The retinoblastoma gene and its product are targeted by ICBP90: a key mechanism in the G1/S transition during the cell cycle
The retinoblastoma gene and its product are targeted by ICBP90: a key mechanism in the G1/S transition during the cell cycle
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DOI：
10.1038/sj.onc.1208878
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发表时间：
2005-11-01
期刊：
影响因子：
8
通讯作者：
Bronner, C
中科院分区：
文献类型：
--
作者：
Jeanblanc, M;Mousli, M;Bronner, C
视网膜母细胞瘤蛋白（pRB）由RB1基因编码，其启动子含有ICBP90 （90 kDa的倒置CCAAT盒子结合蛋白）的几个假定结合位点，ICBP90是拓扑异构酶II α基因的转录调节因子。ICBP90在其初级序列中有两个公认的pRB结合位点。在这里，我们发现pRB和ICBP90在增殖的人肺成纤维细胞和增殖或融合的Jurkat细胞的细胞提取物中共同免疫沉淀。GST下拉实验和免疫细胞化学，在G1期后期细胞同步后，证实了这种相互作用。ICBP90过表达可诱导肺组织pRB表达下调。成纤维细胞mRNA减少的结果。DNA染色质免疫沉淀实验表明，ICBP90在甲基化状态下与RB1基因启动子结合。ICBP90过表达可增加血清饥饿肺成纤维细胞S期和G2/M期细胞组分。增加拓扑异构酶IIa的表达。总之，这些结果表明，ICBP90在蛋白质和基因转录水平上调控pRB，从而有利于进入细胞的S期。我们提出，在癌细胞中发现的ICBP90过表达参与了癌变过程中检查点控制的改变。
The retinoblastoma protein (pRB) is encoded by the RB1 gene whose promoter contains several putative binding sites for ICBP90 (Inverted CCAAT box Binding Protein of 90 kDa), a transcriptional regulator of the topoisomerase II alpha gene. ICBP90 has two consensus binding sites for pRB in its primary sequence. Here, we show that pRB and ICBP90 co-immunoprecipitate in cell extracts of proliferating human lung fibroblasts and of proliferating or confluent Jurkat cells. GST pull-down assays and immunocytochemistry, after cell synchronization in late G1 phase, con. firmed this interaction. Overexpression of ICBP90 induces downregulation of pRB expression in lung. fibroblasts as a result of mRNA decrease. DNA chromatin immunoprecipitation experiment shows that ICBP90 binds to the RB1 gene promoter under its methylated status. Overexpression of ICBP90 increases the S and G2/M phase cell fractions of serum-starved lung fibroblasts as assessed by. flow cytometry analysis and increases topoisomerase IIa expression. Together, these results show that ICBP90 regulates pRB at the protein and gene transcription levels, thus favoring the entry into the S phase of the cells. We propose that ICBP90 overexpression, found in cancer cells, is involved in the altered checkpoint controls occurring in cancerogenesis.