Modulation of the Voltage-gated Potassium Channel (Kv4.3) and the Auxiliary Protein (KChIP3) Interactions by the Current Activator NS5806

KChIP3 (potassium channel interacting protein 3) is a calcium-binding protein that binds at the N terminus of the Kv4 voltage-gated potassium channel through interactions at two contact sites and has been shown to regulate potassium current gating kinetics as well as channel trafficking in cardiac and neuronal cells. Using fluorescence spectroscopy, isothermal calorimetry, and docking simulations we show that the novel potassium current activator, NS5806, binds at a hydrophobic site on the C terminus of KChIP3 in a calcium-dependent manner, with an equilibrium dissociation constant of 2–5 μm in the calcium-bound form. We further determined that the association between KChIP3 and the hydrophobic N terminus of Kv4.3 is calcium-dependent, with an equilibrium dissociation constant in the apo-state of 70 ± 3 μm and 2.7 ± 0.1 μm in the calcium-bound form. NS5806 increases the affinity between KChIP3 and the N terminus of Kv4.3 (K_d = 1.9 ± 0.1 μm) in the presence and absence of calcium. Mutation of Tyr-174 or Phe-218 on KChIP3 abolished the enhancement of Kv4.3 site 1 binding in the apo-state, highlighting the role of these residues in drug and K4.3 binding. Kinetic studies show that NS5806 decreases the rate of dissociation between KChIP3 and the N terminus of K_V4.3. Overall, these studies support the idea that NS5806 directly interacts with KChIP3 and modulates the interactions between this calcium-binding protein and the T1 domain of the Kv4.3 channels through reorientation of helix 10 on KChIP3.     

Involvement of the cAMP response element binding protein, CREB, and cyclin D1 in LPA-induced proliferation of P19 embryonic carcinoma cells

Lysophosphatidic acid (LPA) is a lipid growth factor that induces proliferation of fibroblasts by activating the cAMP response element binding protein (CREB). Here, we further investigated whether LPA induces proliferation of P19 cells, a line of pluripotent embryonic carcinoma cells. 5′-Bromo-2-deoxyuridine incorporation and cell viability assays showed that LPA stimulated proliferation of P19 cells. Immunoblot experiments with P19 cells revealed that the mitogen activated protein kinases, including p-ERK, p38, pAKT, glycogen synthase kinase 3β, and CREB were phosphorylated by treatment with 10 μM LPA. LPA-induced phosphorylation of CREB was efficiently blocked by U0126 and H89, inhibitors of the MAP kinases ERK1/2 and mitogen- and stress-activated protein kinase 1, respectively. Involvement of cyclin D1 in LPA-induced P19 cell proliferation was verified by immunoblot analysis in combination with pharmacological inhibitor treatment. Furthermore, LPA up-regulated CRE-harboring cyclin D1 promoter activity, suggesting that CREB and cyclin D1 play significant roles in LPA-induced proliferation of P19 embryonic carcinoma cells.     

Structure of the ancient TRPY1 channel from Saccharomyces cerevisiae reveals mechanisms of modulation by lipids and calcium

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Scaffold protein Homer 1: Implications for neurological diseases

Homer proteins are commonly known as scaffold proteins at postsynaptic density. Homer 1 is a widely studied member of the Homer protein family, comprising both synaptic structure and mediating postsynaptic signaling transduction. Both an immediate-early gene encoding a Homer 1 variant and a constitutively expressed Homer 1 variant regulate receptor clustering and trafficking, intracellular calcium homeostasis, and intracellular molecule complex formation. Substantial preclinical investigations have implicated that each of these Homer 1 variants are associated with the etiology of many neurological diseases, such as pain, mental retardation syndromes, Alzheimer's disease, schizophrenia, drug-induced addiction, and traumatic brain injury.     

Spectrins: A structural platform for stabilization and activation of membrane channels,receptors and transporters

This review focuses on structure and functions of spectrin as a major component of the membrane skeleton. Recent advances on spectrin function as an interface for signal transduction mediation and a number of data concerning interaction of spectrin with membrane channels, adhesion molecules, receptors and transporters draw a picture of multifaceted protein. Here, we attempted to show the current depiction of multitask role of spectrin in cell physiology. This article is part of a Special Issue entitled: Reciprocal influences between cell cytoskeleton and membrane channels, receptors and transporters. Guest Editor: Jean Claude Hervé.     

Connexins: sensors and regulators of cell cycling

It is nowadays well established that gap junctions are critical gatekeepers of cell proliferation, by controlling the intercellular exchange of essential growth regulators. In recent years, however, it has become clear that the picture is not as simple as originally anticipated, as structural precursors of gap junctions can affect cell cycling by performing actions not related to gap junctional intercellular communication. Indeed, connexin hemichannels also foresee a pathway for cell growth communication, albeit between the intracellular compartment and the extracellular environment, while connexin proteins as such can directly or indirectly influence the production of cell cycle regulators independently of their channel activities. Furthermore, a novel set of connexin-like proteins, the pannexins, have lately joined in as regulators of the cell proliferation process, which they can affect as either single units or as channel entities. In the current paper, these multifaceted aspects of connexin-related signalling in cell cycling are reviewed.     

Bio-informatics based analysis of genes implicated in alcohol mediated liver injury

Alcohol induced liver injury has been studied extensively. Using literature search and bioinformatics tools, the present study characterizes the genes involved in alcohol induced liver injury. The cellular and metabolic processes in which genes involved in alcohol induced liver injury are implicated are also discussed. The genes related to alcohol induced liver injury are also involved in affecting certain molecular functions and metabolism of drugs, besides being associated with diseases. In conclusion, the changes in regulation of genes implicated in alcohol induced liver injury apart from causing alcohol mediated hepatic dysfunction may affect other vital processes in the body.