Identification of functional cAMP-dependent protein kinase in a 'neurite minus' mouse neuroblastoma cell line

We have characterized and quantitated the level of cAMP-dependent protein kinase in the NS-20, N1E-115, N-18 and N1A-103 mouse neuroblastoma clonal cell lines, and we have correlated the occurrence of functional cAMP-dependent protein kinase with the dibutyryl cAMP-induced differentiated functions in these cells. Our results demonstrate the presence of functional cAMP-dependent protein kinase in extracts of all four cell lines examined, including the 'neurite minus' N1A-103 cell line. Dibutyryl cAMP induced neurite outgrowth and acetylcholinesterase activity in the NS-20, N1E-115 and N-18 neuroblastoma cell lines, but not in the N1A-103 cell line. However, dibutyryl cAMP caused a 2-3-fold increase in the R1 regulatory subunit protein and cAMP-phosphodiesterase activity in the 'neurite minus' N1A-103 cells in a manner similar to that of the other three 'neurite positive' cell lines. These results suggest that the biochemical lesion(s) subserving the neurite-minus phenotype of the N1A-103 cells may be distal to the activation of cAMP-dependent protein kinase and is in a biochemical pathway distinct from the induction of R1 regulatory subunit protein and cAMP-phosphodiesterase activity.