Early events in the pancreatic acinar cell critical for development of pancreatitis include activation of the transcription factor nuclear factor κB (NF-κB), abnormal Ca²⁺ responses, and trypsinogen activation. Mechanisms underlying these responses, which can be studied in isolated pancreatic acini stimulated with supraphysiologic doses of cholecystokinin (CCK-8), remain poorly understood. We here report that these responses are regulated by phosphatidylinositide 3-kinase (PI3K) γ.

To inactivate PI3K, we used mice deficient in the catalytic PI3Kγ subunit p110γ as well as the PI3K inhibitors LY294002 and wortmannin. We measured Ca²⁺ responses by using Fura-2, NF-κB-binding activity by electromobility shift assay, IκB degradation by Western blotting, and trypsinogen activation by fluorogenic assay.

CCK-induced intracellular Ca²⁺ mobilization, Ca²⁺ influx, trypsinogen, and NF-κB activation were all diminished in pancreatic acini isolated from p110γ^−/− mice. Both in mouse and rat acini, these responses were inhibited by the PI3K inhibitors. The Ca²⁺ signal and trypsinogen activation were similarly reduced in acini isolated from p110γ^−/− and p110γ^+/− mice compared with wild-type mice. By contrast, NF-κB activation was inhibited in p110γ^−/− acini but not in p110γ^+/− acini. These differences indicate that the mechanism of NF-κB regulation by PI3Kγ differs from those for the Ca²⁺ and trypsinogen responses. CCK-induced responses in p110γ^−/− acini were all further inhibited by LY294002, indicating the involvement of other PI3K isoform(s), in addition to PI3Kγ.

The results show that key pathologic responses of the pancreatic acinar cell are regulated by PI3Kγ and suggest an important role for this PI3K isoform in pancreatitis.