Douet Vanessa, VanWart Christopher M, Heller Matthew B, Reinhard Sabrina, Le Saux Olivier
Department of Cell and Molecular Biology, John A. Burns School of Medicine, University of Hawaii, 651 Ilalo Street, BSB 222, Honolulu, HI 96813, USA.
Biochim Biophys Acta. 2006 Aug-Sep;1759(8-9):426-36. doi: 10.1016/j.bbaexp.2006.08.002. Epub 2006 Aug 11.
Mutations in an ABC transporter gene called ABCC6 are responsible for pseudoxanthoma elasticum (PXE), a rare heritable disease characterized by elastic fiber calcification in skin, ocular and vascular tissues. The presumed function of this ABC transporter is to export metabolites from polarized cells. However, the endogenous substrate(s) are unknown and the exact relationship with elastic fibers is unclear. As ABCC6 is only expressed at high level in liver and kidneys, tissues seemingly unrelated to the PXE phenotype, we explored the transcriptional regulation of the murine Abcc6 gene to define the transcriptional signal conferring tissue specificity and to gather clues on its possible biological function. We cloned 2.9 kb of the mAbcc6 5'-flanking region and several deletion constructs linked to a luciferase reporter gene. We delineated a proximal promoter and a liver-specific enhancer region. We also demonstrated that the proximal region is a TATA-less promoter requiring an intact CCAAT-box and Sp1 binding for its basal activity. By using reporter assays and chromatin immunoprecipitations, we showed that HNF4alpha and surprisingly, NF-E2, enhanced the mAbcc6 promoter activity. The involvement of both HNF4alpha and NF-E2 in the mAbcc6 gene regulation suggests that Abcc6 might be involved in a detoxification processes related to hemoglobin or heme.
一种名为ABCC6的ABC转运蛋白基因突变是引起弹性假黄瘤（PXE）的原因，PXE是一种罕见的遗传性疾病，其特征是皮肤、眼部和血管组织中的弹性纤维钙化。这种ABC转运蛋白的推测功能是从极化细胞中输出代谢物。然而，内源性底物尚不清楚，与弹性纤维的确切关系也不明确。由于ABCC6仅在肝脏和肾脏中高水平表达，而这些组织似乎与PXE表型无关，因此我们探索了小鼠Abcc6基因的转录调控，以确定赋予组织特异性的转录信号，并收集有关其可能生物学功能的线索。我们克隆了2.9 kb的mAbcc6 5'侧翼区域以及几个与荧光素酶报告基因相连的缺失构建体。我们确定了一个近端启动子和一个肝脏特异性增强子区域。我们还证明，近端区域是一个无TATA的启动子，其基础活性需要完整的CCAAT框和Sp1结合。通过使用报告基因检测和染色质免疫沉淀，我们发现HNF4α，令人惊讶的是还有NF-E2，增强了mAbcc6启动子活性。HNF4α和NF-E2都参与mAbcc6基因调控，这表明Abcc6可能参与了与血红蛋白或血红素相关的解毒过程。
