A Role for the p38 Mitogen-activated Protein Kinase/Hsp 27 Pathway in Cholecystokinin-induced Changes in the Actin Cytoskeleton in Rat Pancreatic Acini

Abstract

Cholecystokinin (CCK) and other pancreatic secretagogues have recently been shown to activate signaling kinase cascades in pancreatic acinar cells, leading to the activation of extracellular signal-regulated kinases and Jun N-terminal kinases. We now show the presence of a third kinase cascade activating p38 mitogen-activated protein (MAP) kinase in isolated rat pancreatic acini. CCK and osmotic stress induced by sorbitol activated p38 MAP kinase within minutes; their effects were dosedependent, with maximal activation of 2.8-and 4.4-fold, respectively. The effects of carbachol and bombesin on p38 MAP kinase activity were similar to those of CCK, whereas phorbol ester, epidermal growth factor, and vasoactive intestinal polypeptide stimulated p38 MAP kinase by 2-fold or less. Both CCK and sorbitol also increased the tyrosyl phosphorylation of p38 MAP kinase. Using the specific inhibitor of p38 MAP kinase, SB 203580, we found that p38 MAP kinase activity was required for MAP kinase-activated protein kinase-2 activation in pancreatic acini. SB 203580 reduced the level of basal phosphorylation and blocked the increased phosphorylation of Hsp 27 after stimulation with either CCK or sorbitol. CCK treatment induced an initial rapid decrease in total F-actin content of acini, followed by an increase after 40 min. Preincubation with SB 203580 significantly inhibited these changes in F-actin content. Staining of the actin cytoskeleton with rhodamine-conjugated phalloidin and analysis by confocal fluorescence microscopy showed disruption of the actin cytoskeleton after 10 and 40 min of CCK stimulation. Pretreatment with SB 203580 reduced these changes. These findings demonstrate that the activation of p38 MAP kinase is involved not only in response to stress, but also in physiological signaling by gastrointestinal hormones such as CCK, where activation of G q -coupled receptors stimulates a cascade in which p38 MAP kinase activates MAP kinase-activated protein kinase-2, resulting in Hsp 27 phosphorylation. Activation of p38 MAP kinase, most likely through phosphorylation of Hsp 27, plays a role in the organization of the actin cytoskeleton in pancreatic acini.

Stabilization of Exocytosis by Dynamic F-actin Coating of Zymogen Granules in Pancreatic Acini

“…In contrast to the two-photon imaging, one-photon confocal microscopy was not able to detect such F-actin coating of granules ( Fig. 1, F and G) as a result of the intense light scattering by zymogen granules (10), instead only revealing a rather diffuse spread of F-actin into the cytosol in response to CCK, as described in previous studies (11,23).…”

“…Although this F-actin coat is thought to constitute a barrier to exocytosis (4 -7), secretory granules undergo exocytosis selectively at the apical membrane (8 -10). Redistribution of F-actin is induced during intense secretory activity (4,11,12), but it has remained unknown how F-actin regulates exocytosis in exocrine cells.…”

Disruption of the Murine Protein Kinase Cβ Gene Promotes Gallstone Formation and Alters Biliary Lipid and Hepatic Cholesterol Metabolism

“…Cholecystokinin-induced gallbladder contraction via its receptor is mediated by the activation of G-proteins and subsequent hydrolysis of phosphatidylinositol 4,5-bisphosphate to inositol 1,4,5-trisphosphate and diacylglycerol. Ultimately, these events lead to increased smooth muscle contraction through the PKC, p42/44 MAPK , and p38 MAPK pathways (71)(72)(73). Thus, it is tempting to speculate that enlarged gallbladder size and reduced p38 MAPK activation in PKC␤ Ϫ/Ϫ mice 4 may reflect reduced gallbladder emptying due to a decrease in cholecystokinin signaling.…”

Parallel Regulation of Mitogen-activated Protein Kinase Kinase 3 (MKK3) and MKK6 in Gq-signaling Cascade

“…p38 MAPK pathway has been implicated in various cellular functions such as gene expressions, cytoskeletal regulations, and morphological changes by stimuli through some G q -coupled receptors (57)(58)(59). In this study, we presented some clues for solving the mechanism whereby G q activates MKK3 and MKK6 and in turn p38 MAPK.…”