Submitted on May 9, 2004
Accepted on July 20, 2004
Phosphatidylinositol 3-kinase regulates Ca2+ signaling in pancreatic acinar cells through inhibition of sarco-endoplasmic reticulum Ca2+-ATPase (SERCA)
L. Fischer1, A. S. Gukovskaya2*, S. H. Young3, I. Gukovsky2, A. Lugea2, P. Buechler4, J. M. Penninger5, H. Friess4, and S. J. Pandol2
1 Veterans Affairs Greater Los Angeles Healthcare System, David Geffen School of Medicine, University of California, Los Angeles, CA, USA; Department of Medicine, David Geffen School of Medicine, University of California, Los Angeles, CA, USA; Department of Surgery, University of Heidelberg, Heidelberg, Germany
2 Veterans Affairs Greater Los Angeles Healthcare System, David Geffen School of Medicine, University of California, Los Angeles, CA, USA; Department of Medicine, David Geffen School of Medicine, University of California, Los Angeles, CA, USA
3 Department of Medicine, David Geffen School of Medicine, University of California, Los Angeles, CA, USA
4 Department of Surgery, University of Heidelberg, Heidelberg, Germany
5 Institute for Molecular Biotechnology, Austrian Academy of Sciences, Vienna, Austria
* To whom correspondence should be addressed. E-mail: agukovsk{at}ucla.edu.
Calcium is a key mediator of hormone-induced enzyme secretion in pancreatic acinar cells. At the same time, abnormal Ca2+ responses are associated with pancreatitis. We have recently shown that inhibition of phosphatidylinositol 3-kinase (PI3K) by LY294002 and wortmannin, as well as genetic deletion of the PI3K gamma isoform (PI3K
), regulates Ca2+ responses and the Ca2+-sensitive trypsinogen activation in pancreatic acinar cells. The present study sought to determine the mechanisms of PI3K involvement in Ca2+ responses induced in these cells by cholecystokinin-8 (CCK) and carbachol. The PI3K inhibitors inhibited both Ca2+ influx and mobilization from intracellular stores induced by stimulation of acini with physiologic and pathologic concentrations of CCK, as well as with carbachol. PI3K inhibition facilitated the decay of [Ca2+]i oscillations observed in individual acinar cells. The PI3K inhibitors decreased neither CCK-induced IP3 production nor IP3-induced Ca2+ mobilization suggesting that the effect of PI3K inhibition is not through IP3 or IP3 receptors. PI3K inhibition did not affect Ca2+ mobilization induced by thapsigargin, a specific inhibitor of sarco-endoplasmic reticulum Ca2+-ATPase (SERCA). Moreover, SERCA blockade with thapsigargin abolished the effects of pharmacologic and genetic PI3K inhibition on [Ca2+]i signals, suggesting SERCA as a downstream target of PI3K. Pharmacologic PI3K inhibition as well as genetic deletion of PI3K both increased the amount of Ca2+ in intracellular stores during CCK stimulation. Finally, addition of PI3K product, phosphatidylinositol 3,4,5-trisphosphate, to permeabilized acini significantly attenuated Ca2+ reloading into the ER. The results indicate that PI3K regulates Ca2+ signaling in pancreatic acinar cells through its inhibitory effect on SERCA.
