PKCθ activation in pancreatic acinar cells by gastrointestinal hormones/neurotransmitters and growth factors is needed for stimulation of numerous important cellular signaling cascades

Abstract

The novel PKCθ isoform is highly expressed in T-cells, brain and skeletal muscle and originally thought to have a restricted distribution. It has been extensively studied in T-cells and shown to be important for apoptosis, T-cell activation and proliferation. Recent studies showed its presence in other tissues and importance in insulin signaling, lung surfactant secretion, intestinal barrier permeability, platelet and mast-cell functions. However, little information is available for PKCθ activation by gastrointestinal(GI) hormones/neurotransmitters and growth factors. In the present study we used rat pancreatic acinar cells to explore their ability to activate PKCθ and the possible interactions with important cellular mediators of their actions. Particular attention was paid to cholecystokinin(CCK), a physiological regulator of pancreatic function and important in pathological processes affecting acinar function, like pancreatitis. PKCθ-protein/mRNA were present in the pancreatic acini, and T538-PKCθ phosphorylation/activation was stimulated only by hormones/neurotransmitters activating phospholipase C. PKCθ was activated in time- and dose-related manner by CCK, mediated 30% by high-affinity CCKA-receptor activation. CCK stimulated PKCθ translocation from cytosol to membrane. PKCθ inhibition (by pseudostrate-inhibitor or dominant negative) inhibited CCK- and TPA-stimulation of PKD, Src, RafC, PYK2, p125FAK and IKKα/β, but not basal/stimulated enzyme secretion. Also CCK- and TPA-induced PKCθ activation produced an increment in PKCθ’s direct association with AKT, RafA, RafC and Lyn. These results show for the first time PKCθ presence in pancreatic acinar cells, its activation by some GI hormones/neurotransmitters and involvement in important cell signaling pathways mediating physiological responses (enzyme secretion, proliferation, apoptosis, cytokine expression, and pathological responses like pancreatitis and cancer growth).

Gastrointestinal hormones/neurotransmitters and growth factors can activate P21 activated kinase 2 in pancreatic acinar cells by novel mechanisms

“…We found that the kinetics of CCK-stimulated PAK2 activation was similar to those observed in pancreatic acini with the SFK, Yes, PKC theta, PYK2 and PKD[41,54,77,94] in that it showed a rapid increase, which subsequently partially decreased(by 40%), but was sustained over time. However, it differed from CCK’s activation of p125 FAK or Lyn[39,78], which after initial stimulation decreases markedly to almost basal levels.…”

“…Previous results have demonstrated that numerous GI growth factors (HGF, EGF, bFGF, insulin, IGF and PDGF) are able to interact with specific receptors on pancreatic acinar cells and stimulate growth and/or protein synthesis as well as alter other cellular functions[33,33,54,57,77–79]. We observed activation of PAK2 by EGF, bFGF and PDGF, but not by insulin, IGF-1 and HGF.…”

“…The specificity of the IPA-3 inhibitory effect was supported by the lack of effect of the inactive control Pir 3,5[59,68,104]. These results demonstrate that, although the small GTPases are the principal upstream activator of PAK2 in these cells, there are additional mechanisms of activation that involve PKC and/or SFKs, both which are important CCK signaling pathways in pancreatic acinar cells[58,77,105]. These results differ from that observed in COS7[102], HeLa[9], A2058 human melanoma[19] and colorectal cells[31] where the activation of PAK by different stimuli requires activation of PI3K.…”

Protein kinase C isoforms in the normal pancreas and in pancreatic disease

“…Additionally, PKCθ is an important signaling molecule in pancreatic acinar cells that can be activated by CCK [30], as evidenced by phosphorylation at amino-acid residue T538 and translocation from the cytosol to the plasma membrane [31]. This activation occurs through the CCK A receptor such that most activation occurs through the low affinity state, but about 30% of the activation occurs through the high affinity receptor state [30].…”

“…This activation occurs through the CCK A receptor such that most activation occurs through the low affinity state, but about 30% of the activation occurs through the high affinity receptor state [30]. While PKCθ does not affect amylase release, active PKCθ affects many downstream targets including Src, PYK2, and FAK [30]. …”