6-Methylmercaptopurine riboside is a potent and selective inhibitor of nerve growth factor-activated protein kinase N

C. Volonte, L. A. Greene

Research output: Contribution to journalArticlepeer-review


Protein kinase N (PKN) is a soluble, apparently novel serine protein kinase that is activated by nerve growth factor (NGF) and other agents in PC12 pheochromocytoma cells as well as in several nonneuronal cell lines. Purine analogs, such as 6-thioguanine and 2-aminopurine, have been found to inhibit PKN in vitro. When applied to intact cells, these compounds suppress certain biological responses to NGF, but not others, a finding suggesting the presence of multiple pathways in the NGF mechanism. We report here that 6-methylmercaptopurine riboside (6-MMPR) inhibits NGF-stimulated PKN activity in vitro with an apparent K(i) of ~5 nM. This is ~1,000-fold lower than the K(i) of the most potent purine inhibitor of PKN. Compounds similar to 6-MMPR, but lacking the methyl or riboside groups, were much less potent as PKN inhibitors. A survey of six additional purified protein kinases shows no inhibitory effect of 6-MMPR, thus indicating a good degree of specificity of this compound for PKN. In contrast to NGF-stimulated PKN, a PKN-like activity stimulated in PC12 cells in response to activation of cyclic AMP-dependent protein kinase was nearly insensitive to 6-MMPR. Application of 6-MMPR to intact PC12 cells resulted in blockade of several responses to NGF (neurite regeneration and ornithine decarboxylase induction) but not of several others (rapid enhancement of tyrosine hydroxylase phosphorylation and PKN activation). These findings suggest that 6-MMPR is a potent and selective agent for characterizing PKN in vitro and for assessing its potential role in the multiple pathways of the NGF mechanism of action.

Original languageEnglish
Pages (from-to)700-708
Number of pages9
JournalJournal of Neurochemistry
Issue number2
Publication statusPublished - 1992


  • 6-Methylmercaptopurine riboside
  • Nerve growth factor
  • PC12 cells
  • Protein kinase N
  • Protein kinases

ASJC Scopus subject areas

  • Biochemistry
  • Cellular and Molecular Neuroscience


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