Large-scale human tissue analysis identifies Uroplakin 1a as a putative diagnostic marker for urothelial cancer

Gene of the month: the uroplakins

Uroplakins are a family of membrane-spanning proteins highly specific to the urothelium. There are four uroplakin proteins in humans. These are encoded by the following UPK genes: UPK1A, UPK1B, UPK2 and UPK3 Uroplakin proteins span the apical membrane of umbrella cells of the urothelium, where they associate into urothelial plaques. This provides a barrier function to prevent passage of urine across the urothelium in the renal pelvis, ureters, and bladder. Uroplakins are also involved in developmental processes such as nephrogenesis. The specific localisation of uroplakins within the urothelium means that they are often expressed in primary and metastatic urothelial cell carcinoma and may be used as an immunohistochemical marker of urothelial malignancy.

Loss of Upk1a and Upk1b expression is linked to stage progression in urothelial carcinoma of the bladder

BACKGROUND

Uroplakin-1a (Upk1a) and uroplakin-1b (Upk1b) have recently been identified as diagnostic markers for the distinction of urothelial carcinomas from other solid tumor entities. Both proteins play an important role in the stabilization and strengthening of epithelial cells that line the bladder.

METHODS

To evaluate the prognostic role of uroplakin expression in urothelial carcinomas, more than 2700 urothelial neoplasms were analyzed in a tissue microarray format by immunohistochemistry. To further assess the diagnostic role of uroplakin immunohistochemistry, results were compared with preexisting GATA3 data.

RESULT

The fraction of Upk1a/Upk1b positive cases decreased slightly from pTaG2 low-grade (88% positive for Upk1a/87% positive for Upk1b) and pTaG2 high-grade (92%/89%) to pTaG3 (83%/88%; p > 0.05) and was lower in muscle-invasive (pT2-4) carcinomas (42%/64%; p < 0.0001/p < 0.0001 for pTa vs. pT2-4). Within pT2-4 carcinomas, high expression of Upk1a and Upk1b was linked to nodal metastasis and lymphatic vessel infiltration (p < 0.05) but unrelated to patient outcome. There were significant associations between Upk1a, Upk1b and GATA3 immunostaining (p < 0.0001 each), but 11% of GATA3 negative cancers were Upk1a/b positive and 8% of Upk1a/b negative cancers were GATA3 positive. Absence of GATA3/Upk1a/b staining was significantly linked to poor patient survival in the subgroup of 126 pT4 carcinomas (p = 0.0004) but not in pT2 and pT3 cancers.

CONCLUSIONS

In summary, the results of our study demonstrate that Upk1a and/or Upk1b immunohistochemistry can complement GATA3 for the distinction of urothelial carcinomas. Furthermore, a progressive loss of Upk1a/b expression during stage progression and a prognostic role of the combination GATA3/Upk1a/Upk1b in pT4 carcinomas is evident.