CTp11, a novel member of the family of human cancer/testis antigens.

To identify new genes that may contribute to the metastatic pathway of neoplastic cells, we compared mRNA expression of the parental human melanoma cell line 1F6 and its metastatic variant 1F6m using mRNA differential display. We isolated a cDNA clone that was exclusively expressed in 1F6m. Northern blot analysis on a broader panel of human melanoma cell lines with different metastatic capacity following s.c. inoculation into nude mice demonstrated that the gene was expressed only in the most aggressive, highly metastatic cell lines, giving a band of 0.5 kb. The isolated full length cDNA clone showed an open reading frame of 97 amino acids. To study the subcellular localization of the gene product, COS-1 cells were transfected with cDNA of the gene fused to eGFP. We found the fusion protein to be exclusively present in the nucleus. A computer search showed strong homology with human genomic clones all localized on chromosome X (Xq26.3-Xq27.1) and with several expressed sequence tags, all from testis. Localization of the gene on chromosome X was confirmed by genomic PCR on a panel of human chromosome-specific rodent/human hybrid cell lines. Northern blotting and reverse transcription-PCR on 17 different normal human tissue samples showed that the gene was only expressed in normal testis. Reverse transcription-PCR on a great number of different human tumor cell lines showed expression in 25-30% of the melanoma and bladder carcinoma cell lines. Only 2 of 29 other tumor cell lines were positive. Nested PCR analysis of a series of fresh human melanocytic tumors demonstrated expression in 7 of 10 melanomas tested. No expression was seen in benign melanocytic tumors. In addition to melanoma, some malignant tumors from other histological types were also found to be positive. Based on these data, we conclude that the described gene, CTp11 (cancer/testis-associated protein of 11 kDa), is a novel member of the family of cancer/testis antigens.