The p.E152K-STIM1 mutation deregulates Ca2+ signaling contributing to chronic pancreatitis

Since deregulation of intracellular Ca²⁺ can lead to intracellular trypsin activation, and stromal interaction molecule-1 (STIM1) protein is the main regulator of Ca²⁺ homeostasis in pancreatic acinar cells, we explored the Ca²⁺ signaling in 37 STIM1 variants found in three pancreatitis patient cohorts. Extensive functional analysis of one particular variant, p.E152K, identified in three patients, provided a plausible link between dysregulated Ca²⁺ signaling within pancreatic acinar cells and chronic pancreatitis susceptibility. Specifically, p.E152K, located within the STIM1 EF-hand and sterile α-motif domain, increased the release of Ca²⁺ from the endoplasmic reticulum in patient-derived fibroblasts and transfected HEK293T cells. This event was mediated by altered STIM1-sarco/endoplasmic reticulum calcium transport ATPase (SERCA) conformational change and enhanced SERCA pump activity leading to increased store-operated Ca²⁺ entry (SOCE). In pancreatic AR42J cells expressing the p.E152K variant, Ca²⁺ signaling perturbations correlated with defects in trypsin activation and secretion, and increased cytotoxicity after cholecystokinin stimulation.This article has an associated First Person interview with the first author of the paper.

The lysine derivative aminoadipic acid, a biomarker of protein oxidation and diabetes-risk, induces production of reactive oxygen species and impairs trypsin secretion in mouse pancreatic acinar cells

We have examined the effects of α-aminoadipic acid, an oxidized derivative from the amino acid lysine, on the physiology of mouse pancreatic acinar cells. Changes in intracellular free-Ca²⁺ concentration, the generation of reactive oxygen species, the levels of carbonyls and thiobarbituric-reactive substances, cellular metabolic activity and trypsin secretion were studied. Stimulation of mouse pancreatic cells with cholecystokinin (1 nM) evoked a transient increase in [Ca²⁺]_i. In the presence of α-amoniadipic acid increases in [Ca²⁺]_i were observed. In the presence of the compound, cholecystokinin induced a Ca²⁺ response that was smaller compared with that observed when cholecystokinin was applied alone. Stimulation of cells with cholecystokinin in the absence of Ca²⁺ in the extracellular medium abolished further mobilization of Ca²⁺ by α-aminoadipic acid. In addition, potential pro-oxidant conditions, reflected as increases in ROS generation, oxidation of proteins and lipids, were noted in the presence of α-aminoadipic acid. Finally, the compound impaired trypsin secretion induced by the secretagogue cholecystokinin. We conclude that the oxidized derivative from the amino acid lysine induces pro-oxidative conditions and the impairment of enzyme secretion in pancreatic acinar cells. α-aminoadipic acid thus creates a situation that could potentially lead to disorders in the physiology of the pancreas.

The melatonin receptor antagonist luzindole induces Ca2+ mobilization, reactive oxygen species generation and impairs trypsin secretion in mouse pancreatic acinar cells

BACKGROUND

In this work we studied the effects of the melatonin receptor-antagonist luzindole (1 μM-50 μM) on isolated mouse pancreatic acinar cells.

METHODS

Changes in intracellular free-Ca²⁺ concentration, reactive oxygen species production and trypsin secretion were analyzed.

RESULTS

Luzindole induced increases in [Ca²⁺]_i that diminished CCK-8 induced Ca²⁺ mobilization, compared with that observed when CCK-8 was applied alone. Treatment of cells with thapsigargin (1 μM), in the absence of Ca²⁺ in the extracellular medium, evoked a transient increase in [Ca²⁺]_i. The additional incubation of cells with luzindole (10 μM) failed to induce further mobilization of Ca²⁺. In the presence of luzindole a concentration-dependent increase in ROS generation was observed that decreased in the absence of Ca²⁺ or by pretreatment of cells with melatonin (100 μM). Incubation of pancreatic acinar cells with luzindole (10 μM) impaired CCK-8-induced trypsin secretion. Melatonin was unable to revert the effect of luzindole on CCK-8-induced trypsin secretion.

CONCLUSION

The melatonin receptor-inhibitor luzindole induces Ca²⁺-mediated pro-oxidative conditions and impairment of enzyme secretion, which creates a situation in pancreatic acinar cells that might compromise their function.

GENERAL SIGNIFICANCE

The effects of luzindole that we have observed, might be unspecific and could mislead the observations when it is used to study the actions of melatonin on the gland. Another possibility is that melatonin receptors exhibit a basal or agonist-independent activity in pancreatic acinar cells, which might be modulated by melatonin or luzindole.