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Background: Agonist stimulation of Group I metabotropic glutamate receptors (mGluRs) initiates their coupling to the heterotrimeric G protein, Gαq/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 β-amyloid peptide (Aβ42) 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 IIα (CaMKIIα) as a protein that interacts with the second intracellular loop domain of mGluR5. We show that CaMKIIα interacts with both mGluR1a and mGluR5a in an agonist-independent manner and is co-immunoprecipitated with mGluR5a from hippocampal mouse brain. CaMKIIα 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 Aβ42 oligomers stimulate the association of CaMKIIα with mGluR5a and activate ERK1/2 in an mGluR5a-dependent manner. However, Aβ42 oligomer-stimulated ERK1/2 phosphorylation is not regulated by mGluR5a/CaMKIIα interactions suggesting that agonist and Aβ42 oligomers stabilize distinct mGluR5a activation states that are differentially regulated by CaMKIIα. The expression of both mGluR5a and PrPC together, but not alone resulted in the agonist-stimulated subcellular distribution of CaMKIIα into cytoplasmic puncta. Conclusions: Taken together these results indicate that CaMKIIα selectively regulates mGluR1a and mGluR5a ERK1/2 signaling. As mGluR5 and CaMKIIα are involved in learning and memory and Aβ 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. [ABSTRACT FROM AUTHOR]

In Alzheimer’s disease, the amyloid-b peptide (Ab) interacts with distinct proteins at the cell surface to interfere with synaptic communication. Recent data have implicated the prion protein (PrPC) as a putative receptor for Ab. We show here that Ab oligomers signal in cells in a PrPC-dependent manner, as might be expected if Ab oligomers use PrPC as a receptor. Immunofluorescence, flow cytometry and cell surface protein biotinylation experiments indicated that treatment with Ab oligomers, but not monomers, increased the localization of PrPC at the cell surface in cell lines. These results were reproduced in hippocampal neuronal cultures by labeling cell surface PrPC. In order to understand possible mechanisms involved with this effect of Ab oligomers, we used live cell confocal and total internal reflection microscopy in cell lines. Ab oligomers inhibited the constitutive endocytosis of PrPC, but we also found that after Ab oligomer- treatment PrPC formed more clusters at the cell surface, suggesting the possibility of multiple effects of Ab oligomers. Our experiments show for the first time that Ab oligomers signal in a PrPC-dependent way and that they can affect PrPC trafficking, increasing its localization at the cell surface. [ABSTRACT FROM AUTHOR]

The prion protein (PrPC) has been suggested to operate as a scaffold/ receptor protein in neurons, participating in both physiological and pathological associated events. PrPC, laminin, and metabotropic glutamate receptor 5 (mGluR5) form a protein complex on the plasma membrane that can trigger signaling pathways involved in neuronal differentiation. PrPC and mGluR5 are co-receptors also for β-amyloid oligomers(AβOs)andhavebeenshowntomodulate toxicity and neuronal death in Alzheimer's disease. In the present work, we addressed the potential crosstalk between these two signaling pathways, laminin-PrPC-mGluR5 or AβO-PrPC- mGluR5, as well as their interplay. Herein, we demonstrated that an existing complex containing PrPC-mGluR5 has an important role in AβObinding and activity in neurons. A peptide mimicking the binding site of laminin onto PrPC (Ln-γ1) binds to PrPC and induces intracellular Ca2+ increase in neurons via the complex PrPC-mGluR5. Ln-γ1 promotes internalization of PrPC and mGluR5 and transiently decreases AβO biding to neurons; however, the peptide does not impactAβOtoxicity. Given that mGluR5 is critical for toxic signaling by AβOs and in prion diseases, we tested whether mGlur5 knock-out mice would be susceptible to prion infection. Our results show mild, but significant, effects on disease progression, without affecting survival of mice after infection. These results suggest that PrPC-mGluR5 form a functional response unit by which multiple ligands can trigger signaling. We propose that trafficking of PrPC-mGluR5 may modulate signaling intensity by different PrPC ligands. [ABSTRACT FROM AUTHOR]