New Control Mechanism for Protein Transport in Cells

细胞内蛋白质运输的新控制机制

基本信息

批准号：
14580650
负责人：
OGISHIMA Tadashi
金额：
$ 2.3万
依托单位：
Kyushu University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2002
资助国家：
日本
起止时间：
2002 至 2003
项目状态：
已结题

项目摘要

Outer mitochondrial membrane cytochrome b (OMb) was discovered in rat liver as a homologue of microsomal cytochrome b_5 (b_5). OMb was co-localized in Leydig cells with cytochrome P-450_<17α>, which catalyzes androgengenesis therein, whereas b_5 was undetectable. We have demonstrated that OMb stimulates the 17α-hydroxylase and lyase reactions of P-45O_<17α> under limited but physiological amounts of P-450 reductase, leading to an enhanced production of androstenedione from progesterone. Thus, OMband not b_5, which was believed to be responsible for the activation, was identified as a modulator for androgengenesis in rat testes. This finding prompted us to study the novel physiological functions of OMb. We analyzed the tissue localization of OMb, b_5 and P-45O_<17α> in rats by immunohistochemical staining. In the adrenal cortex OMb and b_5 were mainly present in the outer and inner portions, respectively. In the cerebellum OMb and P-450_<17α> were only detected and co-localized in the Purkinje cell, a major site for neurosteroidogenesis. In cerebrum they were co-localized in the ependymal cells of choroid plexus, which produces the cerebrospinal fluid. OMb was present also in the hippocampus and ganglionic layer. In contrast, b_5 was scarcely observed in the brain. Partially purified Purkinje cells produced testosterone from progesterone, indicating that both P-450_<17α> and 17β-hydroxysteroid dehydrogenase were active in the conversion and suggested that OMb could be responsible for stimulation of P-450_<17α>-catalyzed reactions in the cells. These results imply important functions of OMb in not only ordinary endocrine systems but also in higher life activities.

在大鼠肝脏中发现了线粒体外膜细胞色素 b (OMb)，作为微粒体细胞色素 b_5 (b_5) 的同源物，OMb 与细胞色素 P-450_<17α> 共定位于 Leydig 细胞中，细胞色素 P-450_<17α> 可催化其中的雄激素生成，而 b_5 则检测不到。我们已经证明 OMb 可以刺激 17α-羟化酶和裂解酶反应。 P-45O_<17α>在有限但生理量的P-450还原酶作用下，导致黄体酮雄烯二酮的产生增加，因此，OMband而不是b_5（据信负责激活）被确定为雄激素生成的调节剂。这一发现促使我们研究 OMb 的新生理功能，我们分析了 OMb、b_5 和 OMb 的组织定位。通过免疫组织化学染色，大鼠中的P-45O_<17α>在肾上腺皮质中分别主要存在于外部和内部部分，在小脑中仅检测到OMb和P-450_<17α>并共定位。浦肯野细胞是大脑中神经类固醇生成的主要部位，它们共定位于脉络膜的室管膜细胞中。产生脑脊液的神经丛也存在于海马和神经节层中，相比之下，在大脑中几乎没有观察到部分纯化的浦肯野细胞从孕酮中产生睾酮，这表明 P-450_<17α> 和 17β 都存在。 -羟基类固醇脱氢酶在转化过程中很活跃，表明 OMb 可能负责刺激P-450_<17α>-催化细胞中的反应。这些结果表明OMb不仅在普通内分泌系统中而且在高级生命活动中具有重要功能。