We applied serological analysis of recombinant cDNA expression libraries (SEREX) to cases of esophageal squamous cell carcinoma (SCC) to identify tumor antigens. One of the clones identified was TROP2, which is known as calcium signal transducer. To evaluate the clinical significance of serum anti-TROP2 antibodies (s-TROP2-Abs) in patients with esophageal SCC, the presence of s-TROP2-Abs was analyzed by Western blotting using bacterially expressed TROP2 protein. We found that 23 of 75 (31%) patients were positive for s-TROP2-Abs. Positivity in terms of s-TROP2-Abs showed a significant association with tumor size but not with other clinicopathological features. The protein expression levels of TROP2 were much higher in esophageal SCC cell lines as compared to those in normal esophageal mucosa and its immortalized cells although the mRNA expression levels were not necessarily elevated in malignant cell lines and tissues. Immunohistochemical studies showed that the expression of TROP2 protein in esophageal SCC specimens was noticeably higher than that found in mild hyperplasia of esophageal mucosae. Thus, s-TROP2-Abs seemed useful in the diagnosis of SCC and may be a candidate for serum tumor markers.

Abstract. In order to identify new serum markers of esophageal squamous cell carcinoma (SCC), we performed serological identification of antigens by recombinant cDNA expression cloning (SEREX). E. coli was transformed with a ÏZAPII phage cDNA library prepared from mRNA of an esophageal cancer cell line (T.Tn), and IPTG-induced cDNA products were screened for interaction with antibodies in allogeneic sera of patients with esophageal SCC. We identified myomegalin (MMGL, phosphodiesterase 4D interacting protein/PDE4DIP) as a new SEREX antigen for esophageal SCC. Western blot analysis revealed that serum anti-myomegalin antibodies (s-MMGL-Abs) were present in 43 (47%) of 91 patients, but in only one (2.2%) of 45 healthy controls. Of the 21 patients with stage I disease, 8 (38%) were sero-positive. The positive rate of s-MMGL-Abs was greater than those of other conventional tumor markers. Reverse transcription-PCR analysis suggested that alternative splicing from myomegalin variant 1 to variant 5 may explain, in part, the development of s-MMGL-Abs. Although the presence of s-MMGL-Abs was not related to any clinicopathological features of the patients, multivariate analysis indicated that the presence of s-MMGL-Abs was significantly associated with a favorable prognosis. Consequently, s-MMGL-Abs may be a useful tumor marker to diagnose and establish a prognosis in patients with esophageal SCC. IntroductionEsophageal squamous cell carcinoma (SCC) is a deadly disease. Late presentation in a group of elderly patients with co-morbid illnesses resulted in a poor outcome (1,2). The aggressive behavior of esophageal SCC has been associated with systemic involvement at diagnosis, and the poor prognosis has been attributed largely to a delay in diagnosis (2). Although several serum markers have been reported to be clinically useful for diagnosing esophageal SCC (3,4), these serum markers are limited in terms of detecting early esophageal cancers, except the serum p53 IgG antibody (5,6). In order to identify new tumor-associated antigens that may generate new serum markers for esophageal SCC, we used the method of serological identification of antigens by recombinant cDNA expression cloning (SEREX) which involves the immunoscreening of cDNA libraries prepared from tumor specimens using autologous or allogeneic sera (7). Chen et al (8) and our group (9-13) have succeeded in the identification of several tumor antigens for esophageal SCC. The identification of human tumor antigens recognized by the autologous host is yielding an array of target molecules for the diagnosis, monitoring, and immunotherapy of human cancer (14-16).In the present study, we identified myomegalin as a new SEREX antigen of esophageal SCC, observed that serum anti-myomegalin antibodies (s-MMGL-Abs) were present frequently in esophageal SCC patients, and associated s-MMGL-Abs with a favorable prognosis in patients with esophageal SCC. Materials and methods Human esophageal squamous cell carcinoma cells and tissues.Seven human esophageal squamous cell carcin...

BackgroundDiagnosis of esophageal squamous cell carcinoma (SCC) may improve with early diagnosis. Currently it is difficult to diagnose SCC in the early stage because there is a limited number of tumor markers available.ResultsFifty-two esophageal SCC SEREX antigens were identified by SEREX (serological identification of antigens by recombinant cDNA expression cloning) using a cDNA phage library and sera of patients with esophageal SCC. Sequence analysis revealed that three of these antigens were similar in amino acid sequences, and they were designated as ECSA (esophageal carcinoma SEREX antigen)-1, -2 and -3. The ECSA family was also similar to an EST clone, hepatocellular carcinoma-associated antigen 25a (HCA25a). Serum antibody levels to ECSA-1, -2 and -3 were significantly higher in patients with esophageal SCC than in healthy donors. Based on the conserved amino acid sequences, three peptides were synthesized and used for enzyme-linked immunosorbent assays (ELISA). The serum antibody levels against one of these peptides were significantly higher in patients with esophageal SCC. This peptide sequence was also conserved in FAM119A, GOSR1 and BBS5, suggesting that these are also ECSA family members. Reverse transcription followed by quantitative PCR analysis showed that the mRNA expression levels of ECSA-1, -2 and -3 and FAM119A but not of HCA25a, GOSR1 and BBS5 were frequently elevated in esophageal SCC tissues.ConclusionsWe have identified a new gene family designated ECSA. Serum antibodies against the conserved domain of the ECSA family may be a promising tumor marker for esophageal SCC.

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BackgroundEsophageal squamous cell carcinoma (SCC) represents one of the most malignant tumors. To improve the poor prognosis, it is necessary to diagnose esophageal SCC at early stages using new tumor markers. SEREX (serological identification of antigens by recombinant cDNA expression cloning) is suitable for large-scale screening of tumor antigens and has been applied for various types of human tumors.MethodsTumor markers of esophageal squamous cell carcinoma (SCC) were screened by SEREX method. The presence of serum anti-makorin 1 (MKRN1) antibodies (s-MKRN1-Abs) was examined by Western blotting using bacterially expressed MKRN1 protein. The expression levels of MKRN1 mRNA in tissues were examined by RT-PCR. The biological activity of MKRN1 was examined by transfection of ras-NIH3T3 mouse fibroblasts with MKRN1 cDNA. Major ubiquitinated proteins in MKRN1-transfected cells were identified by immunoprecipitation with anti-ubiquitin antibody followed by mass spectrometry.ResultsMKRN1 was identified as a novel SEREX antigen of esophageal SCC. Although a total of 18 (25%) of 73 patients with esophageal SCC had s-MKRN1-Abs, none of the 43 healthy donors had a detectable level of s-MKRN1-Abs. There was no correlation between the presence of s-MKRN1-Abs and clinicopathological variables other than histological grading. Well-differentiated tumors were associated significantly with the presence of s-MKRN1-Abs in the patients. The mRNA levels of MKRN1 were frequently higher in esophageal SCC tissues than in the peripheral normal esophageal mucosa. Stable transfection of ras-NIH3T3 cells with MKRN1 cDNA induced prominent morphological changes such as enlargement of the cell body and spreading. Ubiquitination of 80- and 82-kDa proteins were clearly observed in MKRN1-transfected cells but not in the parental cells, which were identified as L-FILIP (filamin A interacting protein 1).ConclusionMKRN1 is a novel SEREX antigen of esophageal SCC, and s-NKRN1-Abs can be a candidate of diagnostic markers of esophageal SCC with high specificity. It is plausible that MKRN1 is involved in carcinogenesis of the well-differentiated type of tumors possibly via ubiquitination of L-FILIP.