THYROTROPIN-RELEASING-HORMONE AND EPIDERMAL GROWTH-FACTOR INDUCE HUMAN PROLACTIN EXPRESSION VIA IDENTICAL MULTIPLE CIS ELEMENTS

Pituitary GH3 cells were transfected with different deletion mutants of the human prolactin (hPRL) promoter fused to the CAT reporter gene. The proximal region (-250 to -42) was sufficient to confer stimulation by both thyrotropin-releasing hormone (TRH) and epidermal growth factor (EGF). Further deletion analyses demonstrated the importance of the three proximal Pit-1 binding sites in this response. However, Pit-1 binding oligonucleotides confer neither TRH nor EGF induction to a linked neutral promoter, suggesting that other elements might be involved. We have previously shown that sequence A (-115 to -85) is needed together with Pit- 1 binding sites for full cyclic AMP response of hPRL-CAT. Mutation of this sequence strongly affects TRH and EGF induction. On the other hand, three copies of sequence A confer both TRH and EGF response to a linked neutral promoter. In conclusion, although TRH and EGF activate mostly different intracellular pathways, they mediate transcriptional induction of the hPRL promoter via identical cis elements.