MGC29506 gene, frequently down-regulated in intestinal-type gastric cancer, encodes secreted-type protein with conserved cysteine residues

Microarray analyses is applied for prognosis of gastric cancer, including risk assessments of lymph-node metastasis and peritoneal dissemination. EST AA769445 derived from an unknown gene is reported to be frequently down-regulated in intestinal-type gastric cancer based on microarray analyses. Here, we identified and characterized the gene corresponding to EST AA769445 by using bioinformatics. EST AA769445 overlapped with MGC29506 cDNA (BC021275) and PACAP cDNA (AF338109). MGC29506 protein (189 aa) and PACAP protein (123 aa) were identical in codon 1-59, but were divergent in the C-terminal region due to a frame shift caused by sixteen-base insertion in PACAP cDNA. MGC29506 and PACAP were derived from the same gene, consisting of four exons, due to alternative splicing of alternative splice-acceptor-site type. Fourteen human ESTs were the MGC29506 type, while one human EST was the PACAP type. MGC29506 was the major isoform of the MGC29506/PACAP gene on human chromosome 5q31.2. MGC29506 orthologs in other species were next searched for. AK088094 and AK008016 cDNAs with nucleotide substitutions resulting in four-amino-acid substitutions were derived from mouse Mgc29506 gene. Rat Mgc29506 gene was identified in the rat genome draft sequence AC135285. ESTs AJ396310 and AJ441435 were derived from chicken Mgc29506 gene, while ESTs BW315632 and BW251767 from ciona mgc29506 gene. N-terminal signal peptide, six cysteine residues and other amino acids were conserved among human, mouse, rat, chicken, and ciona MGC29506 proteins. MGC29506 gene, frequently down-regulated in intestinal-type gastric cancer, was found to encode secreted-type protein with six conserved cysteine residues.