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Published on: January 7, 2019
Gain-of-Function Properties of a Dynamin 2 Mutant Implicated in Charcot-Marie-Tooth Disease
Tara C Tassin1, Barbara Barylko1, Per Niklas Hedde2,3
1Department of Pharmacology, U.T. Southwestern Medical Center, Dallas, TX, United States.
Abstract:
Mutations in the gene encoding dynamin 2 (DNM2), a GTPase that catalyzes membrane constriction and fission, are associated with two autosomal-dominant motor disorders, Charcot-Marie-Tooth disease (CMT) and centronuclear myopathy (CNM), which affect nerve and muscle, respectively. Many of these mutations affect the pleckstrin homology domain of DNM2, yet there is almost no overlap between the sets of mutations that cause CMT or CNM. A subset of CMT-linked mutations inhibit the interaction of DNM2 with phosphatidylinositol (4,5) bisphosphate, which is essential for DNM2 function in endocytosis. In contrast, CNM-linked mutations inhibit intramolecular interactions that normally suppress dynamin self-assembly and GTPase activation. Hence, CNM-linked DNM2 mutants form abnormally stable polymers and express enhanced assembly-dependent GTPase activation. These distinct effects of CMT and CNM mutations are consistent with current findings that DNM2-dependent CMT and CNM are loss-of-function and gain-of-function diseases, respectively. In this study, we present evidence that at least one CMT-causing DNM2 mutant (ΔDEE; lacking residues 555DEE557) forms polymers that, like the CNM mutants, are resistant to disassembly and display enhanced GTPase activation. We further show that the ΔDEE mutant undergoes 2-3-fold higher levels of tyrosine phosphorylation than wild-type DNM2. These results suggest that molecular mechanisms underlying the absence of pathogenic overlap between DNM2-dependent CMT and CNM should be re-examined.
Insights
Mutations in dynamin 2 (DNM2) cause Charcot-Marie-Tooth disease (CMT) and centronuclear myopathy (CNM). This study reveals a CMT-linked DNM2 mutant exhibits gain-of-function properties, challenging the distinct loss-of-function model for CMT.
Area of Science:
- Molecular biology
- Genetics
- Cell biology
Background:
- Dynamin 2 (DNM2) mutations cause autosomal-dominant Charcot-Marie-Tooth disease (CMT) and centronuclear myopathy (CNM).
- CMT mutations often impair DNM2's interaction with phosphatidylinositol (4,5) bisphosphate, suggesting loss-of-function.
- CNM mutations typically disrupt intramolecular interactions, leading to enhanced DNM2 self-assembly and GTPase activity, indicating gain-of-function.
Purpose of the Study:
- To investigate the molecular mechanisms of a specific CMT-linked DNM2 mutant (ΔDEE).
- To determine if CMT-associated DNM2 mutants can exhibit gain-of-function characteristics.
- To re-evaluate the distinct pathogenic mechanisms differentiating DNM2-dependent CMT and CNM.
Main Methods:
- Biochemical assays to analyze DNM2 polymer formation and GTPase activity.
- Analysis of tyrosine phosphorylation levels in wild-type and mutant DNM2.
- Characterization of the ΔDEE DNM2 mutant lacking residues 555-557.
Main Results:
- The CMT-linked ΔDEE DNM2 mutant forms polymers resistant to disassembly, similar to CNM mutants.
- The ΔDEE mutant displays enhanced GTPase activation, a gain-of-function characteristic.
- ΔDEE mutant shows significantly increased tyrosine phosphorylation compared to wild-type DNM2.
Conclusions:
- At least one CMT-associated DNM2 mutation can lead to gain-of-function effects.
- The distinction between loss-of-function (CMT) and gain-of-function (CNM) mechanisms in DNM2-related disorders may be less clear-cut.
- These findings necessitate a re-examination of the molecular basis underlying the pathogenic divergence between DNM2-dependent CMT and CNM.
