The transcription factors CREB and c-Fos play key roles in NCAM-mediated neuritogenesis in PC12-E2 cells

The neural cell adhesion molecule (NCAM) stimulates axonal outgrowth by activation of the Ras-mitogen activated protein kinase (MAPK) pathway and by generation of arachidonic acid. We investigated whether the transcription factors, cyclic-AMP response-element binding protein (CREB) and c-Fos play roles in this process by estimating NCAM-dependent neurite outgrowth from PC12-E2 cells grown in co-culture with NCAM-negative or NCAM-positive fibroblasts. PC12-E2 cells were transiently transfected with expression plasmids encoding wild-type or dominant negative forms of CREB and c-Fos or an activated form of the MAPK kinase, MEK2. Alternatively, PC12-E2 cells were treated with arachidonic acid, the cAMP analogue dBcAMP, or protein kinase A (PKA) inhibitors. The negative forms of CREB and c-Fos inhibited neurite outgrowth mediated by NCAM, arachidonic acid, dBcAMP, or MEK2. Neither CREB nor c-Fos could compensate for the inactivation of the other, indicating that both factors are important in NCAM-mediated neuritogenesis. Treatment of primary hippocampal neurons with a synthetic NCAM peptide ligand known to stimulate neurite outgrowth induced phosphorylation of CREB and expression of c-fos. We thus present evidence that NCAM-mediated neurite outgrowth involves a series of signal transduction pathways, including the cAMP/PKA pathway, targeting c-Fos and CREB.