benign prostatic hyperplasia (BPH) and 17 of 17 prostatitis cases (P < 0.0001; odds ratio [OR], 1577; 95% confidence interval (CI), 74-33, 820; relative risk [RR], 25; 95% CI, 6-95). Quantitative immunofluorescence of 3277 cells collected by FNA from 19 CaP cases and 645 cells from 5 cases of BPH showed that the mean content of transglutaminase was 93 femtograms (fg) for the CaP-derived cells and 138 fg for the BPH cells (P < 0.0001). Receiver operating curve analysis of the immunohistochemistry data showed an optimized threshold produced 95% sensitivity with 100% specificity. Growth of LNCaP cells with 5-azacytidine failed to stimulate transglutaminase expression, suggesting that loss of expression was likely not attributable to promoter methylation.

CONCLUSIONS

Measurements of transglutaminase on tissue sections provides additional diagnostic information that is potentially useful for risk assessment of patients with suspicious clinical findings, such as nodules or positive PSA and negative biopsies, without overdetecting disease.

Expression of tissue transglutaminase in human bladder carcinoma

The expression of cell adhesion proteins is frequently deranged in bladder carcinomas. Since tissue transglutaminase (tTG) can increase cellular adhesiveness, its expression was studied in both superficial and invasive transitional cell carcinomas. No expression of tTG was found in normal urothelium or in grade 1-3 papillary tumours without invasion. Expression of tTG was seen in the invasive processes of five grade 3 tumours with microinvasion and in 49 of 63 solid grade 3 and 4 tumours. In six cases, both primary tumours and biopsies from liver metastases were studied. In all these cases, the liver metastases were tTG-negative, while the primary tumours were tTG-negative in five cases and consisted of both tTG-positive and tTG-negative cells in one case. Analysis of tTG protein in tumour extracts by Western blotting showed expression of the 77 kD tTG, with no evidence for expression of the truncated form found in some cell types. It is suggested that tTG, when expressed, contributes to the deranged adhesive properties of the carcinoma cells and may influence the course of invasion. These results also raise the possibility that lack of tTG expression may increase the risk of developing blood-borne metastases.