Shiojima I, Komuro I, Oka T, Hiroi Y, Mizuno T, Takimoto E, Monzen K, Aikawa R, Akazawa H, Yamazaki T, Kudoh S, Yazaki Y
Department of Cardiovascular Medicine, University of Tokyo Graduate School of Medicine, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8655, Japan.
J Biol Chem. 1999 Mar 19;274(12):8231-9. doi: 10.1074/jbc.274.12.8231.
Although the cardiac homeobox gene Csx/Nkx-2.5 is essential for normal heart development, little is known about its regulatory mechanisms. In a search for the downstream target genes of Csx/Nkx-2. 5, we found that the atrial natriuretic peptide (ANP) gene promoter was strongly transactivated by Csx/Nkx-2.5. Deletion and mutational analyses of the ANP promoter revealed that the Csx/Nkx-2.5-binding element (NKE2) located at -240 was required for high level transactivation by Csx/Nkx-2.5. We also found that Csx/Nkx-2.5 and GATA-4 displayed synergistic transcriptional activation of the ANP promoter, and in contrast to previous reports (Durocher, D., Charron, F., Warren, R., Schwartz, R. J., and Nemer, M. (1997) EMBO J. 16, 5687-5696; Lee, Y., Shioi, T., Kasahara, H., Jobe, S. M., Wiese, R. J., Markham, B., and Izumo, S (1998) Mol. Cell. Biol. 18, 3120-3129), this synergism was dependent on binding of Csx/Nkx-2.5 to NKE2, but not on GATA-4-DNA interactions. Although GATA-4 also potentiated the Csx/Nkx-2.5-induced transactivation of the artificial promoter that contains multimerized Csx/Nkx-2.5-binding sites, Csx/Nkx-2.5 reduced the GATA-4-induced transactivation of the GATA-4-dependent promoters. These findings indicate that the cooperative transcriptional regulation mediated by Csx/Nkx-2.5 and GATA-4 is promoter context-dependent and suggest that the complex cis-trans interactions may fine-tune gene expression in cardiac myocytes.
尽管心脏同源框基因Csx/Nkx-2.5对正常心脏发育至关重要，但其调控机制却鲜为人知。在寻找Csx/Nkx-2.5的下游靶基因过程中，我们发现心房利钠肽（ANP）基因启动子被Csx/Nkx-2.5强烈反式激活。对ANP启动子的缺失和突变分析表明，位于-240处的Csx/Nkx-2.5结合元件（NKE2）是Csx/Nkx-2.5高水平反式激活所必需的。我们还发现，Csx/Nkx-2.5和GATA-4对ANP启动子表现出协同转录激活作用，与先前报道（Durocher, D., Charron, F., Warren, R., Schwartz, R. J., and Nemer, M. (1997) EMBO J. 16, 5687-5696; Lee, Y., Shioi, T., Kasahara, H., Jobe, S. M., Wiese, R. J., Markham, B., and Izumo, S (1998) Mol. Cell. Biol. 18, 3120-3129）相反，这种协同作用依赖于Csx/Nkx-2.5与NKE2的结合，而不依赖于GATA-4与DNA的相互作用。尽管GATA-4也增强了Csx/Nkx-2.5诱导的含多个Csx/Nkx-2.5结合位点的人工启动子的反式激活，但Csx/Nkx-2.5降低了GATA-4诱导的GATA-4依赖型启动子的反式激活。这些发现表明，由Csx/Nkx-2.5和GATA-4介导的协同转录调控依赖于启动子背景，并提示复杂的顺式-反式相互作用可能对心肌细胞中的基因表达进行微调。
