Molecular cloning and expression of uroplakins in transitional cell carcinoma

Uroplakins (UPs), urothelium-specific transmembrane proteins, are present only in urothelia and may be good candidates as tumor markers specific for transitional cell carcinomas (TCCs). We investigated the expression of UP genes in the tissues and peripheral blood of patients with TCCs.

We determined the nucleotide sequences of UPs by a polymerase chain reaction (PCR)-based method. We then investigated UP gene expression in tissues from 12 patients with TCC by reverse transcription (RT)-PCR. We also investigated UP gene expression in peripheral blood of 12 other patients with TCC by nested RT-PCR. Polyclonal and monoclonal antibodies against UPs were generated using synthesized polypeptides and recombinant protein, respectively, as immunogens.

We determined the nucleotide sequence of human UP-Ib, UP-II, and UP-III cDNAs and produced gene-specific primer pairs for each and for UP-Ia. UP genes were expressed in both cancerous and non-cancerous urothelia taken from all patients examined (as detected by RT-PCR). The detection sensitivity of our assay system was such that 1 cancer cell could be detected in 5 mL of peripheral blood. UP gene-expression was also detected in the peripheral blood of 3 patients with metastatic TCC, but not from 9 patients with non-metastatic TCC or from 3 healthy volunteers. Antibodies against both UP-Ia and UP-Ib reacted with the cell membrane of TCCs.

UPs may be employed as tumor markers for TCCs, because they are highly conserved and well expressed in non-cancerous and cancerous cells. Furthermore, detection of UP gene expression in blood by nested RT-PCR may provide helpful information in the diagnosis and management of TCCs. We are currently expanding an immunohistochemical study by targeting a larger number of patients to examine the clinical usefulness of these antibodies.