2',3'cyclic nucleotide-3'-phosphodiesterase in peripheral nerve myelin is phosphorylated by a phorbol ester-sensitive protein kinase

Abstract

2',3' cyclic nucleotide-3'-phosphodiesterase (CNP) is phosphorylated in the peripheral nervous system after immunoprecipitation of myelin proteins radiolabeled in vivo, in nerve slices and in a cell-free system. Only radiolabeled phosphoserine was detected after partial acid hydrolysis of immunoprecipitated CNP. Two major phosphopeptides were resolved by two dimensional electrophoresis-chromatography after digestion with trypsin of CNP phosphorylated in the nerve slices. Phosphorylation of CNP was not stimulated a) by forskolin in the nerve slices and b) after incubation of purified nerve myelin with cAMP. However, CNP phosphorylation was increased after incubation of PNS myelin with catalytic unit of protein kinase A. Phosphorylation of the central nervous system myelin CNP was dramatically stimulated by cAMP. These results suggest that PKA may be absent from peripheral nerve myelin or CNP may not be accessible to this enzyme in the PNS. Incubation of nerve slices with phorbol 12 myristate-13-acetate caused a marked increase in the phosphorylation of CNP. These results provide strong evidence that CNP is phosphorylated in the PNS and its phosphorylation in vivo is in all probability regulated by protein kinase C.