Constitutive steroidogenesis in ovine large luteal cells may be mediated by tonically active protein kinase A

Randy Lloyd Bogan, Gordon D. Niswender

Research output: Contribution to journalArticle

13 Citations (Scopus)

Abstract

The mechanisms responsible for the increased basal rates of progesterone secretion from large steroidogenic luteal cells (LLC) relative to small steroidogenic luteal cells (SLC) have not been clearly defined. To determine if protein kinase A (PKA) is tonically active in LLC, the adenylate cyclase activator forskolin and a specific PKA inhibitor (PKI) were utilized in a 2 X 2 factorial treatment with each steroidogenic cell type. Progesterone and cAMP production were quantified after the different treatments. In addition, the effects of the treatments on the concentrations and relative phosphorylation status of the steroidogenic acute regulatory (STAR) protein in the two cell types were determined as a measure of PKA activity. Treatment with PKI blocked forskolin-induced increases in progesterone secretion by SLC without affecting the production of cAMP. The treatment of LLC with PKI significantly decreased basal progesterone secretion in the presence or absence of forskolin, indicating that the high level of steroidogenesis in this cell type requires PKA activity. There were no differences in the steady-state concentrations of STAR protein in either cell type after treatment. However, the percentage of relative STAR phosphorylation was higher in the LLC than in SLC, and PKI treatment significantly decreased the phosphorylation of STAR in the LLC. The relative phosphorylation status of STAR and the concentrations of progesterone in the media were significantly correlated with the treatments in both cell types. The amount of progesterone secreted per picogram of cAMP was higher in the LLC than in the SLC, and this was accompanied by a significant increase in the ratio of relative STAR phosphorylation to the steady-state concentration of STAR protein. These data are compatible with the theory that LLC are constitutively steroidogenic, partly because they have tonically active PKA. In addition, the phosphorylation of STAR appears to be a primary activity of PKA in both types of ovine steroidogenic luteal cells.

Original languageEnglish (US)
Pages (from-to)209-216
Number of pages8
JournalBiology of Reproduction
Volume77
Issue number2
DOIs
StatePublished - Aug 2007
Externally publishedYes

Fingerprint

Luteal Cells
Cyclic AMP-Dependent Protein Kinases
Sheep
Progesterone
Phosphorylation
Colforsin
Protein Kinase Inhibitors
Adenylyl Cyclases

Keywords

  • Corpus luteum
  • Kinases
  • Mechanisms of hormone action
  • Phosphorylation
  • Progesterone
  • Steroidogenesis
  • Steroidogenic acute regulatory protein

ASJC Scopus subject areas

  • Cell Biology
  • Developmental Biology
  • Embryology

Cite this

Constitutive steroidogenesis in ovine large luteal cells may be mediated by tonically active protein kinase A. / Bogan, Randy Lloyd; Niswender, Gordon D.

In: Biology of Reproduction, Vol. 77, No. 2, 08.2007, p. 209-216.

Research output: Contribution to journalArticle

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abstract = "The mechanisms responsible for the increased basal rates of progesterone secretion from large steroidogenic luteal cells (LLC) relative to small steroidogenic luteal cells (SLC) have not been clearly defined. To determine if protein kinase A (PKA) is tonically active in LLC, the adenylate cyclase activator forskolin and a specific PKA inhibitor (PKI) were utilized in a 2 X 2 factorial treatment with each steroidogenic cell type. Progesterone and cAMP production were quantified after the different treatments. In addition, the effects of the treatments on the concentrations and relative phosphorylation status of the steroidogenic acute regulatory (STAR) protein in the two cell types were determined as a measure of PKA activity. Treatment with PKI blocked forskolin-induced increases in progesterone secretion by SLC without affecting the production of cAMP. The treatment of LLC with PKI significantly decreased basal progesterone secretion in the presence or absence of forskolin, indicating that the high level of steroidogenesis in this cell type requires PKA activity. There were no differences in the steady-state concentrations of STAR protein in either cell type after treatment. However, the percentage of relative STAR phosphorylation was higher in the LLC than in SLC, and PKI treatment significantly decreased the phosphorylation of STAR in the LLC. The relative phosphorylation status of STAR and the concentrations of progesterone in the media were significantly correlated with the treatments in both cell types. The amount of progesterone secreted per picogram of cAMP was higher in the LLC than in the SLC, and this was accompanied by a significant increase in the ratio of relative STAR phosphorylation to the steady-state concentration of STAR protein. These data are compatible with the theory that LLC are constitutively steroidogenic, partly because they have tonically active PKA. In addition, the phosphorylation of STAR appears to be a primary activity of PKA in both types of ovine steroidogenic luteal cells.",
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