The Cellular Prion Protein Interacts with the Tissue Non-Specific Alkaline Phosphatase in Membrane Microdomains of Bioaminergic Neuronal Cells

Abstract

BackgroundThe cellular prion protein, PrPC, is GPI anchored and abundant in lipid rafts. The absolute requirement of PrPC in neurodegeneration associated to prion diseases is well established. However, the function of this ubiquitous protein is still puzzling. Our previous work using the 1C11 neuronal model, provided evidence that PrPC acts as a cell surface receptor. Besides a ubiquitous signaling function of PrPC, we have described a neuronal specificity pointing to a role of PrPC in neuronal homeostasis. 1C11 cells, upon appropriate induction, engage into neuronal differentiation programs, giving rise either to serotonergic (1C115-HT) or noradrenergic (1C11NE) derivatives.Methodology/Principal FindingsThe neuronal specificity of PrPC signaling prompted us to search for PrPC partners in 1C11-derived bioaminergic neuronal cells. We show here by immunoprecipitation an association of PrPC with an 80 kDa protein identified by mass spectrometry as the tissue non-specific alkaline phosphatase (TNAP). This interaction occurs in lipid rafts and is restricted to 1C11-derived neuronal progenies. Our data indicate that TNAP is implemented during the differentiation programs of 1C115-HT and 1C11NE cells and is active at their cell surface. Noteworthy, TNAP may contribute to the regulation of serotonin or catecholamine synthesis in 1C115-HT and 1C11NE bioaminergic cells by controlling pyridoxal phosphate levels. Finally, TNAP activity is shown to modulate the phosphorylation status of laminin and thereby its interaction with PrP.Conclusion/SignificanceThe identification of a novel PrPC partner in lipid rafts of neuronal cells favors the idea of a role of PrP in multiple functions. Because PrPC and laminin functionally interact to support neuronal differentiation and memory consolidation, our findings introduce TNAP as a functional protagonist in the PrPC-laminin interplay. The partnership between TNAP and PrPC in neuronal cells may provide new clues as to the neurospecificity of PrPC function.

Cellular function and molecular structure of ecto-nucleotidases

“…Furthermore, intestinal AP has been implicated in fatty acid transport in enterocytes [463]. Moreover, AP can dephosphorylate extracellular proteins at physiological pH [508][509][510][511][512][513]. Calf IAP is widely used in molecular biology to dephosphorylate nucleic acids.…”

“…This interaction takes place in lipid rafts of cultured neuroepithelial cell lines (1C11) that can be differentiated towards a serotonergic (1C11 5-HT ) or noradrenergic (1C11 NE ) phenotype. Since TNAP can dephosphorylate laminin, it is hypothesized that TNAP acts as a functional protagonist in the PrP C interplay [511].…”

Tissue Non-specific Alkaline Phosphatase (TNAP) in Vessels of the Brain

“…On the other hand, neuronal cells and BCECs exclusively express the bone TNAP transcript in human, marmoset, rat and mouse. In fine, TNAP is the only AP isoform found in the brain (Ermonval et al 2009). This characteristic was also noted in several in vitro models of mammalian BBBs (Meyer et al 1990;Nakazato et al 1997;Sobue et al 1999).…”

“…However, despite its known phosphomonoesterase activity, TNAP's putative ability to dephosphorylate protein targets remains subject to debate. Direct proof of TNAP's action on the phosphorylation state of laminin has been reported (Ermonval et al 2009) but contrasts with evidence to show that TNAP does not modulate the phosphorylation of plasma membrane proteins (Fedde et al 1993). In Alzheimer's disease (AD), hyperphosphorylation of the tau protein plays a key role in progression of AD.…”

Tetramisole and Levamisole Suppress Neuronal Activity Independently from Their Inhibitory Action on Tissue Non-specific Alkaline Phosphatase in Mouse Cortex

“…Indeed, although early studies (Landow et al 1942;Bourne 1943) did not report AP activity at the neuronal level in mammals-except in the spinal cord and medulla -, later studies demonstrated significant AP activity in multiple brain structures of various mammalian species. The pharmacological profile of this neuronal AP activity suggested it resulted from TNAP activity (Fonta et al 2004;Langer et al 2008) and it has recently been formally ascribed to TNAP gene expression (Ermonval et al 2009;Brun-Heath et al 2011).…”