Related Experiment Video
Updated: Dec 30, 2025
Next Generation Sequencing for the Detection of Actionable Mutations in Solid and Liquid Tumors
Published on: September 20, 2016
MPL mutations in essential thrombocythemia uncover a common path of activation with eltrombopag dependent on W491
Gabriel Levy1,2,3,4, Serge Carillo5, Benjamin Papoular6
1de Duve Institute, Université Catholique de Louvain, Brussels, Belgium.
Abstract:
Mutations in the MPL gene encoding the human thrombopoietin receptor (TpoR) drive sporadic and familial essential thrombocythemias (ETs). We identified 2 ET patients harboring double mutations in cis in MPL, namely, L498W-H499C and H499Y-S505N. Using biochemical and signaling assays along with partial saturation mutagenesis, we showed that L498W is an activating mutation potentiated by H499C and that H499C and H499Y enhance the activity of the canonical S505N mutation. L498W and H499C can activate a truncated TpoR mutant, which lacks the extracellular domain, indicating these mutations act on the transmembrane (TM) cytosolic domain. Using a protein complementation assay, we showed that L498W and H499C strongly drive dimerization of TpoR. Activation by tryptophan substitution is exquisitely specific for position 498. Using structure-guided mutagenesis, we identified upstream amino acid W491 as a key residue required for activation by L498W or canonical activating mutations such as S505N and W515K, as well as by eltrombopag. Structural data point to a common dimerization and activation path for TpoR via its TM domain that is shared between the small-molecule agonist eltrombopag and canonical and novel activating TpoR mutations that all depend on W491, a potentially accessible extracellular residue that could become a target for therapeutic intervention.
Insights
Novel MPL gene mutations, L498W-H499C and H499Y-S505N, drive essential thrombocythemia by activating the thrombopoietin receptor (TpoR) transmembrane domain. These mutations, along with eltrombopag, converge on residue W491 for TpoR activation and dimerization.
Area of Science:
- Molecular Biology
- Hematology
- Genetics
Background:
- Mutations in the MPL gene, encoding the human thrombopoietin receptor (TpoR), are key drivers of essential thrombocythemias (ETs).
- Understanding the precise mechanisms of TpoR activation by these mutations is crucial for developing targeted therapies.
Purpose of the Study:
- To investigate the functional impact of novel double MPL mutations (L498W-H499C and H499Y-S505N) found in ET patients.
- To elucidate the molecular mechanisms underlying TpoR activation by these mutations, focusing on the transmembrane domain.
Main Methods:
- Biochemical and signaling assays
- Partial saturation mutagenesis
- Protein complementation assay
- Structure-guided mutagenesis
Main Results:
- Identified two novel cis double MPL mutations: L498W-H499C and H499Y-S505N.
- Demonstrated that L498W is an activating mutation, potentiated by H499C, and that H499C/H499Y enhance S505N activity.
- Showed that L498W and H499C activate TpoR via the transmembrane (TM) cytosolic domain and strongly promote TpoR dimerization.
- Identified W491 as a critical residue for activation by novel and canonical MPL mutations, as well as by eltrombopag.
Conclusions:
- Novel MPL mutations activate TpoR through its TM domain, promoting receptor dimerization.
- Activation pathways for novel MPL mutations, canonical mutations, and eltrombopag converge on W491.
- W491 represents a potential therapeutic target for ET treatment.
More Related Videos
04:36Comet Assay to Quantify DNA Damage in FLT3 Mutant-expressing 32D Cells after Exposure to Type I and Type II FLT3 Inhibitors
Published on: October 17, 2025
10:41Wild-type Blocking PCR Combined with Direct Sequencing as a Highly Sensitive Method for Detection of Low-Frequency Somatic Mutations
Published on: March 29, 2017