SUMO-1 dependent and independent mechanisms of PML body assembly and disassembly.
Published: 2005
Language: eng
Number of pages: 220
Description: Numerous discrete domains called nuclear bodies exist within the mammalian nucleus, which exhibit dynamic properties and are hypothesized to have critical roles in normal cellular function. Little is known about the mechanisms governing the formation and stability of nuclear bodies. Here, we used promyelocytic leukemia (PML) body as a paradigm to study the assembly/disassembly and stability of nuclear domains. Our aims included the analysis of underlying cause(s) for PML positional stability and to determine if chromatin contacts were influencing PML body integrity. We used environmental stresses (heat shock and heavy metal shock) to determine that PML bodies dissociate as supra-molecular complexes. We termed these small PML-containing structures, which lack PML-associated proteins as microstructures. These components were dynamic and moved by constrained diffusion. Ultrastructural analysis indicated that the mobility of microstructures was due to a lack of functional contact with other nucleoplasmic structures. During recovery from stress, microstructures fused with each other and parental PML bodies, coincident with increased levels of SUMO-1. During recovery, the position and the rank order size of PML bodies was conserved prior to and following recovery of cells from stress, indicating a non-random mechanism of PML body position and size conservation. Over-expression of SUMO-1 prevented the stress-mediated breakdown of PML bodies, indicating that PML body stability is partially dependent on SUMO-1. Direct transcriptional repression of cells by pharmaceutical agents also caused PML bodies to dissociate into supra-molecular complexes containing PML protein. These structures, however, contained detectable levels of SUMO-1. PML body breakdown was also observed in cells undergoing chromatin condensation as a result of chromatin cleavage, either in the early stages of apoptosis or by direct digestion by DNasel. Over-expression of SUMO-1 did not protect PML bodies from dissociating under these conditions, indicating that a second mechanism, independent of SUMO-1, is involved in PML body stability through PML interactions with the surrounding chromatin. Together, these finding indicate that both post-translational modification and the surrounding chromatin are involved in PML body assembly/disassembly and the maintenance of PML body integrity and may provide information to the formation, positional stability and dynamics of other nuclear bodies.
Notes: Thesis (Ph.D.)--University of Toronto, 2005.

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Source: Dissertation Abstracts International, Volume: 66-06, Section: B, page: 3049.