Interactions of Progesterone-Dependent Endometrial Nuclear Factors with the Promoter of the Rabbit Uteroglobin Gene

We have studied thein vitrointeractions of a promoter fragment of the rabbit uteroglobin (UG) gene with endometrial nuclear factors from either control rabbits or progesterone-treated animals, a treatment that induces the transcription of the gene in the endometrium. Nuclear factors from liver, which does not express UG, were also compared. Using DNase I footprinting, several protected zones were observed on the promoter; some of these were common to all three nuclear extracts, whereas others seemed to be specific to progesterone treated endometrium. One of these footprints was over the TATA box region. A 28-bp synthetic oligonucleotide encompassing the sequence of that region was used as a probe in electrophoretic mobility shift assays (EMSA) and UV-crosslinking assays. In EMSA experiments, endometrial nuclear extracts, but not liver extracts, generated a major retarded complex that was strongly increased following progesterone stimulation. Competition experiments with unlabeled mutated versions of the probe showed that sequences 3′ downstream from the TATA box (but not this motif) were responsible for the formation of the complex. UV-crosslinking experiments indicated that the probe interacted with two progesterone-dependent nuclear proteins of 55 and 60 kDa, different from the TATA box-binding protein. The results suggest that progesterone induction of the UG gene in the endometrium might be mediated by both general and tissue-specific nuclear factors.