NERVE GROWTH FACTOR-ACTIVATED PROTEIN-KINASE-N MODULATES THE CAMP-DEPENDENT PROTEIN-KINASE

Protein kinase N (PKN) is a serine/threonine protein kinase rapidly ac tivated by nerve growth factor (NGF) and other agents in various cell lines, The possible involvement of PKN in the multiple pathways of the NGF mechanism of action was previously established through the use of purine analogs, some of which are apparently specific inhibitors of t his kinase. Since a PKN-like activity is modulated in several cell lin es by cAMP analogs and this activation requires the activity of cAMP-d ependent protein kinase, the aim of the present work is to investigate possible interactions between PKN and C-PKA, Preincubation of the two kinases in the presence of ATP leads to potentiated phosphorylation o f histone HF1, Kemptide (a substrate for C-PKA, but not for PKN), and several additional substrates. This augmented phosphorylating activity is insensitive to 6-thioguanine (an inhibitor for PKN, but not for C- PKA) and is suppressed both by the Walsh inhibitor and by the regulato ry subunit of PKA, PKN-pretreated C-PKA shows a significant decrease i n K-m for Kemptide and a substantial increase in V-max. C-PKA and PKN are widely expressed enzymes and the possibility of PKN-dependent modu lation of PKA in intact cells would therefore have biological implicat ions for signal transduction mechanisms. (C) 1995 Wiley-Liss, Inc.