Submitted on September 10, 2008
Revised on April 10, 2009
Accepted on April 10, 2009
Phosphorylation of myristoylated alanine-rich C kinase substrate is involved in the cAMP-dependent amylase release in parotid acinar cells
Keitaro Satoh1, Miwako Matsuki-Fukushima1, Bing Qi1, Ming-Yu Guo1, Takanori Narita1, Junko Fujita-Yoshigaki2, and Hiroshi Sugiya1*
1 Nihon University School of Dentistry at Matsudo
2 Nihon University School og Dentistry at Matsudo
* To whom correspondence should be addressed. E-mail: sugiya.hiroshi{at}nihon-u.ac.jp.
Myristoylated alanine-rich C kinase substrate (MARCKS) is known as a major cellular substrate for protein kinase C (PKC). MARCKS has been implicated in the regulation of brain development and postnatal survival, cellular migration and adhesion, as well as phagocytosis, endocytosis and exocytosis. The involvement of MARCKS phosphorylation in secretory function has been reported in Ca2+-mediated exocytosis. In rat parotid acinar cells, the activation of 
-adrenergic receptors provokes exocytotic amylase release via accumulation of intracellular cAMP levels. Here, we studied the involvement of MARCKS phosphorylation in the cAMP-dependent amylase release in rat parotid acinar cells. MARCKS protein was detected in rat parotid acinar cells by Western blotting. The -adrenergic agonist isoproterenol (IPR) induced MARCKS phosphorylation in a time-dependent manner. Translocation of a part of phosphorylated MARCKS from the membrane to the cytosol and enhancement of MARCKS phosphorylation at the apical membrane site induced by IPR were observed by immunohistochemistry. H89, a cAMP-dependent protein kinase (PKA) inhibitor, inhibited the IPR-induced MARCKS phosphorylation. The PKC
inhibitor rottlerin inhibited the IPR-induced MARCKS phosphorylation and amylase release. IPR activated PKC, and the effects of IPR were inhibited by the PKA inhibitors. A MARCKS-related peptide partially inhibited the IPR-induced amylase release. These findings suggest that MARCKS phosphorylation via the activation of PKC, which is downstream of PKA activation, is involved in the cAMP-dependent amylase release in parotid acinar cells.
