cAMP promotes branching of laminin-induced neuronal processes

Laminin is a potent stimulator of neurite outgrowth. We have examined the signal transduction events involved in the neuronal cell response to laminin. Cyclic nucleotides, calcium, and sodium-proton exchange do not appear to be required for the transduction of the laminin signal during neurite outgrowth. Direct measurement of cAMP and cGMP levels shows no changes in NG108-15 cells when cultured on laminin. Exogenous cAMP alone had no effect on either the rate of process formation or process length, but did alter the morphology of laminin-induced neurites. A four-fold increase in the number of branches per neurite and a two-to-three-fold increase in the number of neurites per cell were observed in both NG108-15 and PC12 cells cultured on laminin when either 8-BrcAMP or forskolin was added. The cAMP-induced branching was also observed when PC12 cells were cultured on a laminin-derived synthetic peptide (PA22-2), which contains the neurite-promoting amino acid sequence IKVAV. By immunofluorescence analysis with axonal or dendritic markers, the PC12 processes on laminin and PA22-2 were axonal, not dendritic, and the cAMP-induced morphological changes were due to axonal branching. These data demonstrate that changes in cAMP are not involved in laminin-mediated neurite outgrowth, but cAMP can modulate the effects of laminin.