Dipeptidyl Peptidase-Like Protein 6 Is Required for Normal Electrophysiological Properties of Cerebellar Granule Cells

Department of Neuroscience, Baylor College of Medicine, Houston, Texas 77030, USA.
The Journal of Neuroscience : The Official Journal of the Society for Neuroscience (Impact Factor: 6.34). 06/2010; 30(25):8551-65. DOI: 10.1523/JNEUROSCI.5489-09.2010
Source: PubMed


In cerebellar granule (CG) cells and many other neurons, A-type potassium currents play an important role in regulating neuronal excitability, firing patterns, and activity-dependent plasticity. Protein biochemistry has identified dipeptidyl peptidase-like protein 6 (DPP6) as an auxiliary subunit of Kv4-based A-type channels and thus a potentially important regulator of neuronal excitability. In this study, we used an RNA interference (RNAi) strategy to examine the role DPP6 plays in forming and shaping the electrophysiological properties of CG cells. DPP6 RNAi delivered by lentiviral vectors effectively disrupts DPP6 protein expression in CG cells. In response to the loss of DPP6, I(SA) peak conductance amplitude is reduced by >85% in parallel with a dramatic reduction in the level of I(SA) channel protein complex found in CG cells. The I(SA) channels remaining in CG cells after suppression of DPP6 show alterations in gating similar to Kv4 channels expressed in heterologous systems without DPP6. In addition to these effects on A-type current, we find that loss of DPP6 has additional effects on input resistance and Na(+) channel conductance that combine with the effects on I(SA) to produce a global change in excitability. Overall, DPP6 expression seems to be critical for the expression of a high-frequency electrophysiological phenotype in CG cells by increasing leak conductance, A-type current levels and kinetics, and Na(+) current amplitude.

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    • "Kv4 channels were subsequently found to link to “potassium channel interacting proteins” (KChIP1–4; Fig. 1b), a class of calcium sensor molecules that affect channel translocation and kinetic properties [3, 15, 62, 94, 98, 104, 110, 131]. A second auxillary subunit termed dipeptidyl peptidase-like proteins (DPPs) was identified as membrane spanning proteins that directly interact with the Kv4 α-subunit [30, 38, 54, 56, 59, 87, 88, 99, 103]. While DPPs also exert important effects on baseline properties of Kv4 channels, there is no evidence to date for a role in mediating calcium-dependent effects. "
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    ABSTRACT: The electrical output of neurons relies critically on voltage- and calcium-gated ion channels. The traditional view of ion channels is that they operate independently of each other in the plasma membrane in a manner that could be predicted according to biophysical characteristics of the isolated current. However, there is increasing evidence that channels interact with each other not just functionally but also physically. This is exemplified in the case of Cav3 T-type calcium channels, where new work indicates the ability to form signaling complexes with different types of calcium-gated and even voltage-gated potassium channels. The formation of a Cav3-K complex provides the calcium source required to activate KCa1.1 or KCa3.1 channels and, furthermore, to bestow a calcium-dependent regulation of Kv4 channels via associated KChIP proteins. Here, we review these interactions and discuss their significance in the context of neuronal firing properties.
    Preview · Article · Jan 2014 · Pflügers Archiv - European Journal of Physiology
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    • "To examine the importance of co-regulation of both TASK-3 and ISA channels by DPP6 in shaping CG cell firing and information processing, we constructed channel gating models using QuB for TASK-3(GTASK-3), mDPP6 RNAi insensitive K2P (GK2P), control ISA (GISA(c)) and mDPP6 RNAi residual ISA (GISA(r)) and incorporated these channels as point processes into a single compartment (12.5 µm diameter) NEURON [22] CG cell model [6] (Fig. 5). Due to the electrotonically compact somatodendritic compartment in CG cells a multicompartment dendritic model is not necessary; however, accurately capturing some aspects of CG cell firing may require separate axonal and initial segment compartments that we did not try to model in this study [6], [36]. As described in the Methods, the GISA(c) and GISA(r) models were optimized to fit our recorded CG cell currents (Fig. S1). "
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    ABSTRACT: Dipeptidyl Peptidase-like Protein 6 (DPP6) is widely expressed in the brain where it co-assembles with Kv4 channels and KChIP auxiliary subunits to regulate the amplitude and functional properties of the somatodendritic A-current, ISA. Here we show that in cerebellar granule (CG) cells DPP6 also regulates resting membrane potential and input resistance by increasing the amplitude of the IK(SO) resting membrane current. Pharmacological analysis shows that DPP6 acts through the control of a channel with properties matching the K2P channel TASK-3. Heterologous expression and co-immunoprecipitation shows that DPP6 co-expression with TASK-3 results in the formation of a protein complex that enhances resting membrane potassium conductance. The co-regulation of resting and voltage-gated channels by DPP6 produces coordinate shifts in resting membrane potential and A-current gating that optimize the sensitivity of ISA inactivation gating to subthreshold fluctuations in resting membrane potential.
    Preview · Article · Apr 2013 · PLoS ONE
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    • "Dpp6 is an integral membrane glycoprotein which consists of a large extracellular C-terminal domain, a membrane spanning region, and a short N-terminal domain [17], [18]. It has been suggested that Dpp6 is involved in the modulation of A-type potassium channels in neurons and thus play an important role in synaptic plasticity [19], [20]. Dpp6 is also involved in the maintenance of cell-specific phenotype and its deregulation can result in carcinogenesis. "
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    ABSTRACT: DNA methylation is an important mechanism of gene silencing in mammals catalyzed by a group of DNA methyltransferases including Dnmt1, Dnmt3a, and Dnmt3b which are required for the establishment of genomic methylation patterns during development and differentiation. In this report, we studied the role of DNA methyltransferases during retinoic acid induced neuronal differentiation of P19 cells. We observed an increase in the mRNA and protein level of Dnmt3b, whereas the expression of Dnmt1 and Dnmt3a was decreased after RA treatment of P19 cells which indicated that Dnmt3b is more important during neuronal differentiation of P19 cells. Dnmt3b enriched chromatin library from RA treated P19 cells identified dipeptidyl peptidase 6 (Dpp6) gene as a novel target of Dnmt3b. Further, quantitative ChIP analysis showed that the amount of Dnmt3b recruited on Dpp6 promoter was equal in both RA treated as well as untreated p19 cells. Bisulfite genomic sequencing, COBRA, and methylation specific PCR analysis revealed that Dpp6 promoter was heavily methylated in both RA treated and untreated P19 cells. Dnmt3b was responsible for transcriptional silencing of Dpp6 gene as depletion of Dnmt3b resulted in increased mRNA and protein expression of Dpp6. Consequently, the average methylation of Dpp6 gene promoter was reduced to half in Dnmt3b knockdown cells. In the absence of Dnmt3b, Dnmt3a was associated with Dpp6 gene promoter and regulated its expression and methylation in P19 cells. RA induced neuronal differentiation was inhibited upon ectopic expression of Dpp6 in P19 cells. Taken together, the present study described epigenetic silencing of Dpp6 expression by DNA methylation and established that its ectopic expression can act as negative signal during RA induced neuronal differentiation of P19 cells.
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