title: Mitochondrial proteases act on STARD3 to activate progesterone synthesis in human syncytiotrophoblast.
abstract: BACKGROUND
  STARD1 transports cholesterol into mitochondria of acutely regulated steroidogenic tissue. It has been suggested that STARD3 transports cholesterol in the human placenta, which does not express STARD1. STARD1 is proteolytically activated into a 30-kDa protein. However, the role of proteases in STARD3 modification in the human placenta has not been studied.
  
  
  METHODS
  Progesterone determination and Western blot using anti-STARD3 antibodies showed that mitochondrial proteases cleave STARD3 into a 28-kDa fragment that stimulates progesterone synthesis in isolated syncytiotrophoblast mitochondria. Protease inhibitors decrease STARD3 transformation and steroidogenesis.
  
  
  RESULTS
  STARD3 remained tightly bound to isolated syncytiotrophoblast mitochondria. Simultaneous to the increase in progesterone synthesis, STARD3 was proteolytically processed into four proteins, of which a 28-kDa protein was the most abundant. This protein stimulated mitochondrial progesterone production similarly to truncated-STARD3. Maximum levels of protease activity were observed at pH7.5 and were sensitive to 1,10-phenanthroline, which inhibited steroidogenesis and STARD3 proteolytic cleavage. Addition of 22(R)-hydroxycholesterol increased progesterone synthesis, even in the presence of 1,10-phenanthroline, suggesting that proteolytic products might be involved in mitochondrial cholesterol transport.
  
  
  CONCLUSIONS
  Metalloproteases from human placental mitochondria are involved in steroidogenesis through the proteolytic activation of STARD3. 1,10-Phenanthroline inhibits STARD3 proteolytic cleavage. The 28-kDa protein and the amino terminal truncated-STARD3 stimulate steroidogenesis in a comparable rate, suggesting that both proteins share similar properties, probably the START domain that is involved in cholesterol binding.
  
  
  CONCLUSIONS
  Mitochondrial proteases are involved in syncytiotrophoblast-cell steroidogenesis regulation. Understanding STARD3 activation and its role in progesterone synthesis is crucial to getting insight into its action mechanism in healthy and diseased syncytiotrophoblast cells.
authors.affiliation: Departamento de Bioquímica, Facultad de Medicina, Universidad Nacional Autónoma de México, Mexico.
authors.forename: Mercedes
authors.initials: M
authors.lastname: Esparza-Perusquía
authors.affiliation: Departamento de Bioquímica, Facultad de Medicina, Universidad Nacional Autónoma de México, Mexico.
authors.forename: Sofía
authors.initials: S
authors.lastname: Olvera-Sánchez
authors.affiliation: Departamento de Bioquímica, Facultad de Medicina, Universidad Nacional Autónoma de México, Mexico.
authors.forename: Oscar
authors.initials: O
authors.lastname: Flores-Herrera
authors.affiliation: Departamento de Bioquímica y Biología Molecular, Instituto Nacional de Perinatología "Isidro Espinosa de los Reyes", Mexico.
authors.forename: Héctor
authors.initials: H
authors.lastname: Flores-Herrera
authors.affiliation: Departamento de Bioquímica, Facultad de Medicina, Universidad Nacional Autónoma de México, Mexico.
authors.forename: Alberto
authors.initials: A
authors.lastname: Guevara-Flores
authors.affiliation: Departamento de Bioquímica, Facultad de Medicina, Universidad Nacional Autónoma de México, Mexico.
authors.forename: Juan Pablo
authors.initials: JP
authors.lastname: Pardo
authors.affiliation: Departamento de Bioquímica, Facultad de Medicina, Universidad Nacional Autónoma de México, Mexico.
authors.forename: María Teresa
authors.initials: MT
authors.lastname: Espinosa-García
authors.affiliation: Departamento de Bioquímica, Facultad de Medicina, Universidad Nacional Autónoma de México, Mexico. Electronic address: fedem@bq.unam.mx.
authors.forename: Federico
authors.initials: F
authors.lastname: Martínez
mesh_terms: D015153:Blotting, Western; D002352:Carrier Proteins / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D005260:Female; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008565:Membrane Proteins / Q000378:metabolism*; D008928:Mitochondria / Q000201:enzymology* / Q000378:metabolism; D010101:Oxygen Consumption; D010447:Peptide Hydrolases / Q000378:metabolism*; D010618:Phenanthrolines / Q000494:pharmacology; D010920:Placenta / Q000166:cytology / Q000378:metabolism; D011247:Pregnancy; D011374:Progesterone / Q000096:biosynthesis*; D011480:Protease Inhibitors / Q000494:pharmacology; D059748:Proteolysis / Q000187:drug effects; D053719:Tandem Mass Spectrometry; D014327:Trophoblasts / Q000378:metabolism*
chemical_list: D002352:Carrier Proteins; D008565:Membrane Proteins; D010618:Phenanthrolines; D011480:Protease Inhibitors; C105684:STARD3 protein, human; D011374:Progesterone; D010447:Peptide Hydrolases; C025205:1,10-phenanthroline
keywords: Human syncytiotrophoblast mitochondria; Mitochondrial metalloprotease; Progesterone synthesis; STARD3 protein