Neomorphic leukemia-derived mutations in the TET2 enzyme induce genome instability via a substrate shift from...

Area of Science:

• Epigenetics
• Molecular Biology
• Cancer Research

Background:

• Ten-eleven translocation (TET) enzymes regulate gene transcription by oxidizing 5-methylcytosine (mC) in DNA.
• Mutations in TET2 are common in blood cancers, but their full functional impact remains unclear.

Purpose of the Study:

• To investigate the functional consequences of TET2 mutations found in leukemia patients.
• To explore if these mutations alter TET2's substrate specificity and lead to novel activities.

Main Methods:

• Analysis of patient-derived TET2 mutations for altered substrate specificity.
• Biochemical assays using recombinant TET2 proteins to detect thymine oxidation.
• Cellular studies involving exogenous expression and endogenous knock-in of mutant TET2 in HEK293T and mouse embryonic stem cells.
• Assessment of DNA damage response and mutation accumulation in cells expressing mutant TET2.

Main Results:

• A subset of TET2 mutations alters substrate specificity, enabling oxidation of thymine to 5-hydroxymethyluracil (hmU) and 5-formyluracil (fU).
• Mutant TET2 (e.g., N1387T) expression leads to hmU accumulation, DNA lesions, and transcriptional activation of DNA damage response genes.
• Cells with knock-in mutant TET2 exhibit increased mutation rates and sensitivity to ATR inhibition.

Conclusions:

• Specific patient-derived TET2 mutations acquire neomorphic gain-of-function activities, oxidizing thymine instead of mC.
• This novel activity contributes to DNA damage and genomic instability, offering new insights into TET2-mutant leukemogenesis.