The 28K protein in urinary bladder, squamous metaplasia and urine is triosephosphate isomerase

Abstract Objectives: The objective of this study was to establish the identity of a protein found in high concentrations in squamous metaplasia of the bladder. Design and Methods: The protein was isolated and subjected to a series of physical, chemical, and catalytic studies. Results: In the normal urothelium the protein was confined to a juxtanuclear pattern on the luminal side of the umbrella cells; in squamous metaplasia and squamous cell carcinoma the protein was increased and exhibited a more diffuse intracellular distribution. The protein was found to be identical to triosephosphate isomerase (EC 5.3.1.1; TPI) with respect to its immunological properties, native and subunit molecular weights, electrophoretic mobility, catalytic activity, and amino acid sequence. Conclusions: While the basis for the altered distribution of TPI remains to be established, the increased amounts of the protein in urine or bladder tissue may be indicative of squamous metaplasia, squamous cell carcinoma, or other bladder injuries.