Departamento de Bioquimica, Facultad de Medicina, Universidad Nacional Autónoma de México, Apdo. Postal 70-159, 04510 Mexico City, Mexico.
Placenta. 2011 Mar;32(3):222-9. doi: 10.1016/j.placenta.2010.12.018. Epub 2011 Jan 12.
The human placenta, which does not express the StAR protein, synthesizes large amounts of progesterone. The rate-limiting step for steroidogenesis is the transport of cholesterol which is divided into two steps: 1) cholesterol flux from cytoplasm to outer membrane mitochondria, and 2) cholesterol transport from outer to inner mitochondrial membrane. The proteins mediating placental cholesterol influx have not been clearly identified. We investigated the proteins involved in the transport of cholesterol in syncytiotrophoblast mitochondria from human placenta. Two proteins, one of 30 kDa, and another of 60 kDa, were identified using anti-MLN64 antibodies. The 30 kDa protein corresponds to a fragment of MLN64, and the 60 kDa protein was identified as a heat shock protein. During steroidogenesis, mitochondria released MLN64 protein to supernatant. When this supernatant was added to fresh isolated mitochondria, progesterone synthesis increased; a similar result was obtained with the addition of the recombinant MLN64-START protein. In the presence of flurescein-5-maleimide or N-ethyl-maleimide, the mitochondrial synthesis of progesterone was inhibited in a dose-dependent fashion without changes in mitochondrial respiration. 2D-electrophoretic pattern showed that flurescein-5-maleimide- fluorescence was associated with HSP60. Both MLN64 and HSP60 were identified in mitochondrial contact sites. The results suggest that HSP60 is involved in the steroidogenic metabolism of human placenta. A tight association between MLN64 and HSP60 is suggested for cholesterol transport in the human placenta.
人胎盘不表达 StAR 蛋白,但能合成大量孕激素。类固醇生成的限速步骤是胆固醇的转运,胆固醇转运分为两步:1)胆固醇从细胞质到线粒体外膜的通量,2)胆固醇从线粒体外膜到内膜的转运。介导胎盘胆固醇内流的蛋白质尚未明确鉴定。我们研究了人胎盘合体滋养层线粒体中胆固醇转运涉及的蛋白质。使用抗 MLN64 抗体鉴定到两种蛋白质,一种分子量为 30 kDa,另一种分子量为 60 kDa。30 kDa 的蛋白质对应于 MLN64 的一个片段,60 kDa 的蛋白质被鉴定为热休克蛋白。在类固醇生成过程中,线粒体将 MLN64 蛋白释放到上清液中。当将该上清液添加到新鲜分离的线粒体时,孕激素合成增加;添加重组 MLN64-START 蛋白时也得到了类似的结果。当存在荧光素 5-马来酰亚胺或 N-乙基马来酰亚胺时,线粒体孕激素的合成被剂量依赖性抑制,而线粒体呼吸没有变化。2D 电泳模式显示,荧光素 5-马来酰亚胺荧光与 HSP60 相关。线粒体接触点中均鉴定到 MLN64 和 HSP60。结果表明 HSP60 参与人胎盘的甾体生成代谢。提示 MLN64 和 HSP60 之间存在紧密联系,可能与胆固醇在人胎盘的转运有关。