NTRK1 and urothelial carcinoma: To identify growth-promoting signals that were activated via tyrosine phosphorylation along the receptor-tyrosine-kinase (RTK) pathway thus potentially overcoming the rate-limit step of urothelial carcinoma initiation, we first employed one-dimensional (1-D) SDS-PAGE followed by Western blotting using an antibody against pan-phosphotyrosine capable of reacting with all tyrosine-phosphorylated proteins.