Heterogeneity of cellular proliferation within transitional cell carcinoma: Correlation of protein kinase C alpha/betal expression and activity

A total of 18 histological samples containing both transitional cell carcinoma (TCC) and normal urothelial epithelium were analyzed for protein kinase C (PKC)-alpha and -beta I expression, and for their phosphorylated substrates. The results showed an increased expression of PKC-alpha in 13 out of 18 samples and -beta I in 11 out of 18 TCC samples when compared with normal urothelium. In addition, 11 out of 18 of the TCC tumors displayed heterogeneous expression of the PKC isoenzymes, with different levels of immunosignal in different areas of the tumor. Within the same sample, areas of highest PKC isoenzyme expression also showed highest classical PKC activity, as estimated by immunodetection of phosphorylated forms of PKC substrates. The areas of highest expression of PKC-alpha and/or -beta I isoenzymes showed also the highest number of cells positive for Ki67, an indicator of proliferation. Immunofluorescence and Western blotting demonstrated that in cultured TCC cells, PKC-alpha was located in the cytoplasm, whereas PKC-beta I was located primarily in the nucleus as a 65-kDa fragment and in the cytoplasm as a full-size 79-kDa protein. Our results indicate that increased expression of PKC-alpha and -beta I leads to increased total classical PKC kinase activity and suggest that increased activity of the isoenzymes plays a role in accelerated growth of TCC. Furthermore, these results suggest that even in carcinoma tissue, PKC expression and activity are under strict control.