Using yeast to analyze the human promyelocytic leukemia protein (PML).
Boots Quimby, Vladimir Yong-Gonzalez, Alex Strunnikov, Mary Dasso
LGRD, NIH/NICHD, 9000 Rockville Pike, Bethesda, MD, 20816, USA
PML is a tumor suppressor associated with the t(15;17) chromosomal translocation in acute promyelocytic leukemia. This translocation fuses PML to the RARalpha gene. The PML-RARalpha oncoprotein inhibits RARalpha transcriptional function and also associates with the intact PML protein. PML-RARalpha produces leukemia when expressed in transgenic mice while dominant-negative RARalpha mutants that do not interact with PML do not, emphasizing the importance of PML function in leukemogenesis. PML nucleates the formation of large complexes within the nucleus referred to as PODs. Modification of PML by the small ubiquitin like molecule Sumo1 is required for the recruitment of a subset of proteins to PODs. Although PML has been implicated in control of apoptosis, checkpoint responses to DNA damage, genomic stability and DNA repair the cellular mechanism by which PML controls this broad range of cellular processes remains unclear. To analyze PML function we co-expressed human PML and human Sumo1 in yeast. We demonstrate that PML stimulates self-modification by Sumo1 and that this activity is lost when the ring finger domain of PML is mutated. PML and PML-RARalpha, but not the ring finger domain mutant, partially complement the function of the yeast Sumo E3 ligase proteins indicating that PML exhibits Sumo E3 ligase activity. These data demonstrate a biochemical function for PML that could explain its ability to impact a variety of cellular processes associated with cancer.
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