Microtubule-organizing center-mediated structural atypia in low- and high-grade urothelial carcinoma

Urothelial carcinoma (UC) comprises two subtypes, low grade (LG-UC) and high grade (HG-UC), with different pathological and clinical behavior. LG-UC and HG-UC are classified based on cellular and structural atypia of pathological findings. The mechanisms responsible for maintaining structural atypia, such as the disturbance of nuclear polarity, remain unclear. In this study, we studied microtubule-organizing center (MTOC)-mediated nuclear polarity in UC subtypes. We evaluated six cases with normal urothelium (NU), 10 LG-UC cases, and 10 HG-UC cases by double immunofluorescence staining of γ-tubulin as a marker of MTOC and E-cadherin as a marker of each cell border. The number and position of γ-tubulin dots of expression in more than 100 cells per case were assessed using the spatial relationship with the nucleus and surface-basal axis. We found one γ-tubulin dot in most normal and tumor cells, and more than two γ-tubulin dots in 4.6% of NU cells, 6.1% of LG-UC cells, and 9.8% of HG-UC cells. More than three γ-tubulin dots were found only in 1.2% of HG-UC cells. Surface side positioning of γ-tubulin was found in 77.4% of normal urothelial cells, 63.8% of LG-UC cells, and 39.2% of HG-UC cells, whereas aberrant lateral and basal side positioning of γ-tubulin was found in 22.6% of normal urothelial cells, 36.1% of LG-UC cells, and 60.8% of HG-UC cells. We concluded that numerical and positional aberrations of MTOC in UC cases were strongly correlated with both cellular and structural atypia as well as abnormal cell proliferation.