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HORMONES AND SIGNALING

The novel protein kinase C isoforms - and - modulate caerulein-induced zymogen activation in pancreatic acinar cells

¹Department of Internal Medicine, Section of Digestive Diseases, ²Department of Cell Biology, Veterans Affairs Connecticut Healthcare of West Haven, and Yale University School of Medicine, New Haven, Connecticut and ³Research Center for Alcoholic Liver and Pancreatic Diseases, Veterans Affairs Greater Los Angeles Health Care System and University of California, Los Angeles, California

Submitted 15 January 2008 ; accepted in final form 2 April 2008

Isoforms of protein kinase C (PKC) have been shown to modulate some cellular responses such as pathological 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 AP using PKC activators and inhibitors. Phorbol ester, 12-O-tetradecanoylphorbol-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 physiological and supraphysiological effects of the hormone cholecystokinin, respectively, in preparations of pancreatic acinar cells. Isoform-specific PKC inhibitors for PKC- and PKC- reduced supraphysiological caerulein-induced zymogen activation. Using a cell-free reconstitution system, we showed that inhibition of PKC- and -, reduced zymogen activation in both zymogen granule-enriched and microsomal fractions. In dispersed acinar cells, 100 nM caerulein stimulation caused PKC- and - isoform translocation to microsomal membranes using cell fractionation and immunoblot 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- redistributed from an apical to a supranuclear region following caerulein administration. The signal for PKC- overlapped with granule membrane protein, GRAMP-92, an endosomal/lysosomal marker, in a supranuclear region where zymogen activation takes place. These results indicate that PKC- and - isoforms translocate to specific acinar cell compartments and modulate zymogen activation.

translocation; PKC activator phorbol ester; PKC inhibitor