Regulation of the PRL promoter by Akt through cAMP response element binding protein.
Regulation of the PI3K-protein kinase B/Akt (serine/threonine kinase) cascade by PRL-releasing peptide (PrRP) and insulin in GH3 rat pituitary tumor cells was investigated. PrRP and insulin rapidly and transiently stimulated the activation of Akt, and the PI3K inhibitor wortmannin blocked the PrRP- or insulin-induced activation of Akt. Both pertussis toxin (10 ng/ml), which inactivates Gi/Go proteins, and expression of a peptide derived from the carboxyl terminus of the beta-adrenergic receptor kinase I, which specifically blocks signaling mediated by the betagamma subunits of G proteins, completely blocked the PrRP-induced Akt activation, suggesting that Gi/Go proteins are involved in PrRP-induced Akt activation, as they are in the activation of ERK by PrRP. Moreover, to determine whether a PI3K-Akt cascade regulates rat PRL (rPRL) promoter activity, we transfected the intact rPRL promoter ligated to the firefly luciferase reporter gene into GH3 cells. PrRP and insulin activated the rPRL promoter activity. Pretreatment with wortmannin or cotransfection with a dominant-negative Akt partially but significantly inhibited the induction of the rPRL promoter by PrRP or insulin. Cotransfection with a constitutively active Akt induced the rPRL promoter activity and cotransfection with a dominant-negative cAMP response element-binding protein (CREB) completely abolished the response of the rPRL promoter to the constitutively active Akt. Furthermore, either treatment with PrRP and insulin or transfection with the constitutively active Akt induced the phosphorylation of CREB. These results suggest that PrRP and insulin activate a PI3K-Akt cascade that is necessary to elicit rPRL promoter activity via a CREB-dependent mechanism.
Hayakawa
Jun
J
Department of Obstetrics and Gynecology, Osaka University Medical School, 2-2 Yamadaoka, Suita, Osaka 565-0871, Japan.
Ohmichi
Masahide
M
Tasaka
Keiichi
K
Kanda
Yuki
Y
Adachi
Kazushige
K
Nishio
Yukihiro
Y
Hisamoto
Koji
K
Mabuchi
Seiji
S
Hinuma
Shuji
S
Murata
Yuji
Y
D000818:Animals; D002118:Calcium / Q000502:physiology; D017362:Cyclic AMP Response Element-Binding Protein / Q000502:physiology*; D019204:GTP-Binding Proteins / Q000502:physiology; D007028:Hypothalamic Hormones / Q000502:physiology; D007328:Insulin / Q000502:physiology; D009479:Neuropeptides / Q000502:physiology; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology; D010766:Phosphorylation; D011388:Prolactin / Q000235:genetics*; D056690:Prolactin-Releasing Hormone; D011401:Promoter Regions, Genetic / Q000502:physiology*; D011493:Protein Kinase C / Q000502:physiology; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000502:physiology*; D051057:Proto-Oncogene Proteins c-akt; D050783:Proto-Oncogene Proteins c-ets; D051381:Rats; D014157:Transcription Factors / Q000502:physiology; D014407:Tumor Cells, Cultured
D002118:Calcium; D017362:Cyclic AMP Response Element-Binding Protein; D019204:GTP-Binding Proteins; D007028:Hypothalamic Hormones; D007328:Insulin; D009479:Neuropeptides; D019869:Phosphatidylinositol 3-Kinases; D011388:Prolactin; D056690:Prolactin-Releasing Hormone; D011493:Protein Kinase C; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D050783:Proto-Oncogene Proteins c-ets; D014157:Transcription Factors; C534379:Prlh protein, rat; C494920:Akt1 protein, rat