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Role of SUMO-1-modified PML in nuclear body formation
S Zhong1, S Müller, S Ronchetti
1Department of Human Genetics and Molecular Biology Program, Memorial Sloan-Kettering Cancer Center, Sloan-Kettering Division, Graduate School of Medical Sciences, Cornell University, New York, NY 10021, USA.
Abstract:
The tumor-suppressive promyelocytic leukemia (PML) protein of acute promyelocytic leukemia (APL) has served as one of the defining components of a class of distinctive nuclear bodies (NBs). PML is delocalized from NBs in APL cells and is degraded in cells infected by several viruses. In these cells, NBs are disrupted, leading to the aberrant localization of NB proteins. These results have suggested a critical role for the NB in immune response and tumor suppression and raised the question of whether PML is crucial for the formation or stability of NB. In addition, PML is, among other proteins, covalently modified by SUMO-1. However, the functional relevance of this modification is unclear. Here, we show in primary PML(-/-) cells of various histologic origins, that in the absence of PML, several NB proteins such as Sp100, CBP, ISG20, Daxx, and SUMO-1 fail to accumulate in the NB and acquire aberrant localization patterns. Transfection of PML in PML(-/-) cells causes the relocalization of NB proteins. By contrast, a PML mutant that can no longer be modified by SUMO-1 fails to do so and displays an aberrant nuclear localization pattern. Therefore, PML is required for the proper formation of the NB. Conjugation to SUMO-1 is a prerequisite for PML to exert this function. These data shed new light on both the mechanisms underlying the formation of the NBs and the pathogenesis of APL. (Blood. 2000;95:2748-2752)
Insights
The promyelocytic leukemia (PML) protein is essential for forming nuclear bodies (NBs), which are critical for tumor suppression and immune response. SUMO-1 modification of PML is necessary for its function in NB formation.
Area of Science:
- Cell Biology
- Molecular Biology
- Oncology
Background:
- Nuclear bodies (NBs) are distinct nuclear structures involved in cellular processes.
- The promyelocytic leukemia (PML) protein is a key component of NBs and is implicated in tumor suppression.
- PML's localization to NBs is disrupted in acute promyelocytic leukemia (APL) and viral infections, suggesting a role in cellular defense.
Purpose of the Study:
- To investigate the role of PML in the formation and stability of nuclear bodies.
- To determine if PML is essential for the proper localization of other NB proteins.
- To elucidate the functional significance of SUMO-1 modification of PML.
Main Methods:
- Utilized primary PML(-/-) cells from various origins.
- Observed the localization of NB proteins (Sp100, CBP, ISG20, Daxx, SUMO-1) in PML-deficient cells.
- Assessed the effect of PML re-expression and a SUMO-1-deficient PML mutant on NB protein localization.
Main Results:
- In the absence of PML, several NB proteins failed to accumulate in NBs and showed aberrant localization.
- Re-introduction of PML into PML(-/-) cells restored the proper localization of NB proteins.
- A PML mutant unable to undergo SUMO-1 modification failed to rescue NB protein localization, displaying aberrant nuclear patterns.
Conclusions:
- PML is indispensable for the correct formation and protein composition of nuclear bodies.
- SUMO-1 conjugation to PML is a prerequisite for its function in NB assembly.
- These findings provide insights into NB biogenesis mechanisms and APL pathogenesis.