Linkage of two human pregnancy-specific beta 1-glycoprotein genes: one is associated with hydatidiform mole

Human-specific LAIR2 contributes to the high invasiveness of human extravillous trophoblast cells

The placenta is a temporary vital organ for intra-uterine development and growth. The anatomical structure of the placenta has evolved substantially, resulting in broad inter-species diversity. In particular, human placental extravillous trophoblast cells (EVTs) have evolved aggressive features, although the mechanism underlying this aggressiveness remains elusive. In the present study, we compared the human and mouse homologous gene databases and obtained 2272 human-specific genes, 807 of which are expressed in the placenta according to the UniGene database. Using the human trophoblast cell line HTR8/SVneo, we further verified the expression and function of one of these genes, the leukocyte-associated immunoglobulin-like receptor 2 (LAIR2). This gene shows increased expression during pregnancy and its reduced expression is associated with pregnancy complications. Although LAIR2 was expressed in the human placenta villus and decidua in the first trimester of pregnancy, it was not expressed in mouse tissues. Knockdown of LAIR2 markedly improved cell viability and inhibited the invasive ability of HTR8/SVneo cells. These data suggest that species-specific genes are pivotal to the evolution of a more aggressive human placenta to match the physiological demands of human development. Further investigation is required to obtain evidence on the function of LAIR2 and other specific genes in the placenta, providing insight on the mechanism, properties, and possible applications of this in humans.

Proteomic identification of predictive biomarkers for malignant transformation in complete hydatidiform moles

INTRODUCTION

Protein expression in cells are associated with oncogenesis. This study aims to explore proteomic profiles and discover potential biomarkers that can predict malignant transformation of hydatidiform mole.

METHODS

Retrospective analysis was done in 14 cases of remission hydatidiform mole and 14 cases of hydatidiform mole who later developed malignancy (GTN group). Molar tissues were retrieved from -70 °C frozen tissue. Subsequently, a large-scale proteomic analysis was performed to identify proteins and compare their abundance levels in the preserved molar tissues from these two groups using a dimethyl-labeling technique coupled with liquid chromatography-tandem mass spectrometry (LC-MS/MS).

RESULTS

A total of 2,153 proteins were identified from all samples. 22 and 10 proteins were significantly up-regulated and down-regulated, respectively, in the GTN group compared with the mole group. These altered proteins were found in several biological groups such as cell-cell adhesion, secreted proteins, and ribonucleoproteins. Several hormone-related proteins were among the most up-regulated proteins in the GTN group including choriogonadotropin subunit beta (β-hCG) and alpha (α-hCG), growth/differentiation factor 15, as well as both pregnancy-specific beta-1-glycoproteins 2 and 3. In contrast, protein S100-A11 and l-lactate dehydrogenase A chain, were down-regulated in molar tissue from most patients in the GTN group.

DISCUSSION

This study identified a set of differentially expressed proteins in molar tissues that could potentially be further examined as predictive biomarkers for the malignant transformation of CHMs. A molar proteome database was constructed and can be accessible online at http://sysbio.chula.ac.th/Database/GTD_DB/Supplementary_Data.xlsx.

CEA-Related CAMs

The carcinoembryonic antigen (CEA) family comprises a large number of cellular surface molecules, the CEA-related cell adhesion molecules (CEACAMs), which belong to the Ig superfamily. CEACAMs exhibit a complex expression pattern in normal and malignant tissues. The majority of the CEACAMs are cellular adhesion molecules that are involved in a great variety of distinct cellular processes, for example in the integration of cellular responses through homo- and heterophilic adhesion and interaction with a broad selection of signal regulatory proteins, i.e., integrins or cytoskeletal components and tyrosine kinases. Moreover, expression of CEACAMs affects tumor growth, angiogenesis, cellular differentiation, immune responses, and they serve as receptors for commensal and pathogenic microbes. Recently, new insights into CEACAM structure and function became available, providing further elucidation of their kaleidoscopic functions.

Integrins in the endometrium

The endometrium expresses many of the same integrins displayed by other tissues. Endometrial epithelial cells maintain the ‘classic’ epithelial integrins, including α2, α3, α6, and β4, while the stroma expresses the fibronectin receptor, α5β1. During the menstrual cycle, the endometrium undergoes dynamic changes in morphology in preparation for implantation. With these histological changes are concomitant alterations in integrin expression that appear to ‘frame’ the window of implantation, by the co-expression of glandular αvβ3 and α4β1 during days 20 to 24 of the menstrual cycle. The changes in integrin expression shift from epithelial to stroma predominance late in the menstrual cycle, extending into early pregnancy. Decidual integrins that appear upregulated in pregnancy include α1β1, α3β1, α6β1 and αvβ3. Markers of uterine receptivity hold promise for a better understanding of the implantation process and may help to explain many different types of infertility. These markers will be essential for monitoring and improving infertility therapies. The importance of integrins in the human endometrium now seems well established and promises to be an area of great clinical and basic science activity in the future.

Carcinoembryonic Antigen and Related Molecules in Normal and Transformed Trophoblast

Carcinoembryonic antigen (CEA, CD66e) and CEA-related cell adhesion molecules (CEACAMs) are important mediators in remodeling of diverse human tissues, and modulators of cell proliferation and differentiation. Expression by normal and transformed trophoblast of gestational trophoblastic diseases (GTDs), isolated cytotrophoblast and choriocarcinoma cell lines is presented here. Immunocyto/histochemistry of normal placenta (n=9), invasive mole (n=8), choriocarcinoma (n=7), a placental site trophoblastic tumor, cytotrophoblast in primary culture and JAr and JEG-3 cells was performed using polyclonal anti-CEA and specific monoclonal anti-CEA antibodies. Data were analyzed and scored using Mann-Whitney Test. CEA and CEA-related molecules were identified by Western blot and immunoaffinity chromatography in JAr and JEG-3 cells and extracts of 1st and 3rd trimester of pregnancy tissue and cytotrophoblast cell lysates. CEA is expressed throughout pregnancy, in first trimester predominantly in syncytiotrophoblast, but also in villous cytotrophoblast and extravillous trophoblast. Data presented here demonstrate that CEA is significantly increased in transformed trophoblast of GTDs (p<0.05). Both cytotrophoblast in primary culture and choriocarcinoma cell lines express CEA, with staining of granular deposits in JAr and cell membrane in JEG-3. The results suggest that CEA (CD66e) and other CEA-related protein(s) could be involved in trophoblast differentiation.

2,3,7,8-tetrachlorodibenzo-p-dioxin augments the modulation of gene expression mediated by the thyroid hormone receptor

Previously, we reported on genes whose expression was highly modulated by T3 in the HeLaTR cells that stably expressed the thyroid hormone receptor (TR). In this study, we examined the effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on TR-mediated gene expression. In the HeLaTR cells, T3 induced the expression of the reporter gene in a thyroid hormone responsible element (TRE)-dependent manner. When the cells were cultured in the presence of T3, the addition of TCDD but not 4-hydroxy-2',3,4',5,6'-pentachlorobiphenyl (PCB-OH), bisphenol A (BPA), or di(2-ethylhexyl)phthalate (DEHP) to the culture media further enhanced the T3-induced expression of the reporter gene. RT-PCR revealed that mRNA levels of 4-1BB, fmfc, PSCA, PSG7, RANTES, and TRAF1, which were highly increased by T3, were further elevated in cells exposed to T3 and TCDD. Also, the mRNA level of BMP6, which was decreased by T3, further declined in the cells exposed to both T3 and TCDD. In contrast to the effect of TCDD, PCB-OH suppressed the modulation of these gene expressions by T3. Neither TCDD nor PCB-OH alone affected the expression of 4-1BB, fmfc, PSCA, PSG7, RANTES, TRAF1, or BMP6. These results indicate that TCDD augments the cellular responses to T3 by hyperactivating TR-mediated gene expression, whereas PCB-OH suppresses cellular responses to T3 by negatively regulating it. Based on these findings, enzyme-linked immunosorbent assay (ELISA) for the PSCA protein in the HeLaTR cells was established. Such assays will be useful to monitor the effects of endocrine disrupting chemicals (EDCs) on TR-mediated gene expression.

Thyroid hormone induces the expression of 4-1BB and activation of caspases in a thyroid hormone receptor-dependent manner

Thyroid hormone has various effects on cell proliferation, growth and apoptosis. To gain more insight into the molecular dynamics caused by thyroid hormone, gene expression in HeLaTR cells that constitutively overexpressed the thyroid hormone receptor (TR) was analyzed. Gene expression profiling of the HeLaTR cells with an oligonucleotide microarray yielded 229 genes whose expression was significantly altered by T3. Among these genes, the expression of 4-1BB, which is known to initiate a signal cascade activating NF-kappaB, was significantly up-regulated by T3. Although treatment of the HeLaTR cells with T3 did not induce expression of NF-kappaB reporter luciferase, even in the presence of the 4-1BB-Ligand, it increased the caspase activities. An increase in the caspase activities was also observed in the HeLaTR cells transfected with 4-1BB cDNA, and the 4-1BB-Ligand further increased the caspase activities of the HeLaTR cells overexpressing the 4-1BB. Furthermore, up-regulation of 4-1BB and an increase in caspase activities also occurred in the rat FRTL cells that expressed only authentic TR. These results demonstrate that the expression of 4-1BB serves as the mediator of signals from T3 to activate caspases.

Adeno-associated virus DNA in human gestational trophoblastic disease

Previous studies had shown a correlation between infection with the human adeno-associated virus (AAV) and spontaneous abortion in early pregnancy. Furthermore, AAV DNA had been detected in cells of the human trophoblast lines, Jeg-3, JAr, and BeWo, in cells of the human amnion line, FL, and in trophoblasts from amnion fluids. Infectious AAV virions could be isolated from amnion fluids. To further analyse AAV infection during pregnancy, we tested material from Gestational Trophoblastic Disease for the presence of AAV DNA. With 63 tissue samples from patients from Brazil, including 49 hydatiform moles and 14 choriocarcinomas, nested PCR was performed to detect the presence of AAV DNA. In addition, 15 samples from spontaneous abortions were analysed. AAV DNA was found in 43 samples (28/49 hydatiform moles, 4/14 choriocarcinomas, 11/15 miscarriage material). These findings confirm AAV infection of embryo-derived tissue in humans and further suggest a role of AAV in miscarriage and trophoblastic disease.

Transcription of genes encoding pregnancy-specific glycoproteins is regulated by negative promoter-selective elements

The human pregnancy-specific glycoprotein (PSG) genes comprise a family of 11 highly conserved members whose expression is maximal in placental cells and marginal in other cell types. We have investigated here the molecular basis of PSG regulation by analysing a large regulatory region of the PSG-5 gene in cells that do and do not express these genes. The promoter region (-254 to -43), which does not contain a TATA-box, large GC-rich sequences or a classical initiator, was active in all cell types analysed. Additional upstream sequences up to position -3204 repressed promoter activity. Two independent repressor regions were identified and found to operate effectively in HeLa, COS-7 and HTR8/SVneo placental cells. More significantly, these negatively acting modules failed to repress a heterologous TATA-containing thymidine kinase promoter. Detailed transcriptional and DNA-protein analyses of the proximal repressor region (-605 to -254) revealed the presence of both negative and positive cis-acting elements. Disruption of the repressive functions resulted in an enhanced transcription of the reporter constructs. In conclusion, these results demonstrate that PSG-5 gene transcription is highly repressed by promoter-selective negative regulatory regions and the relief of repression allows enhanced PSG-5 gene transcription irrespective of the cell type. Furthermore, our findings suggest that PSG genes are expressed mainly through a derepression mechanism.

The carcinoembryonic antigen (CEA) family: structures, suggested functions and expression in normal and malignant tissues

The human CEA family has been fully characterized. It comprises 29 genes of which 18 are expressed; 7 belonging to the CEA subgroup and 11 to the pregnancy specific glycoprotein subgroup. CEA is an important tumor marker for colorectal and some other carcinomas. The CEA subgroup members are cell membrane associated and show a complex expression pattern in normal and cancerous tissues with notably CEA showing a selective epithelial expression. Several CEA subgroup members possess cell adhesion properties and the primordial member, biliary glycoprotein, seems to function in signal transduction or regulation of signal transduction possibly in association with other CEA sub-family members. A modified ITAM/ITIM motif is identified in the cytoplasmatic domain of BGP. A role of CEA in innate immunity is envisioned.

Coordinate expression of splice variants of the murine pregnancy-specific glycoprotein (PSG) gene family during placental development

The human and murine pregnancy-specific glycoprotein (PSG) gene families encode a large number of closely related proteins which are abundantly expressed in the fetal trophoblast and secreted into the maternal circulation. Although the presence of a well conserved tripeptide sequence His or Arg-Gly-Asp or Glu or Lys (H/RGD/E/K) similar to the RGD motif found in extracellular matrix proteins hints towards a possible interaction with integrin-type receptors, the function of this group of proteins related to the carcinoembryonic antigen family is still unknown. It is also not clear whether the various members of the PSG family exert the same function. Here we describe the cloning of two splice variants of Cea4 (Cea4a, Cea4b), a murine PSG family member, which lacks the RGD-related consensus motif. Cea4a, like most of the other rodent PSG members, is composed of three immunoglobulin (Ig) variable-like domains (N1-N3) and and one Ig constant-like domain (A). In contrast, Cea4b lacks the N2 domain (N1N3A), demonstrating for the first time that PSG isoforms produced by alternative splicing also exist in mice. The mRNAs coding for Cea4a and Cea4b exhibit the same expression kinetics during placental development as found for two other murine PSGs, Cea2 and Cea3, which contain the RGD-like motif. Expression starts after day 12.5 of embryonic development (E12.5) and maximum steady-state levels are reached around E15.5-E17.5 as determined by RNase protection analyses. At E17.5, PSG transcripts can be detected exclusively in the spongiotrophoblast of the placenta. In addition, PCR analyses revealed that Cea2, Cea3, and Cea4 transcripts are also found in RNA from a pool of embryos (E12-E15) but are absent from a number of adult tissues tested (kidney, lung, testis, ovary, liver, brain, thymus, heart, spleen). These results indicate that the various PSG isoforms exert their function(s) at the same time during placental and embryonic development.

Analyses of cis-acting and trans-acting elements that are crucial to sustain pregnancy-specific glycoprotein gene expression in different cell types

Pregnancy-specific beta 1 glycoprotein genes (PSG) are mainly expressed during human placental development, though their expression has been reported in other normal and pathological tissues, e.g. hydatidiform mole (HM), of distinct origins. However, the molecular components implicated in the regulation of PSG are not well understood. To identify some of the regulatory elements involved in the transcriptional control of PSG expression, the DNA-protein interactions and the basal activities of the TATA-box-less PSG5 promoter were determined in different tissues and cell types. In DNAse-I protection assays, DNA-binding proteins from human term placenta (HTP) protected a region of 27 bp located from nucleotides --150 to --124, overlapping the farthest 5' upstream cap site and resembling an initiator-like element. In electrophoretic mobility shift assays (EMSA), three complexes were detected using nuclear extracts from HTP and an oligonucleotide containing the 27-bp motif. In situ ultraviolet crosslinking analysis of the specific complexes revealed that two proteins of 78.0 kDa and 53.0 kDa are involved in such interactions, in accordance with the bands of 80.0 kDa and 57.5 kDa observed by Southwestern blotting. Competitive EMSA using mutant oligonucleotides with the substitution of 5'ACCCAT3' by 5'GATATC3' within the 27-bp motif revealed that this sequence is fundamental for the formation of the specific DNA-protein complexes. We show in transient transfection experiments performed in HeLa, COS-7 and JEG-3 cells, that such mutation completely abolished the transcriptional activity of the PSG5 promoter, independently of the cell type. Moreover, this mutation disrupted the formation of the specific DNA-protein complexes which were essentially the same as those displayed by HTP. We also determined the binding activities of nucleoproteins derived from placental tissues in earlier developmental and pathological stages, i.e. first trimester placenta (1-TRIM) and HM, respectively, showing that the DNA-binding patterns were different from each other and distinct from those elicited by HTP. Our results indicate that the cis-acting and trans-acting elements analyzed are indispensable to support PSG5 promoter activity in cell lines which do or do not produce PSG. In addition, these elements appear to play a role in the mechanisms involved in PSG basal expression during placental development and differentiation.

Distribution of integrin cell adhesion molecules in endometrial cancer

Integrins are ubiquitous cell adhesion molecules that are involved in maintaining normal tissue morphology and have been implicated in the behavior of certain malignancies. We examined the expression of nine integrin subunits in 38 endometrial adenocarcinomas using immunohistochemistry. The pattern of integrin expression in the cancers was compared with that seen in the endometrium of 20 normal cycling women and 7 postmenopausal women. Integrin expression was correlated with grade, stage, nodal status, depth of invasion, steroid receptor status, and histological pattern. In endometrial cancers there was an inverse relationship between the number of integrins expressed and histological grade (P = 0.011). Of the normally expressed, constitutive endometrial epithelial integrin subunits (alpha 2, alpha 3, alpha 6, and beta 4), the least frequently seen in the cancers was the alpha 3 subunit (44.7%) and the most frequently found was alpha 6 (81.6%). The alpha 5 beta 1 integrin, a fibronectin receptor normally found only on endometrial stromal cells, was seen in 17.8% of cases of these epithelial cancers. In addition, a significant association was found between the loss of the alpha 2 beta 1 integrin and the presence of lymph node metastases (P < 0.001). These data suggest that a decline in integrin expression occurs more frequently in poorly differentiated endometrial cancers and that the loss of specific integrins may be associated with metastatic nodal spread.

Pregnancy specific beta 1-glycoprotein in human intestine

Pregnancy-specific beta 1-glycoprotein (PSG) transcripts have been identified in a number of placental and non-placental tissues. Using a placental PSG cDNA probe to screen a normal human intestinal cDNA library we have isolated 22 hybridizing clones. These clones could be divided into four groups. Nucleotide sequence analysis showed that one group of clones correspond to functional and another group correspond to non-functional PSG cDNAs. The other two groups are homologous to the nonspecific cross-reacting antigen (NCA) and biliary glycoprotein (BGP), both of which are members of the carcinoembryonic antigen (CEA) family. Thus, PSG, NCA and BGP are co-expressed in normal human intestine. RNA and immunoblot analysis, along with polymerase chain reaction amplification further confirm the expression of PSG in human intestinal tissue.

Infidelity in the structure of ectopic transcripts: a novel exon in lymphocyte dystrophin transcripts

Ectopic (or "illegitimate") transcripts have recently become popular as a means of facilitating the study of transcripts normally considered to have a pattern of expression restricted to one or a few tissues. It has been generally assumed that the structure of an ectopic transcript faithfully represents that of its tissue-specific counterpart. We describe here the inclusion of a novel exon in 50% of ectopic dystrophin transcripts from human peripheral blood lymphocytes. The novel sequence resembles a conserved region in the 3' untranslated region of members of the carcinoembryonic antigen gene family and lies within the first intron of the human dystrophin gene. This constitutes a significant departure from the expected in vivo splicing behaviour in an ectopic transcript and suggests that there may be exceptions to the assumption that ectopic transcripts are processed in a similar way to their tissue-specific counterparts.

Nucleotide sequence of a pregnancy-specific beta 1 glycoprotein gene family member. Identification of a functional promoter region and several putative regulatory sequences

The pregnancy-specific beta 1 glycoprotein (PSG) genes encode a group of heterogeneous proteins produced in large amounts by the human syncytiotrophoblast. Their expression seems to be regulated at the transcriptional level during normal pregnancy. In the present work, we isolated from a human placental library a 17 kb genomic fragment corresponding to a member of the PSG multigene family. DNA sequence analysis of 1190 nucleotides upstream of the translational start and of the first intron, revealed the presence of several putative regulatory sequences. In a transient chloramphenicol acetyltransferase expression assay, 5' flanking sequences within 123 nucleotides upstream to the first major transcription initiation site, functioned as a strong promoter in COS-7 cells. Meanwhile, sequences 5' further upstream had the ability to abolish this promoter activity. The sequence analyzed did not contain any obvious TATA-like boxes or G+C-rich regions, suggesting the existence of unique promoter elements implicated in transcription initiation and regulation of this PSG gene family member.

Characterization of a major member of the rat pregnancy-specific glycoprotein family

The gene encoding the human pregnancy-specific glycoprotein (PSG) belongs to a gene subfamily, comprised of the carcinoembryonic antigen (CEA) and PSG subgroups, within the immunoglobulin superfamily. To study the functional roles of PSG during development in an animal model, we isolated and characterized a near full-length cDNA (rnCGM6) encoding a PSG-related protein from a rat placental cDNA library. rnCGM6 is 2,068 bp in length and contains an open reading frame that encodes a 475-amino-acid polypeptide with a predicted molecular mass of 53 kD. The 5' noncoding sequence is 173 nucleotides, and primer-extension experiments demonstrate that the transcriptional initiation site is located 22-24 nucleotides further upstream. The 3' noncoding sequence contains 470 nucleotides which is followed by a poly(A) tail. In contrast to human PSGs, which contain one immunoglobulin variable-like and two to three immunoglobulin constant-like protein domains, rnCGM6 contains three immunoglobulin variable-like domains and one immunoglobulin constant-like domain. rnCGM6 contains six potential N-linked glycosylation sites and, in its carboxyl-terminal domain, a tyrosine protein kinase phosphorylation site. The tyrosine phosphorylation site is conserved among all rat and human PSG members. rnCGM6 hybridized with a major 2.5-kb and two minor 3.0- and 3.5-kb mRNAs, all primarily expressed in the rat placenta. Ribonuclease protection analysis, using probes specific to the 5', middle, and 3' regions of rnCGM6, and the 5' region of a previously identified cDNA, rnCGM1, mainly yielded fully-protected fragments indicating relatively low sequence similarity among rat PSG-related proteins. Northern hybridization and ribonuclease protection assays also suggest that rnCGM6 may be the major PSG member in rat.

Carcinoembryonic antigen gene family: molecular biology and clinical perspectives

The carcinoembryonic antigen (CEA) gene family belongs to the immunoglobulin super-gene family and can be divided into two main subgroups based on sequence comparisons. In humans it is clustered on the long arm of chromosome 19 and consists of approximately 20 genes. The CEA subgroup genes code for CEA and its classical crossreacting antigens, which are mainly membrane-bound, whereas the other subgroup genes encode the pregnancy-specific glycoproteins (PSG), which are secreted. Splice variants of individual genes and differential post-translational modifications of the resulting proteins, e.g., by glycosylation, indicate a high complexity in the number of putative CEA-related molecules. So far, only a limited number of CEA-related antigens in humans have been unequivocally assigned to a specific gene. Rodent CEA-related genes reveal a high sequence divergence and, in part, a completely different domain organization than the human CEA gene family, making it difficult to determine individual gene counterparts. However, rodent CEA-related genes can be assigned to human subgroups based on similarity of expression patterns, which is characteristic for the subgroups. Various functions have been determined for members of the CEA subgroup in vitro, including cell adhesion, bacterial binding, an accessory role for collagen binding or ecto-ATPases activity. Based on all that is known so far on its biology, the clinical outlook for the CEA family has been reassessed.