The Novel Protein Kinase C Isoforms -δ and -ε Modulate Caerulein-induced Zymogen Activation in Pancreatic Acinar Cells

Isoforms of protein kinase C (PKC) have been shown to modulate some cellular responses such as pathologic secretion and generation of inflammatory mediators during acute pancreatitis (AP). We propose that PKC also participates in premature zymogen activation within the pancreatic acinar cell, a key event in the initiation of AP. This hypothesis was examined in in vivo and cellular models of caerulein-induced acute pancreatitis using PKC activators and inhibitors. Phorbol ester, 12Otetradecanoylphorbol-13-acetate (TPA; 200 nM), a known activator of PKC, enhanced zymogen activation at both 0.1 nM and 100 nM caerulein, concentrations which mimic physiologic and supraphysiologic effects of the hormone cholecystokinin (CCK) respectively, in preparations of pancreatic acinar cells. Isoform-specific PKC inhibitors for PKC δ and PKC ε reduced supraphysiologic caerulein-induced zymogen activation. Using a cell-free reconstitution system we showed that inhibition of PKC δ and ε, reduced zymogen activation in both zymogen granule-enriched and microsomal fractions. In dipsersed acinar cells 100 nM caerulein stimulation caused PKC δ and ε isoform translocation to microsomal membranes using cell fractionation and immunblot analysis. PKC translocation was confirmed with in-vivo studies and immunofluorescence microscopy in pancreatic tissues from rats treated with or without 100 nM caerulein. PKC ε redistributed from an apical to a supranuclear region following caerulein administration. The signal for PKC ε overlapped with GRAMP 92, an endosomal/lysosomal marker, in a supranuclear region where zymogen activation takes place. These results indicate that PKC δ and ε isoforms translocate to specific acinar cell compartments and modulate zymogen activation. Page 2 of 43