Disparate leukemia mutations converge on nuclear phase-separated condensates

Area of Science:

• Molecular Biology
• Cancer Biology
• Biochemistry

Background:

• Cancer development involves gene expression alterations driven by mutations.
• Leukemia pathogenesis is linked to aberrant HOXA expression, often caused by nucleoporin gene translocations, KMT2A fusions, or NPM1 mutations.
• The unifying mechanism behind these genetic alterations in leukemia is not well understood.

Purpose of the Study:

• To investigate the role of mutant nucleophosmin 1 (NPM1c) in leukemia.
• To elucidate the mechanistic link between NPM1c mutations and other genetic drivers of leukemia.
• To identify potential therapeutic targets in NPM1c-driven leukemia.

Main Methods:

• Formation and characterization of nuclear condensates in NPM1c-mutated cells, mouse models, and patient samples.
• Assessment of NPM1c phase separation's necessity and sufficiency for recruiting NUP98 and KMT2A.
• Mutagenesis and pharmacological approaches to destabilize NPM1c condensates.
• Biophysical characterization of condensates formed by NPM1c and fusion proteins.

Main Results:

• Mutant NPM1c forms nuclear condensates (phase separation) in various leukemia models.
• NPM1c phase separation is crucial for recruiting NUP98 and KMT2A to these condensates.
• NPM1c condensates are essential for aberrant gene expression, leukemic cell expansion, and maintaining the undifferentiated state.
• Fusion proteins involving nucleoporins and KMT2A form condensates with identical biophysical properties to NPM1c condensates.

Conclusions:

• Mutant NPM1c drives leukemia through the formation of nuclear condensates, termed coordinating bodies (C-bodies).
• These C-bodies act as a hub, recruiting key proteins like NUP98 and KMT2A, and are critical for leukemogenesis.
• C-bodies represent a novel therapeutic vulnerability in leukemia, offering a new target for treatment.