Persistent cAMP-signals Triggered by Internalized G-protein-coupled Receptors

PLoS Biol. 2009 Aug;7(8):e1000172. doi: 10.1371/journal.pbio.1000172. Epub 2009 Aug 18.

Abstract

G-protein-coupled receptors (GPCRs) are generally thought to signal to second messengers like cyclic AMP (cAMP) from the cell surface and to become internalized upon repeated or prolonged stimulation. Once internalized, they are supposed to stop signaling to second messengers but may trigger nonclassical signals such as mitogen-activated protein kinase (MAPK) activation. Here, we show that a GPCR continues to stimulate cAMP production in a sustained manner after internalization. We generated transgenic mice with ubiquitous expression of a fluorescent sensor for cAMP and studied cAMP responses to thyroid-stimulating hormone (TSH) in native, 3-D thyroid follicles isolated from these mice. TSH stimulation caused internalization of the TSH receptors into a pre-Golgi compartment in close association with G-protein alpha(s)-subunits and adenylyl cyclase III. Receptors internalized together with TSH and produced downstream cellular responses that were distinct from those triggered by cell surface receptors. These data suggest that classical paradigms of GPCR signaling may need revision, as they indicate that cAMP signaling by GPCRs may occur both at the cell surface and from intracellular sites, but with different consequences for the cell.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenylyl Cyclases / genetics
  • Adenylyl Cyclases / metabolism
  • Animals
  • Cell Line
  • Cells, Cultured
  • Cyclic AMP / metabolism*
  • Epithelial Cells / cytology
  • Epithelial Cells / metabolism
  • Epithelial Cells / ultrastructure
  • Fluorescent Dyes / metabolism
  • GTP-Binding Protein alpha Subunits / metabolism*
  • Humans
  • Mice
  • Mice, Transgenic
  • Microscopy, Confocal
  • Models, Biological
  • Organic Chemicals / metabolism
  • Receptors, Thyrotropin / metabolism
  • Signal Transduction*
  • Subcellular Fractions / metabolism*
  • Thyroid Gland / cytology
  • Thyroid Gland / metabolism*
  • Thyrotropin / metabolism*
  • Thyrotropin / pharmacology

Substances

  • Alexa594
  • Fluorescent Dyes
  • GTP-Binding Protein alpha Subunits
  • Organic Chemicals
  • Receptors, Thyrotropin
  • Thyrotropin
  • Cyclic AMP
  • Adenylyl Cyclases