Biggs Joseph R, Zhang Youhong, Peterson Luke F, Garcia Marileila, Zhang Dong-Er, Kraft Andrew S
Department of Medicine, P.O. Box 250955, Medical University of South Carolina, 6 Jonathan Lucas Street, Charleston, SC 29425, USA.
Mol Cancer Res. 2005 Jul;3(7):391-401. doi: 10.1158/1541-7786.MCR-04-0184.
The acute myeloid leukemia 1 (AML1) transcription factors are key regulators of hematopoietic differentiation. Cellular AML1c protein is found in the nucleus and can be separated into two fractions, one soluble in buffers containing salt and nonionic detergent and the other insoluble and tightly bound to the nuclear matrix. We find that the AML1c protein is modified by both phosphorylation and ubiquitination. Our studies show that the majority of the ubiquitinated AML1c is associated with the insoluble nuclear matrix. Treatment of cells with the proteasome inhibitor PS341 (Velcade, Bortezomib) increases the levels of ubiquitinated AML1c. Mutation of the four phosphorylation sites necessary for transcriptional regulation (serine 276, serine 293, serine 303, and threonine 300) mimics the effects of the proteasome inhibitor, increasing the levels of ubiquitinated, matrix-bound AML1c. We find that the soluble and insoluble forms of AML1c are degraded at a similar rate. However, mutation of these four serine/threonine residues statistically increases the half-life of the matrix-associated AML1c. Thus, phosphorylation of AML1c on specific serine/threonine residues controls both transcriptional activity and rate of degradation.
急性髓系白血病1（AML1）转录因子是造血分化的关键调节因子。细胞中的AML1c蛋白存在于细胞核中，可分为两部分，一部分可溶于含盐和非离子去污剂的缓冲液，另一部分不溶且紧密结合于核基质。我们发现AML1c蛋白可被磷酸化和泛素化修饰。我们的研究表明，大多数泛素化的AML1c与不溶性核基质相关。用蛋白酶体抑制剂PS341（万珂，硼替佐米）处理细胞可增加泛素化AML1c的水平。转录调控所需的四个磷酸化位点（丝氨酸276、丝氨酸293、丝氨酸303和苏氨酸300）发生突变可模拟蛋白酶体抑制剂的作用，增加泛素化的、与基质结合的AML1c的水平。我们发现AML1c的可溶形式和不溶形式以相似的速率降解。然而，这四个丝氨酸/苏氨酸残基发生突变在统计学上增加了与基质相关的AML1c的半衰期。因此，AML1c在特定丝氨酸/苏氨酸残基上的磷酸化既控制转录活性又控制降解速率。
