McCarthy Kevin M, McDevit Daniel, Andreucci Amy, Reeves Raymond, Nikolajczyk Barbara S
Department of Microbiology, Boston University School of Medicine, Boston, MA 02118, USA.
J Biol Chem. 2003 Oct 24;278(43):42106-14. doi: 10.1074/jbc.M308586200. Epub 2003 Aug 7.
The immunoglobulin heavy chain enhancer, or mu enhancer, is required for B cell development. Only the appropriate combination of transcription factors results in B cell-specific enhancer activation. HMGA1 (formerly (HMG-I(Y)) is a proposed co-activator of the ETS transcription factors required for mu enhancer activity. HMGA1 associates with the ETS factor PU.1, resulting in changes in PU.1 structure, and enhanced transcriptional synergy with Ets-1 on the mu enhancer in nonlymphoid cells. New data show HMGA1 directly interacts with Ets-1 in addition to PU.1. In vitro HMGA1/Ets-1 interaction facilitates Ets-1/mu enhancer binding in the absence of an HMGA1.Ets-1.DNA complex. To address whether HMGA1 is present in the transcriptionally active mu nucleoprotein complex, we completed DNA pull-down assays to detect protein tethering in the context of protein/DNA interaction. Results show that HMGA1 is not tightly associated with mu enhancer DNA through PU.1 or Ets-1, despite strong associations between these proteins in solution. However, chromatin immunoprecipitation assays show HMGA1 associates with the endogenous enhancer in B cells. Furthermore, antisense HMGA1 substantially decreases mu enhancer activity in B cells. Taken together, these data suggest that HMGA1 functions as a transcriptional mu enhancer co-activator in B cells through indirect association with DNA.
免疫球蛋白重链增强子，即μ增强子，是B细胞发育所必需的。只有转录因子的适当组合才能导致B细胞特异性增强子的激活。HMGA1（以前称为HMG-I(Y)）是μ增强子活性所需的ETS转录因子的一种假定的共激活因子。HMGA1与ETS因子PU.1结合，导致PU.1结构发生变化，并增强了与非淋巴细胞中μ增强子上的Ets-1的转录协同作用。新数据表明，HMGA1除了与PU.1相互作用外，还直接与Ets-1相互作用。在体外，HMGA1/Ets-1相互作用在不存在HMGA1.Ets-1.DNA复合物的情况下促进Ets-1与μ增强子的结合。为了研究HMGA1是否存在于转录活性的μ核蛋白复合物中，我们完成了DNA下拉实验，以检测在蛋白质/DNA相互作用背景下的蛋白质拴系情况。结果表明，尽管这些蛋白质在溶液中存在很强的结合，但HMGA1并非通过PU.1或Ets-1与μ增强子DNA紧密结合。然而，染色质免疫沉淀实验表明，HMGA1与B细胞中的内源性增强子相关联。此外，反义HMGA1显著降低了B细胞中μ增强子的活性。综上所述，这些数据表明，HMGA1在B细胞中通过与DNA的间接结合而作为转录μ增强子的共激活因子发挥作用。
