Liver receptor homolog‐1 localization in the nuclear body is regulated by sumoylation and cAMP signaling in rat granulosa cells

Abstract

Liver receptor homolog‐1 (LRH‐1; NR5A2) is an orphan member of the nuclear receptor superfamily, mainly expressed in endoderm‐derived tissues and in the ovary. In ovarian granulosa and luteal cells, LRH‐1 regulates the expression of genes associated with ovarian steroidogenesis. LRH‐1 can be transported to transcriptionally inactive nuclear bodies after conjugation with small ubiquitin‐related modifier (SUMO). In the present study, we investigated the effects of SUMO modification at five lysine residues of LRH‐1 in rat granulosa cells. Lysine 289 could be conjugated with SUMO‐1 in vitro, and the mutation K289R increased transcriptional activity of LRH‐1, suggesting that SUMO conjugation is associated with transcription repression. Coexpression of SUMO‐1 targets LRH‐1 to the dot‐like nuclear bodies, but the effect of lysine mutations on blocking subnuclear localization depended on the cell type. In COS‐7 cells, mutation of either K173 or K289 prevented SUMO‐1‐mediated translocation of LRH‐1 into nuclear bodies and also reduced the conjugation by SUMO‐1, suggesting that K289 and K173 are two important sites involved in SUMO‐1 modification. In granulosa cells, three or more altered lysine residues were required for nucleoplasm retention. This result suggests that multiple lysine residues are targets for SUMO conjugation in vivo and granulosa cells are more sensitive to SUMO‐1‐mediated LRH‐1 localization to nuclear bodies. Nuclear body localization of LRH‐1 was suppressed by forskolin and cholera toxin. Forskolin treatment obviously influences the expression of members involved in the SUMO pathway. The results obtained in the present study suggest that cAMP signaling could change the dynamic process of sumoylation and repress LRH‐1 targeting to nuclear speckles in rat granulosa cells.

Therapeutic potential of Liver Receptor Homolog-1 modulators

“…Phosphorylation of the serine residues 238 and 243 located within the hinge region of LRH-1 via phorbol 12-myristate 13-acetate (PMA), was found to be important for LRH-1 transactivation [107]. Sumoylation of LRH-1 also occurs in the hinge region, allowing for additional control of its activity via regulation of its subcellular localisation [108]. Sumoylated LRH-1 is localised to the transcriptionally inactive nuclear bodies, away from active chromatin.…”

Identification of two functional nuclear localization signals mediating nuclear import of liver receptor homologue-1

“…Furthermore, LRH-1 can replace Oct4 in the reversion of mouse somatic cells to pluripotent cells [45]. This reprogramming capacity of LRH-1 can be enhanced by mutations in SUMO-conjugated lysine residues, which prevents the localization of LRH-1 to transcriptionally inactive nuclear bodies and increases its transactivity [14]. The present study revealed the nuclear transport mechanism of LRH-1 and implied that mutation in residues essential for NLS function could inhibit the nuclear localization of LRH-1 and consequently may influence embryonic development.…”

“…The plasmids pGFP-LRH1 and pMyc-LRH1 have been described previously [14]. After plasmid pGFP-LRH1 was digested with KpnI/BamHI or ClaI/BamHI, the ends were blunted with Klenow and then self-ligated to generate pGFP-LRH1 1-116 and pGFP-LRH1 .…”

“…LRH-1 is always localized to the nucleus in cells [14]. As a nuclear protein, LRH-1 must be imported from the cytoplasm into the nucleus via the nuclear pore complex (NPC).…”

Molecular characterization, expression, polymorphism of NR5A2 and its relationship with litter size in Hu sheep

“…In adult mammals, NR5A2 is predominantly expressed in pre-adipocyte cells and in the liver, intestine, pancreas, ovary and testis (Falender et al, 2003;Liu et al, 2003), and is particularly highly expressed in ovaries (Zhao et al, 2007;Yang et al, 2009). Further study showed that NR5A2 is not expressed in the theca or in stromal cells, but is restricted to the granulosa and luteal cells (Fayad et al, 2004).…”