IGF-I and vasoactive intestinal peptide (VIP) regulate cAMP-response element-binding protein (CREB)-dependent transcription via the mitogen-activated protein kinase (MAPK) pathway in pituitary cells: requirement of Rap1.
In previous studies we demonstrated that vasoactive intestinal peptide (VIP) mediation, and interactions between mitogen-activated protein kinase (MAPK) and cAMP/protein kinase A (PKA) signaling pathways are implicated in insulin-like growth factor I (IGF-I)- and VIP-induced lactotroph proliferation. These facts led us to investigate the intracellular mechanisms involved in IGF-I- and VIP-induced lactotroph proliferation. Exposure of cultured male rat pituitary cells to IGF-I (10(-7) M) or VIP (10(-7) M) stimulated the MAPK cascade. Studies in GH4C1 cells, with an expression vector for Rap1 GTPase-activating protein (Rap1 GAP1), demonstrated reduced VIP-induced MAPK activation, indicating that VIP-dependent activation of the extracellular signal-regulated kinase (ERK) pathway requires PKA-Rap1 signaling. IGF-I induced cAMP-response element (CRE)-binding protein (CREB) phosphorylation through the Ras-MAPK pathway, whereas VIP phosphorylated CREB directly via PKA. The mechanisms that regulate IGF-I-and VIP-CREB-dependent gene transcription were examined using GH4C1 cells transiently transfected with a CRE reporter gene. IGF-I and VIP stimulation of CRE-mediated transcription required activation of both Ras-MAPK and cAMP/PKA signaling. This activation was blocked in the presence of Rap1 GAP1. In summary, we showed that IGF-I and VIP stimulated MAPK activity and the phosphorylation of CREB in pituitary cells. Furthermore, VIP-dependent activation of PKA-Rap1-ERK pathways mediated VIP and IGF-I effects on CREB-dependent transcription in GH4C1 cells. Thus, it is possible that VIP- and IGF-I-induced lactotroph proliferation may involve Rap1.
Fernández
M
M
Servicio de Endocrinología, Hospital Ramón y Cajal, Carretera de Colmenar, Km 9, 28034 Madrid, Spain.
Sánchez-Franco
F
F
Palacios
N
N
Sánchez
I
I
Cacicedo
L
L
D000818:Animals; D015153:Blotting, Western; D002478:Cells, Cultured; D017362:Cyclic AMP Response Element-Binding Protein / Q000235:genetics* / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000502:physiology*; D007150:Immunohistochemistry; D007334:Insulin-Like Growth Factor I / Q000502:physiology*; D008297:Male; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010766:Phosphorylation; D010903:Pituitary Gland, Anterior / Q000201:enzymology / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D014158:Transcription, Genetic / Q000502:physiology*; D014660:Vasoactive Intestinal Peptide / Q000378:metabolism*; D020827:rap1 GTP-Binding Proteins / Q000502:physiology*
D017362:Cyclic AMP Response Element-Binding Protein; D004791:Enzyme Inhibitors; D014660:Vasoactive Intestinal Peptide; D007334:Insulin-Like Growth Factor I; D017868:Cyclic AMP-Dependent Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D020827:rap1 GTP-Binding Proteins