title: PKA tightly bound to human placental mitochondria participates in steroidogenesis and is not modified by cAMP.
abstract: BACKGROUND
  Protein phosphorylation plays an important role in the modulation of steroidogenesis and it depends on the activation of different signaling cascades. Previous data showed that PKA activity is related to steroidogenesis in mitochondria from syncytiotrophoblast of human placenta (HPM). PKA localization and contribution in progesterone synthesis and protein phosphorylation of HPM was assessed in this work.
  
  
  METHODS
  Placental mitochondria and submitochondrial fractions were used. Catalytic and regulatory PKA subunits were identified by Western blot. PKA activity was determined by the incorporation of (32)P into proteins in the presence or absence of specific inhibitors. The effect of PKA activators and inhibitors on steroidogenesis and protein phosphorylation in HPM was tested by radioimmunoassay and autoradiography.
  
  
  RESULTS
  The PKAα catalytic subunit was distributed in all the submitochondrial fractions whereas βII regulatory subunit was the main isoform observed in both the outer and inner membranes of HPM. PKA located in the inner membrane showed the highest activity. Progesterone synthesis and mitochondrial protein phosphorylation are modified by inhibitors of PKA catalytic subunit but are neither sensitive to inhibitors of the regulatory subunit nor to activators of the holoenzyme.
  
  
  CONCLUSIONS
  The lack of response in the presence of PKA activators and inhibitors of the regulatory subunit suggests that the activation of intramitochondrial PKA cannot be prevented or further activated.
  
  
  CONCLUSIONS
  The phosphorylating activity of PKA inside HPM could be an important component of the steroidogenesis transduction cascade, probably exerting its effects by direct phosphorylation of its substrates or by modulating other kinases and phosphatases.
authors.affiliation: Departamento de Bioquímica, Facultad de Medicina, Universidad Nacional Autónoma de México, Apartado Postal 70-159, Coyoacán 04510, Mexico City, Mexico.
authors.forename: E
authors.initials: E
authors.lastname: Gomez-Chang
authors.affiliation: Departamento de Bioquímica, Facultad de Medicina, Universidad Nacional Autónoma de México, Apartado Postal 70-159, Coyoacán 04510, Mexico City, Mexico.
authors.forename: M T
authors.initials: MT
authors.lastname: Espinosa-Garcia
authors.affiliation: Departamento de Bioquímica, Facultad de Medicina, Universidad Nacional Autónoma de México, Apartado Postal 70-159, Coyoacán 04510, Mexico City, Mexico.
authors.forename: S
authors.initials: S
authors.lastname: Olvera-Sanchez
authors.affiliation: Departamento de Bioquímica, Facultad de Medicina, Universidad Nacional Autónoma de México, Apartado Postal 70-159, Coyoacán 04510, Mexico City, Mexico.
authors.forename: O
authors.initials: O
authors.lastname: Flores-Herrera
authors.affiliation: Departamento de Bioquímica, Facultad de Medicina, Universidad Nacional Autónoma de México, Apartado Postal 70-159, Coyoacán 04510, Mexico City, Mexico. Electronic address: fedem@bq.unam.mx.
authors.forename: F
authors.initials: F
authors.lastname: Martinez
mesh_terms: D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D005260:Female; D006801:Humans; D008928:Mitochondria / Q000201:enzymology*; D010761:Phosphorus Radioisotopes; D010766:Phosphorylation; D011247:Pregnancy; D011374:Progesterone / Q000096:biosynthesis*; D014327:Trophoblasts / Q000201:enzymology*
chemical_list: D010761:Phosphorus Radioisotopes; D011374:Progesterone; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases
keywords: Human placenta; PKA activity; Protein phosphorylation; Steroidogenesis; Syncytiotrophoblast mitochondria