Determinants contributing to estrogen-regulated expression of SK3

The rSK3 gene encodes a small conductance Ca²⁺-activated K⁺ channel that is transcriptionally regulated by estrogen. To examine determinants of rSK3 gene expression, the CAP site was defined and the promoter was identified. A 33bp sequence adjacent to the promoter was shown to act as an enhancer in L6 cells that express SK3 and estrogen receptor α (ERα). The 33bp enhancer was unable to stimulate transcription in Cos7 cells that do not express SK3 or ERα. However when cotransfected with ERα and stimulated with 17β-estradiol (E2) the enhancer was activated. Interestingly, expression of ERα in Cos7 cells and E2 treatment was sufficient to induce expression of the endogenous SK3 gene. Only Sp1 and Sp3 specifically bound to the enhancer from Cos7 and L6 nuclear extracts, however, ERα increased Sp1s affinity for the enhancer. The data suggest that estrogen regulates SK3 gene expression through interactions between ERα and Sp1.