Cyclic adenosine 5'-monophosphate-stimulated neurotensin secretion is mediated through Rap1 downstream of both Epac and protein kinase A signaling pathways

Mol Endocrinol. 2007 Jan;21(1):159-71. doi: 10.1210/me.2006-0340. Epub 2006 Oct 26.

Abstract

Neurotensin (NT), a gut peptide, plays important roles in gastrointestinal secretion, inflammation, and growth of normal and neoplastic tissues. cAMP regulates the secretion of hormones via its effector proteins protein kinase A (PKA) or Epac (exchange protein directly activated by cAMP). The small GTPase Rap1 can be activated by both PKA and Epac; however, the role of Rap1 in hormone secretion is unknown. Here, using the BON human endocrine cell line, we found that forskolin (FSK)-stimulated NT secretion was reduced by inhibition of Rap1 expression and activity. FSK-stimulated NT secretion was enhanced by overexpression of either wild-type or constitutively active Rap1. Epac activators and wild-type Epac enhanced NT release and Rap1 activity. In contrast, overexpression of a cAMP binding mutant, EpacR279E, decreased NT release and Rap1 activity. PKA activation increased NT release and Rap1 activity. FSK-stimulated NT release was reduced by PKA inhibition and the dominant negative Rap1N17. NT secretion, stimulated by Epac activation, was reduced by PKA inhibition; NT release, stimulated by PKA activation, was enhanced by wild-type Epac but reduced by the mutant EpacR279E. Finally, prostaglandin E2 (PGE2), a physiological agent that increases cAMP, stimulated NT secretion via cAMP/PKA/Rap1. Importantly, we demonstrate that PKA and Epac mediate the cAMP-induced NT secretion synergistically by converging at the common downstream target protein Rap1. Moreover, PGE2, a potent mediator of inflammation and associated with colorectal carcinogenesis, stimulates NT release suggesting a possible link between PGE2 and NT on intestinal inflammatory disorders and colorectal cancers.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Cell Line, Tumor
  • Colforsin / metabolism
  • Colorectal Neoplasms / metabolism
  • Cyclic AMP / chemistry*
  • Cyclic AMP / metabolism
  • Cyclic AMP-Dependent Protein Kinases / metabolism*
  • Genes, Dominant
  • Guanine Nucleotide Exchange Factors / metabolism*
  • Humans
  • Microscopy, Confocal
  • Models, Biological
  • Mutation
  • Neurotensin / metabolism*
  • Protein Binding
  • Signal Transduction
  • rap1 GTP-Binding Proteins / metabolism*

Substances

  • Guanine Nucleotide Exchange Factors
  • RAP1A protein, human
  • RAPGEF3 protein, human
  • Colforsin
  • Neurotensin
  • Cyclic AMP
  • Cyclic AMP-Dependent Protein Kinases
  • rap1 GTP-Binding Proteins