Ca2+/Calmodulin-dependent protein Kinase II interacts with group I Metabotropic Glutamate and facilitates Receptor Endocytosis and ERK1/2 signaling: role of β-Amyloid

Background: Agonist stimulation of Group I metabotropic glutamate receptors (mGluRs) initiates their coupling to the heterotrimeric G protein, Ga-q/11, resulting in the activation of phospholipase C, the release of Ca2+ from intracellular stores and the subsequent activation of protein kinase C. However, it is now recognized that mGluR5a also functions as a receptor for cellular prion protein (PrPC) and beta-amyloid peptide (A beta 42) oligomers to facilitate intracellular signaling via the resulting protein complex. Intracellular mGluR5a signaling is also regulated by its association with a wide variety of intracellular regulation proteins. Results: In the present study, we utilized mass spectroscopy to identify calmodulin kinase IIa (CaMKIIa) as a protein that interacts with the second intracellular loop domain of mGluR5. We show that CaMKIIa interacts with both mGluR1a and mGluR5a in an agonist-independent manner and is co-immunoprecipitated with mGluR5a from hippocampal mouse brain. CaMKIIa positively regulates both mGluR1a and mGluR5a endocytosis, but selectively attenuates mGluR5a but not mGluR1a-stimulated ERK1/2 phosphorylation in a kinase activity-dependent manner. We also find that A beta 42 oligomers stimulate the association of CaMKIIa with mGluR5a and activate ERK1/2 in an mGluR5a-dependent manner. However, A beta 42 oligomer-stimulated ERK1/ 2 phosphorylation is not regulated by mGluR5a/ CaMKIIa interactions suggesting that agonist and A beta 42 oligomers stabilize distinct mGluR5a activation states that are differentially regulated by CaMKIIa. The expression of both mGluR5a and PrPC together, but not alone resulted in the agonist-stimulated subcellular distribution of CaMKIIa into cytoplasmic puncta. Conclusions: Taken together these results indicate that CaMKIIa selectively regulates mGluR1a and mGluR5a ERK1/ 2 signaling. As mGluR5 and CaMKIIa are involved in learning and memory and A beta and mGluR5 are implicated in Alzheimer's disease, results of these studies could provide insight into potential pharmacological targets for treatment of Alzheimer's disease.