Isoform-specific regulation of the CCAAT/enhancer-binding protein family of transcription factors by 3',5'-cyclic adenosine monophosphate in Sertoli cells

FSH and ApoE4 contribute to Alzheimer's disease-like pathogenesis via C/EBPβ/δ-secretase in female mice

Alzheimer's disease (AD) is the most common dementia. It is known that women with one ApoE4 allele display greater risk and earlier onset of AD compared with men. In mice, we previously showed that follicle-stimulating hormone (FSH), a gonadotropin that rises in post-menopausal females, activates its receptor FSHR in the hippocampus, to drive AD-like pathology and cognitive impairment. Here we show in mice that ApoE4 and FSH jointly trigger AD-like pathogenesis by activating C/EBPβ/δ-secretase signaling. ApoE4 and FSH additively activate C/EBPβ/δ-secretase pathway that mediates APP and Tau proteolytic fragmentation, stimulating Aβ and neurofibrillary tangles. Ovariectomy-provoked AD-like pathologies and cognitive defects in female ApoE4-TR mice are ameliorated by anti-FSH antibody treatment. FSH administration facilitates AD-like pathologies in both young male and female ApoE4-TR mice. Furthermore, FSH stimulates AD-like pathologies and cognitive defects in ApoE4-TR mice, but not ApoE3-TR mice. Our findings suggest that in mice, augmented FSH in females with ApoE4 but not ApoE3 genotype increases vulnerability to AD-like process by activating C/EBPβ/δ-secretase signalling.

C/EBPβ/AEP Signaling Drives Alzheimer's Disease Pathogenesis

Alzheimer's disease (AD) is the most common type of dementia. Almost two-thirds of patients with AD are female. The reason for the higher susceptibility to AD onset in women is unclear. However, hormone changes during the menopausal transition are known to be associated with AD. Most recently, we reported that follicle-stimulating hormone (FSH) promotes AD pathology and enhances cognitive dysfunctions via activating the CCAAT-enhancer-binding protein (C/EBPβ)/asparagine endopeptidase (AEP) pathway. This review summarizes our current understanding of the crucial role of the C/EBPβ/AEP pathway in driving AD pathogenesis by cleaving multiple critical AD players, including APP and Tau, explaining the roles and the mechanisms of FSH in increasing the susceptibility to AD in postmenopausal females. The FSH-C/EBPβ/AEP pathway may serve as a novel therapeutic target for the treatment of AD.

The transcription factors Creb1 and Cebpb regulate Sox9 promoter activity in TM4 Sertoli cells

In Sertoli cells, the Sox9 gene is essential for testicular development and normal spermatogenesis. SOX9 is critical for postnatal Sertoli cells differentiation and proliferation in the testis. However, the molecular mechanisms that specifically regulate its expression are not entirely understood. Sox9 expression is regulated by CREB1 and CEBPB in other biological contexts such as during chondrogenesis and in rat thyroid follicular cells. We hypothesized that Sox9 promoter activity is regulated by CREB1 and CEBPB in Sertoli cells. Our results show that Sox9 expression is dependent on the activation of these transcription factors by the cAMP/PKA signaling pathway in TM4 Sertoli cells. Chromatin immunoprecipitation and promoter/reporter luciferase assays with 5' promoter deletions and site-directed mutagenesis demonstrated that CREB1 is being recruited to a DNA regulatory element at -141 bp of the Sox9 promoter region. Such regulation is dependent on the cAMP/PKA signaling pathway, resulting in phosphorylation of CREB1. Activation of Sox9 expression by CEBPB may involve its recruitment to the proximal promoter region by protein-protein interaction with CREB1. Thus, we have shown that the Sox9 promoter is being regulated by the transcription factors CREB1 and CEBPB in TM4 Sertoli cells and involve their recruitment to the proximal promoter region.

The single-cell chromatin accessibility landscape in mouse perinatal testis development

Spermatogenesis depends on an orchestrated series of developing events in germ cells and full maturation of the somatic microenvironment. To date, the majority of efforts to study cellular heterogeneity in testis has been focused on single-cell gene expression rather than the chromatin landscape shaping gene expression. To advance our understanding of the regulatory programs underlying testicular cell types, we analyzed single-cell chromatin accessibility profiles in more than 25,000 cells from mouse developing testis. We showed that single-cell sequencing assay for transposase-accessible chromatin (scATAC-Seq) allowed us to deconvolve distinct cell populations and identify cis-regulatory elements (CREs) underlying cell-type specification. We identified sets of transcription factors associated with cell type-specific accessibility, revealing novel regulators of cell fate specification and maintenance. Pseudotime reconstruction revealed detailed regulatory dynamics coordinating the sequential developmental progressions of germ cells and somatic cells. This high-resolution dataset also unveiled previously unreported subpopulations within both the Sertoli and Leydig cell groups. Further, we defined candidate target cell types and genes of several genome-wide association study (GWAS) signals, including those associated with testosterone levels and coronary artery disease. Collectively, our data provide a blueprint of the 'regulon' of the mouse male germline and supporting somatic cells.

Implications of adiponectin in linking metabolism to testicular function

Obesity is a major health problem, contributing to the development of various diseases with aging. In humans, obesity has been associated with reduced testosterone production and subfertility. Adipose tissue is an important source of hormones having influences on both metabolism and reproduction. Among them, the production and secretion of adiponectin is inversely correlated to the severity of obesity. The purpose of this review of literature is to present the current state of knowledge on adiponectin research to determine whether this hormone affects reproduction in men. Surprisingly, evidences show negative influences of adiponectin on GnRH secretion from the hypothalamus, LH and FSH secretion from the pituitary and testosterone at the testicular level. Thus far, the involvement of adiponectin in the influence of metabolism on reproduction in men is limited. However, adiponectin and its receptors are expressed by different cell types of the male gonad, including Leydig cells, spermatozoa, and epididymis. In addition, actions of adiponectin at the testicular level have been shown to promote spermatogenesis and sperm maturation. Therefore, autocrine/paracrine actions of adiponectin in the testis may contribute to support male reproductive function.

Transcriptional suppression of Sertoli cell Timp2 in rodents following mono-(2-ethylhexyl) phthalate exposure is regulated by CEBPA and MYC

Our previous studies showed that the prototypical testicular toxic phthalate monoester, mono-(2-ethylhexyl) phthalate (MEHP), suppresses Sertoli cell TIMP2 levels and allows for the activation of MMP2 in seminiferous epithelium. Activation of MMP2 is important for triggering germ cell apoptosis and instigating germ cell detachment from Sertoli cells. These novel findings led us to examine the transcriptional regulation of the Timp2 gene that accounts for the decrease in Sertoli cell TIMP2 levels following MEHP exposure. Sequential deletion of the Timp2 5'-upstream activating sequence (1200 bp) was used to survey transcriptional activation in the Timp2 promoter region in response to MEHP. Results indicate that under control conditions in rat Sertoli cells, CCAAT enhancer-binding protein alpha (CEBPA) acts as a transactivator to initiate Timp2 gene transcription, and its action is deactivated by exposure to MEHP. By contrast, MYC protein acts as an inhibitor of Timp2 gene transcription, and its activity is increased after MEHP treatment. Addition of follicle-stimulating hormone (FSH) to cells causes translocation of CEBPA into the Sertoli cell nucleus and rescues MEHP-suppressed TIMP2 levels. Down-regulation of TIMP2 expression by MEHP exposure is blocked by forskolin (a cAMP-elevating agent), suggesting that the decrease in Sertoli cell TIMP2 expression following MEHP exposure is cAMP-dependent. Taken together, these data indicate that MEHP both disrupts the FSH-stimulated cAMP signaling pathway and activates the inhibitory signaling mediated by MYC protein, to ultimately account for the cellular mechanism underlying the decreased expression of TIMP2 in Sertoli cells.

Activation of protein kinase Calpha by EPAC1 is required for the ERK- and CCAAT/enhancer-binding protein beta-dependent induction of the SOCS-3 gene by cyclic AMP in COS1 cells

We recently found that induction of the anti-inflammatory SOCS-3 gene by cyclic AMP occurs through novel cyclic AMP-dependent protein kinase-independent mechanisms involving activation of CCAAT/enhancer-binding protein (C/EBP) transcription factors, notably C/EBPbeta, by the cyclic AMP GEF EPAC1 and the Rap1 GTPase. In this study we show that down-regulation of phospholipase (PL) Cepsilon with small interfering RNA or blockade of PLC activity with chemical inhibitors ablates exchange protein directly activated by cyclic AMP (EPAC)-dependent induction of SOCS-3 in COS1 cells. Consistent with this, stimulation of cells with 1-oleoyl-2-acetyl-sn-glycerol and phorbol 12-myristate 13-acetate, both cell-permeable analogues of the PLC product diacylglycerol, are sufficient to induce SOCS-3 expression in a Ca2+-dependent manner. Moreover, the diacylglycerol- and Ca2+-dependent protein kinase C (PKC) isoform PKCalpha becomes activated following cyclic AMP elevation or EPAC stimulation. Conversely, down-regulation of PKC activity with chemical inhibitors or small interfering RNA-mediated depletion of PKCalpha or -delta blocks EPAC-dependent SOCS-3 induction. Using the MEK inhibitor U0126, we found that activation of ERK MAPKs is essential for SOCS-3 induction by either cyclic AMP or PKC. C/EBPbeta is known to be phosphorylated and activated by ERK. Accordingly, we found ERK activation to be essential for cyclic AMP-dependent C/EBP activation and C/EBPbeta-dependent SOCS-3 induction by cyclic AMP and PKC. Moreover, overexpression of a mutant form of C/EBPbeta (T235A), which lacks the ERK phosphorylation site, blocks SOCS-3 induction by cyclic AMP and PKC in a dominant-negative manner. Together, these results indicate that EPAC mediates novel regulatory cross-talk between the cyclic AMP and PKC signaling pathways leading to ERK- and C/EBPbeta-dependent induction of the SOCS-3 gene.

Identification of CCAAT/enhancer-binding proteins as exchange protein activated by cAMP-activated transcription factors that mediate the induction of the SOCS-3 gene

The prototypical second messenger cAMP is a key regulator of immune and inflammatory responses. Its ability to inhibit interleukin (IL)-6 responses is due to induction of suppressor of cytokine signaling-3 (SOCS-3), a negative regulator of IL-6 receptor signaling. We have determined previously that SOCS-3 induction by cAMP occurs independently of cAMP-dependent protein kinase, instead requiring the recently identified cAMP sensor exchange protein activated by cAMP 1 (EPAC1). Here we present evidence to suggest that the C/EBP family of transcription factors link EPAC1 activation to SOCS-3 induction. Firstly, selective activation of EPAC in human umbilical vein endothelial cells increased C/EBP DNA binding activity and recruitment of C/EBPbeta to the SOCS-3 promoter. Secondly, knockdown of C/EBPbeta and -delta isoforms abolished both SOCS-3 induction and inhibition of IL-6 signaling in response to cAMP. Thirdly, overexpression of C/EBPalpha, -beta, or -delta potentiated EPAC-mediated accumulation of SOCS-3. Finally, these effects were not restricted to human umbilical vein endothelial cells, because similar phenomena were observed in murine embryonic fibroblasts in which C/EBPbeta or delta had been deleted. In summary, our findings constitute the first description of an EPAC-C/EBP pathway that can control cAMP-mediated changes in gene expression independently of protein kinase A.

Expression of CCAAT/enhancer binding proteins alpha and beta in the porcine ovary and regulation in primary cultures of granulosa cells

CCAAT/enhancer binding proteins alpha and beta (CEBPA/ CEBPB) were evaluated in the porcine ovary during the estrous cycle. CEBPB mRNA was present in antral follicles and was significantly increased in healthy corpora lutea (CL), whereas CEBPA mRNA was constitutively expressed in these structures. Both isoforms of CEBPA (42 and 30 kDa) exhibited greater expression in preovulatory follicles, and the 42-kDa isoform increased in CL, whereas the 30-kDa isoform decreased. All major isoforms of CEBPB (38, 34, and 20 kDa) were expressed, with the 34- and 20-kDa isoforms being more abundant in preovulatory follicles and further increased in CL. The effects of FSH and cAMP analogue on the distribution of CEBP isoforms were evaluated in primary cultures of porcine granulosa cells. FSH and 8-Br-cAMP had little stimulatory effect on isoform distribution, but cAMP treatment for 24 h tended to decrease the 30-kDa form of CEBPA and the 34-kDa form of CEBPB. The 34-kDa form of CEBPB was decreased by the protein kinase A inhibitor H89 at 4 h (with FSH treatment), and by both protein kinase A and phosphatidylinositol 3-kinase inhibitors at 24 h of treatment. In transfected granulosa cells, FSH and cAMP analogue stimulated a CEBP consensus sequence-reporter construct that was blocked by H89. These data implicate protein kinase A as the major regulator of CEBPB isoform distribution and CEBP-mediated transactivation in granulosa cells. The differential expression of specific CEBPA/B isoforms observed in maturing follicles and CL may contribute to changes in follicular cell differentiation and increasing steroidogenic capacity.

The helix-loop-helix inhibitor of differentiation (ID) proteins induce post-mitotic terminally differentiated Sertoli cells to re-enter the cell cycle and proliferate

Prior to puberty the Sertoli cells undergo active cell proliferation, and at the onset of puberty they become a terminally differentiated postmitotic cell population that support spermatogenesis. The molecular mechanisms involved in the postmitotic block of pubertal and adult Sertoli cells are unknown. The four known helix-loop-helix ID proteins (i.e., Id1, Id2, Id3, and Id4) are considered dominant negative regulators of cellular differentiation pathways and act as positive regulators of cellular proliferation. ID proteins are expressed at low levels by postpubertal Sertoli cells and are transiently induced by serum. The hypothesis tested was that ID proteins can induce a terminally differentiated postmitotic Sertoli cell to reenter the cell cycle if they are constitutively expressed. To test this hypothesis, ID1 and ID2 were stably integrated and individually overexpressed in postmitotic rat Sertoli cells. Overexpression of ID1 or ID2 allowed postmitotic Sertoli cells to reenter the cell cycle and undergo mitosis. The cells continued to proliferate even after 300 cell doublings. The functional markers of Sertoli cell differentiation such as transferrin, inhibin alpha, Sert1, and androgen binding protein (ABP) continued to be expressed by the proliferating Sertoli cells, but at lower levels. FSH receptor expression was lost in the proliferating Sertoli cell-Id lines. Some Sertoli cell genes, such as cyclic protein 2 (cathepsin L) and Sry-related HMG box protein-11 (Sox11) increase in expression. At no stage of proliferation did the cells exhibit senescence. The expression profile as determined with a microarray protocol of the Sertoli cell-Id lines suggested an overall increase in cell cycle genes and a decrease in growth inhibitory genes. These results demonstrate that overexpression of ID1 and ID2 genes in a postmitotic, terminally differentiated cell type have the capacity to induce reentry into the cell cycle. The observations are discussed in regards to potential future applications in model systems of terminally differentiated cell types such as neurons or myocytes.

Expression pattern of the CCAAT/enhancer-binding proteins C/EBP-alpha, C/EBP-beta and C/EBP-delta in the human placenta

The human trophoblast has the capacity to invade maternal tissue in a controlled fashion and to produce a wide range of hormones. The transcription factors belonging to the CCAAT/enhancer-binding protein (C/EBP) family are regulators of intracellular processes and mediators of hormone action. C/EBP binding sites have been described in the promoters of several placenta-expressed target genes. In the present study, we used immunohistochemistry and Western-blot analysis to investigate the expression pattern of the three most important members of this family, C/EBP-alpha, -beta, and -delta, in the normal human placenta as well as in isolated trophoblast cell populations. We found C/EBP-alpha and C/EBP-beta expression in the villous syncytiotrophophoblast (ST) and the extravillous (intermediate) trophoblast (EVT), but it was absent from the villous cytotrophoblast (CT). Interestingly, expression of C/EBP-beta continued to be very strong up to the third trimester of pregnancy, especially in the ST. C/EBP-delta showed overall lower expression levels, stronger only in the EVT, while CT/ST showed very low/negative expression. These data show for the first time the expression pattern and tissue localization of C/EBP factors in the human placenta, indicating that these factors (especially C/EBP-beta) may play important roles in the regulation of placenta-specific genes and processes.

GATA-1 testis activation region is essential for Sertoli cell-specific expression of GATA-1 gene in transgenic mouse

BACKGROUND

The erythroid transcription factor GATA-1 is also expressed in Sertoli cells of the testis. The testicular expression of GATA-1 is regulated in a developmental and spermatogenic stage-specific manner. To further clarify the regulatory mechanisms of testicular GATA-1 gene expression, we carried out transgenic reporter gene expression analyses.

RESULTS

We found that GATA-1 expression in Sertoli cells is markedly decreased concomitant with the emergence of elongated spermatids in the seminiferous tubules. Transgenic reporter mouse analyses revealed that a 15 kb GATA-1 genomic region is sufficient to recapitulate the gene expression profile in Sertoli cells. While the GATA-1 haematopoietic enhancer and the proximal first exon are included within the 15 kb genomic region, these regulatory elements are not essential for GATA-1 expression in Sertoli cells. Further analyses using deletion constructs revealed that a 1.5 kb region 5' to the GATA-1 haematopoietic enhancer is essential for gene expression in Sertoli cells and this region is referred to as the GATA-1 testis activation region.

CONCLUSION

These results thus demonstrated that the GATA-1 testis activation region is essential for Sertoli cell-specific expression of GATA-1 gene. The 15 kb genomic region is applicable and useful for the expression vector system specific for adult Sertoli cells in stage VII to IX.

Regulation of glypican-1, syndecan-1 and syndecan-4 mRNAs expression by follicle-stimulating hormone, cAMP increase and calcium influx during rat Sertoli cell development

In seminiferous tubules, Sertoli cells provide structural and nutritional support for the developing germinal cells. Cell- to-cell signaling and cell adhesion require proteoglycans expressed at the cell membrane. A preliminary biochemical and structural approach indicated that cell surface proteoglycans are mostly heparan sulfate proteoglycans (HSPG). Glypican-1, syndecans-1 and -4 were identified using a molecular approach. Their differential regulation was demonstrated in immature rat Sertoli cells. Follicle-stimulating hormone (FSH) is the main regulator of Sertoli cell function. Signal transduction triggered by FSH involves both an increased intracellular cAMP synthesis and a calcium influx. This study demonstrates that FSH, through its second messengers (increase in intracellular cAMP and intracellular calcium), downregulated the glypican-1 mRNA expression in Sertoli cells from 20-day-old rats. On the other hand, syndecan-1 mRNA expression is not modulated by FSH as it would result from the antagonistic effects of increased intracellular cAMP and intracellular calcium levels. Finally, syndecan-4 mRNA expression is not regulated by this pathway. The present study was extended during Sertoli cell development. Indeed, Sertoli cells undergo extensive changes during the postnatal period both in structure and function. These important transformations are critical for the establishment of spermatogenesis and development of the adult pattern of testicular function. Our data indicated that the regulation of HSPG mRNA expression is HSPG-specific and depends on the Sertoli cell developmental stage.

USF2 inhibits C/EBP-mediated transcriptional regulation of the RIIbeta subunit of cAMP-dependent protein kinase

BACKGROUND

Cyclic AMP-dependent protein kinase (PKA) plays a central role in regulation of energy metabolism. Upon stimulation of testicular Sertoli cells by follicle stimulating hormone (FSH), glycolysis is activated to increase the production of nutrients for the germ cells, and a new regulatory subunit of cAMP-dependent protein kinase, RIIbeta, is induced. We have previously shown that production of the transcription factor C/EBPbeta is rapidly increased by FSH and cAMP in primary Sertoli cell cultures, and that C/EBPbeta induces the RIIbeta promoter.

RESULTS

In this work we show that USF1, USF2 and truncated USF isoforms bind to a conserved E-box in the RIIbeta gene. Interestingly, overexpression of USF2, but not USF1, led to inhibition of both cAMP- and C/EBPbeta-mediated induction of RIIbeta. Furthermore, Western blots show that a novel USF1 isoform is induced by cAMP in Sertoli cells.

CONCLUSIONS

These results indicate that the expression of various USF isoforms may be regulated by cAMP, and that the interplay between USF and C/EBPbeta is important for cAMP-mediated regulation of RIIbeta expression. The counteracting effects of USF2 and C/EBPbeta observed on the RIIbeta promoter is in accordance with the hypothesis that C/EBP and USF play opposite roles in regulation of glucose metabolism.

Sp1 and Egr1 regulate transcription of the Dmrt1 gene in Sertoli cells

Dmrt1 is a recently described gene that is specifically expressed in the gonads and is required for postnatal testis differentiation. Here, we describe the transcriptional mechanisms regulating the Dmrt1 proximal promoter in testicular Sertoli cells. A genomic clone containing exon 1 of the rat Dmrt1 gene and more than 9 kilobases of 5' flanking sequence was isolated and characterized. Several prominent transcriptional start sites were identified, with the major site located 102 bases from the translational start. The Dmrt1 5' flanking region from -5000 to +74 was transcriptionally active in primary Sertoli cells, and deletion analysis of this fragment identified 2 major regions needed for full Dmrt1 promoter function. These regions were located between -3200 and -2000 base pairs (bp) and downstream of -150 bp relative to the major transcriptional start site. DNase I footprint analysis of the region downstream of -150 bp revealed 3 regions that are bound by proteins from Sertoli cell nuclear extracts. Site-directed mutagenesis of these regions identified 2 elements that activate the Dmrt1 promoter and 2 that repress it. The positive elements bind the transcription factors Sp1, Sp3, and Egr1, suggesting that these transcription factors play a critical role in Dmrt1 regulation in the testis.

CCAAT/enhancer binding protein beta regulates expression of the cystatin-related epididymal spermatogenic (Cres) gene

The CRES protein is a member of the cystatin superfamily of cysteine protease inhibitors with restricted expression in stage-specific germ cells, proximal caput epididymidis, and anterior pituitary gonadotroph cells. To elucidate the molecular mechanisms regulating the highly restricted expression of the cres gene, we have sequenced 1.6 kilobases of mouse cres 5' flanking sequence and performed studies to examine the cres gene promoter. Two putative CCAAT/enhancer binding protein (C/EBP) transcription factor binding motifs exist within the first 135 base pairs of cres promoter. Furthermore, our studies demonstrate that cres mRNA levels are dramatically reduced in the epididymides of C/EBP beta-deficient mice. These data suggest that the C/EBP family of transcription factors, in particular C/EBP beta, plays a role in the regulation of cres gene expression. In support of this finding, Northern blot analysis showed that C/EBP beta is the predominant C/EBP family member expressed in the L beta T2 gonadotroph cell line and the proximal caput epididymidis. Also, gel shift and supershift assays demonstrated that C/EBP beta protein in nuclear extracts from L beta T2 gonadotroph cells and epididymal cells bound to the two C/EBP sites in the cres promoter. Finally, to test the in vivo function of the C/EBP sites in cres gene expression, transfection studies were performed in L beta T2 gonadotroph cells and two heterologous cell systems. These experiments showed a significant reduction of cres transactivation when either C/EBP sites were mutated, and no transC/EBP activation of the cres promoter when both C/EBP sites were mutated. Taken together, these studies demonstrate that the C/EBP beta transcription factor is necessary for high levels of cres gene expression in the proximal caput epididymidis and anterior pituitary gonadotroph cells.

Molecular characterization of the Xenopus CCAAT-enhancer binding protein beta gene promoter

Transcription factors belonging to the CCAAT-enhancer binding protein (C/EBP) family play key roles in the regulation of genes implicated in the control of growth, differentiation, metabolism, and inflammation. The recent limited studies on the promoter regions of C/EBP genes, particularly C/EBPalpha, have indicated the potential existence of species-specific regulatory mechanisms. It is therefore essential that the promoter regions of different C/EBP genes from a wide range of species are investigated in detail. As an important step toward this goal, we report here the characterization of the Xenopus laevis C/EBPbeta gene promoter. Sequence analysis showed that the 1.6-kb promoter region contained putative binding sites for several transcription factors that have previously been implicated in the regulation of the C/EBPs, including C/EBP, CREB, Myb, STAT, and USF. The -288/+91 promoter region was capable of directing high levels of expression in the hepatoma Hep3B cell line. In addition, this minimal promoter could be autoregulated by both C/EBPalpha and C/EBPbeta and activated by lipopolysaccharide, interleukin-6 and CREB. These results therefore demonstrate that several aspects of C/EBPbeta regulation in mammals have been highly conserved in amphibians. However, a comparison of C/EBPbeta gene promoters characterized to date does indicate the existence of species-specific differences in autoregulation.

Hormonal regulation and differential actions of the helix-loop-helix transcriptional inhibitors of differentiation (Id1, Id2, Id3, and Id4) in Sertoli cells

The testicular Sertoli cells support spermatogenesis by providing a microenvironment and structural support for the developing germ cells. Sertoli cell functions are regulated by the gonadotropin FSH. Sertoli cells become a terminally differentiated nongrowing cell population in the adult. In response to FSH, the Sertoli cells express a large number of differentiated gene products, such as transferrin, which transports iron to the developing germ cells. Previously, members of the basic helix-loop-helix (bHLH) family of transcription factors have been shown to influence FSH-mediated gene expression in Sertoli cells. The functions of the bHLH proteins are modulated by Id (inhibitor of differentiation) proteins, which lack the DNA-binding basic domain. The Id proteins form transcriptionally inactive dimers with bHLH proteins and thus regulate cell proliferation and differentiation. The current study investigated the expression and function of Id proteins in the postmitotic Sertoli cell. Freshly isolated and cultured Sertoli cells coexpress all four isoforms of Id (Id1, Id2, Id3, and Id4), as determined by immunoprecipitation with isoform-specific anti-Id antibodies, RT-PCR, and Northern blot analysis. Id2 and Id3 expression levels seem higher than Id1. Interestingly, the expression of Id4 in Sertoli cells is only detectable after stimulation with FSH or cAMP. The Id1 expression is down-regulated by FSH and cAMP, whereas Id2 and Id3 levels remain unchanged in response to FSH. In contrast, serum induces the expression of Id1, Id2, and Id3. Treatment of Sertoli cells with serum significantly reduces the expression of the larger 4-kb Id4 transcript and promotes the presence of a novel 1.3-kb transcript of Id4. The regulatory role of FSH in the expression of all four isoforms of Id is mimicked by a cAMP analog, suggesting that the actions of FSH are mediated through the protein kinase A pathway. An antisense approach was used to study the functional significance of Id proteins in Sertoli cells. Antisense to Id1 stimulated transferrin promoter activity in a transient transfection assay. Interestingly, an antisense to Id2 down-regulated transferrin promoter activity. Id3 and Id4 antisense oligonucleotides had no effect on FSH-mediated transferrin promoter activation. Contrary to the hypothesis that Id proteins have redundant functions, the results of the current study suggest that Id1, Id2, Id3, and Id4 are differentially regulated and may have distinct functions. Id1 may act to maintain Sertoli cell growth potential, whereas Id2 and Id4 may be involved in the differentiation and hormone regulation of Sertoli cells.

Interleukin-6-induced tethering of STAT3 to the LAP/C/EBPbeta promoter suggests a new mechanism of transcriptional regulation by STAT3

LAP/C/EBPbeta is a member of the C/EBP family of transcription factors and contributes to the regulation of the acute phase response in hepatocytes. Here we show that IL-6 controls LAP/C/EBPbeta gene transcription and identify an IL-6 responsive element in the LAP/C/EBPbeta promoter, which contains no STAT3 DNA binding motif. However, luciferase reporter gene assays showed that STAT3 activation through the gp130 signal transducer molecule is involved in mediating IL-6-dependent LAP/C/EBPbeta transcription. Southwestern analysis indicated that IL-6 induces binding of a 68-kDa protein to the recently characterized CRE-like elements in the LAP/C/EBPbeta promoter. Transfection experiments using promoter constructs with mutated CRE-like elements revealed that these sites confer IL-6 responsiveness. Further analysis using STAT1/STAT3 chimeras identified specific domains of the protein that are required for the IL-6-dependent increase in LAP/C/EBPbeta gene transcription. Overexpression of the amino-terminal domain of STAT3 blocked the IL-6-mediated response, suggesting that the STAT3 amino terminus has an important function in IL-6-mediated transcription of the LAP/C/EBPbeta gene. These data lead to a model of how tethering STAT3 to a DNA-bound complex contributes to IL-6-dependent LAP/C/EBPbeta gene transcription. Our analysis describes a new mechanism by which STAT3 controls gene transcription and which has direct implication for the acute phase response in liver cells.

GATA factors differentially activate multiple gonadal promoters through conserved GATA regulatory elements

The GATA factors are a group of transcriptional regulators that play essential roles in cell differentiation, organ morphogenesis, and tissue-specific gene expression during development. The six vertebrate GATA factors are expressed in a broad spectrum of tissues, including the hemopoietic system, heart, gut, brain, placenta, pituitary, and gonads. Interestingly, GATA-like DNA-binding proteins are found in the gonads of several species, ranging from lower invertebrates to humans, thus supporting an evolutionary conserved and crucial role for these factors in gonadal development and function. Indeed, GATA factors are expressed from the onset of gonadal development and are later found in multiple cell lineages of both the testis and ovary. We now report that GATA-4 differentially activates transcription of several genes expressed in the gonads that encode either steroidogenic enzymes (steroidogenic acute regulatory protein and aromatase), hormones (inhibin alpha and Müllerian inhibiting substance) and a transcription factor (SF-1) known to be essential for gonadal development and function. Thus, our results identify GATA-4 as an important regulator of gonadal gene transcription where its specificity of action is mediated through synergistic interactions with other transcription factors such as SF-1.

SF-1 (steroidogenic factor-1), C/EBPbeta (CCAAT/enhancer binding protein), and ubiquitous transcription factors NF1 (nuclear factor 1) and Sp1 (selective promoter factor 1) are required for regulation of the mouse aldose reductase-like gene (AKR1B7) expression in adrenocortical cells

The MVDP (mouse vas deferens protein) gene encodes an aldose reductase-like protein (AKR1B7) that is responsible for detoxifying isocaproaldehyde generated by steroidogenesis. In adrenocortical cell cultures, hormonal regulation of MVDP gene occurs through the cAMP pathway. We show that in adrenals, the pituitary hormone ACTH regulates MVDP gene expression in a coordinate fashion with steroidogenic genes. Cell transfection and DNA-binding studies were used to investigate the molecular mechanisms underlying MVDP gene regulation in Y1 adrenocortical cells. Progressive deletions of upstream regulatory regions identified a -121/+41 fragment that was sufficient for basal and cAMP-mediated transcriptional activities. Gel shift assays showed that CTF1/nuclear factor 1 (NF1), CCAAT enhancer binding protein-ss (C/EBPss), and selective promoter factor 1 (Sp1) factors bound to cis-acting elements at positions -76, -61, and -52, respectively. We report that the cell-specific steroidogenic factor-1 (SF-1) interacts specifically with a novel regulatory element located in the downstream half-site of the proximal androgen response element (AREp) at position -102. Functional analysis of SF-1 and NF1 sites in the -121/+41 promoter showed that mutation of one of them decreases both constitutive and forskolin-stimulated promoter activity without affecting the fold induction (forskolin stimulated/basal). Individual mutations of C/EBP and Sp1 sites resulted in a loss of more than 50% of the cAMP-dependent induction. When both sites were mutated simultaneously, cAMP responsiveness was nearly abolished. Thus, in adrenocortical cells, both SF-1 and NF1 are required for high expression of the MVDP promoter while Sp1 and C/EBPss functionally interact in an additive manner to mediate cAMP-dependent regulation. Furthermore, we report that MVDP gene regulation is impaired in stably transfected Y1 clones expressing DAX-1. Taken together, our findings suggest that detoxifying enzymes of the aldose reductase family may constitute new potential targets for regulators of adrenal and gonadal differentiation and function, e.g. SF-1 and DAX-1.

Protein kinase A-dependent stimulation of rat type II secreted phospholipase A(2) gene transcription involves C/EBP-beta and -delta in vascular smooth muscle cells

Type II secreted phospholipase A(2) (sPLA(2)) releases precursors of important inflammatory lipid mediators from phospholipids. Some observations have indicated that the sPLA(2), which has been implicated in chronic inflammatory conditions such as arthritis, contributes to atherosclerosis in the arterial wall. sPLA(2) was not detected in control vascular smooth muscle cells (VSMC). Treatment of VSMC with agents that increase intracellular cAMP (eg, forskolin, dibutyryl [db]-cAMP) resulted in a time- and concentration-dependent increase in sPLA(2) gene expression. Semiquantitative reverse transcriptase polymerase chain reaction (RT-PCR) showed a marked dose-dependent inhibition of forskolin-induced mRNA by protein kinase A inhibitor. Electrophoretic mobility shift analysis of nuclear proteins from forskolin-treated and db-cAMP-treated VSMC with C/EBP consensus oligonucleotides and C/EBP oligonucleotides from the rat promoter revealed greater binding than in control VSMC. Incubation of VSMC with H89, a specific protein kinase inhibitor, also blocked the binding of nuclear C/EBP to the C/EBP site of the rat promoter induced by db-cAMP and forskolin. Binding was unchanged with the use of CRE consensus oligonucleotides. Antibodies revealed the specific formation of C/EBP/DNA complexes, the majority of which were supershifted by C/EBP-ss and -delta antibodies. Functional activation of C/EBP was confirmed by a luciferase reporter gene assay. A construct comprising 4 tandem repeat copies of the C/EBP element from the rat sPLA(2) promoter linked to luciferase was transcriptionally activated in VSMC by cotransfection with expression vector for the protein kinase A catalytic subunit. It was also significantly activated in transfected VSMC treated by forskolin or db-cAMP. H89 inhibited this activations. We therefore conclude that the increases in sPLA(2) mRNA and enzyme activity produced by cAMP-elevating agents is controlled by a mechanism involving nuclear C/EBP-ss and -delta acting through a protein kinase A signaling pathway.

Isolation and characterization of the promoter region of the rat vasopressin V1b receptor gene

Regulation of pituitary vasopressin V1b receptors plays a critical role in regulating pituitary adrenocorticotropic hormone (ACTH) secretion during adaptation to stress. The objective of this study was to isolate the promoter regulatory region of the V1b receptor gene to better understand the molecular mechanisms involved in V1b receptor regulation. Screening of a rat genomic library using probes directed to the coding region and to the 5'UTR of the rat V1b receptor resulted in the isolation of several clones containing the 5'upstream regions of the V1b receptor cDNA. Sequencing of an 11.2 Kb fragment revealed 8.2 Kb upsteam of the reported cDNA sequence, which contains a putative promoter regulatory region. The 3' end of the clone contained 1472 base pairs corresponding to the recognized cDNA sequence, followed by 1506 bp of unknown sequence located at the end of the sixth transmembrane domain, probably corresponding to an intron, characteristic of these family of receptors. An additional 161 bp intron was found in the 5'UTR, similar to that described in the rat oxytocin receptor gene. 5'RACE and RNase protection analysis mapped two major putative transcription start points at -830 and -861 bp from the starting methionine. Analysis of the putative promoter region showed no indication of a proximal TATA box, but the presence of a CACA box, a GAGA box, several AP-1 and AP-2 sites and a cluster of Sp1 sites upstream of the AP-2 sites. A luciferase construct containing a 2.1-kb of putative promoter, and part of the 5'UTR including the first intron, showed promoter activity when transfected into COS-7, CHO and PC12 cell lines but not in AtT-20 cells. A similar construct without the intron and distal 5'UTR sequence has no promoter activity in the same cell lines. In summary, the V1b receptor gene contains at least 3 exons and 2 introns. The 5'flanking sequence contains several potential sites for transcriptional regulation, and induced luciferace activity only in constructs containing intron 1, suggesting that the latter is important for receptor gene activation. The data provide bases for future analysis of the regulatory elements controlling V1b receptor transcription.

Regulation of tissue inhibitor of metalloproteinases-1 in rat Sertoli cells: induction by germ cell residual bodies, interleukin-1alpha, and second messengers

In the testis, FSH has been shown to induce the expression and secretion of tissue inhibitor of metalloproteinases-1 (TIMP-1) from Sertoli cells in vitro. This study was performed to elucidate further the cellular origin of testicular TIMP-1 and its expression by hormonal and paracrine factors. This is the first report on the expression of testicular TIMP-1 in vivo. TIMP-1 mRNA in whole testis was decreased after hypophysectomy and strongly increased by the injection of FSH-S17 to hypophysectomized rats. Primary cultures of both peritubular and Sertoli cells showed basal expression of TIMP-1 mRNA. In contrast, we were unable to detect TIMP-1 mRNA in Leydig cells, freshly isolated immature germ cells (primary spermatocytes and spermatids), or residual bodies. We further show that treatment of Sertoli cells with 8-(4-chlorophenyl)thio-cAMP (8-CPTcAMP) in combination with 12-O-tetradecanoylphorbol 13-acetate (TPA) or Ca(2+) inducers (calcium ionophore A23187 or thapsigargin) had additive (TPA) and synergistic effects (Ca(2+)) on the level of TIMP-1 mRNA and secreted protein. We also show that both the level of TIMP-1 mRNA and secreted protein from Sertoli cells were strongly increased by residual bodies, as well as by the cytokine interleukin-1alpha. TIMP-1 was not up-regulated by either 8-CPTcAMP or interleukin-1alpha in peritubular cells. In contrast to the regulated secretory fraction of TIMP-1, we also detected constitutively expressed immunoreactive TIMP-1 in the nucleus of Sertoli cells, suggesting a role of nuclear TIMP-1 in these cells. In conclusion, our data show that secretion of TIMP-1 from Sertoli cells is highly regulated by hormonal and local processes in the testis, indicating that TIMP-1 is of physiological importance during both testicular development and spermatogenesis.

CCAAT/enhancer-binding proteins regulate expression of the human steroidogenic acute regulatory protein (StAR) gene

Two putative CCAAT/enhancer-binding protein (C/EBP) response elements were identified in the proximal promoter of the human steroidogenic acute regulatory protein (StAR) gene, which encodes a key protein-regulating steroid hormone synthesis. Expression of C/EBPalpha and -beta increased StAR promoter activity in COS-1 and HepG2 cells. Cotransfection of C/EBPalpha or -beta and steroidogenic factor 1, a transcription factor required for cAMP regulation of StAR expression, into COS-1 augmented 8-bromoadenosine 3':5'-cyclic monophosphate (8-Br-cAMP)-stimulated promoter activity. When the putative C/EBP response elements were mutated, individually or together, a pronounced decline in basal StAR promoter activity in human granulosa-lutein cells resulted, but the fold stimulation of promoter activity by 8-Br-cAMP was unaffected. Recombinant C/EBPalpha and -beta bound to the two identified sequences but not the mutated elements. Human granulosa-lutein cell nuclear extracts also bound these elements but not the mutated sequences. An antibody to C/EBPbeta, but not C/EBPalpha, supershifted the nuclear protein complex associated with the more distal element. The complex formed by nuclear extracts with the proximal element was not supershifted by either antibody. Western blot analysis revealed the presence of C/EBPalpha and C/EBPbeta in human granulosa-lutein cell nuclear extracts. C/EBPbeta levels were up-regulated 3-fold by 8-Br-cAMP treatment. Our studies demonstrate a role for C/EBPbeta as well as yet to be identified proteins, which can bind to C/EBP response elements, in the regulation of StAR gene expression and suggest a mechanism by which C/EBPbeta participates in the cAMP regulation of StAR gene transcription.

CCAAT/enhancer-binding proteins are mediators in the protein kinase A-dependent activation of the decidual prolactin promoter

In the course of decidualization, human endometrial stromal cells (ESC) activate the alternative upstream promoter of the decidual prolactin (dPRL) gene. The dPRL promoter is induced by the protein kinase A pathway in a delayed fashion via the region -332/-270 which contains two overlapping consensus binding sequences, B and D, for CCAAT/enhancer-binding proteins (C/EBP). Here we show that sites B and D both bind C/EBPbeta and -delta from ESC nuclear extracts. When decidualization of cultured ESC was induced by treatment with 8-Br-cAMP, complex formation on sites B and D was enhanced. Western blot analysis revealed an elevation of both C/EBPbeta isoforms, liver-enriched activator protein and liver-enriched inhibitory protein, with a delayed onset between 8 and 24 h of cAMP treatment, while C/EBPdelta expression remained unaffected. Cyclic AMP-mediated activation of dPRL promoter construct dPRL-332/luc3 was abrogated by mutation of sites B and D at -310/-285. An expression vector for liver-enriched activator protein potently induced transcription of dPRL-332/luc3 and further enhanced cAMP-mediated induction, while liver-enriched inhibitory protein expression vector abolished the cAMP response, implying that C/EBPs serve as mediators in the delayed cAMP signal transduction to the dPRL promoter. The ratio between activating and repressing isoforms is likely to dictate the transcriptional output.