Down-regulation of heme oxygenase-2 is associated with the increased expression of heme oxygenase-1 in human cell lines
Down-regulation of heme oxygenase-2 is associated with the increased expression of heme oxygenase-1 in human cell lines
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DOI：
10.1111/j.1742-4658.2006.05526.x
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发表时间：
2006-12-01
期刊：
影响因子：
5.4
通讯作者：
Shibahara, Shigeki
中科院分区：
文献类型：
--
作者：
Ding, Yuanying;Zhang, Yong Z.;Shibahara, Shigeki
细胞内血红素浓度的维持部分是由血红素氧化酶催化的血红素降解。血红素加氧酶由两个结构相关的同工酶HO-1和HO-2组成。最近的研究已经确定HO-2是一种潜在的氧传感器。为了进一步了解HO-2在血红素稳态中的调节作用，我们分析了HO-2的表达谱以及用特异性短干扰RNA （siRNA）敲低HO-2在人类细胞中的生化后果。HO-2 mRNA和蛋白在8种人类癌细胞系中均有表达，HO-1在5种细胞系中均有表达，包括HeLa宫颈癌和HepG2肝癌。用siRNA抑制HO-2 （siHO-2）下调HO-2的表达，可诱导HeLa和HepG2细胞在mRNA和蛋白水平上表达HO-1。而HO-1表达下调对HO-2表达无明显影响。HO-2敲除使HeLa细胞HO-1 mRNA的半衰期延长2倍。在HeLa细胞中的瞬时转染实验显示，4.5 kb的人HO-1基因启动子通过选择性敲低HO-2以序列依赖的方式被激活。此外，HO-2敲低仅在暴露于外源性血红素时才会引起HeLa和HepG2细胞中的血红素积累。HO-2敲低可能模拟某种生理变化，这在维持细胞血红素稳态中很重要。这些结果表明，HO-2可能下调HO-1的表达，从而指导HO-1和HO-2的协调表达。
Intracellular heme concentrations are maintained in part by heme degradation, which is catalyzed by heme oxygenase. Heme oxygenase consists of two structurally related isozymes, HO-1 and HO-2. Recent studies have identified HO-2 as a potential oxygen sensor. To gain further insights into the regulatory role of HO-2 in heme homeostasis, we analyzed the expression profiles of HO-2 and the biochemical consequences of HO-2 knockdown with specific short interfering RNA (siRNA) in human cells. Both HO-2 mRNA and protein are expressed in the eight human cancer cell lines examined, and HO-1 expression is detectable in five of the cell lines, including HeLa cervical cancer and HepG2 hepatoma. Down-regulation of HO-2 expression with siRNA against HO-2 (siHO-2) caused induction of HO-1 expression at both mRNA and protein levels in HeLa and HepG2 cells. In contrast, knockdown of HO-1 expression did not noticeably influence HO-2 expression. HO-2 knockdown prolonged the half-life of HO-1 mRNA twofold in HeLa cells. Transient transfection assays in HeLa cells revealed that the 4.5-kb human HO-1 gene promoter was activated with selective knockdown of HO-2 in a sequence-dependent manner. Moreover, HO-2 knockdown caused heme accumulation in HeLa and HepG2 cells only when exposed to exogenous hemin. HO-2 knockdown may mimic a certain physiological change that is important in the maintenance of cellular heme homeostasis. These results suggest that HO-2 may down-regulate the expression of HO-1, thereby directing the co-ordinated expression of HO-1 and HO-2.