The c-jun proto-oncogene codes for an important component of the AP-1 transcription factor complex which regulates the expression of many genes. This paper demonstrates that the steady state c-jun mRNA level in the avian oviduct is markedly decreased to 50% of control values within 30 minutes after estrogen injection into the animals. In the avian liver, the level is rapidly increased over 10 fold. Nuclear run-off transcription analysis demonstrates that the decrease in the c-jun mRNA levels in the avian oviduct occurs at least in part at the level of transcription. These changes are reproducible in repeat experiments. This response in the avian oviduct is unique since 1) it is the first demonstration of a steroid effect on c-jun expression in any animal system, 2) the changes in c-jun mRNA occur much more rapidly than most steroid responsive genes, and 3) it is the rare demonstration of an estrogen inhibition of the expression of a gene. A role for the c-jun proto-oncogene as an early regulatory gene in the cascade model for steroid action is proposed.
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