The I(1)-imidazoline receptor in PC12 pheochromocytoma cells reverses NGF-induced ERK activation and induces MKP-2 phosphatase

Brain Res. 2003 Aug 1;980(1):71-9. doi: 10.1016/s0006-8993(03)02893-2.


We sought to further elucidate signal transduction pathways for the I(1)-imidazoline receptor in PC12 cells and their interaction with the well-characterized signaling events triggered by nerve growth factor (NGF) in these cells. Stimulation of the I(1)-imidazoline receptor with moxonidine, a centrally acting antihypertensive, increased by greater than two-fold the proportion of ERK-1 and ERK-2 in the phosphorylated active form. Similarly, NGF elicited a five-fold increase in activated ERKs. Surprisingly, treatment of NGF-treated cells with moxonidine completely reversed activation of ERK. Moxonidine-induced inhibition of ERK activation in NGF-treated cells was dose-dependent, followed a limited time course and could be blocked by the I(1)-antagonist efaroxan. These data suggested possible deactivation of ERK by specific phosphatases. Therefore, we assayed levels of MKP-2, a dual specificity phosphatase whose substrates include ERK. Moxonidine and NGF both increased levels of MKP-2 by three-fold. These effects were additive, as both agents together increased MKP-2 by a total of six-fold. Moxonidine-induced induction of MKP-2 was time- and dose-dependent and could be blocked by the I(1)-antagonist efaroxan or by D609, an inhibitor of phosphatidylcholine-selective phospholipase C known to block downstream signaling events coupled to I(1)-receptors. Thus, I(1)-receptors can abrogate the primary signaling cascade activated by NGF, most likely by increasing levels of a specific phosphatase to return dually phosphorylated ERK to its unphosphorylated state.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Antihypertensive Agents / pharmacology
  • Blotting, Western
  • Dose-Response Relationship, Drug
  • Imidazoles / pharmacology
  • Imidazoline Receptors
  • Mitogen-Activated Protein Kinases / metabolism*
  • Nerve Growth Factor / metabolism*
  • PC12 Cells / drug effects*
  • PC12 Cells / enzymology*
  • Phosphoric Monoester Hydrolases / metabolism*
  • Rats
  • Receptors, Drug / agonists
  • Receptors, Drug / metabolism*
  • Signal Transduction


  • Antihypertensive Agents
  • Imidazoles
  • Imidazoline Receptors
  • Receptors, Drug
  • imidazoline I1 receptors
  • Nerve Growth Factor
  • moxonidine
  • Mitogen-Activated Protein Kinases
  • Phosphoric Monoester Hydrolases