title: Disruption of astrocytic glutamine turnover by manganese is mediated by the protein kinase C pathway.
abstract: Manganese (Mn) is a trace element essential for normal human development and is required for the proper functioning of a variety of physiological processes. Chronic exposure to Mn can cause manganism, a neurodegenerative disorder resembling idiopathic Parkinson's disease (PD). Mn(II) neurotoxicity is characterized by astrocytic impairment both in the expression and activity of glutamine (Gln) transporters. Because protein kinase C (PKC) activation leads to the downregulation of a number of neurotransmitter transporters and Mn(II) increases PKC activity, we hypothesized that the PKC signaling pathway contributes to the Mn(II)-mediated disruption of Gln turnover. Our results have shown that Mn exposure increases the phosphorylation of both the PKCα and PKCδ isoforms. PKC activity was also shown to be increased in response to Mn(II) treatment. Corroborating our earlier observations, Mn(II) also caused a decrease in Gln uptake. This effect was blocked by PKC inhibitors. Notably, PKC activation caused a decrease in Gln uptake mediated by systems ASC and N, but had no effect on the activities of systems A and L. Exposure to α-phorbol 12-myristate 13-acetate significantly decreased SNAT3 (system N) and ASCT2 (system ASC) protein levels. Additionally, a co-immunoprecipitation study demonstrated the association of SNAT3 and ASCT2 with the PKCδ isoform, and Western blotting revealed the Mn(II)-mediated activation of PKCδ by proteolytic cleavage. PKC activation was also found to increase SNAT3 and ubiquitin ligase Nedd4-2 binding and to induce hyperubiquitination. Taken together, these findings demonstrate that the Mn(II)-induced dysregulation of Gln homeostasis in astrocytes involves PKCδ signaling accompanied by an increase in ubiquitin-mediated proteolysis.
authors.affiliation: Department of Pediatrics, Vanderbilt University Medical Center, Nashville, Tennessee, USA.
authors.forename: Marta
authors.initials: M
authors.lastname: Sidoryk-Wegrzynowicz
authors.forename: Eunsook
authors.initials: E
authors.lastname: Lee
authors.forename: Ni
authors.initials: N
authors.lastname: Mingwei
authors.forename: Michael
authors.initials: M
authors.lastname: Aschner
mesh_terms: D026962:Amino Acid Transport System ASC / Q000096:biosynthesis / Q000235:genetics; D026921:Amino Acid Transport Systems, Neutral / Q000378:metabolism; D000818:Animals; D001253:Astrocytes / Q000378:metabolism*; D019921:Biotinylation; D015153:Blotting, Western; D002478:Cells, Cultured; D002712:Chlorides / Q000633:toxicity; D056827:Endosomal Sorting Complexes Required for Transport / Q000378:metabolism; D005973:Glutamine / Q000378:metabolism*; D047468:Immunoprecipitation; D017895:Manganese Compounds; D020149:Manganese Poisoning / Q000201:enzymology / Q000378:metabolism*; D008565:Membrane Proteins / Q000096:biosynthesis; D015778:Minor Histocompatibility Antigens; D000075702:Nedd4 Ubiquitin Protein Ligases; D011493:Protein Kinase C / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D060888:Real-Time Polymerase Chain Reaction; D015398:Signal Transduction / Q000502:physiology; D025801:Ubiquitin / Q000502:physiology; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism
chemical_list: D026962:Amino Acid Transport System ASC; D026921:Amino Acid Transport Systems, Neutral; D002712:Chlorides; D056827:Endosomal Sorting Complexes Required for Transport; D017895:Manganese Compounds; D008565:Membrane Proteins; D015778:Minor Histocompatibility Antigens; C498849:Slc1a5 protein, rat; D025801:Ubiquitin; C403222:system N protein 1; D005973:Glutamine; C000618479:NEDD4L protein, rat; D000075702:Nedd4 Ubiquitin Protein Ligases; C000618483:Nedd4 protein, human; C000618484:Nedd4 protein, rat; C000618485:Nedd4L protein, human; D044767:Ubiquitin-Protein Ligases; D011493:Protein Kinase C; C025340:manganese chloride