Department of Biological Chemistry, University of California, Irvine, California 92697, USA.
J Biol Chem. 2010 Feb 12;285(7):4464-71. doi: 10.1074/jbc.M109.062265. Epub 2009 Dec 10.
The high mobility group AT-hook 2 (HMGA2), a DNA architectural protein, is highly regulated during development and plays an important role in tumorigenesis. Indeed, HMGA2 was overexpressed in many different kinds of tumors. However, the mechanisms regulating HMGA2 expression remain elusive. Using microarray analysis, we found that HMGA2, along with a dozen of other genes, was co-repressed by ZBRK1, BRCA1, and CtIP. BRCA1 exerts its transcriptional repression activity through interaction with the transcriptional repressor ZBRK1 in the central domain, and with CtIP in the C-terminal BRCT domain. Here, we show that ZBRK1, BRCA1, and CtIP form a repression complex that coordinately regulates HMGA2 expression via a ZBRK1 recognition site in the HMGA2 promoter. Depletion of any of the proteins in this complex via adenoviral RNA interference in MCF10A mammary epithelial cells activates HMGA2 expression, resulting in increased colony formation in soft agar. Similarly, depletion of ZBRK1, or ectopic overexpression of HMGA2, in MCF10A cells induces abnormal acinar size with increased cell number and inhibits normal acinar formation. Consistently, many BRCA1-deficient mouse breast tumors express higher levels of HMGA2 than BRCA1-proficient tumors. These results suggest that activation of HMGA2 gene expression through derepression of the ZBRK1/BRCA1/CtIP complex is a significant step in accelerating breast tumorigenesis.
高迁移率族 AT 钩 2（HMGA2）是一种 DNA 结构蛋白，在发育过程中受到高度调控，在肿瘤发生中发挥重要作用。事实上，HMGA2 在许多不同类型的肿瘤中过度表达。然而，调节 HMGA2 表达的机制仍不清楚。通过微阵列分析，我们发现 HMGA2 与十几个其他基因一起被 ZBRK1、BRCA1 和 CtIP 共同抑制。BRCA1 通过与中央结构域中的转录抑制因子 ZBRK1 以及 C 末端 BRCT 结构域中的 CtIP 相互作用来发挥其转录抑制活性。在这里，我们表明 ZBRK1、BRCA1 和 CtIP 形成一个抑制复合物，通过 HMGA2 启动子中的 ZBRK1 识别位点协同调节 HMGA2 的表达。通过腺病毒 RNA 干扰在 MCF10A 乳腺上皮细胞中耗尽该复合物中的任何一种蛋白质，都会激活 HMGA2 的表达，导致软琼脂中集落形成增加。同样，在 MCF10A 细胞中耗尽 ZBRK1 或异位过表达 HMGA2 会诱导异常的小泡大小，增加细胞数量并抑制正常的小泡形成。一致地，许多 BRCA1 缺陷型小鼠乳腺癌比 BRCA1 功能正常的肿瘤表达更高水平的 HMGA2。这些结果表明，通过去抑制 ZBRK1/BRCA1/CtIP 复合物来激活 HMGA2 基因表达是加速乳腺癌发生的重要步骤。
