All-trans- and 9-cis-retinoic acids activate the human cyclooxynase-2 gene: a role for DR1 as RARE or RXRE.

The human COX-2 promoter contains a direct repeat 1 (DR1) which was shown to confer responsiveness to PPARs. We found that in AN(3)CA and F9 cells, this hCOX-2 DR1 mediates responsiveness to all-trans-retinoic acid (tRA) or 9-cis-retinoic acid (9cRA), but this effect was suppressed by PPARδ. Truncated PPARδ lacking the activation domain AF2 cannot suppress RA-induced activation of the hCOX-2 gene via DR1, suggesting that cofactor recruitment by AF2 is required for the suppression by PPARδ. Gel shift assay showed that PPAR/RXR, RARß/RXR, and RXR/RXR, bind to hCOX-2 DR1, revealing the promiscuity of this DR1. Particularly, RXR homodimer was able to bind to this DR1 only in the presence of 9cRA. Our results established that tRA and 9cRA are potent inducers of hCOX-2 and that the hCOX-2 DR1 could either serve as RARE or RXRE depending on cellular contexts.

Transduction of the MPG-tagged fusion protein into mammalian cells and oocytes depends on amiloride-sensitive endocytic pathway.

BACKGROUND: MPG is a cell-permeable peptide with proven efficiency to deliver macromolecular cargoes into cells. In this work, we examined the efficacy of MPG as an N-terminal tag in a fusion protein to deliver a protein cargo and its mechanism of transduction. RESULTS: We examined transduction of MPG-EGFP fusion protein by live imaging, flow cytometry, along with combination of cell biological and pharmacological methods. We show that MPG-EGFP fusion proteins efficiently enter various mammalian cells within a few minutes and are co-localized with FM4-64, a general marker of endosomes. The transduction of MPG-EGFP occurs rapidly and is inhibited at a low temperature. The entry of MPG-EGFP is inhibited by amiloride, but cytochalasin D and methyl-beta-cyclodextrin did not inhibit the entry, suggesting that macropinocytosis is not involved in the transduction. Overexpression of a mutant form of dynamin partially reduced the transduction of MPG-EGFP. The partial blockade of MPG-EGFP transduction by a dynamin mutant is abolished by the treatment of amiloride. MPG-EGFP transduction is also observed in the mammalian oocytes. CONCLUSION: The results show that the transduction of MPG fusion protein utilizes endocytic pathway(s) which is amiloride-sensitive and partially dynamin-dependent. Collectively, the MPG fusion protein could be further developed as a novel tool of "protein therapeutics", with potentials to be used in various cell systems including mammalian oocytes.

Etv5, an ETS transcription factor, is expressed in granulosa and cumulus cells and serves as a transcriptional regulator of the cyclooxygenase-2.

Etv4, Etv1, and Etv5 are members of Etv4 subfamily of E26 transformation-specific (Ets) transcription factors that are known to influence a host of biological processes. We previously showed that Etv5, expressed in Sertoli cells, plays a crucial role in maintaining spermatogonial stem cell niche in the mouse testis. However, it is not yet known whether Etv4 family members are expressed in the ovary or play any role in ovarian functions. Here, we show that Etv5 and Etv4 are expressed in mouse ovaries in granulosa and cumulus cells during folliculogenesis. Both Etv5 and Etv4 mRNAs are also detected in cumulus-oocyte complexes (COCs) and denuded oocytes. Notably, Etv4 is highly expressed in the cumulus cells of ovulated COCs at 16-h post-human chorionic gonadotropin. Cyclooxygenase-2 (PTGS2), a rate-limiting enzyme for prostaglandin synthesis, is critical for oocyte maturation and ovulation. Since several putative Ets-binding sites are present in the PTGS2 promoter, we examined whether Etv5 influences Ptgs2 transcriptional activity. Indeed, we found that addition of Etv5 increases the transcriptional activity of the 3.2-kb mouse Ptgs2 promoter by 2.5-fold in luciferase reporter assays. Collectively, the results show that Etv4 and Etv5 are expressed in granulosa and cumulus cells during folliculogenesis and ovulation, suggesting that they influence cellular events in the ovary by regulating downstream genes such as Ptgs2.

Utilization of DR1 as true RARE in regulating the Ssm, a novel retinoic acid-target gene in the mouse testis.

Various nuclear receptors form dimers to activate target genes via specific response elements located within promoters or enhancers. Retinoid X receptor (RXR) serves as a dimerization partner for many nuclear receptors including retinoic acid receptor (RAR) and peroxisome proliferator-activated receptor (PPAR). Dimers show differential preference towards directly repeated response elements with 1-5 nucleotide spacing, and direct repeat 1 (DR1) is a promiscuous element which recruits RAR/RXR, RXR/RXR, and PPAR/RXR in vitro. In the present investigation, we report identification of a novel RAR/RXR target gene which is regulated by DR1s in the promoter region. This gene, namely spermatocyte-specific marker (Ssm), recruits all the three combinations of nuclear receptors in vitro, but in vivo regulation is observed by trans-retinoic acid-activated RAR/RXR dimer. Indeed, chromatin immunoprecipitation experiment demonstrates binding of RARbeta and RXRalpha in the promoter region of the Ssm. Interestingly, expression of Ssm is almost exclusively observed in spermatocytes in the adult mouse testis, where RA signaling is known to regulate developmental program of male germ cells. The results show that Ssm is a RAR/RXR target gene uniquely using DR1 and exhibits stage-specific expression in the mouse testis with potential function in later stages of spermatogenesis. This finding exemplifies usage of DR1s as retinoic acid response element (RARE) under a specific in vivo context.

Progesterone supplementation extends uterine receptivity for blastocyst implantation in mice.

We previously showed that blastocyst can initiate implantation beyond the normal 'window' of uterine receptivity on day 5 of pregnancy and pseudopregnancy (PSP) in mice. In this study, we investigated whether uterine receptivity for blastocyst implantation can be further extended on day 6 of PSP and the role of progesterone (P(4)) on this event. Embryo transfers, experimentally induced decidualization, in situ hybridization and [(3)H]thymidine incorporation were performed. Blastocysts initiate attachment reaction within 48 h when transferred on day 5, but not on day 6 of PSP. Likewise, decidualization reaction occurred on days 4 and 5 of PSP, but completely failed on day 6. However, P(4) supplementation partially retains uterine receptivity for blastocyst implantation and decidualization on day 6 of PSP. In addition, certain indicators of uterine receptivity, such as cell proliferation profile and expression patterns of implantation-related genes were similarly observed on days 4 and 5 of PSP, but not on day 6. Consistent with embryo transfer and decidualization, exogenous administration of P(4) partially restores these indicators on day 6 of PSP. We concluded that critical physiological changes occur between days 4 and 5 of PSP, leading to uterine non-receptivity on day 6, but P(4) is able to extend the uterine receptivity through day 6.

Differential expression of the PEA3 subfamily of ETS transcription factors in the mouse ovary and peri-implantation uterus.

The objective of the present investigation was to examine the spatio-temporal expression of three members of the ETS family of transcription factors, ERM, ER81, and PEA3, in the peri-implantation mouse uterus and in the ovary. These three factors belong to the PEA3 subfamily and are known to mediate diverse functions ranging from neuronal development to tumor progression. As transcription factors, they regulate the expression of a number of genes with various biological functions. Since several genes with known roles in the reproductive processes have been shown to be under the regulation of one of these factors, we sought to investigate the expression of ERM, ER81, and PEA3 in the mouse ovary and uterus. Quantitative RT-PCR analyses showed that ERM, ER81, and PEA3 were all expressed in the peri-implantation mouse uterus, with higher levels of expression on days 4 and 5 of pregnancy. To determine the cell type-specific expression of these factors, we employed in situ hybridization, the results of which revealed that ERM was expressed in both the epithelium and the stroma on days 4 and 5 of pregnancy. Uterine glands showed a high expression of ERM on those days. ERM was also highly expressed in the corpora lutea of the mouse ovary. Both ER81 and PEA3 were expressed at low levels in the stroma on days 4 and 5. On day 8, while ERM and PEA3 were mainly expressed in the embryo and were at low levels in the maternal decidua in a diffused pattern, ER81 was highly expressed in the vascular bed of the mesometrial deciduum. Both ER81 and PEA3 were undetectable in the mouse ovary. Collectively, these data show that ERM is implicated in the early event of implantation as well as in ovarian functions, while ER81 is involved in the establishment of the maternal vasculature for subsequent placental development. PEA3 is apparently an embryonic factor for early embryogenesis.

Transcriptional cofactors exhibit differential preference toward peroxisome proliferator-activated receptors alpha and delta in uterine cells.

We previously showed that peroxisome proliferator-activated receptor delta (PPARdelta) is crucial for embryo implantation as a receptor for cyclooxygenase-2-derived prostacyclin in mice. PPARs belong to the nuclear receptor superfamily. They form heterodimer with a retinoid X receptor, recruit transcriptional cofactors, and bind to a specific recognition element for regulation of target genes. Although cofactors are generally shared by various nuclear receptors, some are involved in cell-specific events. The objective of this investigation was to examine interactions of transcriptional cofactors with PPARdelta in uterine cells for its effectiveness in regulating gene expression. We chose two uterine cellular systems: periimplantation mouse uterus and AN(3)CA human uterine cell line. As examined by in situ hybridization, steroid receptor coactivator (SRC)-2, SRC-3, PPAR-interacting protein, receptor-interacting protein 140 (RIP140), nuclear receptor corepressor (N-CoR), and silencing mediator for retinoid and thyroid hormone receptor (SMRT) exhibit overlapping expression with that of PPARdelta in the periimplantation mouse uterus. Glutathione-S-transferase (GST) pull-down assays show that PPARdelta physically interacts with SRC 1-3, RIP140, PPAR-binding protein, N-CoR, and SMRT in the absence of ligands, suggesting their potent interactions with PPARdelta. Transient transfection assays in AN(3)CA cells show that among members of the SRC family, only SRC-2 serves as a true coactivator for PPARdelta, whereas all SRC members could enhance PPARalpha-induced transcriptional activation. Interestingly, N-CoR and SMRT potently repress PPARdelta-induced transcriptional activation but fail to repress PPARalpha activity. RIP140 is effective in repressing basal and PPAR-induced transcriptional activation. Collectively, the results suggest that gene regulation by PPARdelta in the uterine cells uniquely responds to SRC-2, N-CoR, SMRT, or RIP140, and these interactions may be operative during implantation when these cofactors are abundantly expressed.