Deregulation of the cytoplasmic tyrosine kinase cSrc in the absence of a truncating mutation at codon 531 in human bladder carcinoma

The involvement of the cytoplasmic tyrosine kinase cSrc was investigated in human bladder carcinogenesis. Kinase activity was determined in tissue lys ates from bladder transitional cell carcinoma (TCC) relative to normal epit helia. Strong kinase activation was observed at all stages of carcinogenesi s with a peak at the stage pT1, where tumor cells disrupt the basement memb rane and invade the submucosa. In agreement with a role for cSrc in cell in vasion, immunocytochemistry analysis showed a strong staining of invading c ells. An increase in cSrc protein level were also found in most tumor sampl es, however, it did not correlate with an increase in activity (r = 0.44) s uggesting that cSrc is deregulated in these tumors. Indeed, high Src activi ty was affinity-purified from a column (IRSVSSDGHE(p)YIYVDP-Affigel 10) tha t specifically retains active Src. Enzymatic regulation involves the C-term inus, recently found mutated at codon 531 in a subset of advanced human col on cancers. However, no such mutations were detected in TCC, suggesting the existence of other mechanisms for kinase activation. (C) 2000 Academic Pre ss.