Estrogen receptors beta4 and Beta5 are full length functionally distinct ERβ isoforms -: Cloning from human ovary and functional characterization

We describe here the cloning and functional characterization of two unique ER isoforms, ER beta 4 and ER beta 5. The full length ER beta 4 and ER beta 5 were identified by asymmetric PCR using human ovary cDNA, cloning, and sequence analyses. Both receptors share identical sequences with ER beta 1 from exon 1 to exon 7. In the place of exon 8, ER beta 4 has unique sequences arising from a region downstream of the ER beta gene and upstream of the SYNE2 gene. ER beta 5 has sequences arising from retention of the 5' end of the intron between exon 7 and 8. Both receptors bind promoter sequences on DNA but do not bind estrogen. They translocate to the nucleus and exhibit three to four times higher estrogen-independent transcriptional activity than ER beta 1. When co-transfected with ER alpha, they predominantly form heterodimers and negatively regulate its transcriptional activity. Estrogen-independent transcriptional activity of ER beta 5, but not ER beta 4, was inhibited by ER alpha, demonstrating for the first time that ER alpha regulates ER beta. Tissue-specific expression of ER beta 4 and ER beta 5, together with their ligand-independent transcriptional properties and ER alpha modulating activities, could have a number of implications in seemingly unlinked biological processes regulated by estrogen.