Thyrotropin-releasing hormone stimulates in parallel jun B and c-fos messenger ribonucleic acids in GH3B6 pituitary cells: comparison with PRL secretion.

The hypothalamic neuropeptide TRH stimulates PRL release and PRL gene transcription in GH3B6 rat pituitary cells. In this model, TRH also raises c-fos proto-oncogene mRNA levels. c-fos is assumed to be involved in the transduction of external signals to the nucleus as a component of AP1 transcription factor, a complex that contains a member of the jun proto-oncogene family. Hence, the main aim of this study was to look for the expression of c-jun, jun B, and jun D proto-oncogenes in TRH-stimulated GH3B6 cells, compared to c-fos mRNA levels and PRL secretion. This was performed using serum-starved cells. Northern blotting and dot blotting revealed that jun B mRNA were expressed at noticeable levels in control cells and were strongly stimulated by TRH. This stimulation was dose-dependent and exhibited an early peak and a long-lasting plateau phase stabilized at 4 h, similar to TRH-induced c-fos mRNA induction. c-jun mRNA was expressed at minute levels in control cells and was transiently stimulated by TRH. The jun D message was not detected. TRH-induced jun B and c-fos responses were characteristic of immediate early genes as shown by the superinduction observed under cycloheximide treatment and the total inhibition elicited by actinomycin D. Finally, the responses to serum at 30 min and 4 h revealed differences among the proto-oncogenes studied and indicate that the action of TRH is specific.(ABSTRACT TRUNCATED AT 250 WORDS)