RING tetramerization is required for nuclear body biogenesis and PML sumoylation

Area of Science:

• Cellular Biology
• Molecular Oncology
• Structural Biology

Background:

• ProMyelocytic Leukemia nuclear bodies (PML NBs) are critical stress-regulated domains involved in acute promyelocytic leukemia (APL) eradication.
• Most TRIM proteins utilize ubiquitin E2 enzymes and gain ligase activity through RING dimerization.
• PML, however, interacts with UBC9, the SUMO E2 enzyme, suggesting a distinct mechanism.

Purpose of the Study:

• To elucidate the structural basis of PML nuclear body assembly and function.
• To investigate the role of PML RING domain interactions in sumoylation and leukemogenesis.
• To understand the mechanism of TRIM-PML interactions with E2 enzymes.

Main Methods:

• X-ray crystallography to determine the structure of the PML RING domain.
• Small-angle X-ray scattering (SAXS) for characterizing PML oligomerization in solution.
• In vivo and ex vivo assays to assess the functional impact of PML mutations on leukemogenesis and differentiation.

Main Results:

• PML RING domain tetramerizes through conserved PML-specific sequences, essential for NB assembly and sumoylation.
• Conserved residues involved in TRIM RING dimerization also stabilize PML tetramers.
• Impaired PML RING tetramerization abrogates PML/RARA-driven leukemogenesis and arsenic-induced differentiation.

Conclusions:

• PML RING tetramerization is a fundamental step in the macro-molecular scaffolding of PML nuclear bodies.
• Higher-order RING interactions facilitate efficient UBC9 recruitment, altering TRIM-mediated post-translational modifications.
• This mechanism highlights a novel aspect of TRIM protein function and its role in cancer biology.