TrkB Variants with Deletions in the Leucine-rich Motifs of the Extracellular Domain*
- From the School of Biological and Medical Sciences, University of St. Andrews, St. Andrews, Fife KY16 9AJ, Scotland
Abstract
We have isolated two novel variants involving the extracellular domain of TrkB from developing sensory neurons. These variants are generated by alternative splicing and lack two or all three of the leucine-rich motifs. Each of these variants is expressed as isoforms that possess or lack the intracellular tyrosine kinase domain. Fibroblast cell lines stably expressing these variants do not bind any of the TrkB ligands (brain-derived neurotrophic factor, neurotrophin-3, and neurotrophin-4/5) and neither survive nor undergo morphological transformation in response to neurotrophins. These results demonstrate that the leucine-rich motifs in TrkB are essential for ligand binding and signaling and indicate that the extracellular immunoglobulin-like domains alone are insufficient to confer neurotrophin binding to TrkB.
Footnotes
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↵* This work was supported by a grant from the Wellcome Trust.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
The nucleotide sequence(s) reported in this paper has been submitted to the GenBank™/EMBL Data Bank with accession number(s) M33385 and X17647.
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↵‡ Present address: Engelhardt Institute of Molecular Biology, Russian Academy of Sciences, Vavilov St. 32, Moscow 117 984, Russia.
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↵§ To whom correspondence should be addressed: School of Biological and Medical Sciences, Bute Medical Bldgs., University of St. Andrews, St. Andrews, Fife KY16 9AJ, Scotland. Tel.: 44-1334-463-219; Fax: 44-1334-463-217; E-mail: amd2{at}st-and.ac.uk.
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↵1 The abbreviations used are: NGF, nerve growth factor; BDNF, brain-derived neurotrophic factor; NT3, neurotrophin-3; NT4/5, neurotrophin-4/5; LRM(s), leucine-rich motif(s); PCR, polymerase chain reaction; bp, base pair(s); DMEM, Dulbecco’s modified Eagle’s medium; MTT, 3-(4,5-dimethyl thiazol-2-yl)-2,5-diphenyl tetrazolium bromide.
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- Received October 22, 1996.
- Revision received March 5, 1997.
