The regulation of glycine transporter GLYT1 is mainly mediated by protein kinase Cα in C6 glioma cells

Department of Dental Pharmacology, Hiroshima University Graduate School of Biomedical Sciences, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8553, Japan.
Neurochemistry International (Impact Factor: 3.09). 09/2008; 53(6-8):248-54. DOI: 10.1016/j.neuint.2008.08.002
Source: PubMed

ABSTRACT Glycine has been shown to possess important functions as a bidirectional neurotransmitter. At synaptic clefts, the concentration of glycine is tightly regulated by the uptake of glycine released from nerve terminals into glial cells by the transporter GLYT1. It has been recently demonstrated that protein kinase C (PKC) mediates the downregulation of GLYT1 activity in several cell systems. However, it remains to be elucidated which subtypes of PKC might be important in the regulation of GLYT1 activity. In this study, we attempted to make clear the mechanism of the phorbol 12-myristate 13-acetate (PMA)-suppressed uptake of glycine in C6 glioma cells which have the native expression of GLYT1. In C6 cells, the expression of PKCalpha, PKCdelta, and PKCvarepsilon of the PMA-activated subtypes was detected. The PMA-suppressed action was fully reversed by the removal of both extracellular and intracellular Ca(2+). Furthermore, the inhibitory effects of PMA or thymeleatoxin (THX), which is a selective activator of conventional PKC (cPKC), were blocked by the downregulation of all PKCs expressed in C6 cells by long-term incubation with THX, or pretreatment with GF109203X or Gö6983, which are broad inhibitors of PKC, or Gö6976, a selective inhibitor of cPKC. On the other hand, treatment of C6 cells with ingenol, a selective activator of novel PKCs, especially PKCdelta and PKCvarepsilon, did not affect the transport of glycine. Silencing of PKCdelta expression by using RNA interference or pretreatment with the inhibitor peptide for PKCvarepsilon had no effect on the PMA-suppressed uptake of glycine. Together, these results suggest PKCalpha to be a crucial factor in the regulation of glycine transport in C6 cells.

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    • "For EAAC1, PKC seems to increase the surface expression together with PI3-kinase, whereas PP2A dephosphorylation elicits the internalization. Also the glycine transporter is being regulated by PKC (49–51). As PKC is ubiquitously expressed but strictly compartmentalized, its subcellular activation is differentially executed through a myriad of signal pathways, accounting for a large and diverse part of total phosphorylation phenomena in all cell types. "
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    • "Different quantities of total lysate from PAE and C6 glioma cells were subjected to Western blotting with anti-PKC antibodies from different sources. As mentioned above, PKCα was detected in control and PAE cell lysates with the anti-PKCα antibody, consistent with earlier observations in C6 glioma cells by Morioka et al. (Morioka et al., 2008). By contrast, blotting with monoclonal (E3) or a polyclonal (C-16, not shown) anti PKCβ1 antibodies readily detected a ∼75 kDa band in controls and C6 glioma cells corresponding to PKCβ1, showing the expression of this isozyme and to similar levels in both C6 and PAE cells. "
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