Hayashi Shunsuke, Omata Yoshiaki, Sakamoto Hiroshi, Higashimoto Yuichiro, Hara Takayuki, Sagara Yasuhiro, Noguchi Masato
Department of Medical Biochemistry, Kurume University School of Medicine, 67 Asahi-machi, Kurume 830-0011, Japan.
Gene. 2004 Jul 21;336(2):241-50. doi: 10.1016/j.gene.2004.04.002.
Heme oxygenase (HO) is an enzyme responsible for the physiological degradation of heme to produce iron, CO and biliverdin. The released iron is recycled and represents the major source of this metal in heme homeostasis. A putative role as messenger in a signaling pathway is suggested for CO. Biliverdin, together with bilirubin, may function as an antioxidant. Thus far, three isoforms of HO, HO-1, HO-2 and HO-3 have been described. While HO-1 and HO-2 have been extensively investigated, HO-3 is still an elusive and poorly understood isoform. In this study, we examined the structure of the rat HO-3 gene with genomic PCR. However, we failed to isolate the reported HO-3 gene but, instead, found two HO-3-related genes, tentatively named HO-3a and HO-3b, whose sequences differed slightly from each other. Neither gene had any introns and consisted only of exon 2 through 5 of the HO-2 gene, though their sequences were not completely identical with that of HO-2. A stop codon was introduced within the coding regions of these genes due to frame-shift. The nucleotide sequence of their 5'-upstream region largely agreed with long interspersed nuclear element 3. No HO-3-related mRNAs were amplified by RT-PCR, and no HO-3-related proteins were detected in tissues by Western blot analysis. Our results suggested that there are no functional HO-3 genes in rat and that the HO-3a and HO-3b genes are processed pseudogenes derived from HO-2 transcripts.
血红素加氧酶(HO)是一种负责血红素生理降解以产生铁、一氧化碳和胆绿素的酶。释放出的铁被循环利用,是血红素稳态中这种金属的主要来源。一氧化碳被认为在信号通路中可能作为一种信使发挥作用。胆绿素与胆红素一起可能具有抗氧化功能。到目前为止,已经描述了HO的三种同工型,即HO-1、HO-2和HO-3。虽然HO-1和HO-2已被广泛研究,但HO-3仍然是一种难以捉摸且了解甚少的同工型。在本研究中,我们用基因组PCR检测了大鼠HO-3基因的结构。然而,我们未能分离出报道的HO-3基因,而是发现了两个与HO-3相关的基因,暂命名为HO-3a和HO-3b,它们的序列彼此略有不同。这两个基因都没有内含子,仅由HO-2基因的外显子2至5组成,尽管它们的序列与HO-2并不完全相同。由于移码,在这些基因的编码区内引入了一个终止密码子。它们5'上游区域的核苷酸序列与长散在核元件3基本一致。通过逆转录聚合酶链反应(RT-PCR)未扩增出与HO-3相关的mRNA,通过蛋白质免疫印迹分析在组织中也未检测到与HO-3相关的蛋白质。我们的结果表明大鼠中不存在功能性的HO-3基因,并且HO-3a和HO-3b基因是源自HO-2转录本的加工假基因。