Identification and molecular characterization of NUCB2 as potential gastric cancer antigen

Zane Slucka BSc 1, Aija Line MSc 1, Aivars Stengrevics MD 2, Geng Li PhD 3, Eriks Jankevics PhD 1 and Robert C. Rees PhD 3

1 Biomedical Research and Study Centre, University of Latvia, Riga, Latvia; 2 Latvian Oncology Center, Riga, Latvia; 3 Department of Life Sciences, Nottingham Trent University, Nottingham, UK

AIMS: We applied serological screening method, called SEREX to identify new cancer-associated genes in human gastric cancer. Fourteen distinct serum-reactive cDNA clones were isolated, including NUCB2 – a multifunctional calcium binding protein. The aim of this study was to evaluate possible reasons of NUCB2 immunogenicity. METHODS: NUCB2 clone was isolated by immunoscreening of gastric cancer cDNA expression library with patient’s sera. NUCB2 was characterized by comparing DNA sequences in cancer patients and donors, mRNA tissue distribution and comparison of mRNA levels between gastric cancer and adjacent tissue specimens by RT-PCR and the frequency of antibody responses in allogeneic sera. RESULTS: Analysis of DNA sequences from cancerous and adjacent tissues revealed a DNA polymorphism - a 3-nucleotide deletion at 3’ end of the NUCB2 coding region. Majority of cancer patients and only one from ten donors analyzed were heterozygous at this locus. Comparative RT-PCR analysis showed consistently decreased mRNA levels in 50% of tumors in comparison with adjacent normal tissues. No antibody response to NUCB2 gene product was detected in sera from 35 healthy donors. CONCLUSIONS: NUCB2 have been proposed to be involved in the regulation of survival and death of postmitotic cells by controlling calcium homeostasis in the cell. We have found NUCB2 gene product to be immunogenic in gastric cancer patient. An unusual DNA polymorphism – a 3-nucleotide deletion – was observed with very high frequency among gastric cancer patients, moreover the expression of NUCB2 is downregulated in 50% gastric tumors.

KEY WORDS: Tumor antigens, .

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Paper presented at the International Symposium on Predictive Oncology and Intervention Strategies; Paris, France; February 9 - 12, 2002; in the section on Predictive Markers.