Amyloid beta protein (25-35) phosphorylates MARCKS through tyrosine kinase-activated protein kinase C signaling pathway in microglia

Myristoylated alanine-rich C kinase substrate (MARCKS) is a widely distribu ted specific protein kinase C (PKC) substrate and has been implicated in me mbrane trafficking, cell motility, secretion, cell cycle, and transformatio n. We found that amyloid beta protein (A beta) (25-35) and A beta (1-40) ph osphorylate MARCKS in primary cultured rat microglia. Treatment of microgli a with A beta (25-35) at 10 nM or 12-O-tetradecanoylphorbol 13-acetate (1.6 nM) led to phosphorylation of MARCKS, an event inhibited by PKC inhibitors , staurosporine, calphostin C, and chelerythrine. The A beta (25-35)-induce d phosphorylation of MARCKS was inhibited by pretreatment with the tyrosine kinase inhibitors genistein and herbimycin A, but not with pertussis toxin , PKC isoforms alpha, delta, and epsilon were identified in microglia by im munocytochemistry and western blots using isoform-specific antibodies. PKC- delta was tyrosine-phosphorylated by the treatment of microglia for 10 min with A beta (25-35) at 10 nM. Other PKC isoforms alpha and epsilon were tyr osine-phosphorylated by A beta (25-35), but only to a small extent. We prop ose that a tyrosine kinase-activated PKC pathway is involved in the A beta (25-35)-induced phosphorylation of MARCKS in rat microglia.