RAPID DOWN-REGULATION OF C-JUN PROTOONCOGENE TRANSCRIPTION BY PROGESTERONE IN THE AVIAN OVIDUCT

Previous work in this and other laboratories has shown that steroids r apidly regulate the expression of nuclear protooncogenes. In this pres ent study, we have investigated the effect of progesterone (Pg) on the expression of c-jun in the avian oviduct system and its promoter acti vity in avian liver cells. Pg treatment of estrogen-withdrawn chickens brings about a decrease in the steady state mRNA level of the protoon cogene c-jun within 30 min. This decrease is steroid dose dependent an d gene specific. Using nuclear run-off transcription analyses, this ra pid regulation was shown to occur at the level of gene transcription, as the rate of c-jun transcription decreases by more than 80% within 1 5 min after progesterone treatment. As expected, ovalbumin gene transc ription is increased only after a lag period of 4 h following Pg treat ment. In other studies, we have linked the c-jun promoter sequences be tween -1000 and +192 to chloramphenicol acetyltransferase reporter gen e and cotransfected them into transformed avian liver cells along with the expression vector for the Pg receptor. Pg treatment of these cell s causes a decrease in chloramphenicol acetyltransferase gene expressi on, albeit to a lesser extent than Pg inhibition of c-jun gene transcr iption. These results suggest that the 5'-domain of the chicken c-jun gene contains sequence elements that negatively regulate c-jun promote r activity in response to Pg.