Human trypsinogens in the pancreas and in cancer

This study led to the development of monoclonal antibodies and time-resolved immunofluorometric methods recognizing human trypsinogen-1 and -2, respectively. Using these methods in normal sera the concentration of trypsinogen-1 was found to be higher than that of trypsinogen-2. However, in acute pancreatitis the concentration of serum trypsinogen-2 was 50-fold higher than in controls, whereas the difference in trypsinogen-1 concentration was only 15-fold. Serum samples from patients who had undergone pancreatoduodenectomy contained trypsinogen-2, while trypsinogen-1 was detected in only one of nine samples. Furthermore, in human ovarian cyst fluids tumor-associated trypsinogen-2 (TAT-2) is the predominant isoenzyme and in mucinous cyst fluids the levels of TAT-2 were associated with malignancy. These results suggest that (i) trypsinogen-2 could be used as a diagnostic marker for acute pancreatitis, (ii) its expression is not restricted to the pancreas, and (iii) TAT could be involved in ovarian tumor dissemination and breakage of tissue barriers. In ion exchange chromatography, isoelectric variants of the trypsinogen isoenzymes were seen. Mass spectrometric analysis of these revealed that pancreatic trypsinogens are sulfated at tyrosine 154 (Tyr154), whereas TAT-2 from a colon carcinoma cell line is not. Tyr154 is located within the primary substrate binding pocket of trypsin. Thus, Tyr154 sulfation is likely to influence substrate binding. The previously known differences in charge and substrate binding between pancreatic and tumor-associated trypsinogens are suggested to be caused by sulfation of Tyr154 in pancreatic trypsinogens.