A ROLE FOR THE P38 MITOGEN-ACTIVATED PROTEIN-KINASE HSP-27 PATHWAY INCHOLECYSTOKININ-INDUCED CHANGES IN THE ACTIN CYTOSKELETON IN RAT PANCREATIC ACINI

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 ki nases and Jun N-terminal kinases. We now show the presence of a third kinase cascade activating p38 mitogen-activated protein (MAP) kinase i n isolated rat pancreatic acini, CCK and osmotic stress induced by sor bitol activated p38 MAP kinase within minutes; their effects were dose -dependent, with maximal activation of 2.8- and 4.4-fold, respectively . The effects of carbachol and bombesin on p38 MAP kinase activity wer e similar to those of CCK, whereas phorbol eater, epidermal growth fac tor, and vasoactive intestinal polypeptide stimulated p38 MAP kinase b y 8-fold or less. Both CCK and sorbitol also increased the tyrosyl pho sphorylation of p38 MAP kinase. Using the specific inhibitor of p38 MA P kinase, SE 203580, we found that p38 MAP kinase activity was require d for MAP kinase-activated protein kinase-a activation in pancreatic a cini. SE 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 t otal F-actin content of acini, followed by an increase after 40 min. P reincubation with SE 203580 significantly inhibited these changes in F -actin content. Staining of the actin cytoskeleton with rhodamine-conj ugated phalloidin and analysis by confocal fluorescence microscopy sho wed disruption of the actin cytoskeleton after 10 and 40 min of CCK st imulation. Pretreatment with SE 203580 reduced these changes. These fi ndings demonstrate that the activation of p38 MAP kinase is involved n ot only in response to stress, but also in physiological signaling by gastrointestinal hormones such as CCK, where activation of G(q)-couple d receptors stimulates a cascade in which pas MAP kinase activates MAP kinase-activated protein kinase-2, resulting in Hsp 27 phosphorylatio n. Activation of p38 MAP kinase, most likely through phosphorylation o f Hsp 27, plays a role in the organization of the actin cytoskeleton i n pancreatic acini.