Cloning of the complete gene for carcinoembryonic antigen: analysis of its promoter indicates a region conveying cell type-specific expression

A Novel ssDNA Aptamer Targeting Carcinoembryonic Antigen: Selection and Characterization

One of the major causes of a drastically shorter life expectancy and one of the most prevalent diseases in the world today is cancer. Given the data on the rise in cancer cases throughout the world, it is obvious that, despite the diagnostic techniques currently being used, there is a pressing need to develop precise and sensitive techniques for early diagnosis of the disease. A high degree of affinity and specificity towards particular targets is maintained by the short nucleic acid molecules known as aptamers. Aptamers outperform antibodies due to their unique benefits, such as their simplicity in synthesis and modification, lack of toxicity, and long-term stability. Utilizing an accurate recognition element and a robust signal transduction mechanism, molecular diagnostics can be extremely sensitive and specific. In this study, development of new single-stranded DNA aptamers against CEA for use in cancer diagnostics was accomplished using SELEX and NGS methods. As a result of 12 iterative SELEX rounds, nine aptamer candidates against CEA were developed. NGS comparative analysis revealed that round twelve had an enriched number of aptamers that were specifically bound, as opposed to round eight. Among the selected nine sequences characterized by bioinformatics analysis and ELONA, an aptamer sequence with the highest specificity and affinity for the target protein was identified and further examined. Aptamer sequence (6) was screened in a concentration-dependent assay, specificity analysis was performed, and its potential secondary and tertiary structures were predicted, which enabled us to test one of the possible putative interactions with CEA. Finally, aptamer sequence (6) labelled with a Cy5 fluorescent tag was used in confocal microscopy to observe its binding towards the CEA expressed in HT-29 human colon adenocarcinoma cell line.

CEA-Regulated Oncolytic Virus Anticancer Therapy: A Promising Strategy for Rare Solid Tumors

BACKGROUND

Rare solid tumors have attracted much more attention due to the great unmet clinical need, limited treatment options, and poor prognosis. As the most thoroughly studied tumor marker, carcinoembryonic antigen (CEA) can not only overexpress in various common solid tumors, but also in several rare solid tumors. Oncolytic virus therapy has achieved excellent anticancer effects in the past decades. Due to the specific high expression of CEA in certain tumor tissues, but not in normal tissues, CEA has been applied to improve the tumor specificity of gene expression.

METHODS

The studies of CEA expression in rare solid tumors and CEA-regulated oncolytic virus therapy were reviewed.

RESULTS

We showed the types of rare solid tumors with overexpression of CEA. Elevated serum CEA levels can indicate the diagnosis, response of surgery or system therapy, distal metastasis, recurrence, and survival. Due to high tumor specificity, CEA-regulated OA therapy has demonstrated a surprising antitumor effect for common CEA-positive tumors in preclinical trials Conclusion: These data suggested that CEA could be a diagnostic and prognostic biomarker for several rare solid tumors. We proposed the hypothesis that CEA-regulated oncolytic virus therapy could be a promising therapeutic strategy for CEA-positive rare solid tumors.

Anti-colorectal cancer effect of interleukin-2 and interferon-β fusion gene driven by carcinoembryonic antigen promoter

This study was designed to investigate the antitumor effects of combined interleukin-2/interferon-β-based gene therapy in colorectal cancer. Transfection of the fusion gene expression plasmid induced significant apoptosis of Lovo cells. Additionally, the fusion gene exhibited strong inhibitory activity against tumor growth and apoptosis when being injected into the nude mice implanted with human colon cancer cells. Furthermore, the tail-vein injection showed a more notable effect than direct injection into tumor. These results suggest that the combined interleukin-2/interferon-β-based gene therapy with the carcinoembryonic antigen promoter might be an effective antitumor strategy.

Potent and specific antitumor effect for colorectal cancer by CEA and Rb double regulated oncolytic adenovirus harboring ST13 gene

Cancer Targeting Gene-Viro-Therapy (CTGVT) is constructed by inserting an antitumor gene into an oncolytic virus (OV). It is actually an OV-gene therapy, which has much better antitumor effect than either gene therapy alone or virotherapy alone in our previously published papers. This study is a modification of CTGVT by inserting a colorectal cancer (CRC) specific suppressor gene, ST13, into a CRC specific oncolytic virus, the Ad·CEA·E1A(Δ24), to construct the Ad·(ST13)·CEA·E1A(Δ24) for increasing the targeting tropism to colorectal cancer and it was briefly named as CTGVT-CRC. Although many studies on CEA promoter and ST13 gene were reported but no construct has been performed to combine both of them as a new strategy for colorectal cancer (CRC) specific therapy. In addition to the CRC specificity, the antitumor effect of Ad·(ST13)·CEA·E1A(Δ24) was also excellent and got nearly complete inhibition (not eradication) of CRC xenograft since ST13 was an effective antitumor gene with less toxicity, and a Chinese patent (No. 201110319434.4) was available for this study. Ad·(ST13)·CEA·E1A(Δ24) caused cell apoptosis through P38 MAPK (i.e. P38) which upregulated CHOP and ATF2 expression. The mitochondrial medicated apoptosis pathway was activated by the increase of caspase 9 and caspase 3 expression.

Differentiating rectal carcinoma by an immunohistological analysis of carcinomas of pelvic organs based on the NCBI Literature Survey and the Human Protein Atlas database

The treatments and prognoses of pelvic organ carcinomas differ, depending on whether the primary tumor originated in the rectum, urinary bladder, prostate, ovary, or uterus; therefore, it is essential to diagnose pathologically the primary origin and stages of these tumors. To establish the panels of immunohistochemical markers for differential diagnosis, we reviewed 91 of the NCBI articles on these topics and found that the results correlated closely with those of the public protein database, the Human Protein Atlas. The results revealed the panels of immunohistochemical markers for the differential diagnosis of rectal adenocarcinoma, in which [+] designates positivity in rectal adenocarcinoma and [-] designates negativity in rectal adenocarcinoma: from bladder adenocarcinoma, CDX2[+], VIL1[+], KRT7[-], THBD[-] and UPK3A[-]; from prostate adenocarcinoma, CDX2[+], VIL1[+], CEACAM5[+], KLK3(PSA)[-], ACPP(PAP)[-] and SLC45A3(prostein)[-]; and from ovarian mucinous adenocarcinoma, CEACAM5[+], VIL1[+], CDX2[+], KRT7[-] and MUC5AC[-]. The panels of markers distinguishing ovarian serous adenocarcinoma, cervical carcinoma, and endometrial adenocarcinoma were also represented. Such a comprehensive review on the differential diagnosis of carcinomas of pelvic organs has not been reported before. Thus, much information has been accumulated in public databases to provide an invaluable resource for clinicians and researchers.

Quantitative analysis of TEM-8 and CEA tumor markers indicating free tumor cells in the peripheral blood of colorectal cancer patients

BACKGROUND

Colorectal cancer (CRC) remains the third most common cancer in the world. Approximately in 50 percent of patients, metastatic disease is a major cause of death. Therefore, early diagnosis of CRC is crucial for a successful outcome. For the detection of circulating cancer cells, this study applied a sensitive method that employed specific tumor markers for early detection.

METHODS

A total of 80 blood samples from 40 CRC patients and 40 age-matched healthy controls were collected for the study. The circulating mRNA levels of two CRC tumor markers, tumor endothelial marker 8 (TEM-8) and carcinoembryogenic antigen (CEA) were evaluated using an absolute quantitative real-time PCR assay in a Stratagene Mx-3000P real-time PCR system. GAPDH was used as the endogenous control.

RESULTS

TEM-8 and CEA were primarily detected more in the CRC patients rather than in the controls: 22/40 vs 9/40, p=0.009 and 30/40 vs 11/40, p=0.00054, respectively. In the CRC patients, the mRNA level of these markers was significantly higher in comparison to the normal controls (p=0.018 and 0.01). The overall sensitivity of this panel was 65% with a specificity of 75%. Statistical analysis for demographic variants did not reach significant values.

CONCLUSIONS

TEM-8 and CEA markers were detected more frequently and in significantly higher levels in the blood samples of patients compared with samples from age-matched healthy controls. The copy number of CEA and TEM-8 mRNA, as detected by a real-time quantitative PCR, appears to be a promising marker for evaluating the risk of tumor spread.

Recombinant carcinoembryonic antigen as a reporter gene for molecular imaging

PURPOSE

Reporter genes can provide a way of noninvasively assessing gene activity in vivo. However, current reporter gene strategies may be limited by the immunogenicity of foreign reporter proteins, endogenous expression, or unwanted biological activity. We have developed a reporter gene based on carcinoembryonic antigen (CEA), a human protein with limited normal tissue expression.

METHODS

To construct a CEA reporter gene for PET, a CEA minigene (N-A3) was fused to the extracellular and transmembrane domains of the human Fc gamma RIIb receptor. The NA3-Fc gamma RIIb recombinant gene, driven by a CMV promoter, was transfected in Jurkat (human T cell leukemia) cells. Expression was analyzed by flow cytometry, immunohistochemistry (IHC), and microPET imaging.

RESULTS

Flow cytometry identified Jurkat clones stably expressing NA3-Fc gamma RIIb at low, medium, and high levels. High and medium NA3-Fc gamma RIIb expression could also be detected by Western blot. Reporter gene positive and negative Jurkat cells were used to establish xenografts in athymic mice. IHC showed staining of the tumor with high reporter gene expression; medium and low N-A3 expression was not detected. MicroPET imaging, using an anti-CEA (124)I-labeled single-chain Fv-Fc antibody fragment, demonstrated that only high N-A3 expression could be detected. Specific accumulation of activity was visualized at the N-A3 positive tumor as early as 4 h. MicroPET image quantitation showed tumor activity of 1.8 +/- 0.2, 15.2 +/- 1.3, and 4.6 +/- 1.2 percent injected dose per gram (%ID/g) at 4, 20, and 48 h, respectively. Biodistribution at 48 h demonstrated tumor uptake of 4.8 +/- 0.8%ID/g.

CONCLUSION

The CEA N-A3 minigene has the potential to be used as a reporter gene for imaging cells in vivo.

In vitro evaluation of cancer-specific NF-kappaB-CEA enhancer-promoter system for 5-fluorouracil prodrug gene therapy in colon cancer cell lines

Nuclear factor-kappa B (NF-κB) is a transcription factor with high transcriptional activity in cancer cells. In this study, we developed a novel enhancer–promoter system, κB4-CEA205, in which the basal carcinoembryonic antigen (CEA) promoter sequence (CEA205) was placed downstream of the four tandem-linked NF-κB DNA-binding sites (κB4). In combination with a κB4 enhancer, the transcriptional activity of the CEA promoter was significantly enhanced (three- to eight-fold) in cancer cell lines but not in normal cells. In cancer cell lines, the transcriptional activity of κB4-CEA205 was comparable with that of the SV40 promoter. We also constructed vectors in which the thymidine phosphorylase (TP) cDNA was under the control of CEA205, κB4, κB4-CEA205 and CMV promoters, respectively. TP protein and enzyme activity were detected at comparable levels in κB4-CEA205- and CMV-driven TP cDNA-transfected cancer cell lines (H630 and RKO). The κB4-TP and CEA205-TP-transfected cell lines, respectively, only demonstrated negligible and low levels of TP protein and enzyme activity. Both CMV- and κB4-CEA205-driven TP cDNA transiently transfected cells were 8- to 10-fold sensitised to 5-fluorouracil (5-FU) prodrug, 5′-deoxy-5-fluorouradine (5′-DFUR), in contrast to only 1.5- to 2-fold sensitised by the κB4- and CEA205-driven TP cDNA-transfected cells. The bystander killing effect of CMV- and κB4-CEA205-driven TP cDNA-transfected cells was comparable. This is the first report that indicates that the NF-κB DNA-binding site could be used as a novel cancer-specific enhancer to improve cancer-specific promoter activity in gene-directed enzyme prodrug therapy.

Transcription activity of ectogenic human carcinoembryonic antigen promoter in lung adenocarcinoma cells A549

The transcription activity of ectogenic human carcinoembryonic antigen (CEA) promoter in lung adenocarcinoma cells A549 was investigated for the further gene-targeting therapy. The reporter gene green fluorescent protein (GFP) driven by CEA promoter and human cytomegalovirus (CMV) promoter were relatively constructed and named plasmid pCEA-EGFP and pCMV-GFP respectively. The intensity of fluorescence was detected by fluorescence microscope and flow cytometry analysis after the pCEA-GFP and pSNAV-GFP plasmids were transfected into A549 cells through liposome respectively. The results showed (4.08+/-0.63) % of the A549 cells transfected with pCEA-AFP plasmid expressed, significantly lower than that of the A549 cells transfected with pCMV-GFP [(43.27+/-3.54) %]. It was suggested that ectogenic human CEA promoter in lung adenocarcinoma cells A549 was weakly expressed. The distinct specificity of CEA promoter in CEA high expression cells was regarded as a tool in selective gene therapy, but the transcription activity of ectogenic human CEA promoter was needed to increase in the future.

Expression of CD44v6 gene in normal human peripheral blood

AIM: To investigate if CD44v6 could be used as a molecular marker of cancer progression and metastasis through the detection of CD44v6 gene expression in normal human peripheral blood.

METHODS: RNA was extracted from the peripheral blood mononuclear cells of 50 healthy donors, the expression of CD44v6 was investigated using reverse transcriptase-polymerase chain reaction (RT-PCR).

RESULTS: CD44v6 mRNA was detected in 58% of healthy volunteers under the proper controls.

CONCLUSION: Our results suggest that the measurement of CD44v6 expression in peripheral blood by RT-PCR is not suitable for detection of circulating tumor cells.

Expression of the carcinoembryonic antigen gene is inhibited by SOX9 in human colon carcinoma cells

The human carcinoembryonic antigen (CEA) is overexpressed in many types of human cancers and is commonly used as a clinical marker. In colon cancer, this overexpression protects cells against apoptosis and contributes to carcinogenesis. Therefore, CEA-expressing cells as well as CEA expression itself constitute potential therapeutic targets. In this report, we show that the transcription factor SOX9 down-regulates CEA gene expression and, as a probable consequence, induces apoptosis in the human colon carcinoma cell line HT29Cl.16E.

Molecular detection of disseminated tumor cells in the peripheral blood in patients with gastrointestinal cancer

PURPOSE

In this study, 62 preoperative peripheral blood samples from patients with gastrointestinal carcinomas, 12 healthy volunteers, and ten patients with inflammatory gastrointestinal diseases were analyzed for the determination of CEA, CK19, and CK20 mRNA expression in peripheral blood, and its clinical significance was evaluated.

METHODS

Nested reverse transcriptase-polymerase chain reaction (nested RT-PCR) was used to analyze CEA, CK19, and CK20 mRNA expression in peripheral blood. Fresh tumor tissues from patients with colorectal cancer (n=15) were used as a positive control.

RESULTS

Among 62 blood samples from patients with gastrointestinal cancer, the expression of CEA, CK19, and CK20 mRNA was 51.6% (32/62), 35.5% (22/62), and 48.4% (30/62), respectively. 74.2% (46/62) were positive for at least one marker. Fifteen tumor tissues were all positive for CEA, CK19, and CK20 mRNA. Only one blood sample from patients with no gastrointestinal carcinoma was positive for CEA mRNA.

CONCLUSION

Our results indicate that the molecular detection of circulating tumor cells in peripheral blood in patients with gastrointestinal carcinoma was significantly correlated with its malignant biological properties, and may be helpful in the selection of clinical treatment and judgment of prognosis.

Differential expression of carcinoembryonic antigen (CEA) splice variants in whole blood of colon cancer patients and healthy volunteers: implication for the detection of circulating colon cancer cells

Quantification of circulating cancer cells in whole blood samples by real time quantitative RT-PCR might be of clinical value for monitoring therapeutic effectiveness. In colon cancer patients, carcinoembrynic antigen (CEA) and cytokeratin 20 (CK20) have been frequently used for RT-PCR based tumor cell detection, but the specificity in particular for CEA has been questioned. In this study, we compared real-time RT-PCR for CEA and CK20 and analysed patients with metastatic disease (n=32) and healthy volunteers (n=17). CK20 mean values were elevated in cancer patients (P<0.001) and defined a subgroup (38%) who showed CK20 levels at least 100-fold above the highest value of the healthy control group. In contrast, only two cancer patients (6%) showed elevated CEA levels. Samples of the healthy control group showed exclusively a CEA-PCR product of 79 degrees C melting temperature. Thirty per cent of the colon cancer patients showed an additional product of 82 degrees C melting temperature. The 82 degrees C product was identical with the amplification product of CEA-cDNA and cDNA from different colon cancer cell lines. Colon cancer cells were spiked into normal blood in 10-fold dilutions that resulted in a dose dependent shift of the melt curve from 79 degrees C to the 82 degrees C. Sequencing of the PCR products showed that white blood cells express a splice variant of CEA, which hinders detection of tumor cell cDNA in whole blood samples. Our findings have implications for the use of CEA as a diagnostic molecule (e.g. by RT-PCR). The discovery of a physiologically expressed CEA splice variant might lead to a better understanding of the biological function of CEA and its family members.

Impact of cytokeratin-20 and carcinoembryonic antigen mRNA detection by RT-PCR in regional lymph nodes of patients with colorectal cancer

The reported rates for tumour cell involvement in the locoregional lymph nodes of colorectal cancer vary greatly, depending on the method used and case selection. In order to further evaluate the clinical value of molecular biologic detection of tumour cells we investigated 102 histologically tumour-free (pN0) regional lymph nodes from 51 consecutive, completely resected (UICC R0) colorectal carcinoma specimens for the presence of tumour cell mRNA by RT-PCR specific for carcinoembryonic antigen (CEA) and cytokeratin 20 (CK-20). Two lymph nodes located nearest to the primary tumour were investigated in each case. CK-20 mRNA was found in 31 of 51 patients (60.8%) and CEA mRNA in 30 of 51 patients (58.8%), respectively. Identical transcription patterns of CK-20 and CEA mRNA (both positive or both negative) were found in 38 of 51 patients (74.5%). There was a significantly higher proportion of cases with CEA positivity in the lymph nodes of tubulopapillary than of mucinous adenocarcinomas (P< 0.03). Detection of CK-20 and CEA mRNA correlated in nine of 12 cases (75.0%) with the risk of tumour recurrence (not significant) and showed a tendency towards shorter disease-free survival by univariate analysis (not significant). Our data indicate that CK-20 and CEA mRNA detection by RT-PCR may prove useful for the prediction of tumour recurrence of patients with pN0 colorectal carcinoma, although neither reach statistical significance in this series of patients.

Ribozyme as an approach for growth suppression of human pancreatic cancer

Ribozymes (catalytic RNAs, RNA enzymes) are effective modulators of gene expression because of their simple structure, site-specific cleavage activity, and catalytic potential, and have potentially important implications for cancer gene therapy. Point mutations in the K-ras oncogene are found in approx 90% of human pancreatic carcinomas, and can be used as potential targets for specific ribozyme-mediated reversal of the malignant phenotype. In this study, we focused on in vitro manipulation of ribozyme targeting of the mutated K-ras oncogene in a human pancreatic carcinoma cell line. We evaluated the efficacy of an anti-K-ras hammerhead ribozyme targeted against GUU-mutated codon 12 of the K-ras gene in cultured pancreatic carcinoma cell lines. The anti-K-ras ribozyme significantly reduced cellular K-ras mRNA level (GUU-mutated codon 12) when the ribozyme was transfected into the Capan-1 pancreatic carcinoma cells. The ribozyme inhibited proliferation of the transfected Capan-1 cells. These results suggested that this ribozyme is capable of reversing the malignant phenotype in human pancreatic carcinoma cells.

Structure of the gene for congenital nephrotic syndrome of the finnish type (NPHS1) and characterization of mutations

Congenital nephrotic syndrome of the Finnish type (NPHS1) is an autosomal recessive disorder that is caused by mutations in the recently discovered nephrin gene, NPHS1 (AF035835). The disease, which belongs to the Finnish disease heritage, exists predominantly in Finland, but many cases have been observed elsewhere in Europe and North America. The nephrin gene consists of 29 exons spanning 26 kb in the chromosomal region 19q13.1. In the present study, the genomic structure of the nephrin gene was analyzed, and 35 NPHS1 patients were screened for the presence of mutations in the gene. A total of 32 novel mutations, including deletions; insertions; nonsense, missense, and splicing mutations; and two common polymorphisms were found. Only two Swedish and four Finnish patients had the typical Finnish mutations: a 2-bp deletion in exon 2 (Finmajor) or a nonsense mutation in exon 26 (Finminor). In seven cases, no mutations were found in the coding region of the NPHS1 gene or in the immediate 5'-flanking region. These patients may have mutations elsewhere in the promoter, in intron areas, or in a gene encoding another protein that interacts with nephrin.

Non-radioactive hybridization in microwells using enzyme linked immune sorbent assay for detection of RT-PCR-amplified CK19- and CEA-mRNA

PCR enzyme linked immune sorbent assay (ELISA) was developed for detection of RT-PCR-amplified cytokeratin 19 (CK19) mRNA and carcinoembryonic antigen (CEA) mRNA. The non-radioactive hybridization was performed in a streptavidin-coated microwell with digoxigenin-labeled PCR products and with biotin-labeled capture probe. PCR ELISA was proved to be expedient, simple, sensitive and safe for identification of CK19-, CEA-RT-PCR products. These results were proven by sequencing.

Detection of colonic cells in peripheral blood of colorectal cancer patients by means of reverse transcriptase and polymerase chain reaction

Circulating tumour cells play a central role in the metastatic process, but little is known about the relationship between this cellular subpopulation and the development of secondary disease. This study was aimed at assessing the presence of colonic cells in peripheral blood of patients with colorectal cancer in different evolutionary stages, by means of reverse transcriptase polymerase chain reaction (RT-PCR) targeted to carcinoembryonic antigen (CEA) mRNA. In vitro sensitivity was established in a recovery experiment by preparing serial colorectal cancer cell dilutions. Thereafter, 95 colorectal cancer patients and a control group including healthy subjects (n=11), patients with other gastrointestinal neoplasms (n=11) or inflammatory bowel disease (n=9) were analysed. Specific cDNA primers for CEA transcripts were used to apply RT-PCR to peripheral blood samples. Tumour cells were detected down to five cells per 10 ml blood, thus indicating a sensitivity limit of approximately one tumour cell per 10(7) white blood cells. CEA mRNA expression was detected in 39 out of 95 colorectal cancer patients (41.1%), there being a significant correlation with the presence of distant metastases at inclusion. None of the healthy volunteers and only 1 of 11 patients (9.1%) with other gastrointestinal neoplasms had detectable CEA mRNA in peripheral blood. By contrast, CEA mRNA was detected in five of the nine patients (55.6%) with inflammatory bowel disease. These results confirm that it is feasible to amplify CEA mRNA in the peripheral blood, its presence being almost certainly derived from circulating malignant cells in colorectal cancer patients. However, CEA mRNA detectable in blood of patients with inflammatory bowel disease suggests the presence of circulating non-neoplastic colonic epithelial cells.

Targeted gene transfer for adenocarcinoma using a combination of tumor-specific antibody and tissue-specific promoter

We have developed a highly specific gene transfer method for adenocarcinoma using a monoclonal antibody against tumor-specific antigen coupled with a plasmid containing the carcinoembryonic antigen (CEA)-specific promoter. The chimeric CEA promoter (CC promoter), which contained an enhancer from the immediate early gene of cytomegalovirus and the CEA promoter, achieved 4- to 5-fold higher transgene expression in CEA-producing cells than the original CEA promoter while maintaining CEA specificity. Furthermore, a complex of a monoclonal antibody against Lewis Y antigen (LYA), the CC promoter-containing plasmid and cationic liposomes (DOTAP) achieved specific gene expression in CEA-producing and LYA-positive adenocarcinoma cell lines that was 200-fold more efficient than in CEA-non-producing and LYA-negative cell lines during a short in vitro incubation. This strategy may be applicable for clinical gene therapy.

In vivo adenovirus-mediated prodrug gene therapy for carcinoembryonic antigen-producing pancreatic cancer

In gene therapy for malignancy, the herpes simplex virus thymidine kinase (HSVtk)-ganciclovir (GCV) system has been widely used. For pancreatic cancer targeting, we estimated the therapeutic efficacy of gene transduction by an adenovirus-carrying HSVtk gene under the control of a carcinoembryonic antigen (CEA) promoter (AdCEAtk) followed by systemic administration of GCV. Four cell lines, CEA-producing Su.86.86. BxPC-3 (pancreatic cancer cells), MKN45 (gastric cancer cells) and CEA-nonproducing HeLa, were used for analysis of GCV sensitivity induced by adenoviral gene transduction. To evaluate the therapeutic efficacy of AdCEAtk and GCV administration in human CEA-positive pancreatic cancer in vivo, a subcutaneously implanted tumor-bearing nude mouse model was used. When the HSVtk gene was transduced with a ubiquitous promoter into these cells, increase of the GCV sensitivity was independent of CEA-production. In contrast, when the cells were transduced with a CEA promoter, the cell-killing effect of GCV was increased in only CEA-producing cells. For in vivo analysis, AdCEAtk was delivered into subcutaneously established tumors of Su.86.86 cells. Immunohistochemical staining of the tumor showed that HSVtk protein was expressed only in tumor cells, and tumor growth was markedly suppressed by administration of GCV. These results suggest that the adenovirus-mediated transfer of HSVtk gene with CEA promoter specifically increases the GCV sensitivity of CEA-producing pancreatic cancer cells in vitro and in vivo. This strategy may provide a useful tool for treating pancreatic cancer, especially CEA-producing tumor cells.

Transcripts from opposite strands of gamma satellite DNA are differentially expressed during mouse development

Using in vitro immuno-selected retinoic acid response elements, we have isolated mouse genomic clones containing major (gamma) satellite DNA repeats that are considered as typical of chromosome centromeres. Several cDNA clones were then isolated from a F9 cell cDNA library and were found to harbor variants of the 234-base pair consensus gamma satellite monomer. In Northern analysis, these satellite DNA sequences hybridized predominantly to an approximately 1.8-kb RNA species in polyadenylated RNA from P19 cells. These transcripts were strongly repressed by retinoic acid, and nuclear run-on assays revealed that this repression was, at least in part, mediated at the transcriptional level. Satellite transcripts were also detected in HeLa cells, where they were similarly down-regulated by retinoids. Heterogeneously sized satellite transcripts were detected in RNA from specific mouse tissues, such as fetuses (but not placenta), adult liver, and testis. In situ hybridization analysis revealed that satellite transcripts are generated from opposite DNA strands and are differentially expressed in cells of the developing central nervous system as well as in adult liver and testis. These data may have implications on retinoic acid-mediated transcriptional regulation and centromere function.

Bgp2, a new member of the carcinoembryonic antigen-related gene family, encodes an alternative receptor for mouse hepatitis viruses

Murine coronaviruses such as mouse hepatitis virus (MHV) infect mouse cells via cellular receptors that are isoforms of biliary glycoprotein (Bgp) of the carcinoembryonic antigen gene family (G. S. Dveksler, C. W. Dieffenbach, C. B. Cardellichio, K. McCuaig, M. N. Pensiero, G.-S. Jiang, N. Beauchemin, and K. V. Holmes, J. Virol. 67:1-8, 1993). The Bgp isoforms are generated through alternative splicing of the mouse Bgp1 gene that has two allelic forms called MHVR (or mmCGM1), expressed in MHV-susceptible mouse strains, and mmCGM2, expressed in SJL/J mice, which are resistant to MHV. We here report the cloning and characterization of a new Bgp-related gene designated Bgp2. The Bgp2 cDNA allowed the prediction of a 271-amino-acid glycoprotein with two immunoglobulin domains, a transmembrane, and a putative cytoplasmic tail. There is considerable divergence in the amino acid sequences of the N-terminal domains of the proteins coded by the Bgp1 gene from that of the Bgp2-encoded protein. RNase protection assays and RNA PCR showed that Bgp2 was expressed in BALB/c kidney, colon, and brain tissue, in SJL/J colon and liver tissue, in BALB/c and CD1 spleen tissue, in C3H macrophages, and in mouse rectal carcinoma CMT-93 cells. When Bgp2-transfected hamster cells were challenged with MHV-A59, MHV-JHM, or MHV-3, the Bgp2-encoded protein served as a functional MHV receptor, although with a lower efficiency than that of the MHVR glycoprotein. The Bgp2-mediated virus infection could not be inhibited by monoclonal antibody CC1 that is specific for the N-terminal domain of MHVR. Although CMT-93 cells express both MHVR and Bgp2, infection with the three strains of MHV was blocked by pretreatment with monoclonal antibody CC1, suggesting that MHVR was the only functional receptor in these cells. Thus, a novel murine Bgp gene has been identified that can be coexpressed in inbred mice with the Bgp1 glycoproteins and that can serve as a receptor for MHV strains when expressed in transfected hamster cells.

Genomic organization of the melanoma-associated glycoprotein MUC18: implications for the evolution of the immunoglobulin domains

The cell surface glycoprotein MUC18, a member of the immunoglobulin superfamily and homologous to several cell adhesion molecules, is associated with tumor progression and the development of metastasis in human malignant melanoma. Immunohistochemical and Northern blot analysis revealed that expression of the antigen is restricted to advanced primary and metastatic melanomas and to cell lines of the neuroectodermal lineage. The genomic sequence encoding the cell surface antigen spans approximately 14 kb and consists of 16 exons. The organization of the gene, which is related to that of the neural cell adhesion molecule N-CAM, shows a structure where each immunoglobulin-related domain is encoded by more than one exon. Sequencing of the putative MUC18 promoter region revealed a G + C-rich promoter lacking conventional TATA and CAAT boxes. Several motifs for binding of transcription factor Sp1 are present in the regulatory region, and only a single transcription start site within a presumed initiator sequence was identified. Sequence elements which might confer melanocyte-specific expression were not detected. Instead, recognition sequences for the transcription factors CREB, AP-2, and c-Myb, as well as CArG-box motifs, were observed. These elements may contribute to the differential regulation of the MUC18 gene in normal and malignant tissues and suggest a role for this putative adhesion molecule in neural crest cells during embryonic development.

Expression of the Bgp gene and characterization of mouse colon biliary glycoprotein isoforms

The biliary glycoprotein (BGP)-encoding gene is a member of the human carcinoembryonic antigen (CEA) gene family. We have now cloned several mouse Bgp cDNAs from an outbred CDR-1 mouse colon cDNA library, as well as by reverse transcription-PCR amplification of colon RNA. The distinguishing features of the deduced Bgp protein isoforms are found in the two divergent N-terminal domains, the highly conserved internal C2-set immunoglobulin domains, and an intracytoplasmic domain of either 10 or 73 amino acids (aa). The cDNA structures suggest that these mRNAs are produced through alternative splicing of a Bgp gene and the usage of multiple transcriptional terminators. The Bgp deduced aa sequences are highly homologous to several well characterized rat hepatocyte proteins such as the cell CAM105/ecto-ATPase/pp120/HA4 proteins. Oligodeoxyribonucleotide probes representing the various cDNA isoform domains revealed predominant transcripts of 1.8, 3.1 and 4.0 kb on Northern analyses of mouse colon RNA; some of these bands are actually composed of several co-migrating transcripts. The transcripts encoding the long intracytoplasmic-tailed Bgp proteins are expressed at one-tenth the relative abundance of the shorter-tailed species. We have previously demonstrated that several mouse Bgp cDNAs, when transfected into eukaryotic cells, express BGP proteins at the cell surface and function in vitro as cell adhesion molecules, much like their human and rat counterparts. The expression of the many Bgp isoforms at the surface of epithelial cells, such as colon, suggests that these proteins play a determinant role, through self- or heterologous contact, in renewal and/or differentiation of their epithelia.

Assembly and analysis of cosmid contigs in the CEA-gene family region of human chromosome 19

The carcinoembryonic antigen (CEA)-like genes are members of a large gene family which is part of the immunoglobulin superfamily. The CEA family is divided into two major subgroups, the CEA-subgroup and the pregnancy-specific glycoprotein (PSG)-subgroup. In the course of an effort to develop a set of overlapping cosmids spanning human chromosome 19, we identified 245 cosmids in a human chromosome 19 cosmid library (6-7X redundant) by hybridization with an IgC-like domain fragment of the CEA gene. A fluorescence-based restriction enzyme digest fingerprinting strategy was used to assemble 212 probe-positive cosmids, along with 115 additional cosmids from a collection of approximately 8,000 randomly selected cosmids, into five contigs. Two of the contigs contain CEA-subgroup genes while the remaining three contigs contain PSG-subgroup genes. These five contigs range in size from 100 kb to over 300 kb and span an estimated 1 Mb. The CEA-like gene family was determined by fluorescence in situ hybridization to map in the q13.1-q13.2 region of human chromosome 19. Analysis of the two CEA-subgroup contigs provided verification of the contig assembly strategy and insight into the organization of 9 CEA-subgroup genes.

Characterization of murine carcinoembryonic antigen gene family members

The carcinoembryonic antigen (CEA) is a human tumor marker whose gene belongs to a family with more than 20 members. This gene family codes for a group of proteins with in vitro cell adhesion properties and for a group of abundantly expressed pregnancy-specific glycoproteins (PSG) with unknown functions. As a basis for in vivo functional studies, we have started to analyze the murine CEA gene family and have identified five new members (Cea-2 to Cea-6). cDNA clones were isolated for Cea-2, Cea-3, and Cea-6. The deduced amino acid sequences of Cea-2 and Cea-6 indicate three IgV-like (N), followed by one IgC-like (A) domain (N1-N2-N3-A). We have also partially characterized the Cea-2 gene and two additional ones, Cea-4 and Cea-5. Cea-2 and Cea-4 are separated by only 16 kb, suggesting a close linkage of murine CEA-related genes, as found for the human CEA gene family. Cea-5 was located to the proximal region of mouse Chromosome (Chr) 7, which is syntenic to part of human Chr 19, containing the human CEA gene family cluster. Cea-2, Cea-3, and a Cea-4-like gene are differentially transcribed in the placenta during pregnancy, but not in other organs tested. This expression pattern strongly suggests that they represent counterparts of the human PSG subgroup members, despite the presence of multiple IgV-like domains, a feature not found for human PSGs. The more distantly related Cea-5 seems to be ubiquitously expressed. The putative promoter region of Cea-2 lacks typical TATA- or CAAT-boxes, but contains other conserved motifs that could play a role in the initiation of transcription.

Isolation and characterization of the genomic human CD7 gene: structural similarity with the murine Thy-1 gene

The human CD7 molecule is a 40-kDa member of the immunoglobulin gene superfamily that is expressed on T-lymphoid and myeloid precursors in fetal liver and bone marrow. CD7 is also expressed on T lymphocytes in multiple stages of T-cell development, including a major subset of mature peripheral T cells. In this paper we report the isolation and characterization of the human CD7 gene and 5' flanking region. Sequence analysis revealed that the CD7 gene comprises four exons that span 3.5 kilobases. The 5' flanking region (506 base pairs) has a high G + C content and no "TATA" or "CCAAT" elements. DNase I sensitivity analysis of chromatin from the CD7+ progenitor cell leukemia line, DU528, and the CD7-, CD4+, CD8+, TCR alpha beta + T-cell line, DU980 (where TCR is the T-cell receptor), revealed two distinct hypersensitive sites 5' of the CD7 gene. Hypersensitive site 1, present in the DU980 T-cell line, was located 4.5 kilobases upstream of the presumed CD7 transcription initiation site. Only DNase I hypersensitive site 2, which mapped to the promoter region, was found in the DU528 line. Comparison of the organization of the CD7 gene with that of other members of the immunoglobulin gene superfamily revealed that the human CD7 gene most closely resembles the murine Thy-1 gene. Both CD7 and Thy-1 are encoded by small genes with four exons, contain TATA-less promoters, and have a similar functional organization. These structural similarities suggest that human CD7 and murine Thy-1 may be functional homologues.