Identification and characterization of two novel splicing isoforms of human estrogen-related receptor beta.

CONTEXT: Estrogen-related receptor beta (ERRbeta) was one of the first two orphan nuclear receptors reported and is believed to play important roles in estrogen-regulated pathways. Embryo lethality of ERRbeta-null mice indicated that ERRbeta is essential for embryo development.
OBJECTIVE: Two novel splicing isoforms of human (h) ERRbeta, hERRbeta2-Delta10 and short-form hERRbeta, were identified during the cloning of previously reported hERRbeta-hERRbeta2. We aim to investigate the functional differences of these three human ERRbeta-splicing isoforms. RESULTS AND
CONCLUSIONS: A genomic sequence comparison within and flanking the ERRbeta genes of eight species demonstrated that short-form hERRbeta lacks an F domain and is the matched homolog of mouse and rat ERRbeta proteins in humans. However, hERRbeta2-Delta10 and the previously reported hERRbeta2 isoforms are primate specific. RT-PCR analysis showed that short-form hERRbeta has a wide distribution in the 24 of 27 human tissues and cell lines tested, whereas hERRbeta2 and hERRbeta2-Delta10 were only expressed in testis and kidney. The three human ERRbeta-splicing isoforms have different transcriptional activities when measured on an estrogen response element-driven luciferase reporter in transfection assays. The localization of a nuclear localization signal of short-form hERRbeta was also determined. Interestingly, the F domain of hERRbeta2 alters the function of the nuclear localization signal. Therefore, the ERRbeta isoforms are likely to have diverse biological functions in vivo, and characterizing the three isoforms of ERRbeta will lead to an understanding of the multiple levels of gene regulation involved in steroid receptor-signaling pathways in humans and may provide novel therapeutic targets for human diseases.