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Updated: Jun 15, 2025
A Deep-sequencing-assisted, Spontaneous Suppressor Screen in the Fission Yeast Schizosaccharomyces pombe
Published on: March 7, 2019
Novel mechanisms of MITF regulation identified in a mouse suppressor screen
Hong Nhung Vu1, Matti Már Valdimarsson2, Sara Sigurbjörnsdóttir1
1Department of Biochemistry and Molecular Biology, BioMedical Center, Faculty of Medicine, University of Iceland, Sturlugata 8, 102, Reykjavík, Iceland.
Abstract:
MITF, a basic Helix-Loop-Helix Zipper (bHLHZip) transcription factor, plays vital roles in melanocyte development and functions as an oncogene. We perform a genetic screen for suppressors of the Mitf-associated pigmentation phenotype in mice and identify an intragenic Mitf mutation that terminates MITF at the K316 SUMOylation site, leading to loss of the C-end intrinsically disordered region (IDR). The resulting protein is more nuclear but less stable than wild-type MITF and retains DNA-binding ability. As a dimer, it can translocate wild-type and mutant MITF partners into the nucleus, improving its own stability thus ensuring nuclear MITF supply. smFRET analysis shows interactions between K316 SUMOylation and S409 phosphorylation sites across monomers; these interactions largely explain the observed effects. The recurrent melanoma-associated E318K mutation in MITF, which affects K316 SUMOylation, also alters protein regulation in concert with S409. This suggests that residues K316 and S409 of MITF are impacted by SUMOylation and phosphorylation, respectively, mediating effects on nuclear localization and stability through conformational changes. Our work provides a novel mechanism of genetic suppression, and an example of how apparently deleterious mutations lead to normal phenotypes.
Insights
A genetic screen identified a mutation in the Microphthalmia-associated Transcription Factor (MITF) that enhances nuclear localization and stability. This discovery reveals a novel mechanism for genetic suppression, explaining how mutations can lead to normal phenotypes.
Area of Science:
- Molecular Biology
- Genetics
- Cell Biology
Background:
- Microphthalmia-associated Transcription Factor (MITF) is crucial for melanocyte development and acts as an oncogene.
- Understanding MITF regulation is key to comprehending pigmentation and melanoma.
- Genetic screens are powerful tools for identifying novel regulatory mechanisms.
Purpose of the Study:
- To identify genetic suppressors of Mitf-associated pigmentation defects.
- To elucidate the molecular mechanisms underlying MITF regulation and its impact on phenotype.
- To investigate the interplay between MITF mutations, SUMOylation, and phosphorylation.
Main Methods:
- Genetic screening in mice to identify suppressors of Mitf pigmentation phenotype.
- Characterization of an intragenic Mitf mutation affecting the K316 SUMOylation site.
- Biochemical and biophysical analyses, including smFRET, to study protein interactions and localization.
- Analysis of melanoma-associated mutations in MITF.
Main Results:
- An intragenic Mitf mutation was identified, leading to MITF truncation at the K316 SUMOylation site and loss of the C-terminal intrinsically disordered region (IDR).
- The truncated MITF protein exhibits increased nuclear localization and altered stability, while retaining DNA-binding ability.
- The mutant MITF dimer can stabilize wild-type and mutant MITF partners in the nucleus, ensuring nuclear MITF supply.
- Interactions between K316 SUMOylation and S409 phosphorylation sites across monomers were observed, explaining the phenotypic effects.
- The melanoma-associated E318K mutation impacts K316 SUMOylation and interacts with S409 phosphorylation.
Conclusions:
- MITF SUMOylation at K316 and phosphorylation at S409 are critical regulatory sites influencing nuclear localization and stability through conformational changes.
- A novel mechanism of genetic suppression involving MITF truncation and altered protein-protein interactions was discovered.
- Deleterious mutations can paradoxically lead to normal phenotypes through compensatory regulatory mechanisms.
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