Expression Parameters of the Polycomb Group Proteins BMI1, SUZ12, RING1 and CBX7 in Urothelial Carcinoma of the Bladder and Their Prognostic Relevance

Background: The polycomb group (PCG) proteins are epigenetic transcriptional repressors involved in the control of cellular proliferation and oncogenesis. This study aimed at examining whether mRNA tumor levels of the PCG family members BMI1, SUZ12, RING1, and CBX7 relate to histopathological parameters in urothelial carcinomas of the bladder and whether they may provide prognostic information following tumor resection.

Methods: The relative gene expression of BMI1, SUZ12, RING1, and CBX7 was analyzed by real-time RT-PCR in tumor tissue obtained from 93 patients with urothelial carcinoma of the bladder undergoing surgical treatment. Expression data was correlated with pathological variables and outcome.

Results: PCG family members BMI1, SUZ12, RING1, and CBX7 are commonly expressed in urothelial carcinomas of the bladder. The relative CBX7 mRNA expression levels gradually decreased from superficial (pTa) to invasive (pT1) and finally to muscle-invasive (> or =pT2) tumors (p = 0.008). Furthermore, CBX7 expression was statistically significantly correlated with tumor grade (p = 0.04). No correlation of mRNA levels with histopathological tumor features or tumor recurrence was observed for the other PCG components investigated.

Conclusion: Expression levels of CBX7 inversely correlate with the progression of tumor stage and grade in urothelial carcinomas of the bladder, suggesting that downregulation of CBX7 indicates aggressive urothelial carcinoma phenotype.