title: MARCKS protein is a key molecule regulating mucin secretion by human airway epithelial cells in vitro.
abstract: Hypersecretion of airway mucin characterizes numerous respiratory diseases. Although diverse pathological stimuli can provoke exocytotic release of mucin from secretory cells of the airway epithelium, mechanisms involved remain obscure. This report describes a new paradigm for the intracellular signaling mechanism regulating airway mucin secretion. Direct evidence is provided that the myristoylated alanine-rich C kinase substrate (MARCKS) is a central regulatory molecule linking secretagogue stimulation at the cell surface to mucin granule release by differentiated normal human bronchial epithelial cells in vitro. Down-regulation of MARCKS expression or disruption of MARCKS function in these cells inhibits the secretory response to subsequent stimulation. The intracellular mechanism controlling this secretory process involves cooperative action of two separate protein kinases, protein kinase C and cGMP-dependent protein kinase. Upon stimulation, activated protein kinase C phosphorylates MARCKS, causing translocation of MARCKS from the plasma membrane to the cytoplasm, where it is then dephosphorylated by a protein phosphatase 2A that is activated by cGMP-dependent protein kinase, and associates with both actin and myosin. Dephosphorylated cytoplasmic MARCKS would also be free to interact with mucin granule membranes and thus could link granules to the contractile cytoskeleton, mediating their movement to the cell periphery and subsequent exocytosis. These findings suggest several novel intracellular targets for pharmacological intervention in disorders involving aberrant secretion of respiratory mucin and may relate to other lesions involving exocytosis of membrane-bound granules in various cells and tissues.
authors.affiliation: Department of Anatomy, Physiological Sciences and Radiology, College of Veterinary Medicine, North Carolina State University, Raleigh, North Carolina 27606, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Li
authors.forename: L D
authors.initials: LD
authors.lastname: Martin
authors.forename: G
authors.initials: G
authors.lastname: Spizz
authors.forename: K B
authors.initials: KB
authors.lastname: Adler
mesh_terms: D000199:Actins / Q000378:metabolism; D000595:Amino Acid Sequence; D017869:Cyclic GMP-Dependent Protein Kinases / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D015536:Down-Regulation; D004789:Enzyme Activation; D004847:Epithelial Cells / Q000201:enzymology / Q000378:metabolism; D005089:Exocytosis; D006801:Humans; D066298:In Vitro Techniques; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D008969:Molecular Sequence Data; D009077:Mucins / Q000378:metabolism*; D009218:Myosins / Q000378:metabolism; D000076250:Myristoylated Alanine-Rich C Kinase Substrate; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism*; D011506:Proteins / Q000502:physiology*; D014132:Trachea / Q000166:cytology / Q000201:enzymology / Q000378:metabolism*
chemical_list: D000199:Actins; D047908:Intracellular Signaling Peptides and Proteins; C000619710:MARCKS protein, human; D008565:Membrane Proteins; D009077:Mucins; D011506:Proteins; D000076250:Myristoylated Alanine-Rich C Kinase Substrate; D017869:Cyclic GMP-Dependent Protein Kinases; D011493:Protein Kinase C; D009218:Myosins