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The Journal of Neuroscience, May 13, 2009, 29(19):6250-6265; doi:10.1523/JNEUROSCI.0856-09.2009
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Cellular/Molecular
Alternatively Spliced Isoforms of TRIP8b Differentially Control h Channel Trafficking and Function
Alan S. Lewis,1 Emily Schwartz,1 C. Savio Chan,2 Yoav Noam,3,4,5 Minyoung Shin,1 Wytse J. Wadman,5 D. James Surmeier,2 Tallie Z. Baram,3,4 Robert L. Macdonald,6,7,8 andDane M. Chetkovich1,2 1The Ken & Ruth Davee Department of Neurology and Clinical Neurosciences and 2Department of Physiology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois 60611, Departments of 3Anatomy & Neurobiology, and 4Pediatrics, University of California, Irvine, Irvine, California 92697-4475, 5Swammerdam Institute for Life Sciences, Center for NeuroScience, University of Amsterdam, 1098 SM Amsterdam, The Netherlands, and Departments of 6Neurology, 7Pharmacology, and 8Molecular Physiology and Biophysics, Vanderbilt University Medical Center, Nashville, Tennessee 37212
Correspondence should be addressed to Dr. Dane M. Chetkovich, Ruth & Ken Davee Department of Neurology and Clinical Neuroscience, Feinberg School of Medicine, Northwestern University, 303 East Chicago Avenue, Ward 10-201, Chicago, IL 60611-3008. Email: d-chetkovich{at}northwestern.edu
Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels (h channels) are the molecular basis for the current, Ih, which contributes crucially to intrinsic neuronal excitability. The subcellular localization and biophysical properties of h channels govern their function, but the mechanisms controlling these characteristics, and especially the potential role of auxiliary subunits or other binding proteins, remain unclear. We focused on TRIP8b, an h channel-interacting protein that colocalizes with HCN1 in cortical and hippocampal pyramidal neuron dendrites, and found that it exists in multiple alternative splice variants with distinct effects on h channel trafficking and function. The developmentally regulated splice variants of TRIP8b all shared dual, C terminus-located interaction sites with HCN1. When coexpressed with HCN1 in heterologous cells individual TRIP8b isoforms similarly modulated gating of Ih, causing a hyperpolarizing shift in voltage dependence of channel activation, but differentially upregulated or downregulated Ih current density and HCN1 surface expression. In hippocampal neurons, coexpression of TRIP8b isoforms with HCN1 produced isoform-specific changes of HCN1 localization. Interestingly, the TRIP8b isoforms most abundant in the brain are those predicted to enhance h channel surface expression. Indeed, shRNA knockdown of TRIP8b in hippocampal neurons significantly reduced native Ih. Thus, although TRIP8b exists in multiple splice isoforms, our data suggest that the predominant role of this protein in brain is to promote h channel surface expression and enhance Ih. Because Ih expression is altered in models of several diseases, including temporal lobe epilepsy, TRIP8b may play a role in both normal neuronal function and in aberrant neuronal excitability associated with neurological disease.
Received March 19, 2009; accepted April 11, 2009.
Correspondence should be addressed to Dr. Dane M. Chetkovich, Ruth & Ken Davee Department of Neurology and Clinical Neuroscience, Feinberg School of Medicine, Northwestern University, 303 East Chicago Avenue, Ward 10-201, Chicago, IL 60611-3008. Email: d-chetkovich{at}northwestern.edu
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