Multifaceted modulation of K+ channels by protein-tyrosine phosphatase ε tunes neuronal excitability

Roles of KCNA2 in Neurological Diseases: from Physiology to Pathology

Potassium voltage-gated channel subfamily a member 2 (Kv1.2, encoded by KCNA2) is highly expressed in the central and peripheral nervous systems. Based on the patch clamp studies, gain-of function (GOF), loss-of-function (LOF), and a mixed type (GOF/LOF) variants can cause different conditions/disorders. KCNA2-related neurological diseases include epilepsy, intellectual disability (ID), attention deficit/hyperactive disorder (ADHD), autism spectrum disorder (ASD), pain as well as autoimmune and movement disorders. Currently, the molecular mechanisms for the reported variants in causing diverse disorders are unknown. Consequently, this review brings up to date the related information regarding the structure and function of Kv1.2 channel, expression patterns, neuronal localizations, and tetramerization as well as important cell and animal models. In addition, it provides updates on human genetic variants, genotype-phenotype correlations especially highlighting the deep insight into clinical prognosis of KCNA2-related developmental and epileptic encephalopathy, mechanisms, and the potential treatment targets for all KCNA2-related neurological disorders.

Tuning the Protein Phosphorylation by Receptor Type Protein Tyrosine Phosphatase Epsilon (PTPRE) in Normal and Cancer Cells

Tyrosine phosphorylation is an important post-translation modification of proteins that is controlled by tyrosine kinases and phosphatases. Disruption of the balance between the activity of tyrosine kinases and phosphatases may result in diseases. Receptor type protein tyrosine phosphatase epsilon (PTPRE) is closely related with receptor type protein tyrosine phosphatase alpha (PTPRA). PTPRE has been studied in osteoclast cells, nerve cells, hematopoietic cells, cancer cells and others, and it has different functions among various tissues. In this review, we summarized the current knowledge about the regulation of PTPRE on cellular signal transduction and its function under normal and pathological conditions.

Activation of zebrafish Src family kinases by the prion protein is an amyloid-β-sensitive signal that prevents the endocytosis and degradation of E-cadherin/β-catenin complexes in vivo

Background

Prions and amyloid-β (Aβ) oligomers trigger neurodegeneration by hijacking a poorly understood cellular signal mediated by the prion protein (PrP) at the plasma membrane. In early zebrafish embryos, PrP-1-dependent signals control cell-cell adhesion via a tyrosine phosphorylation-dependent mechanism.

Results

Here we report that the Src family kinases (SFKs) Fyn and Yes act downstream of PrP-1 to prevent the endocytosis and degradation of E-cadherin/β-catenin adhesion complexes in vivo. Accordingly, knockdown of PrP-1 or Fyn/Yes cause similar zebrafish gastrulation phenotypes, whereas Fyn/Yes expression rescues the PrP-1 knockdown phenotype. We also show that zebrafish and mouse PrPs positively regulate the activity of Src kinases and that these have an unexpected positive effect on E-cadherin-mediated cell adhesion. Interestingly, while PrP knockdown impairs β-catenin adhesive function, PrP overexpression enhances it, thereby antagonizing its nuclear, wnt-related signaling activity and disturbing embryonic dorsoventral specification. The ability of mouse PrP to influence these events in zebrafish embryos requires its neuroprotective, polybasic N-terminus but not its neurotoxicity-associated central region. Remarkably, human Aβ oligomers up-regulate the PrP-1/SFK/E-cadherin/β-catenin pathway in zebrafish embryonic cells, mimicking a PrP gain-of-function scenario.

Conclusions

Our gain- and loss-of-function experiments in zebrafish suggest that PrP and SFKs enhance the cell surface stability of embryonic adherens junctions via the same complex mechanism through which they over-activate neuroreceptors that trigger synaptic damage. The profound impact of this pathway on early zebrafish development makes these embryos an ideal model to study the cellular and molecular events affected by neurotoxic PrP mutations and ligands in vivo. In particular, our finding that human Aβ oligomers activate the zebrafish PrP/SFK/E-cadherin pathway opens the possibility of using fish embryos to rapidly screen for novel therapeutic targets and compounds against prion- and Alzheimer's-related neurodegeneration. Altogether, our data illustrate PrP-dependent signals relevant to embryonic development, neuronal physiology and neurological disease.

Electronic supplementary material

The online version of this article (doi:10.1186/s13024-016-0076-5) contains supplementary material, which is available to authorized users.

Regulation of the neuronal KCNQ2 channel by Src--a dual rearrangement of the cytosolic termini underlies bidirectional regulation of gating

Neuronal M-type K(+) channels are heteromers of KCNQ2 and KCNQ3 subunits, and are found in cell bodies, dendrites and the axon initial segment, regulating the firing properties of neurons. By contrast, presynaptic KCNQ2 homomeric channels directly regulate neurotransmitter release. Previously, we have described a mechanism for gating downregulation of KCNQ2 homomeric channels by calmodulin and syntaxin1A. Here, we describe a new mechanism for regulation of KCNQ2 channel gating that is modulated by Src, a non-receptor tyrosine kinase. In this mechanism, two concurrent distinct structural rearrangements of the cytosolic termini induce two opposing effects: upregulation of the single-channel open probability, mediated by an N-terminal tyrosine, and reduction in functional channels, mediated by a C-terminal tyrosine. In contrast, Src-mediated regulation of KCNQ3 homomeric channels, shown previously to be achieved through the corresponding tyrosine residues, involves the N-terminal-tyrosine-mediated downregulation of the open probability, rather than an upregulation. We argue that the dual bidirectional regulation of KCNQ2 functionality by Src, mediated through two separate sites, means that KCNQ2 can be modified by cellular factors that might specifically interact with either one of the sites, with potential significance in the fine-tuning of neurotransmitters release at nerve terminals.

Comparison of the gene expression profiles of human fetal cortical astrocytes with pluripotent stem cell derived neural stem cells identifies human astrocyte markers and signaling pathways and transcription factors active in human astrocytes

Astrocytes are the most abundant cell type in the central nervous system (CNS) and have a multitude of functions that include maintenance of CNS homeostasis, trophic support of neurons, detoxification, and immune surveillance. It has only recently been appreciated that astrocyte dysfunction is a primary cause of many neurological disorders. Despite their importance in disease very little is known about global gene expression for human astrocytes. We have performed a microarray expression analysis of human fetal astrocytes to identify genes and signaling pathways that are important for astrocyte development and maintenance. Our analysis confirmed that the fetal astrocytes express high levels of the core astrocyte marker GFAP and the transcription factors from the NFI family which have been shown to play important roles in astrocyte development. A group of novel markers were identified that distinguish fetal astrocytes from pluripotent stem cell-derived neural stem cells (NSCs) and NSC-derived neurons. As in murine astrocytes, the Notch signaling pathway appears to be particularly important for cell fate decisions between the astrocyte and neuronal lineages in human astrocytes. These findings unveil the repertoire of genes expressed in human astrocytes and serve as a basis for further studies to better understand astrocyte biology, especially as it relates to disease.

5-HT2 receptors-mediated modulation of voltage-gated K+ channels and neurophysiopathological correlates

The activity of voltage-gated K(+) channels (Kv) can be dynamically modulated by several events, including neurotransmitter stimulated biochemical cascades mediated by G protein-coupled receptors such as 5-HT2 receptors (5-HT2Rs). Activation of 5-HT2A/CR inhibits the Shaker-like K(+) channels Kv1.1 and Kv1.2, and this modulation involves the dual coordination of both RPTPα and distinct tyrosine kinases coupled to this receptor; 5-HT2Rs-mediated modulation of Kv channels controls glutamate release onto prefrontal cortex neurons that might play critical roles in neurophysiological, neurological, and psychiatric conditions. Noticeably, hallucinogens modulate Kv channel activity, acting at 5-HT2R. Hence, comprehensive knowledge of 5-HT2R signaling through modulation of distinct K(+) channels is a pivotal step in the direction that will enable scientists to discover novel 5-HT functions and dysfunctions in the brain and to identify original therapeutic targets.

Central regulation of metabolism by protein tyrosine phosphatases

Protein tyrosine phosphatases (PTPs) are important regulators of intracellular signaling pathways via the dephosphorylation of phosphotyrosyl residues on various receptor and non-receptor substrates. The phosphorylation state of central nervous system (CNS) signaling components underlies the molecular mechanisms of a variety of physiological functions including the control of energy balance and glucose homeostasis. In this review, we summarize the current evidence implicating PTPs as central regulators of metabolism, specifically highlighting their interactions with the neuronal leptin and insulin signaling pathways. We discuss the role of a number of PTPs (PTP1B, SHP2, TCPTP, RPTPe, and PTEN), reviewing the findings from genetic mouse models and in vitro studies which highlight these phosphatases as key central regulators of energy homeostasis.