Insulin activation of rat prolactin promoter activity.

The role of insulin regulation of rat prolactin (rPRL) gene transcription was studied using GH4 rat pituitary tumor cells transiently transfected with plasmids containing proximal rPRL promoter fragments ligated to the reporter gene luciferase. Here we show that insulin, at nanomolar concentrations, has a rapid effect on the rPRL promoter stimulating its activity about 1.8-fold within 4h after hormone addition. Furthermore, we have mapped the rPRL promoter element responsible for mediating insulin hormone action between positions -212 and +73. The stimulation of rPRL gene transcription by insulin was abolished when insulin doses extended into the micromolar range. Thus, rPRL promoter sequences downstream of -212 are sufficient to mediate increased rPRL gene transcription in response to insulin.