Extracellular carbohydrate-signal triggering cAMP-dependent protein kinase-dependent neuronal actin-reorganization

Cell surface glycoconjugates are thought to mediate cell-cell recognition and to play roles in neuronal development and functions. We demonstrated here that exposure of neuronal cells to nanomolar levels of glyco-chains with an N-acetylgalactosamine (GaINAc) residue at the non-reducing termini (GaINAc-S) such as GaINAcbeta4(Neu5Acalpha3)GaIbeta4GIcCer (GM2) ganglioside, its ollgosaccharide portion, GaINAcbeta4GaIbeta4GlcCer (Gg(3)) Cer, GaINAcalpha3GaINAcbeta3GaIalpha4GaIbeta4GIcCer (Gb(5)) Cer (Forssman hapten) and alpha1-4 linked oligomers of GaINAc, induced a rapid and transient activation of cAMP-dependent protein kinase (PKA) in subplasmalemma. The treatment was accompanied by peripheral actin polymerization and filopodia formation in NG108-15 cells and primary cultured hippocampal neurons, but not in glial cells. A cAMP-dependent protein kinase (PKA) selective inhibitor and an adenylate cyclase inhibitor blocked both PKA activation and the subsequent filopodia formation. A small GTPase cdc42 was a potential downstream target of GaINAc-S-activated PKA. These results suggest that extracellular GaINAc-S serve as potential regulators of the filopodia formation in neuronal cells by triggering the activation of PKA followed by cdc42 up-regulation via a cell surface receptor-like component. Filopodia formation induced by GaINAc-S may have a physiological relevance because long-term exposure to GaINAc-S enhanced F-actin-rich dendrite generation of primary cultured hippocampal neurons, and PKA-dependent dendritic outgrowth and branch formation of primary cultured cerebellar Purkinje neurons, in which actin isoforms were localized to motile structures in dendrites. These findings provide evidence for a novel GaINAc/PKA-signaling cascade in regulating some neuronal maturation. (C) 2003 IBRO. Published by Elsevier Ltd. All rights reserved.