Characterization of C21ORF100 as a Novel Prostate Differentiation Antigen

Differentiation antigens are immunogenic proteins expressed in specific cell lineages or at specific stages of differentiation ina particular tissue. Generally, their expression in normal cells is preserved after neoplasic transformation and this feature hasmade such molecules potential candidates for cancer immunotherapy. Using alignments between expressed sequence tags(ESTs) and the human chromosome 21 sequence, we have identified a novel gene, named C21orf100, which is exclusivelyexpressed in normal prostate and codes for a putative protein of 55 amino acids. Objective: To characterize C21orf100 as anovel prostate differentiation antigen. Material and Methods: C21orf100 mRNA expression was determined by RT-PCR in 22normal tissues and in 65 samples from melanomas and prostate, thyroid, stomach, uterus and breast tumors. The existenceof a humoral immune response against C21orf100 protein in prostate cancer patients was evaluated by immunoblotting usinga His-tagged recombinant protein. Results: As expected for a differentiation antigen, C21orf100 mRNA expression waspredominantly detected in both normal and tumor prostate samples. Antibodies against C21orf100 recombinant protein weredetected in 1 out of 50 (2%) plasma samples from prostate cancer patients and were not detected in the plasma from healthyblood donors. Conclusion: The restricted expression pattern and the detection of antibodies in prostate cancer patients suggestthat C21orf100 is a novel prostate differentiation antigen. However, due to the low frequency of antibody response againstC21orf100 detected among prostate cancer patients, further analysis is necessary to evaluate its potential for cancerimmunotherapy.

Identification and complete sequencing of novel human transcripts through the use of mouse orthologs and testis cDNA sequences

The correct identification of all human genes, and their derived transcripts, has not yet been achieved, and it remains one of the major aims of the worldwide genomics community. Computational programs suggest the existence of 30,000 to 40,000 human genes. However, definitive gene identification can only be achieved by experimental approaches. We used two distinct methodologies, one based on the alignment of mouse orthologous sequences to the human genome, and another based on the construction of a high-quality human testis cDNA library, in an attempt to identify new human transcripts within the human genome sequence. We generated 47 complete human transcript sequences, comprising 27 unannotated and 20 annotated sequences. Eight of these transcripts are variants of previously known genes. These transcripts were characterized according to size, number of exons, and chromosomal localization, and a search for protein domains was undertaken based on their putative open reading frames. In silico expression analysis suggests that some of these transcripts are expressed at low levels and in a restricted set of tissues.

A novel human G protein-coupled receptor is over-expressed in prostate cancer

G protein-coupled receptors (GPCRs) are involved in a large variety of physiological functions. The number of known members that belong to this large family of receptors has been rapidly increasing. Now, with the availability of the human genome sequence databases, further family members are being identified. We describe the identification of a novel GPCR that shows no significant amino acid identity to any one of the known members of the GPCR superfamily. The gene expression pattern of this receptor is restricted: in normal tissues it is confined to the nervous system and testis, but we also detected gene expression in several tumor types, most notably prostate cancer, suggesting a potential role for this gene as a marker for this disease.