Cholecystokinin (CCK) is a gastrointestinal hormone that induces exocytotic amylase release in pancreatic acinar cells. The activation of protein kinase C (PKC) is involved in the CCK-induced pancreatic amylase release. Myristoylated alanine-rich C kinase substrate (MARCKS) is a ubiquitously expressed substrate of PKC. MARCKS has been implicated in membrane trafficking in several cell types. The phosphorylation of MARCKS by PKC results in the translocation of MARCKS from the membrane to the cytosol. Here, we studied the involvement of MARCKS in the CCK-induced amylase release in rat pancreatic acini. Employing Western blotting, we detected MARCKS protein in the rat pancreatic acini. CCK induced MARCKS phosphorylation. A PKC-δ inhibitor, rottlerin, inhibited the CCK-induced MARCKS phosphorylation and amylase release. In the translocation assay, we also observed CCK-induced PKC-δ activation. An immunohistochemistry study showed that CCK induced MARCKS translocation from the membrane to the cytosol. When acini were lysed by a detergent, Triton X-100, CCK partially induced displacement of the MARCKS from the GM1a-rich detergent-resistant membrane fractions (DRMs) in which Syntaxin2 is distributed. A MARCKS-related peptide inhibited the CCK-induced amylase release. These findings suggest that MARCKS phosphorylation by PKC-δ and then MARCKS translocation from the GM1a-rich DRMs to the cytosol are involved in the CCK-induced amylase release in pancreatic acinar cells.

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Salivary glands have the ability to regenerate, yet the origin and markers of stem/progenitor cells involved in this regeneration are still unclear. We have previously reported that the expression of cytokeratin 5, which is considered as a marker of both basal/myoepithelial and progenitor cells in salivary glands, was enhanced by tissue injury. In this study, to identify more specific markers for progenitor cells of salivary glands, we examined the expression and localization of nestin in damaged tissues by duct ligation. Changes in mouse parotid glands after unilateral obstruction of the main excretory duct were analyzed histologically, with immunoblot analysis, and with immunohistochemical staining. Atrophy of acinar cells was observed on the side of duct ligation with hematoxylin and eosin staining. On the other hand, the contralateral side and sham-operated salivary glands did not change morphologically. The amount of nestin protein on the ligated side was increased and was significantly higher than on the contralateral side at day 4. Immunohistochemical staining demonstrated nestin-positive cells in the ducts and the atrophied acinar cells and around them. And some cells expressed both nestin and cytokeratin 5. Ki-67-positive cells were also increased at day 4 on the ligated side, indicating that proliferation of progenitor cells begins simultaneously with the increase in nestin. These results suggest that nestin may be a useful marker of progenitor cells in salivary glands.