Molecular cloning and characterization of a gene which is overexpressed in human ovarian tumors.

摘要

A cDNA corresponding to a novel human gene, tumor-associated diagnostic gene 7 (TADG7), was cloned from a serous cystadenocarcinoma of ovary. The relative level of TADG7 mRNA expression, as measured by a semi-quantitative polymerase chain reaction (PCR), indicated that the TADG7 gene is frequently overexpressed in malignant ovarian tumors at a level equivalent to two-fold or higher than that of normal ovary. The frequency of overexpression of the TADG7 mRNA in ovarian tumors is 93.7% as compared to 0-10% in normal ovary. TADG7 was very frequently overexpressed in serous cancer of the ovary which showed on average a 5.3-fold overexpression compared to normal ovary. In addition, stage I ovarian tumors, including the majority of benign and low malignant potential tumors, showed a moderately high frequency of overexpression (57.1-71.4%). Northern blot analysis indicated that the TADG7 gene has two major transcripts (1.8 kb and 2.7 kb) in most tissues, however fetal brain showed an additional minor transcript (4.5 kb). The cloned cDNA contains a 1,609 nucleotide sequence, which probably corresponds to the 1.8 kb transcript. An open reading frame encoding 184 amino acids was found in the 1,609 bp cDNA. The predicted TADG7 protein appeared to be a novel protein of unknown biological function. However, a possible correlation of the TADG7 protein to receptor-tyrosine kinases (RTKs) was suggested from the results of a protein domain (motif) analysis and a sequence homology search. The TADG7 protein appeared to contain two potential signature sequences of RTK including the ATP-binding domain. In addition, the protein contains six potential phosphorylation sites for protein kinases (PKA and PKC), and three potential myristylation sites. The amino acid sequence of the TADG7 showed a 21-22% sequence identity to the extracellular ligand binding domain of RTKs (Class III). The TADG7 gene and its translated protein product may be useful for early diagnosis and/or the treatment of ovarian cancer patients.