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, ERβ4 and ERβ5. The full length ERβ4 and ERβ5 were identified by asymmetric PCR using human ovary cDNA, cloning, and sequence analyses. Both receptors share identical sequences with ERβ1 from exon 1 to exon 7. In the place of exon 8, ERβ4 has unique sequences arising from a region downstream of the ERβ gene and upstream of the SYNE2 gene. ERβ5 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 ERβ1. When co-transfected with ERα, they predominantly form heterodimers and negatively regulate its transcriptional activity. Estrogen-independent transcriptional activity of ERβ5, but not ERβ4, was inhibited by ERα, demonstrating for the first time that ERα regulates ERβ. Tissue-specific expression of ERβ4 and ERβ5, together with their ligand-independent transcriptional properties and ERα modulating activities, could have a number of implications in seemingly unlinked biological processes regulated by estrogen. [ABSTRACT FROM AUTHOR]