Elevated expression of pp60c-src in low grade human bladder carcinoma.

The results presented in this report demonstrate that the tyrosine-specific protein kinase activity of pp60c-src is elevated over that recorded in normal bladder mucosa in a subset of human bladder carcinomas. Increased kinase activity was observed mainly in low grade bladder lesions and was associated, at least in part, with elevated levels of pp60c-src expression. Extension of this analysis to a panel of human bladder carcinoma cell lines confirmed previous observations of low pp60c-src kinase activity in three lines established from high grade (GIII) bladder tumors and revealed increased kinase activity in three alternative bladder lines derived from GI or GII tumors. Use of an anti-phosphotyrosine antibody in Western blot analysis revealed the presence of novel phosphotyrosyl cellular substrates in human bladder cell lines and tumors displaying elevated pp60c-src kinase activity. These observations suggest an association for the src protooncogene in urothelial cell differentiation events.