Transcriptional regulation of pim-1 by prolactin: independence of a requirement for Jak2/Stat signaling.

Lactogen-dependent Nb2 cell lines have been widely employed to investigate signaling mechanisms coupled to prolactin receptor (PRLR)-stimulated transcription of hormone-responsive genes. We previously reported that PRL rapidly induced expression of the immediate-early protooncogene, pim-1. In the present report, we describe experiments conducted to evaluate PRL-stimulated transcription of pim-1 as well as potential PRLR-linked signaling mechanisms leading to promoter activation. Results from promoter/reporter experiments and electrophoretic mobility gel shift analysis indicated that two elements (distal element, -427 to -336 bp, and proximal element, -104 to -1 bp) positively regulated PRL-stimulated pim-1 promoter activity while it appeared to be repressed by factor binding to a NF-1 half site located between these positive elements. Deletion of gamma-interferon activation sequences did not reduce the effect of PRL to activate the promoter. Results from pharmacological antagonism of several signaling mechanisms indicated that PRLR activation of the pim-1 promoter reflected contributions from the ras-MAPK and PI-3 kinase pathways. Together these observations suggest that PRLR stimulation of pim-1 transcription occurs independently of a requirement for signaling through a Jak2/Stat mechanism.