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Synaptic Activity and Muscle Contraction Increases PDK1 and PKCβI Phosphorylation in the Presynaptic Membrane of the Neuromuscular Junction.

Frontiers in molecular neuroscience | 2017

Conventional protein kinase C βI (cPKCβI) is a conventional protein kinase C (PKC) isoform directly involved in the regulation of neurotransmitter release in the neuromuscular junction (NMJ). It is located exclusively at the nerve terminal and both synaptic activity and muscle contraction modulate its protein levels and phosphorylation. cPKCβI molecular maturation includes a series of phosphorylation steps, the first of which is mediated by phosphoinositide-dependent kinase 1 (PDK1). Here, we sought to localize PDK1 in the NMJ and investigate the hypothesis that synaptic activity and muscle contraction regulate in parallel PDK1 and cPKCβI phosphorylation in the membrane fraction. To differentiate the presynaptic and postsynaptic activities, we abolished muscle contraction with μ-conotoxin GIIIB (μ-CgTx-GIIIB) in some experiments before stimulation of the phrenic nerve (1 Hz, 30 min). Then, we analyzed total and membrane/cytosol fractions of skeletal muscle by Western blotting. Results showed that PDK1 is located exclusively in the nerve terminal of the NMJ. After nerve stimulation with and without coincident muscle contraction, total PDK1 and phosphorylated PDK1 (pPDK1) protein levels remained unaltered. However, synaptic activity specifically enhanced phosphorylation of PDK1 in the membrane, an important subcellular location for PDK1 function. This increase in pPDK1 coincides with a significant increase in the phosphorylation of its substrate cPKCβI also in the membrane fraction. Moreover, muscle contraction maintains PDK1 and pPDK1 but increases cPKCβI protein levels and its phosphorylation. Thus, even though PDK1 activity is maintained, pcPKCβI levels increase in concordance with total cPKCβI. Together, these results indicate that neuromuscular activity could induce the membrane targeting of pPDK1 in the nerve terminal of the NMJ to promote the phosphorylation of the cPKCβI, which is involved in ACh release.

Pubmed ID: 28890686 RIS Download

Associated grants

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GE Healthcare (tool)

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PKB Kinase (E-3) (antibody)

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This monoclonal targets PDPK1

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PKB Kinase (E-3) (antibody)

RRID:AB_626657

This monoclonal targets PDPK1

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HotHsd:SD (organism)

RRID:RGD_5508397

Rattus norvegicus with name HotHsd:SD from RGD.

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PKC betaI Antibody (C-16) (antibody)

RRID:AB_2168968

This polyclonal targets Prkcb

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Adobe Photoshop (software resource)

RRID:SCR_014199

Software for image processing, analysis, and editing. The software includes features such as touch capabilities, a customizable toolbar, 2D and 3D image merging, and Cloud access and options.

View all literature mentions

ImageJ (software resource)

RRID:SCR_003070

Open source Java based image processing software program designed for scientific multidimensional images. ImageJ has been transformed to ImageJ2 application to improve data engine to be sufficient to analyze modern datasets.

View all literature mentions

S100 (antibody)

RRID:AB_10013383

This polyclonal targets S100 isolated from cow brain.

View all literature mentions

Anti-Mouse IgG (whole molecule)-Peroxidase antibody produced in rabbit (antibody)

RRID:AB_258431

This polyclonal targets Mouse IgG (whole molecule)-Peroxidase antibody produced in rabbit

View all literature mentions

Phospho-PDK1 (Ser241) Antibody (antibody)

RRID:AB_2161919

This unknown targets PDK1, phospho (Ser241)

View all literature mentions

GAPDH (A-14) (antibody)

RRID:AB_641101

This polyclonal targets GAPDH

View all literature mentions

PKB Kinase (E-3) (antibody)

RRID:AB_626657

This monoclonal targets PDPK1

View all literature mentions