Article

Deletion of CASK in mice is lethal and impairs synaptic function.

Department of Neuroscience, University of Texas Southwestern Medical Center, Dallas, TX 75390-9111, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.81). 03/2007; 104(7):2525-30. DOI: 10.1073/pnas.0611003104
Source: PubMed

ABSTRACT CASK is an evolutionarily conserved multidomain protein composed of an N-terminal Ca2+/calmodulin-kinase domain, central PDZ and SH3 domains, and a C-terminal guanylate kinase domain. Many potential activities for CASK have been suggested, including functions in scaffolding the synapse, in organizing ion channels, and in regulating neuronal gene transcription. To better define the physiological importance of CASK, we have now analyzed CASK "knockdown" mice in which CASK expression was suppressed by approximately 70%, and CASK knockout (KO) mice, in which CASK expression was abolished. CASK knockdown mice are viable but smaller than WT mice, whereas CASK KO mice die at first day after birth. CASK KO mice exhibit no major developmental abnormalities apart from a partially penetrant cleft palate syndrome. In CASK-deficient neurons, the levels of the CASK-interacting proteins Mints, Veli/Mals, and neurexins are decreased, whereas the level of neuroligin 1 (which binds to neurexins that in turn bind to CASK) is increased. Neurons lacking CASK display overall normal electrical properties and form ultrastructurally normal synapses. However, glutamatergic spontaneous synaptic release events are increased, and GABAergic synaptic release events are decreased in CASK-deficient neurons. In contrast to spontaneous neurotransmitter release, evoked release exhibited no major changes. Our data suggest that CASK, the only member of the membrane-associated guanylate kinase protein family that contains a Ca2+/calmodulin-dependent kinase domain, is required for mouse survival and performs a selectively essential function without being in itself required for core activities of neurons, such as membrane excitability, Ca2+-triggered presynaptic release, or postsynaptic receptor functions.

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    • "CASK is important for P2X3 protein expression CASK is molecular scaffold playing a major role in the assembly of multiprotein complexes at specialized regions of neuronal plasma membranes (Butz et al. 1998; Borg et al. 1999) and is associated with pre-and post-synaptic proteins and cytoskelethon (Hata et al. 1996; Butz et al. 1998; Hsueh et al. 1998; Biederer and S€ udhof 2000; Jeyifous et al. 2009). Hence, CASK is reported to be involved in different neuronal functions, including synaptic strength, vesicle release, and receptor expression and trafficking as well as neuronal development (Olsen et al. 2005): indeed, its genetic ablation is lethal to mice (Atasoy et al. 2007). Our present data revealed for the first time that, in trigeminal ganglion neurons, CASK was widely expressed by P2X3-positive neurons, suggesting its potential role in sensory neuron physiology and nociceptive activity. "
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    ABSTRACT: AbstractATP‐gated P2X3 receptors of sensory ganglion neurons are important transducers of painful stimuli and are modulated by extracellular algogenic substances, via changes in the receptor phosphorylation state. The present study investigated the role of calcium/calmodulin‐dependent serine protein kinase (CASK) in interacting and controlling P2X3 receptor expression and function in mouse trigeminal ganglia. Most ganglion neurons in situ or in culture co‐expressed P2X3 and CASK. CASK was immunoprecipitated with P2X3 receptors from trigeminal ganglia and from P2X3/CASK‐cotransfected human embryonic kidney (HEK) cells. Recombinant P2X3/CASK expression in HEK cells increased serine phosphorylation of P2X3 receptors, typically associated with receptor upregulation. CASK deletion mutants also enhanced P2X3 subunit expression. After silencing CASK, cell surface P2X3 receptor expression was decreased, which is consistent with depressed P2X3 currents. The reduction in P2X3 expression levels was reversed by the proteasomal inhibitor MG‐132. Moreover, neuronal CASK/P2X3 interaction was up‐regulated by nerve growth factor (NGF) signaling and down‐regulated by P2X3 agonist‐induced desensitization. These data suggest a novel interaction between CASK and P2X3 receptors with positive outcome for receptor stability and function. As CASK‐mediated control of P2X3 receptors was dependent on the receptor activation state, CASK represents an intracellular gateway to regulate purinergic nociceptive signaling.
    Journal of Neurochemistry 07/2013; 126(1). DOI:10.1111/jnc.12272 · 4.24 Impact Factor
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    • "These include an N-terminal calcium/calmodulin kinase domain, two L27 domains, PDZ and SH3 domains, and a C-terminal guanylate kinase domain. CASK is enriched at the neuronal synapse where it plays important roles in regulating trafficking, targeting, and signaling of ion channels [21] [22]. "
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    ABSTRACT: Alternative pre-mRNA splicing has a major impact on cellular functions and development with the potential to fine-tune cellular localization, posttranslational modification, interaction properties, and expression levels of cognate proteins. The plasticity of regulation sets the stage for cells to adjust the relative levels of spliced mRNA isoforms in response to stress or stimulation. As part of an exon profiling analysis of mouse cortical neurons stimulated with high KCl to induce membrane depolarization, we detected a previously unrecognized exon (E24a) of the CASK gene, which encodes for a conserved peptide insertion in the guanylate kinase interaction domain. Comparative sequence analysis shows that E24a appeared selectively in mammalian CASK genes as part of a >3,000 base pair intron insertion. We demonstrate that a combination of a naturally defective 5' splice site and negative regulation by several splicing factors, including SC35 (SRSF2) and ASF/SF2 (SRSF1), drives E24a skipping in most cell types. However, this negative regulation is countered with an observed increase in E24a inclusion after neuronal stimulation and NMDA receptor signaling. Taken together, E24a is typically a skipped exon, which awakens during neuronal stimulation with the potential to diversify the protein interaction properties of the CASK polypeptide.
    Journal of nucleic acids 09/2012; 2012:816237. DOI:10.1155/2012/816237
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    • "The central role that CASK plays in the development of mammals is demonstrated by the lethal phenotype of CASK null mutants (Atasoy et al., 2007; Najm et al., 2008). Mild mutations (e.g., point substitutions, truncations of internal fragments, or decreased Figure 4. Molecular Details of the Interfaces of the Liprin-a2_LH/ "
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    ABSTRACT: Liprins are highly conserved scaffold proteins that regulate cell adhesion, cell migration, and synapse development by binding to diverse target proteins. The molecular basis governing liprin/target interactions is poorly understood. The liprin-α2/CASK complex structure solved here reveals that the three SAM domains of liprin-α form an integrated supramodule that binds to the CASK kinase-like domain. As supported by biochemical and cellular studies, the interaction between liprin-α and CASK is unique to vertebrates, implying that the liprin-α/CASK interaction is likely to regulate higher-order brain functions in mammals. Consistently, we demonstrate that three recently identified X-linked mental retardation mutants of CASK are defective in binding to liprin-α. We also solved the liprin-α/liprin-β SAM domain complex structure, which uncovers the mechanism underlying liprin heterodimerizaion. Finally, formation of the CASK/liprin-α/liprin-β ternary complex suggests that liprins can mediate assembly of target proteins into large protein complexes capable of regulating numerous cellular activities.
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