A role for nuclear factor interleukin-3 (NFIL3), a critical transcriptional repressor, in down-regulation of periovulatory gene expression

The LH surge triggers dramatic transcriptional changes in genes associated with ovulation and luteinization. The present study investigated the spatiotemporal expression of nuclear factor interleukin-3 (NFIL3), a transcriptional regulator of the bZIP transcription factor superfamily, and its potential role in the ovary during the periovulatory period. NFIL3, also known as E4-binding protein 4 or NFIL3/E4BP4, was originally identified as a transcriptional repressor based on its DNA-binding activity at the promoter of the gene encoding the adenovirus E4 protein. Immature female rats were injected with PMSG, treated with hCG, and ovaries or granulosa cells were collected at various times after hCG. Nfil3 mRNA was highly induced both in intact ovaries and granulosa cells after hCG treatment. In situ hybridization demonstrated that Nfil3 mRNA was highly induced in theca-interstitial cells at 4-8 h after hCG, localized to granulosa cells at 12 h, and decreased at 24 h. Over-expression of NFIL3 in granulosa cells inhibited the induction of prostaglandin-endoperoxide synthase 2 (Ptgs2), progesterone receptor (Pgr), epiregulin (Ereg), and amphiregulin (Areg) and down regulated levels of prostaglandin E2. The inhibitory effect on Ptgs2 induction was reversed by NFIL3 siRNA treatment. In theca-interstitial cells the expression of hydroxyprostaglandin dehydrogenase 15-(NAD) (Hpgd) was also inhibited by NFIL3 over-expression. Data from luciferase assays demonstrated that NFIL3 over-expression decreased the induction of the Ptgs2 and Areg promoter activity. EMSA and ChIP analyses indicated that NFIL3 binds to the promoter region containing the DNA binding sites of CREB and C/EBP?. In summary, hCG induction of NFIL3 expression may modulate the process of ovulation and theca-interstitial and granulosa cell differentiation by regulating expression of PTGS2, PGR, AREG, EREG, and HPGD, potentially through interactions with CREB and C/EBP? on their target gene promoters.

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Li F, Liu J, Jo M, Curry TE Jr