DIFFERENTIAL UP-REGULATION OF GAP JUNCTION CONNEXIN-26 GENE IN MAMMARY AND UTERINE TISSUES - THE ROLE OF SP TRANSCRIPTION FACTORS

The mRNA and protein expressions of connexin 26 (Cx26) in rat mammary gland and uterus can be up-regulated during pregnancy as well as by th e administration of human CG (hCG). In the present study, we found tha t the time course and magnitude of Cx26 induction by hCG was different in these two tissues. The molecular mechanism underscoring this diffe rence was therefore investigated. We had previously demonstrated that both Sp1 and Sp3 transcription factors play a functional role in Cx26 expression. By the electrophoretic mobility shift assay, nuclear extra cts from both virgin mammary gland and uterus were capable of binding to a labeled oligonucleotide probe that contained the proximal GC box and formed three protein-DNA complexes (C1, C2, and C3). In the mammar y gland, pregnancy enhanced the intensity of all three complexes, wher eas in the uterine tissue there was a decrease in the C2 and C3 comple xes and an emergence of a new major component, C4 complex. In the supe rshift study, the C1 complex could be supershifted only by an antibody against Spl, whereas C2, C3, and C4 could all be supershifted by an a ntibody against Sp3, suggesting a potential presence of Sp3 isoforms o f various sizes. We therefore conclude that the basal Sp profiles in v irgin mammary gland and uterine tissue are similar. However, in respon se to pregnancy, the changes in Sp profile are tissue specific and may account for the temporal and quantitative differences between these t wo tissues in Cx26 induction.