Induction of Krox-24 by Endogenous Cannabinoid Type 1 Receptors in Neuro2A Cells Is Mediated by the MEK-ERK MAPK Pathway and Is Suppressed by the Phosphatidylinositol 3-Kinase Pathway

E Scott Graham,Emma L Scotter,Nicola Ball,Pritika Narayan,Michelle Glass,Mike Dragunow

doi:10.1074/jbc.m602516200

Abstract

Neuro2a cells endogenously express cannabinoid type 1 (CB1) receptors. CB1 stimulation with HU210 activated ERK and induced the transcription factor Krox-24. A functional MEK-ERK pathway is an important requirement for CB1-mediated Krox-24 induction as blockade of MEK signaling by UO126 reduces both basal and CB1-mediated activation of Krox-24. CB1 receptor stimulation did not activate either JNK or p38 MAPK pathways or the pro-proliferation phosphatidylinositol 3-kinase (PI3K)-Akt pathway. However, serum removal or blockade of PI3K signaling by LY294002 transiently stimulated basal Krox-24 expression and increased CB1-mediated induction of Krox-24. This was consistent with a transient increase in pMEK, pERK, and pCREB levels following PI3K blockade. These data demonstrate that CB1-mediated activation of the Krox-24 transcription factor is negatively regulated through the PI3K-Akt pathway and reveals several points of signaling cross-talk between these two important kinase pathways.

Highlights

In the brain the cannabinoid type 1 (CB1)2 receptor is largely responsible for mediating the effects of endocannabinoids and cannabinoid drugs like ⌬9-tetrahydrocannabinol (THC)
We have demonstrated that CB1 can selectively activate the ERK pathway, which is crucially required for CB1-mediated Krox-24 induction
We did not detect endogenous CB1 receptors in human SK-N-SH cells or PC12 cells. These results were confirmed by Northern analysis, which demonstrated the existence of three abundant CB1 mRNA transcripts of 9.0, 6.0, and 1.5 kb

Summary

Introduction

In the brain the cannabinoid type 1 (CB1)2 receptor is largely responsible for mediating the effects of endocannabinoids and cannabinoid drugs like ⌬9-tetrahydrocannabinol (THC). We found krox-24 mRNA levels to be elevated in Neuro2a cells 40 – 60 min after CB1 stimulation with 100 nM HU210 by Northern analysis (Fig. 3a). CB1 Receptor-mediated Krox-24 Activation Is pERK MAPK-dependent—We investigated how CB1 signaling pathways were coupled to the up-regulation of Krox-24 levels in Neuro2a cells.

Results

Conclusion