Alterations of the ocular surface epithelial MUC16 and goblet cell MUC5AC in patients with atopic keratoconjunctivitis

BACKGROUND

An increased understanding of the ocular surface at cellular level in the conjunctiva and the cornea may help explain the pathogenesis and the subsequent clinical appearance of atopic ocular allergies, which may be potentially blinding.

PURPOSE

To investigate the MUC16 and MUC5AC alterations, tear function and the ocular surface disorder in patients with atopic keratoconjunctivitis (AKC).

METHODS

Thirty-six eyes of 18 AKC patients as well as 28 eyes of 14 age- and sex-matched normal subjects were studied. The subjects underwent corneal sensitivity measurements, Schirmer test, tear film break-up time (BUT), fluorescein and Rose-Bengal staining of the ocular surface, conjunctival impression cytology and brush cytology. Impression cytology samples underwent periodic acid schiff and immunohistochemical staining with MUC16 and MUC5AC antibodies. Brush cytology specimens underwent evaluation for inflammatory cell numbers and quantitative real-time polymerase chain reaction (PCR) for MUC16 and MUC5AC mRNA expression.

RESULTS

The mean corneal sensitivity and BUT values were significantly lower in patients with AKC, compared with controls (P < 0.001). Brush cytology specimens from AKC patients revealed significantly higher numbers of inflammatory cells (P < 0.001). Specimens from patient eyes showed positive staining for MUC5AC and MUC16. MUC16 mRNA expression was significantly upregulated with significant downregulation of MUC5AC mRNA expression in eyes with AKC compared with the eyes of control subjects.

CONCLUSION

Ocular surface inflammation, decline in corneal sensitivity, tear film instability, changes in conjunctival epithelial MUC5AC and MUC16 mRNA expressions were thought to be important in the pathogenesis of atopic ocular surface disease.

Regulation of membrane-associated mucins in the human corneal epithelial cells by dexamethasone

PURPOSE

To study the influence of dexamethasone on membrane-associated mucins produced by human corneal epithelial cells.

METHODS

Human corneal epithelial cells were cultured in medium supplemented with various concentrations of dexamethasone (ranging from 10 to 10 M). Reverse transcription-polymerase chain reaction (RT-PCR) and Western blot analysis using monoclonal antibodies specific for human MUC1 (HMFG-1), MUC4 (1G8), and MUC16 (OC125) were performed to evaluate the effect of dexamethasone on membrane-associated mucin expression. The effect of glucocorticoid receptor antagonist (RU38486) on dexamethasone-induced mucin expression was estimated.

RESULTS

RT-PCR revealed that MUC1 and MUC16 gene expression were upregulated 48 hours after addition of dexamethasone and that MUC4 gene expression was downregulated in the same condition. Western blot analysis showed that MUC1 and MUC16 proteins were increased after addition of dexamethasone. However, MUC4 was not detected by anti-MUC4 monoclonal antibody (1G8) for ASGP-2 under our conditions. Treatment with RU38486 inhibited the changes of MUC1, MUC4, and MUC16 by dexamethasone; thus, the effect of dexamethasone on mucin expression is mediated by glucocorticoid receptors.

CONCLUSIONS

This study shows that MUC1, MUC4, and MUC16 are regulated differently by dexamethasone in human corneal epithelial cells. External application of dexamethasone might affect the precorneal mucin.

Multi-layered culture of primary human conjunctival epithelial cells producing MUC5AC

The purpose of our study was to establish a system for culturing normal human conjunctival epithelial (NHCE) cells under serum-free culture conditions without compromising their ability to differentiate into a mucous epithelium. To this end, small pieces of normal conjunctiva were biopsied from patients undergoing cataract surgery. Obtained NHCE cells were cultured in bronchial epithelial growth medium (BEGM) under serum free culture conditions and passage 3 cells were air-lifted. Cultured NHCE cells displayed typical epithelial morphology. Expression of cytokeratin 19 and conjunctival epithelial specific carbohydrate residue were detected. Air-lifted NHCE cells demonstrated an increase in stratification and differentiation into goblet cells up to 3weeks under air-liquid interface (ALI) culture condition. NHCE cells expressed MUC1, MUC4, MUC16, and MUC5AC mRNA, and MUC5AC production and secretion increased in a time dependent manner after culture under ALI conditions. Exposure of cells to proinflammatory cytokines (TNF-alpha or IFN-gamma) resulted in upregulation of MUC1, MUC4, MUC16, and MUC5AC gene expression. In conclusion, differentiated NHCE cells showed features of a multi-layered conjunctival epithelium, including goblet cells, and retained functional characteristics similar to those seen in vivo. This cell culture system can better facilitate investigation of conjunctival epithelial cell biology and goblet cell differentiation.

Early CA-125 fluctuations in patients with recurrent ovarian cancer receiving chemotherapy

The objective of this study was to analyze retrospective populations with recurrent ovarian cancer to assess differences in CA-125 patterns during chemotherapy. The populations included all patients treated between January 1994 and January 2004, who received liposomal doxorubicin and topotecan, and all patients treated between July 1997 and June 2001, who received carboplatin. Prognostic variables were abstracted from the medical records. Eighty-nine patients received liposomal doxorubicin and topotecan therapy and 21 received carboplatin; of these, 59 (liposomal doxorubicin), 60 (topotecan), and 17 (carboplatin) patients had evaluable CA-125 patterns. Patients given liposomal doxorubicin were more likely to have received only one or two cycles of therapy (37/89 [42%]) than patients receiving either carboplatin (5/21 [24%]) or topotecan (20/89[22%]). In cycle 1, CA-125 increases in patients were carboplatin, 4/17 (24%); liposomal doxorubicin, 41/59 (69%); and topotecan, 11/60 (18%). In cycle 2, CA-125 increases were carboplatin, 2/16 (13%); liposomal doxorubicin, 19/37 (51%); and topotecan, 9/50 (18%). In cycle 3, CA-125 increases were carboplatin, 0/12 (0%); liposomal doxorubicin, 7/23 (30%); and topotecan, 6/38 (16%). Of patients having any CA-125 decrease and given two or more cycles, fewer declines were seen in those given liposomal doxorubicin precycle 2 (18/35[51%]) than in those given carboplatin (13/16[81%]) or topotecan (49/56[88%]). The most prominent delay in CA-125 decline was in patients given liposomal doxorubicin compared with those given topotecan or carboplatin. In the entire population, only 3 of 107 (2.8%) patients demonstrated first CA-125 decline precycle 4. Discontinuation of therapy solely on the basis of early CA-125 increase (precycle 3), particularly with liposomal doxorubicin chemotherapy, may exclude some patients who will benefit from continued therapy.

Carcinomas of ovary and lung with clear cell features: can immunohistochemistry help in differential diagnosis?

Metastatic lung carcinomas with clear cell morphology can be confused with primary ovarian clear cell carcinomas. We performed immunohistochemical stains in 14 cases of non-small cell lung carcinomas with clear cell features and 14 cases of ovarian clear cell carcinomas using a panel of markers, including thyroid transcription factor 1 (TTF-1), carcinoembryonic antigen (CEA), Wilms tumor gene 1, octamer-binding transcription factor 4 (OCT-4), cancer antigen 125 (CA-125), estrogen receptor, and progesterone receptor. Among non-small cell lung carcinomas with clear cell features, 87.5% of adenocarcinomas (or 50% overall frequency in lung carcinomas) were positive for TTF-1, whereas none of the ovarian clear cell carcinomas were positive (P = 0.002). All 14 ovarian clear cell carcinomas stained for CA-125 as compared with 1 non-small cell lung carcinoma (P < 0.001). On the other hand, 85% of non-small cell lung carcinomas stained for CEA, whereas none of the ovarian clear cell carcinomas did (P < 0.001). Interestingly, 4 ovarian clear cell carcinomas (28%) showed positive staining for the germ cell marker OCT-4. Either lung or ovarian carcinomas stained for Wilms tumor gene 1, estrogen receptor, or progesterone receptor very infrequently; and the difference between the 2 groups was not statistically significant. Our results suggest that an immunohistochemical panel consisting of TTF-1, CEA, CA-125, and OCT-4 is helpful in distinguishing most pulmonary and ovarian carcinomas with clear cell features.

MUC16 in the lacrimal apparatus

The aim of the present study was to determine the possible expression of the mucin MUC16 in the lacrimal apparatus. Expression and distribution of MUC16 in lacrimal gland, accessory lacrimal glands, and nasolacrimal ducts was monitored by RT-PCR and immunohistochemistry. MUC16 was expressed and detected in all tissues investigated. Comparable to conjunctiva and cornea it was membrane-anchored in accessory lacrimal glands whereas in lacrimal gland acinar cells and columnar cells of the nasolacrimal ducts it was stored in intracytoplasmic vesicles without membrane-association. Subepithelial serous glands of the nasolacrimal ducts revealed staining of the secretion product. Intracelluar production of MUC16 is present in lacrimal gland and epithelial cells of the nasolacrimal ducts but it is not clear whether this MUC16 is secreted. MUC16 seems to be shedded or secreted from the epithelial surface of subepithelial serous glands of the nasolacrimal ducts. Our results show that MUC16 is present in the whole lacrimal apparatus. Its distribution pattern suggests different physiological functions with regard to tear film physiology and tear outflow. Moreover, the results demonstrate the existence of so far not recognized qualitative differences in the secretion product of main lacrimal gland and accessory lacrimal glands (glands of Krause).

Mesothelin-MUC16 binding is a high affinity, N-glycan dependent interaction that facilitates peritoneal metastasis of ovarian tumors

Background

The mucin MUC16 and the glycosylphosphatidylinositol anchored glycoprotein mesothelin likely facilitate the peritoneal metastasis of ovarian tumors. The biochemical basis and the kinetics of the binding between these two glycoproteins are not clearly understood. Here we have addressed this deficit and provide further evidence supporting the role of the MUC16-mesothelin interaction in facilitating cell-cell binding under conditions that mimic the peritoneal environment.

Results

In this study we utilize recombinant-Fc tagged human mesothelin to measure the binding kinetics of this glycoprotein to MUC16 expressed on the ovarian tumor cell line OVCAR-3. OVCAR-3 derived sublines that did not express MUC16 showed no affinity for mesothelin. In a flow cytometry-based assay mesothelin binds with very high affinity to the MUC16 on the OVCAR-3 cells with an apparent K_d of 5–10 nM. Maximum interaction occurs within 5 mins of incubation of the recombinant mesothelin with the OVCAR-3 cells and significant binding is observed even after 10 sec. A five-fold molar excess of soluble MUC16 was unable to completely inhibit the binding of mesothelin to the OVCAR-3 cells. Oxidation of the MUC16 glycans, removal of its N-linked oligosaccharides, and treatment of the mucin with wheat germ agglutinin and erythroagglutinating phytohemagglutinin abrogates its binding to mesothelin. These observations suggest that at least a subset of the MUC16-asscociated N-glycans is required for binding to mesothelin. We also demonstrate that MUC16 positive ovarian tumor cells exhibit increased adherence to A431 cells transfected with mesothelin (A431-Meso⁺). Only minimal adhesion is observed between MUC16 knockdown cells and A431-Meso⁺ cells. The binding between the MUC16 expressing ovarian tumor cells and the A431-Meso⁺ cells occurs even in the presence of ascites from patients with ovarian cancer.

Conclusion

The strong binding kinetics of the mesothelin-MUC16 interaction and the cell adhesion between ovarian tumor cells and A431-Meso+ even in the presence of peritoneal fluid strongly support the importance of these two glycoproteins in the peritoneal metastasis of ovarian tumors. The demonstration that N-linked glycans are essential for mediating mesothlein-MUC16 binding may lead to novel therapeutic targets to control the spread of ovarian carcinoma.

Distinct evolution of the human carcinoma-associated transmembrane mucins, MUC1, MUC4 AND MUC16

The MUC family of mucins consists of secreted and membrane-bound forms. Overexpression of the membrane-bound family members, MUC1 (CA15-3), MUC4 and MUC16 (CA125), is found in diverse human carcinomas. However, despite being classified in the same family, little is known about the genetic origins of the carcinoma-associated mucins. The present results show that MUC1 homologs are restricted to mammalian species. MUC1 has no sequence similarity with the other membrane-bound mucins, except for the presence of a sea urchin sperm protein-enterokinase-agrin (SEA) domain. The results indicate that the MUC1 SEA domain originated from heparin sulfate proteoglycan of basement membrane (HSPG2; perlecan), an inducer of tumor cell growth. MUC4 has no SEA domain, but does have (i) a NIDO domain that evolved from an ancestor common to nidogen, and (ii) AMOP and VWD domains that originated from an ancestor common to the Sushi-domain containing protein. MUC16 contains multiple SEA domains that are found in a chicken gene and were subsequently repeated through duplication events. The SEA domains in MUC16 appear to have evolved from agrin before the divergence of birds and mammals. These findings indicate that MUC1, MUC4 and MUC16 evolved from distinct ancestors and that the membrane-bound mucins consist of different subgroups based on their genetic backgrounds.

Impact of short-term exposure of commercial eyedrops preserved with benzalkonium chloride on precorneal mucin

PURPOSE

The aim of this study is to investigate the short-term effects of benzalkonium chloride (BAC), a preservative used in many ophthalmic topical solutions, on precorneal mucin in humans.

METHODS

Immortalized human corneal-limbal epithelial (HCLE) cells were exposed to eyedrops containing BAC solutions at 0.0025% and 0.01% concentrations for a period of 15 min. Human corneal epithelium was acquired with consent, as a byproduct of elective excimer photorefractive keratectomy procedures after application of Ocuflox eyedrops (0.3% ofloxacin with 0.0025% BAC) for 1 week before surgery. The relative expression of the MUC1 and MUC16 mucin gene was determined by conventional and real-time reverse transcription-polymerase chain reaction (RT-PCR). Monoclonal antibodies for MUC1 (HMFG-1) and MUC16 (OC125) were used in western blot analysis to detect MUC1 and MUC16. Human corneas exposed to 0.01% BAC solutions were examined by transmission electron microscopy.

RESULTS

The expression of MUC1 and MUC16 gene transcripts was not changed after exposure to BAC in HCLE cells and human corneal epithelium. However, MUC1 and MUC16 were reduced after exposure to BAC in HCLE cells and human corneal epithelium. Transmission electron microscopy of the anterior corneal surface revealed fixation of the mucous layer after exposure to 0.01% BAC for 5 or 15 min; prolonged exposure (60 min) to 0.01% BAC destroys the mucous layer.

CONCLUSIONS

This study demonstrates that short-term exposure to BAC can alter the precorneal mucin.

Characterization of antibodies to CA 125 that bind preferentially to the cell-associated form of the antigen

OBJECTIVE

Antibodies to CA 125 have been used to predict relapse of ovarian cancer, but have performed poorly as therapeutic agents. One rationale for this is antibody binding to circulating shed antigen. Our aim in this study was to develop antibodies to human CA 125 that have enhanced selectivity for the cell-associated form of the antigen.

METHODS

Monoclonal antibodies were raised to a recombinant fragment of CA 125 that included sequence proximal to the putative membrane attachment site. Antibodies were characterized in terms of their binding site, affinity and selectivity for cell-associated CA 125.

RESULTS

In assays using patient-derived CA 125, a subset of high-affinity (KD <5 nM) monoclonal antibodies demonstrated a 10- to greater than 200-fold increase in selectivity for cell-associated CA 125 when compared with controls. Based on mapping of the various monoclonal antibodies obtained, it was determined that shedding of CA 125 most likely occurs in the most C-terminal repeat domain.

CONCLUSION

Results from competition analysis using patient-derived shed antigen predict that the antibodies described in this study may have significantly enhanced tumor-targeting properties when compared with existing antibodies to CA 125 in a tumor environment having high concentrations (>10,000 CA 125 units) of shed CA 125.

From gene profiling to diagnostic markers: IL-18 and FGF-2 complement CA125 as serum-based markers in epithelial ovarian cancer

We used an oligonucleotide-based DNA microarray to identify potential markers in 39 primary cultures of ovarian cancer specimens compared with 11 primary cultures of normal ovarian epithelia. Differential gene expression of IL-18 and FGF-2 was validated on a subset of samples by quantitative PCR and by IHC, using an independent tissue array of 90 cores of 20 normal ovarian surface epithelia and 70 EOCs representing different grades and pathologies of ovarian disease. We further compared, by ELISA, these two markers with CA125 in sera from 25 cancer-free and 47 ovarian cancer patients. IL-18 and FGF-2 proteins were significantly elevated in tumor tissues (p<0.04) and sera (p<0.05) from patients with ovarian cancer. In combination, the three markers (IL-18, FGF-2, and CA125) showed similar sensitivity in scoring for ovarian cancer (35/45 patients) compared to that of CA125 alone (37/45) and significantly improved the specificity of detection (20/25 patients) compared to each marker individually (15/25 for CA125; 18/25 FGF-2; 16/25 for IL-18). In conclusion we show that a combination of the three serum markers (IL-18, FGF-2 and CA125) is associated with EOC, with higher specificity than CA125 alone. Prospective studies with a large cohort of susceptible ovarian cancer patients will be required to expand these findings.

Effect of retinoic acid on gene expression in human conjunctival epithelium: secretory phospholipase A2 mediates retinoic acid induction of MUC16

PURPOSE

How vitamin A contributes to the maintenance of the wet-surfaced phenotype at the ocular surface is not well understood. This study sought to identify vitamin A-responsive genes in ocular surface epithelia using gene microarray analysis of cultures of a human conjunctival epithelial (HCjE) cell line grown with all-trans-retinoic acid (RA). The analysis showed that secretory phospholipase A(2) group IIA (sPLA(2)-IIA) was the gene most upregulated by RA, followed by the membrane-associated mucin MUC16 at a later time point. Since eicosanoids, the product of arachidonic acid generated by the PLA(2) family, have been shown to increase mucin production, this study sought to determine whether sPLA(2) mediates the RA induction of MUC16.

METHODS

HCjE cells were cultured with or without RA for 3, 6, 24, and 48 hours. Complementary RNA prepared from RNA of the HCjE cells was hybridized to human gene chips and analyzed using commercial software. Microarray data on mucin expression were validated by real-time PCR. To investigate whether sPLA(2) is associated with RA-induced MUC16 upregulation, HCjE cells were incubated with RA and the broad-spectrum PLA(2) inhibitor aristolochic acid (ArA) or the specific sPLA(2)-IIA inhibitor LY315920, followed by analysis of MUC16 mRNA and protein by real-time PCR and Western blot analysis.

RESULTS

After RA addition, 28 transcripts were upregulated and 6 downregulated by more than twofold (P < 0.01) at both 3 and 6 hours (early phase). Eighty gene transcripts were upregulated and 45 downregulated at both 24 and 48 hours (late phase). Group IIA sPLA(2), significantly upregulated by 24 hours, and MUC16 were the most upregulated RNAs by RA at 48 hours. sPLA(2) upregulation by RA was confirmed by Western blot analysis. When HCjE cells were incubated with RA plus ArA or specific inhibitor of sPLA(2)-IIA, LY315920, the RA-induced MUC16 mRNA was significantly reduced (P < 0.01).

CONCLUSIONS

The RA-associated upregulation of membrane-associated mucin MUC16 at late phase appears to be through sPLA(2)-IIA. Upregulation of this hydrophilic membrane-associated mucin may be one of the important mechanisms by which vitamin A facilitates maintenance of the wet-surfaced phenotype on the ocular surface.

Introducing the MUC16 gene: implications for prevention and early detection in epithelial ovarian cancer

More than 24,000 women in the United States are diagnosed with ovarian cancer every year, and half of these women die from their disease. Stage 1 ovarian cancer is curable in 95% of cases; however, due to inadequate screening tools and lack of symptoms in early disease, ovarian cancer is generally at Stage 3 or 4 when finally diagnosed. CA125 is a tumor antigen used to monitor the progression and regression of epithelial ovarian cancer. When its levels are elevated postsurgery (hysterectomy/salpingo-oophorectomy with or without peritoneal washings and lymph node biopsy) and postchemotherapy, it is suggestive of recurrent disease. Due to its similarly elevated levels in some nonmalignant conditions, however, it is not specific enough to be used for population screening. The CA125 molecule is considered a very large glycoprotein because of its molecular weight, and it has three domains: the carboxy terminal domain, the extracellular domain, and the amino terminal domain. MUC16 is the gene that encodes the peptide moiety of the CA125 molecule. MUC16 domains provide novel opportunities to develop new assays and refine current tools to improve the sensitivity and specificity of CA125 for population-based screening guidelines.

Differential regulation of membrane-associated mucins in the human ocular surface epithelium

PURPOSE

Membrane-associated mucins present in the apical cells of the ocular surface epithelium (MUC1, -4, and -16) are believed to contribute to the maintenance of a hydrated and wet-surfaced epithelial phenotype. Serum and retinoic acid (RA) have been used to treat drying ocular surface diseases. The goal of this study was to determine whether serum or RA regulates the production of membrane-associated mucins in human conjunctival epithelial cells.

METHODS

A telomerase-immortalized human conjunctival epithelial cell line (HCjE) was used. Cells were cultured in serum-free medium to confluence and then cultured with either 10% calf serum or with 100 nM RA for 0 to 72 hours. Conventional RT-PCR was used to determine the expression of retinoic acid receptors (RARs) and quantitative real-time PCR was used to investigate the mRNA expression of MUC1, -4, and -16. Protein levels were assayed by immunoblot analysis, using the antibodies HMFG-2, 1G8, or OC125, which are specific to MUC1, -4 and -16, respectively. To determine whether RA-associated MUC4 mRNA induction is a direct or indirect effect, HCjE cells were treated with RA and the protein synthesis inhibitor cycloheximide (1.0 microg/mL) for 12 hours.

RESULTS

MUC1 and -16, but not -4, mRNAs were detectable in HCjE cells grown in serum-free medium. Real-time PCR revealed that MUC4 mRNA was significantly induced by serum 3 hours after its addition, and that MUC1 and MUC16 mRNA levels were significantly upregulated at 72 hours. Western blot analysis demonstrated that the MUC1, -4, and -16 proteins increased over time after addition of serum. Conventional RT-PCR analysis demonstrated that RAR-alpha and -gamma mRNA were expressed in native human conjunctival tissue as well as in the HCjE cells. Treatment with RA upregulated the expression of both MUC4 and -16 mRNA and protein, but MUC1 was unaffected. Because the protein synthesis inhibitor cycloheximide did not prevent the RA-associated induction of MUC4 mRNA, the action of RA on the MUC4 promoter may be direct.

CONCLUSIONS

The membrane-associated mucins of the ocular surface epithelia, MUC1, -4, and -16, are differentially regulated by serum and RA in the telomerase-immortalized human conjunctival epithelial cell line. Serum derived from vessels in the conjunctiva may play an important role in mucin regulation in the ocular surface epithelia. These data also support the clinical efficacy of autologous serum and RA application in patients with ocular surface diseases. Furthermore, the data suggest that MUC4 and -16 are particularly important hydrophilic molecules involved in maintenance of a healthy ocular surface.

Characterization of novel human ovarian cancer-specific transcripts (HOSTs) identified by serial analysis of gene expression

A better understanding of changes in gene expression during ovarian tumorigenesis and the identification of specific tumor markers may lead to novel strategies for diagnosis and therapy for this disease. Using our serial analysis of gene expression (SAGE) data, as well as public SAGE databases that contained a total of 137 SAGE libraries representing a wide variety of normal and neoplastic tissues, we identified five novel SAGE tags specifically expressed in ovarian cancer. Database analysis, cloning and, sequencing of the corresponding expressed sequence tags revealed details about these transcripts that we named human ovarian cancer-specific transcripts (HOSTs). HOST1 was found to be identical to the gene encoding ovarian marker CA125 (MUC16). HOST2 is a novel gene containing multiple copies of retroviral-related sequences without an obvious open reading frame. HOST3 encodes the tight-junction protein claudin-16 (CLDN16). HOST4 encodes a poorly characterized proteoglycan link protein (LP), and HOST5 codes for a type II sodium-dependent phosphate transporter (SLC34A2). Except for MUC16, these genes have not previously been shown to be expressed in ovarian or other cancers. Northern blot analysis confirmed that HOST genes are rarely expressed in normal tissues or nonovarian cancers, but are frequently expressed in ovarian cancer-derived cell lines and primary tumors. Moreover, HOST genes are upregulated in all four major subtypes of ovarian cancer compared to cultivated ovarian surface epithelial cells, as concluded by real-time reverse transcription (RT)-PCR using a panel of microdissected ovarian tumors. The sodium-dependent phosphate transporter (HOST5/SLC34A2) expression was associated with increased differentiation in ovarian serous tumors. While the roles of HOSTs in ovarian malignant transformation remain unclear, we propose that HOSTs may represent alternative targets for diagnosis and therapy and of this deadly disease.

CA125 and UQCRFS1 FISH studies of ovarian carcinoma

OBJECTIVE

With the gene CA125 having recently been cloned, we chose to investigate the gene copy number of various ovarian cancer samples by FISH. As a control we chose BACs close to the chromosome 19 centromere. One of these BACs carries the gene UQCRFS1.

METHODS

We developed FISH probes for CA125 and the UQCRFS1 region. We studied 22 touch preparations and 14 paraffin-embedded samples of ovarian carcinomas with known CA125 serum levels, two ovarian cancer cell lines, and one ascites sample from an ovarian cancer patient. The average copy number per cell of both probes was calculated. Metaphase analyses were done on cell lines and ascites cells to localize the signals.

RESULTS

The CA125 gene mapped to 19p13.2. Three of 22 (13.6%) touch preparations and 1 of 14 (7.1%) paraffin samples had amplified levels of CA125. The cell lines and ascites sample did not have amplified CA125. Unexpectedly, 3 of 22 (13.6%) touch preparations, 1 of 14 (7.1%) paraffin samples, one cell line, and the ascites sample had amplification of the UQCRFS1 region. The amplification of the UQCRFS1 region occurred in the form of homogeneously staining regions (HSRs). Only one sample had coamplification of CA125 and UQCRFS1.

CONCLUSIONS

CA125 was only sometimes modestly amplified in ovarian carcinoma, even when the serum CA125 level was highly elevated. Unexpectedly, the UQCRFS1 region was also sometimes amplified as HSRs. The UQCRFS1 protein is also known as complex III of the mitochondrial respiratory chain. This product may have an important role in malignant cells.

[Normal human conjunctival epithelium expresses MUC13, MUC15, MUC16 and MUC17 mucin genes]

PURPOSE

The ocular surface epithelia express at least five mucin genes of the total of 17 human mucin genes that have been identified so far. This study was designed to determine the expression profile of mucin genes in conjunctival impression cytology (CIC) samples from healthy subjects.

METHODS

Two polyethersulfone filters were applied to the superior conjunctiva of both eyes from eight healthy donors. Polymerase chain reaction (PCR) was performed using isolated and retrotranscripted total RNA obtained from the CIC samples to study the expression of all known human mucin genes. Following amplification, PCR products were electrophoresed on 1.5% agarose gel and stained with ethidium bromide to confirm that only a single band was obtained when amplifying all cDNAs with the convenient primers.

RESULTS

Transcripts of the previously reported conjunctival mucin genes MUC1, MUC2, MUC4, MUC5AC, and MUC7 were detected in all samples. In addition, transcripts of MUC13, MUC15, MUC16 and MUC17 mucin genes also were detected. Amplified products by conventional PCR showed the expected amplicon size. Transcripts of MUC3A, MUC3B, MUC5B, MUC6, MUC8, MUC11, and MUC12 mucin genes were not detected.

CONCLUSION

The expression of four additional mucin mRNA (MUC13, MUC15, MUC16, and MUC17) has been proved in human conjunctival epithelium from healthy donors for the first time. The function of these genes remains to be further elucidated.

MUC16 mucin is expressed by the human ocular surface epithelia and carries the H185 carbohydrate epitope

PURPOSE

H185 antibody has been shown to recognize a carbohydrate epitope on a membrane-associated mucin in the apical surfaces of the corneal and conjunctival epithelia. The distribution of this antibody is altered on the surfaces of conjunctival epithelial cells of dry eye patients. The purpose of this work was to determine whether the H185 antibody recognizes the recently cloned membrane-associated mucin MUC16 (formerly CA125 antigen).

METHODS

To determine whether ocular surface epithelia express MUC16, the relative expression of the MUC16 mucin gene was determined by real-time PCR on reverse transcription products from RNA isolated from human corneal and conjunctival tissues, as well as from immortalized human corneal-limbal epithelial cell (HCLE) cultures. To determine the distribution of MUC16 mRNA and protein in the ocular surface epithelia, in situ hybridization and immunohistochemistry were performed on sections of corneal and conjunctival epithelia using, respectively, a MUC16 antisense oligoprobe and the antibodies OC125, VK-8, and R16 raised against the MUC16 mucin. Determination of whether MUC1 and MUC16 mucins carry the H185 carbohydrate epitope was achieved with the respective mucins isolated from HCLE protein extracts, using one- or two-step immunoprecipitation assays and immunodepletion experiments followed by Western blot analysis.

RESULTS

MUC16 mucin transcripts were detected in the human ocular surface epithelia and in corneal cell cultures. MUC16 mRNA and protein localized to the apical cell layers of the cornea and to the suprabasal region of the conjunctival epithelium. In HCLE cultures, MUC16 protein was detected in apical cells of islands of stratified cells. Immunofluorescence microscopy demonstrated exact colocalization of the MUC16 mucin and the H185 carbohydrate epitope in sections of human corneal tissue. Immunoprecipitated MUC16 mucin was recognized by the H185 antibody and vice versa, indicating that MUC16 mucin carries the H185 epitope. Immunodepletion with H185 antibody resulted in no OC125 antibody reactivity. No cross-reactivity between immunoprecipitated MUC1 and the H185 antibody was observed.

CONCLUSIONS

This study demonstrates that the membrane-associated mucin MUC16 is expressed by the human ocular surface epithelia and that MUC16 carries the H185 carbohydrate epitope. Future studies on the expression of MUC16 and the characterization of the molecular structure of the H185 carbohydrate epitope will determine their biological significance on the healthy ocular surface and in dry eye syndrome.

The CA 125 gene: a newly discovered extension of the glycosylated N-terminal domain doubles the size of this extracellular superstructure

CA 125 is a well-established marker for patients diagnosed with ovarian carcinoma. It is clearly elaborated in serous cystadenocarcinomas and less likely to be expressed in mucinous tumors. It has been 20 years since CA 125 was first recognized and it is only in recent years (the past 2) that some progress has been made toward cloning the gene, providing the basis for an understanding of the functional role of this molecule in embryonic development and neoplastic transformation. It is now clear that CA 125 is a large glycoprotein which is anchored to the epithelium by a transmembrane domain and is released into the extracellular space by enzymatic cleavage. Here, we describe a further major extension to the glycosylated extracellular amino terminal domain of this molecule. These additional data in association with our previous understanding of this molecule will provide the basis for our ability to understand the physiologic function of this molecule in biologic development and pathologic transformation.

Ovarian cancer antigen CA125 is encoded by the MUC16 mucin gene

Serum assays based on the CA125 antigen are widely used in the monitoring of patients with ovarian cancer; however very little is known about the molecular nature of the CA125 antigen. We recently cloned a partial cDNA (designated MUC16) that codes for a new mucin that is a strong candidate for being the CA125 antigen. This assignment has now been confirmed by transfecting a partial MUC16 cDNA into 2 CA125-negative cell lines and demonstrating the synthesis of CA125 by 3 different assays. Of the 3 antibodies (OC125, M11 and VK-8) tested on the transfected cells, only the first 2 were strongly positive, indicating the differential expression of the CA125 epitopes in these cells. The cloning and expression of CA125 antigen opens the way to an understanding of its function in normal and malignant cells.

CA 125: the end of the beginning

CA 125, a high-molecular-weight mucin, was first defined in 1981 by the monoclonal antibody OC125. Until recently, it has defied many attempts to purify it from a variety of sources, although many research groups have successfully raised antibodies that bind to CA 125. Nevertheless, CA 125 has demonstrated its considerable value as a marker in monitoring patients with ovarian cancer. This year, two research groups have succeeded in cloning the high-molecular-weight mucin CA 125. Their findings are summarized and the significance discussed in light of existing data from the human genome.

The CA 125 gene: an extracellular superstructure dominated by repeat sequences

CA 125 has long presented problems to both clinicians and investigators because there was no definitive information on its structure and function. Here, we describe our work on cloning the CA 125 gene with the anticipation that such information will provide the basis for understanding its structure and its physiologic role in both normal and malignant tissues. The CA 125 protein core is composed of a short cytoplasmic tail, a transmembrane domain and an extraordinarily large glycosylated extracellular structure. This structure is dominated by a repeat domain composed of 156 amino acid repeat units which encompass the epitope binding sites. The molecule also includes an amino terminal domain of serine/threonine-rich sequences which would account for most of the O-glycosylation known to be present in CA 125. CA 125 is an unusually large transmembrane glycoprotein. Its release from the surface of the cell is most probably dependent on cytoplasmic phosphorylation followed by proteolytic cleavage. The extracellular domain is characterized by a large number of repeat units (probably 60+) which encompass an interactive disulfide bridged cysteine-loop and the site of OC125 and M11 binding. Sequencing the gene provides us with the ability to initiate the quest to understand the biological function of CA 125.

Molecular Cloning of the CA125 Ovarian Cancer Antigen

CA125 is an ovarian cancer antigen that is the basis for a widely used serum assay for the monitoring of patients with ovarian cancer; however, detailed information on its biochemical and molecular nature is lacking. We now report the isolation of a long, but partial, cDNA that corresponds to the CA125 antigen. A rabbit polyclonal antibody produced to purified CA125 antigen was used to screen a lambdaZAP cDNA library from OVCAR-3 cells in Escherichia coli. The longest insert from the 54 positive isolated clones had a 5797-base pair sequence containing a stop codon and a poly(A) sequence but no clear 5' initiation sequence. The deduced amino acid sequence has many of the attributes of a mucin molecule and was designated CA125/MUC16 (gene MUC16). These features include a high serine, threonine, and proline content in an N-terminal region of nine partially conserved tandem repeats (156 amino acids each) and a C-terminal region non-tandem repeat sequence containing a possible transmembrane region and a potential tyrosine phosphorylation site. Northern blotting showed that the level of MUC16 mRNA correlated with the expression of CA125 in a panel of cell lines. The molecular cloning of the CA125 antigen will lead to a better understanding of its role in ovarian cancer.

Regulation of CA 125 expression in cultured human carcinoma cells

CA 125 shedding is not a constitutive and stable process but may be affected by cell cycle and cell proliferation as well as by various growth factors and cytokines. Interferons, interleukin-1 beta, tumor necrosis factor-alpha and transforming growth factor-alpha have been shown to induce while glucocorticoids and transforming growth factor-beta have been shown to suppress the release of the tumor marker CA 125 from ovarian carcinoma cells. Several endogenous as well as exogenous factors may affect CA 125 biosynthesis; however, a major question remains whether this observed modulation of CA 125 expression in vitro is of clinical importance.

Immunohistochemistry of CA 125. Unusual expression in normal tissues, distribution in the human fetus and questions around its application in diagnostic pathology

CA 125 is known as the marker that is most strongly associated with epithelial gynecological tumors. Compared to the number of publications on its use in serum assays, the application in immunohistochemistry is still limited. The availability of many good antibodies that perform well in formalin-fixed paraffin-embedded tissue opens good possibilities for a wider use. Outside the gynecological tract several other structures may react positive for CA 125. Among these are the lung and breast but also the epithelial cells of the conjunctiva and to some extent prostate glandular epithelium. In the fetus reactions can be found in the serosal linings of body cavities but also in the esophagus and skin. In diagnostic pathology CA 125 plays a role in identifying the primary locations of metastatic carcinoma of unknown origin. It is recommended to use CA 125 antibodies not in a solitary setting but in combination with CEA, BRST-2 and Vimentin to discriminate best between the most frequent sites of origin of metastatic carcinoma. Regular analysis of sensitivity/specificity ratios in a balanced population, representing the composition of the patient population seen in daily practice, should be performed to evaluate the position of CA 125 in diagnostic immunohistochemistry.

Production of a single-chain fragment of the murine anti-idiotypic antibody ACA125 as phage-displayed and soluble antibody by recombinant phage antibody technique

The F(ab')2 fragment of the murine monoclonal anti-idiotypic antibody ACA125 mimicking the tumor-associated antigen CA125 is used as a vaccine for the induction of an anti-tumoral immunity in patients with ovarian carcinoma. We tried to generate a single-chain fragment (ScFv) composed of ACA125 heavy- and light-chain variable domains connected by a polypeptide linker as an alternative to the corresponding F(ab')2 fragment. Heavy- and light-chain genes of antibody-producing mouse hybridoma cell line were amplified separately and assembled into a ScFv gene with linker DNA by the polymerase chain reaction (PCR). The ScFv gene was ligated into the phagemid vector pCANTAB5E, which allows the production of both phage-displayed and soluble ScFv. Transformed Escherichia coli TG1 cells were infected with M13K07 helper phage to yield recombinant phage, which display ScFv fragments as a g3p fusion protein on the surface of the filamentous phage M13. Recombinant phages could be selected by binding to the idiotypic antibody OC125 after one round of panning and directly used to reinfect E. coli TG1 cells. The E. coli nonsuppressor strain HB2151 was infected with an antigen-positive phage clone, previously screened by enzyme-linked immunosorbent assay (ELISA), to express soluble ScFv fragments. Functional soluble ScFv binding to the idiotypic antibody OC125 F(ab')2 could be detected in the bacterial periplasm by Western blot and ELISA. The variable heavy- and light-chain genes of the ACA125 ScFv fragment were further sequenced and compared with known antibody sequences.

Isolation of the murine Nbr1 gene adjacent to the murine Brca1 gene

The human NBR1 cDNA has previously been identified using polyclonal sera to CA125, an ovarian tumor antigen used in monitoring ovarian cancer. The gene was mapped to the BRCA1 region on chromosome 17q21 and subsequently found to lie in close proximity to the recently identified BRCA1 gene. The NBR1 protein has a B-box motif but the function of the protein is as yet unknown. To investigate the function and importance of this gene, we have studied the conservation of this gene in other species and in particular in the mouse. We have isolated murine Nbr1 cDNA and genomic clones. Translation of the cDNA sequence indicates that the protein is highly conserved, being 89% similar and 84% identical to the human. Analysis of the murine Nbr1 genomic clones indicates that it maps less than 1 kb from the Brca1 gene and that, unlike that in human, this region is not duplicated.