Modulation of inositol 1,4,5-triphosphate concentration by prolyl endopeptidase inhibition

Prolyl endopeptidase (PEP) is a proline-specific oligopeptidase with a reported effect on learning and memory in different rat model systems. Using the astroglioma cell line U343, PEP expression was reduced by an antisense technique. Measuring different second-messenger concentrations revealed an inverse correlation between inositol 1,4,5-triphosphate [Ins(1,4,5)P-3] concentration and PEP expression in the generated antisense cell lines. However, no effect on cAMP generation was observed. In addition, complete suppression of PEP activity by the specific inhibitor, Fmoc-Ala-Pyrr-CN (5 muM) nduced in U343 and other cell lines an enhanced, but delayed, increase in Ins(1,4,5)P-3 concentration. This indicates that the proteolytic activity of PEP is responsible for the observed effect. Furthermore, the reduced PEP activity was found to amplify Substance P-mediated stimulation of Ins(1,4,5)P-3. The effect of reduced PEP activity on second-messenger concentration indicates a novel intracellular function of this peptidase, which may have an impact on the reported cognitive enhancements due to PEP inhibition.