Cyclic adenosine 5'-monophosphate-stimulated neurotensin secretion is mediated through Rap1 downstream of both Epac and protein kinase A signaling pathways.
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.
Li
Jing
J
Department of Surgery, The University of Texas Medical Branch, Galveston, Texas 77555-0536, USA.
O'Connor
Kathleen L
KL
Cheng
Xiaodong
X
Mei
Fang C
FC
Uchida
Tatsuo
T
Townsend
Courtney M
CM
Evers
B Mark
BM
D045744:Cell Line, Tumor; D005576:Colforsin / Q000378:metabolism; D015179:Colorectal Neoplasms / Q000378:metabolism; D000242:Cyclic AMP / Q000737:chemistry* / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D005799:Genes, Dominant; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism*; D006801:Humans; D018613:Microscopy, Confocal; D008954:Models, Biological; D009154:Mutation; D009496:Neurotensin / Q000378:metabolism*; D011485:Protein Binding; D015398:Signal Transduction; D020827:rap1 GTP-Binding Proteins / Q000378:metabolism*
D020662:Guanine Nucleotide Exchange Factors; C430803:RAP1A protein, human; C116122:RAPGEF3 protein, human; D005576:Colforsin; D009496:Neurotensin; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D020827:rap1 GTP-Binding Proteins