Substance P-induced elevation of intracellular calcium in transfected Chinese hamster ovary cells: role of inositol trisphosphate

Role of calcium in substance P-induced chemokine synthesis in mouse pancreatic acinar cells

BACKGROUND AND PURPOSE

Substance P (SP) and chemokines play critical roles in acute pancreatitis. SP elevates cytosolic calcium in pancreatic acinar cells and elevated cytosolic calcium is thought to be an early event in the pathogenesis of acute pancreatitis. SP induces production of chemokines MCP-1, MIP-1alpha and MIP-2 in pancreatic acinar cells, however the exact mechanism by which SP stimulates the production of these pro-inflammatory mediators remain undetermined. The aim of the present study is to investigate the role of calcium in SP-induced chemokine production in pancreatic acinar cells and to establish the signal transduction mechanisms involved.

EXPERIMENTAL APPROACH

An in vitro model of isolated mouse pancreatic acinar cells was used. Western blotting analysis, ELISA and calcium measurement were performed.

KEY RESULTS

SP increased chemokine secretion through the activation of PKCalpha/betaII, MAPKinases (ERK and JNK), NFkappaB and AP-1 in pancreatic acinar cells. These effects were blocked by pretreatment of the cells with the specific calcium chelator BAPTA-AM. Moreover, SP-induced activation of PKCalpha/betaII, ERK, JNK, NF-kappaB, AP-1 and chemokine production was inhibited by the specific phospholipase C inhibitor U73122.

CONCLUSIONS AND IMPLICATIONS

SP-induced chemokine production in pancreatic acinar cells resulted from PLC-induced elevated intracellular calcium and PKCalpha/betaII activation, subsequently leading to the activation of MAPKinases (ERK and JNK) and transcription factors NF-kappaB and AP-1. The present study demonstrates the critical role of calcium in SP-induced chemokine production in pancreatic acinar cells. Drugs targeting the SP-calcium mediated signaling pathways could prove beneficial in improving the treatment of acute pancreatitis.

A substance P (neurokinin-1) receptor mutant carboxyl-terminally truncated to resemble a naturally occurring receptor isoform displays enhanced responsiveness and resistance to desensitization

Two isoforms of the substance P (SP) receptor, differing in the length of the cytoplasmic carboxyl-terminus by approximately 8 kDa, have been detected previously in rat salivary glands and other tissues. The binding and functional properties of these two isoforms have been investigated using full-length (407 amino acids) and carboxyl-terminally truncated (324 amino acids) rat SP receptors transfected stably into Chinese hamster ovary cells. Both the full-length and the truncated receptor bound radiolabeled SP with a similar Kd ( approximately 0.1 nM). The average number of high affinity SP binding sites per cell was 1.0 x 10(5) and 0.3 x 10(5) for the full-length and the truncated SP receptor, respectively. In both cell lines, SP induced a rapid but transient increase in cytosolic calcium concentration ([Ca2+]i), which consisted of the release of Ca2+ from intracellular stores and the influx of extracellular Ca2+. Both components are dependent on phospholipase C activation. Although the full-length and the truncated receptor utilize the same calcium pathways, they differ in their EC50 values (0.28 nM for the full-length; 0.07 nM for the truncated). These differences in responsiveness may be related to the observed differences in receptor desensitization. The truncated receptor, in contrast to the full-length receptor, does not undergo rapid and long-lasting desensitization. Cells possessing the short isoform of the SP receptor would thus be expected to exhibit a prolonged responsiveness.