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Melatonin Inhibits the Activation of Cyclic AMP-Dependent Protein Kinase in Cultured Pars Tuberalis Cells from Ovine

D G Hazlerigg1, P J Morgan, W Lawson

  • 1Department of Anatomy, University of Cambridge, Downing Street, Cambridge CB2 3DY, UK.

Journal of Neuroendocrinology
|February 14, 2009
PubMed

Insights

Melatonin potently inhibits cyclic AMP-dependent protein kinase (PKA) activation in ovine pars tuberalis cells. This suggests melatonin regulates cellular functions in this tissue by dephosphorylating specific proteins.

Area of Science:

  • Endocrinology
  • Molecular Biology
  • Cell Signaling

Background:

  • Melatonin is a key hormone regulating circadian rhythms and reproductive functions.
  • The pars tuberalis plays a crucial role in mediating photoperiodic information to the neuroendocrine system.
  • Cyclic AMP (cAMP)-dependent protein kinase (PKA) is a central mediator of intracellular signaling pathways.

Purpose of the Study:

  • To investigate the effect of melatonin on the activation of PKA in ovine pars tuberalis cells.
  • To determine the dose-dependency and mechanism of melatonin's action on PKA.
  • To elucidate the role of melatonin in cAMP-mediated signal transduction within this specific tissue.

Main Methods:

  • Primary cultures of ovine pars tuberalis cells were used.
  • Forskolin was employed to activate PKA.
  • Melatonin's effect on forskolin-induced PKA activation was assessed.
  • Photoaffinity labeling with 8N(3)-[(32)P]cAMP was performed to identify PKA subunits.

Main Results:

  • Forskolin rapidly and dose-dependently activated PKA.
  • Melatonin significantly inhibited forskolin-induced PKA activation in a dose-dependent manner (ED(50) 10(-10)M).
  • Melatonin also rapidly deactivated PKA in cells already stimulated with forskolin.
  • Photoaffinity labeling identified regulatory subunits of PKA I and PKA II.

Conclusions:

  • Melatonin acts as a potent inhibitory regulator of cAMP-mediated signal transduction in the ovine pars tuberalis.
  • The cellular effects of melatonin in this tissue are likely mediated through the dephosphorylation of specific substrate proteins.
  • These findings highlight a novel mechanism for melatonin's action in the pars tuberalis.

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