ARPP-39, a membrane-associated substrate for cyclic AMP-dependent protein kinase present in neostriatal neurons.

This study describes a cyclic AMP-regulated phosphoprotein that displays a distinct cellular and regional distribution in rat brain. The protein is found only in neostriatal regions, where it is enriched in nerve cells and not in afferent or efferent axons or in glial cells. On subcellular fractionation, it appears tightly associated with particulate components, possibly the synaptic plasma membrane fraction. The protein may therefore be specifically enriched in dendrites and/or somata of neostriatal neurons. Following phosphorylation in vitro with [gamma-32P]ATP and cyclic AMP-dependent protein kinase, the protein contains phosphoseryl residues on multiple thermolytic peptides. The specific cellular and subcellular localization we have observed suggests that this protein, termed ARPP-39 (cyclic AMP-regulated phosphoprotein, M(r) = 39,000) may be important in receptor-regulated, cyclic AMP-mediated functions in distinct neostriatal neurons.