Cai D H, Wang D, Keefer J, Yeamans C, Hensley K, Friedman A D
Division of Pediatric Oncology, Johns Hopkins University School of Medicine, Baltimore, MD 21231, USA.
Oncogene. 2008 Apr 24;27(19):2772-9. doi: 10.1038/sj.onc.1210940. Epub 2007 Nov 19.
The basic-region leucine zipper (BR-LZ or bZIP) transcription factors dimerize via their LZ domains to position the adjacent BRs for DNA binding. Members of the C/EBP, AP-1 and CREB/ATF bZIP subfamilies form homodimeric or heterodimeric complexes with other members of the same subset and bind-specific DNA motifs. Here we demonstrate that C/EBPalpha also zippers with AP-1 proteins and that this interaction allows contact with novel DNA elements and induction of monocyte lineage commitment in myeloid progenitors. A leucine zipper swap:gel shift assay demonstrates that C/EBPalpha zippers with c-Jun, JunB or c-Fos, but not with c-Maf or MafB. To evaluate activities of specific homodimers or heterodimers we utilized LZs with acid (LZE) or basic (LZK) residues in their salt bridge positions. C/EBPalphaLZE:C/EBPalphaLZK preferentially binds a C/EBP site, c-JunLZE:c-FosLZK an AP-1 site and C/EBPalphaLZE:c-JunLZK a hybrid element identified as TTGCGTCAT by oligonucleotide selection. In murine myeloid progenitors, C/EBPalpha:c-Jun or C/EBPalpha:c-Fos LZE:LZK heterodimers induce monocyte lineage commitment with markedly increased potency compared with C/EBPalpha or c-Jun homodimers or c-Jun:c-Fos heterodimers, demonstrating a positive functional consequence of C/EBP:AP-1 bZIP subfamily interaction. C/EBPalpha:cJun binds and activates the endogenous PU.1 promoter, providing one mechanism for induction of monopoiesis by this complex.
碱性区域亮氨酸拉链（BR-LZ或bZIP）转录因子通过其LZ结构域二聚化，以使相邻的BR定位用于DNA结合。C/EBP、AP-1和CREB/ATF bZIP亚家族的成员与同一亚组的其他成员形成同二聚体或异二聚体复合物，并结合特异性DNA基序。在这里，我们证明C/EBPα也能与AP-1蛋白形成拉链结构，并且这种相互作用允许与新的DNA元件接触，并诱导髓系祖细胞向单核细胞系分化。亮氨酸拉链交换：凝胶迁移试验表明，C/EBPα能与c-Jun、JunB或c-Fos形成拉链结构，但不能与c-Maf或MafB形成拉链结构。为了评估特定同二聚体或异二聚体的活性，我们在其盐桥位置使用了带有酸性（LZE）或碱性（LZK）残基的LZ。C/EBPαLZE:C/EBPαLZK优先结合一个C/EBP位点，c-JunLZE:c-FosLZK结合一个AP-1位点，而C/EBPαLZE:c-JunLZK结合一个通过寡核苷酸筛选鉴定为TTGCGTCAT的杂交元件。在小鼠髓系祖细胞中，与C/EBPα或c-Jun同二聚体或c-Jun:c-Fos异二聚体相比，C/EBPα:c-Jun或C/EBPα:c-Fos LZE:LZK异二聚体诱导单核细胞系分化的能力显著增强，这证明了C/EBP:AP-1 bZIP亚家族相互作用具有积极的功能后果。C/EBPα:cJun结合并激活内源性PU.1启动子，为该复合物诱导单核细胞生成提供了一种机制。
