Prolactin-releasing peptide activation of the prolactin promoter is differentially mediated by extracellular signal-regulated protein kinase and c-Jun N-terminal protein kinase

Regulation of the mitogen-activated protein kinase (MAPK) family by prolact in-releasing peptide (PrRP) in both GH3 rat pituitary tumor cells and prima ry cultures of rat anterior pituitary cells was investigated. PrRP rapidly and transiently activated extracellular signal-regulated protein kinase (ER K) in both types of cells. Both pertussis toxin, which inactivates G(i)/G(o ), proteins, and exogenous expression of a peptide derived from the carboxy l terminus of the beta-adrenergic receptor kinase I, which specifically blo cks signaling mediated by the beta gamma 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 cell ular protein kinase C did not significantly inhibit the PrRP-induced ERK ac tivation, suggesting that a protein kinase C-independent pathway is mainly involved. PrRP-induced ERK activation was not dependent on either extracell ular Ca2+ or intracellular Ca2+. 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 transf ected the intact rPRL promoter ligated to the firefly luciferase reporter g ene into GH3 cells. PrRP activated the rPRL promoter activity in a time-dep endent manner. Co-transfection with a catalytically inactive form of a MAPK construct or a dominant negative JNK, partially but significantly inhibite d 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 activi ty in an Ets-dependent mechanism.