Prolactin-releasing Peptide Activation of the Prolactin Promoter Is Differentially Mediated by Extracellular Signal-regulated Protein Kinase and c-Jun N-terminal Protein Kinase

Akiko Kimura,Masahide Ohmichi,Keiichi Tasaka,Yuki Kanda,Hiromasa Ikegami,Jun Hayakawa,Koji Hisamoto,Ken-Ichirou Morishige,Shuji Hinuma,Hirohisa Kurachi,Yuji Murata

doi:10.1074/jbc.275.5.3667

Abstract

Regulation of the mitogen-activated protein kinase (MAPK) family by prolactin-releasing peptide (PrRP) in both GH3 rat pituitary tumor cells and primary cultures of rat anterior pituitary cells was investigated. PrRP rapidly and transiently activated extracellular signal-regulated protein kinase (ERK) in both types of cells. Both pertussis toxin, which inactivates G(i)/G(o) proteins, and exogenous 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 ERK activation, suggesting the involvement of G(i)/G(o) proteins in the PrRP-induced ERK activation. Down-regulation of cellular protein kinase C did not significantly inhibit the PrRP-induced ERK activation, suggesting that a protein kinase C-independent pathway is mainly involved. PrRP-induced ERK activation was not dependent on either extracellular Ca(2+) or intracellular Ca(2+). However, the ERK cascade was not the only route by which PrRP communicated with the nucleus. JNK was also shown to be significantly activated in response to PrRP. JNK activation in response to PrRP was slower than ERK activation. Moreover, to determine whether a MAPK family cascade regulates rat prolactin (rPRL) promoter activity, we transfected the intact rPRL promoter ligated to the firefly luciferase reporter gene into GH3 cells. PrRP activated the rPRL promoter activity in a time-dependent manner. Co-transfection with a catalytically inactive form of a MAPK construct or a dominant negative JNK, partially but significantly inhibited the induction of the rPRL promoter by PrRP. Furthermore, co-transfection with a dominant negative Ets completely abolished the response of the rPRL promoter to PrRP. These results suggest that PrRP differentially activates ERK and JNK, and both cascades are necessary to elicit rPRL promoter activity in an Ets-dependent mechanism.

Highlights

Prolactin (PRL)1 is important in pregnancy and lactation in mammals, and is involved in the development of the mammary glands and the promotion of milk synthesis [1]
Co-transfection with a dominant negative Ets completely abolished the response of the rat PRL (rPRL) promoter to prolactin-releasing peptide” (PrRP). These results suggest that PrRP differentially activates extracellular signal-regulated kinase (ERK) and Jun N-terminal kinase (JNK), and both cascades are necessary to elicit rPRL promoter activity in an Ets-dependent mechanism
3, lane 5) induced ERK activation. These results suggest that activation of ERK by Thyrotropinreleasing hormone (TRH) is mainly mediated by protein kinase C (PKC) and activation of ERK by PrRP is partly mediated by PKC

Summary

Introduction

Prolactin (PRL)1 is important in pregnancy and lactation in mammals, and is involved in the development of the mammary glands and the promotion of milk synthesis [1]. These facts led us to examine whether PrRP stimulates the activity of ERK or JNK, and whether each of these cascades plays a role in the transcriptional activation of the rat PRL (rPRL) gene in GH3 cells. The effect of extracellular and intracellular Ca2ϩ on PrRP-induced ERK activation was examined in primary cultures of rat anterior pituitary cells (Fig. 4B).

Results

Conclusion