Browsing by Author "Kahanovitch, Uri"
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- A Collision Coupling Model Governs the Activation of Neuronal GIRK1/2 Channels by Muscarinic-2 ReceptorsBerlin, Shai; Artzy, Etay; Handklo-Jamal, Reem; Kahanovitch, Uri; Parnas, Hanna; Dascal, Nathan; Yakubovich, Daniel (2020-08-12)The G protein-activated Inwardly Rectifying K+-channel (GIRK) modulates heart rate and neuronal excitability. Following G-Protein Coupled Receptor (GPCR)-mediated activation of heterotrimeric G proteins (G alpha beta gamma), opening of the channel is obtained by direct binding of G beta gamma subunits. Interestingly, GIRKs are solely activated by G beta gamma subunits released from G alpha(i/o)-coupled GPCRs, despite the fact that all receptor types, for instance G alpha(q)-coupled, are also able to provide G beta gamma subunits. It is proposed that this specificity and fast kinetics of activation stem from pre-coupling (or pre-assembly) of proteins within this signaling cascade. However, many studies, including our own, point towards a diffusion-limited mechanism, namely collision coupling. Here, we set out to address this long-standing question by combining electrophysiology, imaging, and mathematical modeling. Muscarinic-2 receptors (M2R) and neuronal GIRK1/2 channels were coexpressed inXenopus laevisoocytes, where we monitored protein surface expression, current amplitude, and activation kinetics. Densities of expressed M2R were assessed using a fluorescently labeled GIRK channel as a molecular ruler. We then incorporated our results, along with available kinetic data reported for the G-protein cycle and for GIRK1/2 activation, to generate a comprehensive mathematical model for the M2R-G-protein-GIRK1/2 signaling cascade. We find that, without assuming any irreversible interactions, our collision coupling kinetic model faithfully reproduces the rate of channel activation, the changes in agonist-evoked currents and the acceleration of channel activation by increased receptor densities.
- Glial Dysfunction in MeCP2 Deficiency Models: Implications for Rett SyndromeKahanovitch, Uri; Patterson, Kelsey C.; Hernandez, Raymundo D.; Olsen, Michelle L. (MDPI, 2019-08-05)Rett syndrome (RTT) is a rare, X-linked neurodevelopmental disorder typically affecting females, resulting in a range of symptoms including autistic features, intellectual impairment, motor deterioration, and autonomic abnormalities. RTT is primarily caused by the genetic mutation of the Mecp2 gene. Initially considered a neuronal disease, recent research shows that glial dysfunction contributes to the RTT disease phenotype. In the following manuscript, we review the evidence regarding glial dysfunction and its effects on disease etiology.
- Glial SIK3: A central player in ion and volume homeostasis in Drosophila peripheral nervesKahanovitch, Uri; Olsen, Michelle L. (Rockefeller University Press, 2019-12-01)The electrical properties of neuronal cells rely on gradients of ions across their membranes and the extracellular fluid (ECF) in which they are bathed. Little is known regarding how the ECF volume and content is maintained. In this issue, Li et al. (2019. J. Cell Biol. https://doi.org/10.1083/jcb.201907138) identify the kinase SIK3 in glia as a key signal transduction regulator in ion and volume homeostasis in Drosophila peripheral nerves.
- MeCP2 Deficiency Leads to Loss of Glial Kir4.1Kahanovitch, Uri; Cuddapah, Vishnu A.; Pacheco, Natasha L.; Holt, Leanne M.; Murphy, Daniel K.; Percy, Alan K.; Olsen, Michelle L. (Society for Neuroscience, 2018)Rett syndrome is a devastating neurodevelopmental disorder that affects 1 in 10,000–25,000 females. Mutations in methyl-CpG-binding protein 2 (MeCP2), a transcriptional regulator, are responsible for >95% of RTT cases. Recent work has shown that astrocytes contribute significantly to the disorder, although their contribution to this disease is not known. Here, we demonstrate that the critical astrocyte K⁺ channel Kir4.1 is a novel molecular target of MeCP2. MeCP2 deficiency leads to decreased Kcnj10/Kir4.1 mRNA levels, protein expression, and currents. These findings provide novel mechanistic insight and begin to elucidate the role of astrocytes in this disorder.
- Mutual action by Gγ and Gβ for optimal activation of GIRK channels in a channel subunit-specific mannerTabak, Galit; Keren-Raifman, Tal; Kahanovitch, Uri; Dascal, Nathan (Nature Publishing Group, 2019-01-24)The tetrameric G protein-gated K+ channels (GIRKs) mediate inhibitory effects of neurotransmitters that activate Gi/o-coupled receptors. GIRKs are activated by binding of the Gβγ dimer, via contacts with Gβ. Gγ underlies membrane targeting of Gβγ, but has not been implicated in channel gating. We observed that, in Xenopus oocytes, expression of Gγ alone activated homotetrameric GIRK1* and heterotetrameric GIRK1/3 channels, without affecting the surface expression of GIRK or Gβ. Gγ and Gβ acted interdependently: the effect of Gγ required the presence of ambient Gβ and was enhanced by low doses of coexpressed Gβ, whereas excess of either Gβ or Gγ imparted suboptimal activation, possibly by sequestering the other subunit “away” from the channel. The unique distal C-terminus of GIRK1, G1-dCT, was important but insufficient for Gγ action. Notably, GIRK2 and GIRK1/2 were not activated by Gγ. Our results suggest that Gγ regulates GIRK1* and GIRK1/3 channel’s gating, aiding Gβ to trigger the channel’s opening. We hypothesize that Gγ helps to relax the inhibitory effect of a gating element (“lock”) encompassed, in part, by the G1-dCT; GIRK2 acts to occlude the effect of Gγ, either by setting in motion the same mechanism as Gγ, or by triggering an opposing gating effect. © 2019, The Author(s).