Functional synergy between the transcription factor Sp1 and the estrogen receptor.

A GC-rich oligonucleotide containing an estrogen responsive element (ERE) half-site from the heat shock protein 27 (Hsp 27) gene promoter (−105 to −84) [i.e. GGGCGGG(N)10GGTCA; Sp1(N)10ERE] forms a complex with the Sp1 and estrogen receptor (ER) proteins. Moreover, promoter-reporter constructs containing this sequence (−108 to −84 or −108 to +23) are also estrogen-responsive. Mutation of the ERE half-site in the Hsp 27-derived oligonucleotides did not result in loss of estrogen responsiveness in transient transfection studies, suggesting that estrogen inducibility was mediated through the Sp1-DNA motif. Gel mobility shift assays using 32P-labeled wild type and ERE mutant Sp1(N)10ERE and consensus Sp1 oligonucleotides showed that Sp1 protein formed a DNA-protein complex with all three nucleotides, and the intensities of retarded bands were enhanced by coincubation with wild type ER and 11C-ER, which does not contain the DNA-binding domain. ER mutants in which N-terminal (19C-ER) and C-terminal (15C-ER) reg...