Protein Kinase Cδ Regulates Airway Mucin Secretion via Phosphorylation of MARCKS Protein

Mucin hypersecretion is a major pathological feature of many respiratory diseases, yet cellular mechanisms regulating secretion of mucin have not been fully elucidated. Previously, we reported that mucin hypersecretion induced by human neutrophil elastase involves activation of protein kinase C (PKC), specifically the δ-isoform (PKCδ). Here, we further investigated the role of PKCδ in mucin hypersecretion using both primary human bronchial epithelial cells and the human bronchial epithelial 1 cell line as in vitro model systems. Phorbol-12-myristate-13-acetate (PMA)-induced mucin hypersecretion was significantly attenuated by rottlerin, a PKCδ-selective inhibitor. Rottlerin also reduced PMA- or human neutrophil elastase-induced phosphorylation of myristoylated alanine-rich C kinase substrate (MARCKS) protein in these cells. Both secretion and MARCKS phosphorylation were significantly enhanced by the PKCδ activator bryostatin 1. A dominant-negative PKCδ construct (pEGFP-N1/PKCδK376R) transfected into human bronchial epithelial 1 cells significantly attenuated both PMA-induced mucin secretion and phosphorylation of MARCKS, whereas transfection of a wild-type construct increased PKCδ and enhanced mucin secretion and MARCKS phosphorylation. Similar transfections of a dominant-negative or wild-type PKCε construct did not affect either mucin secretion or MARCKS phosphorylation. The results suggest that PKCδ plays an important role in mucin secretion by airway epithelium via regulation of MARCKS phosphorylation.