title: Pathogenic mechanism of the FIG4 mutation responsible for Charcot-Marie-Tooth disease CMT4J.
abstract: CMT4J is a severe form of Charcot-Marie-Tooth neuropathy caused by mutation of the phosphoinositide phosphatase FIG4/SAC3. Affected individuals are compound heterozygotes carrying the missense allele FIG4-I41T in combination with a null allele. Analysis using the yeast two-hybrid system demonstrated that the I41T mutation impairs interaction of FIG4 with the scaffold protein VAC14. The critical role of this interaction was confirmed by the demonstration of loss of FIG4 protein in VAC14 null mice. We developed a mouse model of CMT4J by expressing a Fig4-I41T cDNA transgene on the Fig4 null background. Expression of the mutant transcript at a level 5 × higher than endogenous Fig4 completely rescued lethality, whereas 2 × expression gave only partial rescue, providing a model of the human disease. The level of FIG4-I41T protein in transgenic tissues is only 2% of that predicted by the transcript level, as a consequence of the protein instability caused by impaired interaction of the mutant protein with VAC14. Analysis of patient fibroblasts demonstrated a comparably low level of mutant I41T protein. The abundance of FIG4-I41T protein in cultured cells is increased by treatment with the proteasome inhibitor MG-132. The data demonstrate that FIG4-I41T is a hypomorphic allele encoding a protein that is unstable in vivo. Expression of FIG4-I41T protein at 10% of normal level is sufficient for long-term survival, suggesting that patients with CMT4J could be treated by increased production or stabilization of the mutant protein. The transgenic model will be useful for testing in vivo interventions to increase the abundance of the mutant protein.
authors.affiliation: Department of Human Genetics, University of Michigan, Ann Arbor, Michigan, USA.
authors.forename: Guy M
authors.initials: GM
authors.lastname: Lenk
authors.forename: Cole J
authors.initials: CJ
authors.lastname: Ferguson
authors.forename: Clement Y
authors.initials: CY
authors.lastname: Chow
authors.forename: Natsuko
authors.initials: N
authors.lastname: Jin
authors.forename: Julie M
authors.initials: JM
authors.lastname: Jones
authors.forename: Adrienne E
authors.initials: AE
authors.lastname: Grant
authors.forename: Sergey N
authors.initials: SN
authors.lastname: Zolov
authors.forename: Jesse J
authors.initials: JJ
authors.lastname: Winters
authors.forename: Roman J
authors.initials: RJ
authors.lastname: Giger
authors.forename: James J
authors.initials: JJ
authors.lastname: Dowling
authors.forename: Lois S
authors.initials: LS
authors.lastname: Weisman
authors.forename: Miriam H
authors.initials: MH
authors.lastname: Meisler
mesh_terms: D000483:Alleles; D000818:Animals; D001343:Autophagy / Q000235:genetics; D002607:Charcot-Marie-Tooth Disease / Q000235:genetics* / Q000378:metabolism; D005347:Fibroblasts / Q000378:metabolism; D005420:Flavoproteins / Q000235:genetics* / Q000378:metabolism; D005911:Gliosis / Q000235:genetics; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism; D008565:Membrane Proteins; D051379:Mice; D008822:Mice, Transgenic; D023421:Models, Animal; D009154:Mutation; D000072180:Phosphoinositide Phosphatases; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D061988:Proteasome Inhibitors; D014162:Transfection
chemical_list: D005420:Flavoproteins; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D061988:Proteasome Inhibitors; C525133:Vac14 protein, mouse; C522216:Fig4 protein, mouse; D000072180:Phosphoinositide Phosphatases; D046988:Proteasome Endopeptidase Complex