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C-terminal domains within human MT1 and MT2 melatonin receptors are involved in internalization processes

Shalini Sethi1, Wendy Adams, John Pollock

  • 1Division of Pharmaceutical Sciences, School of Pharmacy, Bayer School of Natural and Environmental Sciences, Duquesne University, Pittsburgh, PA 15282, USA.

Journal of Pineal Research
|March 18, 2008
PubMed

Insights

Melatonin receptors MT1 and MT2 require specific C-terminal tail domains for function and internalization. Mutating a cysteine residue essential for function, while truncating the tail inhibits both processes.

Area of Science:

  • Molecular pharmacology
  • Cell biology
  • Endocrinology

Background:

  • Melatonin receptors MT1 and MT2 are G-protein-coupled receptors involved in various physiological processes and diseases, including cancer.
  • Understanding the functional domains of these receptors is crucial for developing targeted therapies.
  • The cytoplasmic C-terminal tail is known to play a role in receptor desensitization and signaling.

Purpose of the Study:

  • To investigate the role of specific domains within the cytoplasmic C-terminal tail of MT1 and MT2 receptors in receptor function and desensitization.
  • To elucidate the contribution of a putative palmitoylation site (cysteine residue) and the overall C-terminal tail to receptor internalization and signaling.

Main Methods:

  • Site-directed mutagenesis was used to create specific mutations in the C-terminal tails of MT1 and MT2 receptors.
  • Mutations included altering a cysteine residue (MT1C7.72A, MT2C7.77A) and truncating the C-terminal tail (MT1Y7.64, MT2Y7.64).
  • Receptor binding affinity, internalization via confocal microscopy, and 3',5'-cyclic adenosine monophosphate (cAMP) accumulation assays were performed.

Main Results:

  • Mutations did not affect the binding affinity of 2-[(125)I]-iodomelatonin to MT1 or MT2 receptors.
  • The putative palmitoylation site (cysteine residue) was not essential for receptor internalization but was critical for receptor function (cAMP accumulation).
  • Truncation of the C-terminal tail inhibited both receptor internalization and the cAMP response, highlighting its importance.

Conclusions:

  • The C-terminal tail of MT1 and MT2 receptors is essential for both receptor internalization and cAMP signaling.
  • A specific cysteine residue in the C-terminal tail is crucial for MT1/MT2 receptor function, independent of internalization.
  • These findings provide insights into the molecular mechanisms governing melatonin receptor signaling and desensitization.

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