Abstract
Several deleterious intra-acinar phenomena are simultaneously triggered on initiating acute pancreatitis. These culminate in acinar injury or inflammatory mediator generation in vitro and parenchymal damage in vivo. Supraphysiologic caerulein is one such initiator which simultaneously activates numerous signaling pathways including non-receptor tyrosine kinases such as of the Src family. It also causes a sustained increase in cytosolic calcium- a player thought to be crucial in regulating deleterious phenomena. We have shown Src to be involved in caerulein induced actin remodeling, and caerulein induced changes in the Golgi and post-Golgi trafficking to be involved in trypsinogen activation, which initiates acinar cell injury. However, it remains unclear whether an increase in cytosolic calcium is necessary to initiate acinar injury or if injury can be initiated at basal cytosolic calcium levels by an alternate pathway. To study the interplay between tyrosine kinase signaling and calcium, we treated mouse pancreatic acinar cells with the tyrosine phosphatase inhibitor pervanadate. We studied the effect of the clinically used Src inhibitor Dasatinib (BMS-354825) on pervanadate or caerulein induced changes in Src activation, trypsinogen activation, cell injury, upstream cytosolic calcium, actin and Golgi morphology. Pervanadate, like supraphysiologic caerulein, induced Src activation, redistribution of the F-actin from its normal location in the sub-apical area to the basolateral areas, and caused antegrade fragmentation of the Golgi. These changes, like those induced by supraphysiologic caerulein, were associated with trypsinogen activation and acinar injury, all of which were prevented by Dasatinib. Interestingly, however, pervanadate did not cause an increase in cytosolic calcium, and the caerulein induced increase in cytosolic calcium was not affected by Dasatinib. These findings suggest that intra-acinar deleterious phenomena may be initiated independent of an increase in cytosolic calcium. Other players resulting in acinar injury along with the Src family of tyrosine kinases remain to be explored.
Highlights
Pancreatitis is initiated by numerous insults [1]
In this study we note that pervanadate treatment of acinar cells results in F-actin reorganization, trypsinogen activation and acinar injury independent of an increase in cytosolic calcium
This seems to involve Src since Dasatinib prevents the activation of Src, in addition to inhibiting F-actin reorganization, antegrade fragmentation of the Golgi, trypsinogen activation and acinar injury induced by pervanadate, which on its own does not increase cytosolic calcium levels
Summary
Pancreatitis is initiated by numerous insults [1]. The most commonly used model to study pancreatitis in rodents is the caerulein model. The commonly studied upstream signaling mechanisms include the activation of Src [7], protein kinase C isoforms [8,9], calcium signaling [10,11,12], the calcium dependent protein kinase Pyk2 [13,14], PI3 Kinases [15,16,17], MAP kinases [18,19,20], ERK [21] etc These regulate phenomena such as actin reorganization [22,23,24], caspase activation [5,6], transcription factor activation such as AP-1 [2], translocation of p65 unit of NF-. The increase in intracellular calcium is commonly thought to be ‘‘essential but not sufficient’’ for the initiation of these pathways since calcium chelators do prevent certain crucial steps (e.g. trypsinogen activation, NF-kB activation) [2,32], but agents that increase intracellular calcium alone (e.g. ionomycin or thapsigargin) have been ineffective in activating proinflammatory or cell death phenomena in most studies [2,28,32]
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