Expression of the gene encoding transcription factor cyclic adenosine 3',5'-monophosphate (cAMP) response element-binding protein (CREB): regulation by follicle-stimulating hormone-induced cAMP signaling in primary rat Sertoli cells

Circular RNA Tmcc1 improves astrocytic glutamate metabolism and spatial memory via NF-κB and CREB signaling in a bile duct ligation mouse model: transcriptional and cellular analyses

BACKGROUND

Hepatic encephalopathy-induced hyperammonemia alters astrocytic glutamate metabolism in the brain, which is involved in cognitive decline. To identify specific therapeutic strategies for the treatment of hepatic encephalopathy, various molecular signaling studies, such as non-coding RNA functional study, have been conducted. However, despite several reports of circular RNAs (circRNAs) in the brain, few studies of circRNAs in hepatic encephalopathy-induced neuropathophysiological diseases have been conducted.

METHODS

In this study, we performed RNA sequencing to identify whether the candidate circRNA cirTmcc1 is specifically expressed in the brain cortex in a bile duct ligation (BDL) mouse model of hepatic encephalopathy.

RESULTS

Based on transcriptional and cellular analysis, we investigated the circTmcc1-dysregulation-induced changes in the expression of several genes that are associated with intracellular metabolism and astrocyte function. We found that the circTmcc1 binds with the NF-κB p65-CREB transcriptional complex and regulates the expression of the astrocyte transporter EAAT2. Furthermore, circTmcc1 contributed to the secretion of proinflammatory mediators and glutamate metabolism in astrocytes and subsequently modulated an improvement in spatial memory by mediating neuronal synaptic plasticity.

CONCLUSIONS

Thus, circTmcc1 may be a promising circRNA candidate for targeted interventions to prevent and treat the neuropathophysiological complications that occur due to hepatic encephalopathy.

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.

Gdnf Acts as a Germ Cell-Derived Growth Factor and Regulates the Zebrafish Germ Stem Cell Niche in Autocrine- and Paracrine-Dependent Manners

Glial cell line-derived neurotrophic factor (GDNF) and its receptor (GDNF Family Receptor α1-GFRα1) are well known to mediate spermatogonial stem cell (SSC) proliferation and survival in mammalian testes. In nonmammalian species, Gdnf and Gfrα1 orthologs have been found but their functions remain poorly investigated in the testes. Considering this background, this study aimed to understand the roles of the Gdnf-Gfrα1 signaling pathway in zebrafish testes by combining in vivo, in silico and ex vivo approaches. Our analysis showed that zebrafish exhibit two paralogs for Gndf (gdnfa and gdnfb) and its receptor, Gfrα1 (gfrα1a and gfrα1b), in accordance with a teleost-specific third round of whole genome duplication. Expression analysis further revealed that both ligands and receptors were expressed in zebrafish adult testes. Subsequently, we demonstrated that gdnfa is expressed in the germ cells, while Gfrα1a/Gfrα1b was detected in early spermatogonia (mainly in types A_und and A_diff) and Sertoli cells. Functional ex vivo analysis showed that Gdnf promoted the creation of new available niches by stimulating the proliferation of both type A_und spermatogonia and their surrounding Sertoli cells but without changing pou5f3 mRNA levels. Strikingly, Gdnf also inhibited late spermatogonial differentiation, as shown by the decrease in type B spermatogonia and down-regulation of dazl in a co-treatment with Fsh. Altogether, our data revealed that a germ cell-derived factor is involved in maintaining germ cell stemness through the creation of new available niches, supporting the development of spermatogonial cysts and inhibiting late spermatogonial differentiation in autocrine- and paracrine-dependent manners.

Testicular Hypoplasia with Normal Fertility in Neudesin-Knockout Mice

Neudesin is a secretory protein involved in the brain development during embryonic period and diet-induced development of adipose tissue. Although neudesin is also expressed in the testis, its physiological functions in the testis have not been documented. Therefore, we examined neudesin-encoding neuron-derived neurotrophic factor (Nenf) gene-knockout (Neudesin-KO) mice to clarify the functions of neudesin in the testis. The testicular size of the Neudesin-KO mice was significantly smaller than that of wild-type (WT) mice. However, histological analyses did not reveal any abnormalities in the testis, caput epididymis, and cauda epididymis. Sperm number in the cauda epididymis was comparable between WT and KO mice. Neudesin-KO male mice produced vaginal plugs on paired WT female mice, with a frequency similar to that in WT male mice. A similar number of embryos were developed in the females copulated with WT and Neudesin-KO males. Molecular analysis indicated that the ion transporters Slc19a1 and Kcnk3 were more expressed in the testis of Neudesin-KO mice than in the testis of WT mice, suggesting that the transport of ions and some nutrients in the testis has some abnormalities. Testicular size decreased on postnatal day 6, but not on the day of birth, indicating that neudesin is involved in the postnatal, but not embryonic, development of testis. These results indicate a novel role of neudesin in the development of testis.

FSH mediated cAMP signalling upregulates the expression of Gα subunits in pubertal rat Sertoli cells

Follicle Stimulating Hormone (FSH) acts via FSH-Receptor (FSH-R) by employing cAMP as the dominant secondary messenger in testicular Sertoli cells (Sc) to support spermatogenesis. Binding of FSH to FSH-R, results the recruitment of the intracellular GTP binding proteins, either stimulatory Gαs or inhibitory Gαi that in turn regulate cAMP production in Sc. The cytosolic concentration of cAMP being generated by FSH-R thereafter critically determines the downstream fate of the FSH signalling. The pleiotropic action of FSH due to differential cAMP output during functional maturation of Sc has been well studied. However, the developmental and cellular regulation of the Gα proteins associated with FSH-R is poorly understood in Sc. In the present study, we report the differential transcriptional modulation of the Gα subunit genes by FSH mediated cAMP signalling in neonatal and pubertal rat Sc. Our data suggested that unlike in neonatal Sc, both the basal and FSH/forskolin induced expression of Gαs, Gαi-1, Gαi-2 and Gαi-3 transcripts was significantly (p < 0.05) up-regulated in pubertal Sc. Further investigations involving treatment of Sc with selective Gαi inhibitor pertussis toxin, confirmed the elevated expression of Gi subunits in pubertal Sc. Collectively our results indicated that the high level of Gαi subunits serves as a negative regulator to optimize cAMP production in pubertal Sc.

Molecular Mechanisms and Signaling Pathways Involved in Sertoli Cell Proliferation

Sertoli cells are somatic cells present in seminiferous tubules which have essential roles in regulating spermatogenesis. Considering that each Sertoli cell is able to support a limited number of germ cells, the final number of Sertoli cells reached during the proliferative period determines sperm production capacity. Only immature Sertoli cells, which have not established the blood-testis barrier, proliferate. A number of hormonal cues regulate Sertoli cell proliferation. Among them, FSH, the insulin family of growth factors, activin, and cytokines action must be highlighted. It has been demonstrated that cAMP/PKA, ERK1/2, PI3K/Akt, and mTORC1/p70SK6 pathways are the main signal transduction pathways involved in Sertoli cell proliferation. Additionally, c-Myc and hypoxia inducible factor are transcription factors which participate in the induction by FSH of various genes of relevance in cell cycle progression. Cessation of proliferation is a pre-requisite to Sertoli cell maturation accompanied by the establishment of the blood-testis barrier. With respect to this barrier, the participation of androgens, estrogens, thyroid hormones, retinoic acid and opioids has been reported. Additionally, two central enzymes that are involved in sensing cell energy status have been associated with the suppression of Sertoli cell proliferation, namely AMPK and Sirtuin 1 (SIRT1). Among the molecular mechanisms involved in the cessation of proliferation and in the maturation of Sertoli cells, it is worth mentioning the up-regulation of the cell cycle inhibitors p21Cip1, p27Kip, and p19INK4, and of the gap junction protein connexin 43. A decrease in Sertoli cell proliferation due to administration of certain therapeutic drugs and exposure to xenobiotic agents before puberty has been experimentally demonstrated. This review focuses on the hormones, locally produced factors, signal transduction pathways, and molecular mechanisms controlling Sertoli cell proliferation and maturation. The comprehension of how the final number of Sertoli cells in adulthood is established constitutes a pre-requisite to understand the underlying causes responsible for the progressive decrease in sperm production that has been observed during the last 50 years in humans.

HIV-1 Tat protein promotes neuronal dysregulation by inhibiting E2F transcription factor 3 (E2F3)

Individuals who are infected with HIV-1 accumulate damage to cells and tissues (e.g. neurons) that are not directly infected by the virus. These include changes known as HIV-associated neurodegenerative disorder (HAND), leading to the loss of neuronal functions, including synaptic long-term potentiation (LTP). Several mechanisms have been proposed for HAND, including direct effects of viral proteins such as the Tat protein. Searching for the mechanisms involved, we found here that HIV-1 Tat inhibits E2F transcription factor 3 (E2F3), CAMP-responsive element-binding protein (CREB), and brain-derived neurotropic factor (BDNF) by up-regulating the microRNA miR-34a. These changes rendered murine neurons dysfunctional by promoting neurite retraction, and we also demonstrate that E2F3 is a specific target of miR-34a. Interestingly, bioinformatics analysis revealed the presence of an E2F3-binding site within the CREB promoter, which we validated with ChIP and transient transfection assays. Of note, luciferase reporter assays revealed that E2F3 up-regulates CREB expression and that Tat interferes with this up-regulation. Further, we show that miR-34a inhibition or E2F3 overexpression neutralizes Tat's effects and restores normal distribution of the synaptic protein synaptophysin, confirming that Tat alters these factors, leading to neurite retraction inhibition. Our results suggest that E2F3 is a key player in neuronal functions and may represent a good target for preventing the development of HAND.

Curative GnRHa treatment has an unexpected repressive effect on Sertoli cell specific genes

Background

Follicle stimulating hormone and testosterone stimulate Sertoli cells to support germ cell function and differentiation. During mini-puberty, when gonadotropin (GnRH) stimulates increases in plasma luteinizing hormone (LH) and testosterone levels, gonocytes are transformed into Ad spermatogonia. In cryptorchidism, impaired gonadotropin secretion during mini-puberty results in insufficient LH and testosterone secretion, impaired gonocyte transition to Ad spermatogonia, and perturbed Sertoli cell proliferation. Treatment with a gonadotropin-releasing hormone agonist (GnRHa/Buserelin) induced gonocytes to differentiate into Ad spermatogonia and rescued fertility. The present study evaluated the impact of low LH secretion on Sertoli cell function by comparing differential gene expression data between testes with low LH that lacked Ad spermatogonia (Ad-) and testes that completed mini-puberty (Ad+). Furthermore, we analyzed changes in the transcription of selected Sertoli cell specific genes in response to GnRHa treatment.

Results

Ad- testes showed reduced expression of nine out of 40 selected Sertoli cell specific genes compared to Ad+ testes. GnRHa treatment repressed most of the Sertoli cell specific genes, including the inhibins, but it increased the expression of genes that regulate apoptosis (FASLG) and proliferation (GDNF).

Conclusions

Impaired-minipuberty with decreased LH and testosterone levels affected Ad and Sertoli cell development through positive and negative regulation of morphoregulatory and apoptotic genes. GnRHa treatment had a repressive effect on most Sertoli cell specific genes, which suggested that Sertoli cells underwent a cellular rearrangement. We propose that gonadotropin-dependent increases in FASLG and GDNF expression drove Sertoli cell proliferation and germ cell self-renewal and supported the transition of gonocytes to Ad spermatogonia, independent of inhibins.

The role of testosterone in colorectal carcinoma: pathomechanisms and open questions

Colorectal cancer (CRC) is the fourth commonest type of malignancy after breast, lung and prostate in the USA and accounts for approximately 49,190 deaths annually in USA alone. The 5-year survival rate of CRC has increased over the past decades, in part, due to greater awareness and the widespread implementation of national screening programmes. Recently, a number of studies reported that males have a higher risk of developing CRC due to the action of testosterone. Testosterone is an androgen that is responsible for the development of male secondary sex characteristics and for spermatogenesis. Studies on rats with mutated Apc tumour-suppressor gene subjected to either ovariectomy or orchidectomy exhibit different risks of CRC. Female rats subjected to ovariectomy are at higher risk of CRC, whereas orchidectomised male rats exhibit a lower risk of developing CRC. Sex hormones, in particular estrogen and testosterone, play a significant role in the development of CRC since the anti-neoplastic effect of estrogen lost during ovariectomy increases the risk of females developing CRC. Male mice exposed to testosterone after orchidectomy were also at greater risk than those who were orchidectomised but administered placebo only. Moreover, the recently established role of membrane androgen receptors in regression of CRC via non-genomic androgen-dependent action sets these receptors apart from intracellular androgen receptors (iARs) which themselves promote CRC development. In addition, testosterone-albumin conjugates are selective to membrane androgen receptors (mARs) and lead to apoptosis via caspase-3 activation. Akt kinases promote invasion of colon cancer cells when phosphorylated. These kinases are dephosphorylated upon activation of mARs, thereby reducing colon cancer cell motility and invasiveness. Testosterone similarly plays important roles in human CRC. Long cytosine-adenine-guanine (CAG) repeats in the gene for the androgen receptors have been associated with a poor 5-year survival compared to shorter CAG repeats. Very recently, the measurement of serum unbound testosterone has been suggested as a novel biomarker along with carcinoembryonic antigen in CRC. In conclusion, testosterone may promote the development of CRC via a number of pathways, which may place males at greater risk. Testosterone holds promise as a potential biomarker in CRC risk prediction; however, further studies are required to better define its role in colorectal neoplasia.

NF-κB, CRE and YY1 elements are key functional regulators of CMV promoter-driven transient gene expression in CHO cells

Transient gene expression (TGE) in CHO cells is utilized to produce material for use in early stage drug development. These systems typically utilize the cytomegalovirus (CMV) promoter to drive recombinant gene transcription. In this study, we have mechanistically dissected CMV-mediated TGE in CHO cells in order to identify the key regulators of this process. An in silico analysis of the promoter composition of transcription factor regulatory elements (TFREs) and the CHO cell repertoire of transcription factors identified eight TFREs as likely effectors of CMV activity. We determined the regulatory function of these elements by preventing their cognate transcription factors from binding at the CMV promoter. This was achieved by both scrambling promoter binding site sequences and using decoy molecules to sequester intracellular transcription factors. We determined that the vast majority of CMV activity is mediated by just two discrete TFREs, showing that simultaneous inhibition of NF-κB and CRE-mediated transactivation reduced CMV-driven transient secreted alkaline phosphatase (SEAP) production by over 75%. Further, we identified a mechanism by which CMV-mediated TGE is negatively regulated in CHO cells, showing that inhibition of YY1-mediated transrepression increased SEAP production 1.5-fold. This work enables optimization and control of CMV-mediated TGE in CHO cells, in order to improve transient protein production yields.

Nociceptin and meiosis during spermatogenesis in postnatal testes

Phosphorylated Rec8, a key component of cohesin, mediates the association and disassociation, "dynamics," of chromosomes occurring in synaptonemal complex formation, crossover recombination, and sister chromatid cohesion during meiosis in germ cells. Yet, the extrinsic factors triggering meiotic chromosome dynamics remained unclear. In postnatal testes, follicle-stimulating hormone (FSH) acts directly on somatic Sertoli cells to activate gene expression via an intracellular signaling pathway composed of cAMP, cAMP-dependent protein kinase (PKA), and cAMP-response element-binding protein (CREB), and promotes germ cell development and spermatogenesis indirectly. Yet, the paracrine factors mediating the FSH effects to germ cells remained elusive. We have shown that nociceptin, known as a neuropeptide, is upregulated by FSH signaling through cAMP/PKA/CREB pathway in Sertoli cells of postnatal murine testes. Chromatin immunoprecipitation from Sertoli cells demonstrated that CREB phosphorylated at Ser133 associates with prepronociceptin gene encoding nociceptin. Analyses with Sertoli cells and testes revealed that both prepronociceptin mRNA and the nociceptin peptide are induced after FSH signaling is activated. In addition, the nociceptin peptide is induced in testes after 9 days post partum following FSH surge. Thus, our findings may identify nociceptin as a novel paracrine mediator of the FSH effects in the regulation of spermatogenesis; however, very little has known about the functional role of nociceptin in spermatogenesis. We have shown that nociceptin induces Rec8 phosphorylation, triggering chromosome dynamics, during meiosis in spermatocytes of postnatal murine testes. The nociceptin receptor Oprl-1 is exclusively expressed in the plasma membrane of testicular germ cells, mostly spermatocytes. Treatment of testes with nociceptin resulted in a rapid phosphorylation of Rec8. Injection of nociceptin into mice stimulated Rec8 phosphorylation and meiotic chromosome dynamics in testes, whereas injection of nocistatin, a specific inhibitor for nociceptin, abolished them. Therefore, our findings suggest that nociceptin is a novel extrinsic factor that plays a crucial role in the progress of meiosis during spermatogenesis.

Promoter analysis of the gene encoding GDNF in murine Sertoli cells

GDNF is a Sertoli-cell-derived factor that controls the balance between self-renewal and differentiation of the spermatogonial stem cells. Although research in recent years has concentrated on the impact of GDNF on target germ cells rather little attention has been paid to the molecular control of GDNF expression in Sertoli cells. Here, we aimed to characterize the promoter region of the mouse gdnf gene active in Sertoli cells. We identified the transcriptional start sites and analyzed the promoter activity of the 5'-flanking regions. By in-silico analysis of evolutionarily conserved DNA sequences we identified several putative transcription factor-binding regions. Deletion analysis showed the involvement of the three CRE sites for basal and cAMP-induced expression of gdnf in murine Sertoli cells. These results provide the basis for future studies to analyze how hormonal or paracrine signals modulate the transcriptional activity of gdnf in Sertoli cells.

NF-κB and CREB are required for angiotensin II type 1 receptor upregulation in neurons

Nuclear factor kappa B (NF-κB) and the Ets like gene-1 (Elk-1) are two transcription factors that have been previously established to contribute to the Angiotensin II mediated upregulation of Angiotensin II type 1 receptor (AT1R) in neurons. The cAMP response element binding protein (CREB) is another transcription factor that has also been implicated in AT1R gene transcription. The goal of the current study was to determine if NF-κB and CREB association was required for AT1R upregulation. We hypothesized that the transcription of the AT1R gene occurs via an orchestration of transcription factor interactions including NF-κB, CREB, and Elk-1. The synergistic role of CREB and NFκB in promoting AT1R gene expression was determined using siRNA-mediated silencing of CREB. Electrophorectic Mobility Shift Assay studies employing CREB and NF-κB demonstrated increased protein - DNA binding as a result of Ang II stimulation which was blunted by siRNA silencing of CREB. Upstream inhibition of p38 mitogen activated protein kinase (p38 MAPK) with SB203580 or inhibition of the calmodulin kinase (CAMK) pathway using KN-62 blunted changes in CREB and NF-κB expression. These findings suggest that Ang II may activate multiple signaling pathways involving p38 MAPK leading to the activation of NF-κB and CREB, which feed back to upregulate the AT1R gene. This study provides insight into the molecular mechanisms involving multiple transcription factor activation in a coordinated fashion which may be partially responsible for sympathoexcitation in clinical conditions associated with increased activation of the renin angiotensin system.

Different signal transduction pathways elicited by basic fibroblast growth factor and interleukin 1β regulate CREB phosphorylation in Sertoli cells

BACKGROUND AND AIM

Basic fibroblast growth factor (bFGF) and interleukin 1β (IL1β) belong to the set of intratesticular regulators that provide for the fine-tuning of processes implicated in the maintenance of spermatogenesis. The aim of this study was to investigate if bFGF and IL1β activate CREB, what signaling pathways may be participating and the possible relationship between CREB activation and the regulation of Sertoli cell function.

METHODS

Twenty-day-old rat Sertoli cell cultures were used.

RESULTS

Cultures stimulated with bFGF and IL1β produced a time-dependent increment in phosphorylated CREB levels that reached maximal values in 5- and 15-minute incubations respectively. MEK inhibitors--PD98059 and U0126--blocked the effect of bFGF on phosphorylated CREB while a p38-MAPK inhibitor--SB203580--blocked the effect of IL1β on phosphorylated CREB. A possible correlation between CREB regulation and two Sertoli cell-differentiated functions, Ldh A and transferrin expression, was explored. PD98059 blocked the ability of bFGF to stimulate Ldh A expression and SB203580 blocked the ability of IL1β to stimulate Ldh A expression and LDH activity. Concerning transferrin, PD98059 and U0126 were able to inhibit the ability of bFGF to stimulate its secre tion. On the contrary, SB203580 was unable to block IL1β induced increase in transferrin secretion suggesting that the p38-MAPK pathway does not participate in the mechanism of action of the cytokine to regulate transferrin.

CONCLUSIONS

The results presented herein suggest that CREB is stimulated in response to bFGF and IL1β through p42/p44-MAPK and p38-MAPK pathways and that this transcription factor may be partially responsible for the regulation of Sertoli cell function.

CREB, NF-κB, and NADPH oxidase coordinately upregulate indoxyl sulfate-induced angiotensinogen expression in proximal tubular cells

In chronic kidney disease (CKD), indoxyl sulfate, a uremic toxin, accumulates in serum, and the expression of angiotensinogen (AGT) is upregulated in renal proximal tubular cells. The present study aimed to determine the relationship between indoxyl sulfate and the upregulation of AGT expression in proximal tubular cells. Indoxyl sulfate induced expression of AGT in rat renal cortex and in cultured human proximal tubular cells (HK-2). In proximal tubular cells, indoxyl sulfate induced phosphorylation of cAMP response element-binding protein (CREB) on Ser-133, and small interfering RNA (siRNA) specific to CREB inhibited indoxyl sulfate-induced AGT expression. Our previous study demonstrated that indoxyl sulfate activated nuclear factor-κB (NF-κB) through reactive oxygen species (ROS) production. NF-κB inhibitors (pyrrolidine dithiocarbamate and isohelenin), NF-κB p65 siRNA, an antioxidant [ N-acetylcysteine (NAC)], and a nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibitor [diphenyleneiodonium (DPI)] suppressed indoxyl sulfate-induced AGT expression. Both NAC and DPI suppressed indoxyl sulfate-induced expression of NF-κB p65 and CREB. CREB siRNA suppressed indoxyl sulfate-induced NF-κB p65 expression, whereas both NF-κB inhibitors and NF-κB p65 siRNA prevented indoxyl sulfate-induced CREB expression. Furthermore, we focused on the expression of NADPH oxidase 4 (NOX4), because indoxyl sulfate induced NOX4 expression in vascular smooth muscle cells and vascular endothelial cells. Indoxyl sulfate induced the expression of NOX4 in proximal tubular cells, which was suppressed by NAC, DPI, NF-κB inhibitors, NF-κB p65 siRNA, and CREB siRNA. Taken together, CREB, NF-κB, and NOX4 coordinately upregulate indoxyl sulfate-induced AGT expression in proximal tubular cells.

Phytoestrogen genistein up-regulates endothelial nitric oxide synthase expression via activation of cAMP response element-binding protein in human aortic endothelial cells

We previously reported that genistein, a phytoestrogen, up-regulates endothelial nitric oxide synthase (eNOS) and prevents hypertension in rats that are independent of estrogen signaling machinery. However, how genistein regulates eNOS expression is unknown. In the present study, we show that genistein enhanced eNOS expression and NO synthesis in primary human aortic endothelial cells. Inhibition of extracellular signal regulated kinase, phosphoinositol-3 kinase, or protein kinase C did not affect genistein-enhanced eNOS expression and NO synthesis. However, chemical inhibition of protein kinase A (PKA) or adenoviral transfer of the specific endogenous PKA inhibitor gene completely abolished PKA activity and genistein-stimulated eNOS expression and NO production. Accordingly, genistein induced PKA activity and subsequent phosphorylation of cAMP response element (CRE)-binding protein (CREB) at Ser133. Suppression of CREB by small interfering RNA transfection abolished genistein-enhanced eNOS expression and NO production. Consistently, deletion of the CRE site within human eNOS promoter eliminated genistein-stimulated eNOS promoter activity. These findings provide the first evidence to our knowledge that genistein may play a beneficial role in vascular function through targeting the PKA/CREB/eNOS/NO signaling pathway.

Nociceptin is upregulated by FSH signaling in Sertoli cells in murine testes

In postnatal testes, follicle-stimulating hormone (FSH) acts on somatic Sertoli cells to activate gene expression directly via an intracellular signaling pathway composed of cAMP, cAMP-dependent protein kinase (PKA), and cAMP-response element-binding protein (CREB), and promotes germ cell development indirectly. Yet, the paracrine factors mediating the FSH effects to germ cells remained elusive. Here we show that nociceptin, known as a neuropeptide, is upregulated by FSH through cAMP/PKA/CREB pathway in Sertoli cells in murine testes. Chromatin immunoprecipitation from Sertoli cells shows that CREB phosphorylated at Ser133 associates with prepronociceptin gene encoding nociceptin. Analyses with Sertoli cells and testes demonstrates that both prepronociceptin mRNA and the nociceptin peptide are induced after FSH signaling is activated. In addition, the nociceptin peptide is induced in testes after 9days post partum following FSH surge. Thus, our findings may identify nociceptin as a novel paracrine mediator of the FSH effects in the regulation of spermatogenesis.

17Beta-estradiol signaling and regulation of proliferation and apoptosis of rat Sertoli cells

The aim of the present study was to investigate the intracellular signaling events downstream of the classical estrogen receptors (ESRs) and G protein-coupled estrogen receptor 1 (GPER) involved in regulation of proliferation and apoptosis of rat Sertoli cells, in which we have previously described ESR1, ESR2, and GPER. ESRs play a role in Sertoli cell proliferation, and GPER, but not ESRs, plays a role modulating gene expression involved with apoptosis. The present study shows that 17beta-estradiol (E2) and the GPER-selective agonist G-1 rapidly activate phosphatidylinositol 3-kinase (PIK3)/serine threonine protein kinase (AKT) and cyclic AMP response element-binding (CREB) phosphorylation. E2 and the ESR1-selective agonist 4,4',4″-(4-propyl-(1H)-pyrazole-1,3,5-triyl)trisphenol (PPT) increase the expression of cyclin D1 (CCND1), whereas the ESR2-selective agonist 2,3-bis(4-hydroxyphenyl)-propionitrile (DPN) and G-1 do not change the expression of this protein, suggesting that ESR1 is the upstream receptor regulating Sertoli cell proliferation. E2- or PPT-ESR1, through activation of epidermal growth factor receptor (EGFR)/mitogen-activated protein kinase 3/1 (MAPK3/1) and PIK3 pathways, induces upregulation of CCND1. KG-501, the compound that disrupts the phospho-CREB/CREB binding protein (CBP) complex, does not change E2- or PPT-ESR1-mediated CCND1 expression, suggesting that phospho-CREB/cyclic AMP response element/CBP is not involved in the expression of this protein. E2- or G-1-GPER, through activation of EGFR/MAPK3/1 and PIK3 pathways, may be involved in the upregulation of antiapoptotic proteins BCL2 and BCL2L2. E2- or G-1-GPER/EGFR/MAPK3/1/phospho-CREB decreases BAX expression. Taken together, these results show a differential effect of E2-GPER on the CREB-mediated transcription of proapoptotic and antiapoptotic genes of the same BCL2 gene family. ESR1 and GPER can mediate the rapid E2 actions in the Sertoli cells, which in turn can modulate nuclear transcriptional events important for Sertoli cell function and maintenance of normal testis development and homeostasis. Our findings are important to clarify the role of estrogen in a critical period of testicular development, and to direct further studies, which may contribute to better understanding of the causes of male infertility.

Antiapoptotic actions of exendin-4 against hypoxia and cytokines are augmented by CREB

Islets isolated from cadaveric donor pancreas are functionally viable and can be transplanted in diabetic patients to reduce insulin requirements. This therapeutic approach is less efficient because a significant portion of functional islets is lost due to oxidative stress, inflammation, and hypoxia. Exendin-4, a glucagon-like peptide-1 receptor agonist, is known to improve islet survival through activation of the transcription factor, cAMP response element binding protein (CREB). However, isolated human islets are exposed to several stresses known to down-regulate CREB. The objective of the present study was to determine whether the cytoprotective actions of exendin-4 in human islets can be augmented by increasing the levels of CREB. Simulation of ischemia/reperfusion injury and exposure to hypoxic conditions in cultured human islets resulted in decreased CREB activation and induction of apoptosis. Islets were transduced with adenoviral CREB followed by exposure to exendin-4 as a strategy for improving their survival. This combination increased the levels of several proteins needed for β-cell survival and function, including insulin receptor substrate-2, Bcl-2, and baculoviral IAP repeat-containing 3, and suppressed the expression of proapoptotic and inflammatory genes. A combination of CREB and exendin-4 exerted enhanced antiapoptotic action in cultured islets against hypoxia and cytokines. More significantly, transplantation of human islets transduced with adenoviral CREB and treated with exendin-4 showed improved glycemic control over a 30-d period in diabetic athymic nude mice. These observations have significant implications in the therapeutic potential of exendin-4 and CREB in the islet transplantation setting as well as in preserving β-cell mass of diabetic patients.

Upstream stimulatory factor induces Nr5a1 and Shbg gene expression during the onset of rat Sertoli cell differentiation

Within the testis, each Sertoli cell can support a finite number of developing germ cells. During development, the cessation of Sertoli cell proliferation and the onset of differentiation establish the final number of Sertoli cells and, thus, the total number of sperm that can be produced. The upstream stimulatory factors 1 and 2 (USF1 and USF2, respectively) differentially regulate numerous Sertoli cell genes during differentiation. To identify genes that are activated by USF proteins during differentiation, studies were conducted in Sertoli cells isolated from 5- and 11-day-old rats, representing proliferating and differentiating cells, respectively. Usf1 mRNA and USF1 protein levels were increased between 5 and 11 days after birth. In vitro studies revealed that USF1 and USF2 DNA-binding activity also increased at 11 days for the promoters of four potential target genes, Fshr, Gata4, Nr5a1, and Shbg. Chromatin immunoprecipitation assays confirmed that USF recruitment increased in vivo between 5 and 11 days after birth at the Fshr, Gata4, and Nr5a1 promoters. Expression of Nr5a1 and Shbg, but not of Fshr or Gata4, mRNAs was elevated in 11-day-old Sertoli cells compared with 5-day-old Sertoli cells. Transient transfection of USF1 and USF2 expression vectors up-regulated Nr5a1 and Shbg promoter activity. RNA interference assays demonstrated that USF1 and USF2 contribute to Nr5a1 and Shbg expression in differentiating cells. Together, these data indicate that increased USF levels induce the expression of Nr5a1 and Shbg during the differentiation of Sertoli cells, whereas Fshr and Gata4 expression is not altered by USF proteins during differentiation.

Regulation of Sertoli-germ cell adhesion and sperm release by FSH and nonclassical testosterone signaling

Testosterone and FSH act in synergy to produce the factors required to maximize the production of spermatozoa and male fertility. However, the molecular mechanisms by which these hormones support spermatogenesis are not well established. Recently, we identified a nonclassical mechanism of testosterone signaling in cultured rat Sertoli cells. We found that testosterone binding to the androgen receptor recruits and activates Src tyrosine kinase. Src then causes the activation of the epidermal growth factor receptor, which results in the phosphorylation and activation of the ERK MAPK and the cAMP response element-binding protein transcription factor. In this report, we find that FSH inhibits testosterone-mediated activation of ERK and the MAPK pathway in Sertoli cells via the protein kinase A-mediated inhibition of Raf kinase. In addition, FSH, as well as inhibitors of Src and ERK kinase activity, reduced germ cell attachment to Sertoli cells in culture. Using pathway-specific androgen receptor mutants we found that the nonclassical pathway is required for testosterone-mediated increases in germ cell attachment to Sertoli cells. Studies of seminiferous tubule explants determined that Src kinase, but not ERK kinase, activity is required for the release of sperm from seminiferous tubule explants. These findings suggest the nonclassical testosterone-signaling pathway acts via Src and ERK kinases to facilitate the adhesion of immature germ cells to Sertoli cells and through Src to permit the release of mature spermatozoa. In contrast, FSH acts to limit testosterone-mediated ERK kinase activity and germ cell attachment.

Effects of the A(-115)G variant on CREB1 promoter activity in two brain cell lines: Interactions with gonadal steroids

Major depressive disorder (MDD) is a leading contributor to disease burden worldwide. Previous genetic studies have revealed significant evidence of linkage of the CREB1 region to mood disorders among women from families with recurrent, early-onset MDD (RE-MDD), a severe and familial subtype of MDD. Systematic resequencing of the CREB1 gene in affected members of these families has identified rare sequence variants at positions -656 and -115 that appear to cosegregate with unipolar mood disorders in two large multigenerational families and three small nuclear families, respectively. Results from previous transfection experiments that employed constructs containing the wild-type or variant CREB1 promoters coupled to a reporter gene support the hypothesis that the A(-656) allele contributes to the development of MDD in women by selectively increasing the activity of the CREB1 promoter in brain cell lines exposed to 17 β-estradiol. Analogous transfection experiments described in the current study revealed that the G(-115) promoter variant reduced promoter activity in CATH.a neuronal cells regardless of the hormonal environment, consistent with the observation that increased risk for unipolar mood disorders conferred by this allele was not limited by sex. The effects of CREB1 promoter variants on promoter activity, their influence on the development of mood disorders and related clinical features, and the interaction of their phenotypic expression with sex seem likely to be complex and allele-specific rather than a general property of the CREB1 locus. © 2010 Wiley-Liss, Inc.

Non-classical actions of testosterone and spermatogenesis

Testosterone is essential to maintain spermatogenesis and male fertility. In the absence of testosterone stimulation, spermatogenesis does not proceed beyond the meiosis stage. After withdrawal of testosterone, germ cells that have progressed beyond meiosis detach from supporting Sertoli cells and die, whereas mature sperm cannot be released from Sertoli cells resulting in infertility. The classical mechanism of testosterone action in which testosterone activates gene transcription by causing the androgen receptor to translocate to and bind specific DNA regulatory elements does not appear to fully explain testosterone regulation of spermatogenesis. This review discusses two non-classical testosterone signalling pathways in Sertoli cells and their potential effects on spermatogenesis. Specifically, testosterone-mediated activation of phospholipase C and calcium influx into Sertoli cells is described. Also, testosterone activation of Src, EGF receptor and ERK kinases as well as the activation of the CREB transcription factor and CREB-mediated transcription is reviewed. Regulation of germ cell adhesion to Sertoli cells and release of mature sperm from Sertoli cells by kinases regulated by the non-classical testosterone pathway is discussed. The evidence accumulated suggests that classical and non-classical testosterone signalling contribute to the maintenance of spermatogenesis and male fertility.

Activity of retinoic acid receptor-alpha is directly regulated at its protein kinase A sites in response to follicle-stimulating hormone signaling

Retinoic acid receptor-alpha (RARA) is crucial for germ cell development in the testis, as shown by the degenerated testis in Rara gene knockout mice, which are sterile. Similarly, FSH is known to regulate Sertoli cell proliferation and differentiation, indirectly controlling the quantity of the spermatogenic output. Interestingly, FSH inhibited, via activation of FSH receptor, cAMP, and protein kinase A (PKA), the nuclear localization and transcriptional activity of RARA. Given that retinoic acid, the ligand for RARA, is known to regulate cell proliferation and differentiation, we investigated whether FSH regulates RARA by a direct posttranslational phosphorylation mechanism. Mutagenesis of serine 219 (S219) and S369 at the PKA sites on RARA to either double alanines or double glutamic acids showed that both PKA sites are important for RARA activity. The negative charges at the PKA sites, whether they are from glutamic acids or phosphorylation of serines, decreased the nuclear localization of RARA, heterodimerization with retinoid X receptor-alpha, and the transcriptional activity of the receptor. On the other hand, the double-alanine mutant that cannot be phosphorylated at the 219 and 369 amino acid positions did not respond to cAMP and PKA activation. Wild-type and double-mutant RARA interacted with PKA, but only in the presence of cAMP or FSH. These results together suggest that FSH may regulate cell proliferation and differentiation of Sertoli cells, at least partially, by directly affecting the PKA sites of RARA and controlling the transcriptional function of the receptor.

Effects of the G(-656)A variant on CREB1 promoter activity in a neuronal cell line: interactions with gonadal steroids and stress

Major depressive disorder (MDD) constitutes a major public health problem worldwide and affects women twice as frequently as men. Previous genetic studies have revealed significant evidence of linkage of the cAMP-responsive element-binding protein 1 (CREB1) gene region (2q33-35) to mood disorders among women from families with recurrent, early-onset MDD (RE-MDD), a severe and familial subtype of MDD. A rare G-to-A transition at position -656 in the CREB1 promoter co-segregates with mood disorders in women from these families, implicating CREB1 as a sex-related susceptibility gene for unipolar mood disorders. In the current study, the functional significance of the CREB1 promoter variant was determined using transfection experiments that employed plasmid constructs containing the wild-type or variant CREB1 promoters coupled to a reporter gene. The results support the hypothesis that the A(-656) allele contributes to the development of MDD in women through selective alteration of CREB1 promoter activity by female gonadal steroids in noradrenergic neuronal cells. Furthermore, exaggeration of these effects during a simulated stress condition may be relevant to reported gene-environment interactions that contribute to the emergence of MDD in clinical populations.

USF1/2 transcription factor DNA-binding activity is induced during rat Sertoli cell differentiation

Each Sertoli cell can support a finite number of developing germ cells. During development of the testis, the cessation of Sertoli cell proliferation and the onset of differentiation determine the final number of Sertoli cells and, hence, the number of sperm that can be produced. We hypothesize that the transition from proliferation to differentiation is facilitated by E-box transcription factors that induce the expression of differentiation-promoting genes. The relative activities of E-box proteins were studied in primary Sertoli cells isolated from 5-, 11-, and 20-day-old rats, representing proliferating, differentiating, and differentiated cells, respectively. E-box DNA-binding activity is almost undetectable 5 days after birth but peaks with initiation of differentiation 11 days after birth and remains elevated. Upstream stimulatory factors 1 and 2 (USF1 and USF2) were found to be the predominant E-box proteins present within DNA-protein complexes formed after incubating E-box-containing probes with nuclear extracts from developing Sertoli cells. The known potentiator of Sertoli cell differentiation, thyroxine, increases USF DNA-binding activity in Sertoli cells before differentiation (5-day-old Sertoli cells) but not after differentiation is initiated (11- and 20-day-old Sertoli cells). The developmental-specific increase in USF1 and USF2 DNA-binding activity may facilitate the switch from proliferation to differentiation and, thus, determine the ultimate number of Sertoli cells present within the testes and the upper limit of fertility.

CREB, ATF, and AP-1 transcription factors regulate IFN-gamma secretion by human T cells in response to mycobacterial antigen

IFN-gamma production by T cells is pivotal for defense against many pathogens, and the proximal promoter of IFN-gamma, -73 to -48 bp upstream of the transcription start site, is essential for its expression. However, transcriptional regulation mechanisms through this promoter in primary human cells remain unclear. We studied the effects of cAMP response element binding protein/activating transcription factor (CREB/ATF) and AP-1 transcription factors on the proximal promoter of IFN-gamma in human T cells stimulated with Mycobacterium tuberculosis. Using EMSA, supershift assays, and promoter pulldown assays, we demonstrated that CREB, ATF-2, and c-Jun, but not cyclic AMP response element modulator, ATF-1, or c-Fos, bind to the proximal promoter of IFN-gamma upon stimulation, and coimmunoprecipitation indicated the possibility of interaction among these transcription factors. Chromatin immunoprecipitation confirmed the recruitment of these transcription factors to the IFN-gamma proximal promoter in live Ag-activated T cells. Inhibition of ATF-2 activity in T cells with a dominant-negative ATF-2 peptide or with small interfering RNA markedly reduced the expression of IFN-gamma and decreased the expression of CREB and c-Jun. These findings suggest that CREB, ATF-2, and c-Jun are recruited to the IFN-gamma proximal promoter and that they up-regulate IFN-gamma transcription in response to microbial Ag. Additionally, ATF-2 controls expression of CREB and c-Jun during T cell activation.

Effects of the G(-656)A variant on CREB1 promoter activity in a glial cell line: interactions with gonadal steroids and stress

Major depressive disorder (MDD) constitutes a major public health problem worldwide and affects women twice as frequently as men. Previous genetic studies have revealed significant evidence of linkage of the CREB1 region to mood disorders among women from families with recurrent, early-onset MDD (RE-MDD), a severe and familial subtype of MDD. A rare G to A transition at position -656 in the CREB1 promoter cosegregates with mood disorders in women from these families, implicating CREB1 as a sex-related susceptibility gene for unipolar mood disorders. In the current study, the functional significance of the CREB1 promoter variant was determined using transfection experiments that employed constructs containing the wild-type or variant CREB1 promoters coupled to a reporter gene. The results support the hypothesis that the A(-656) allele contributes to the development of MDD in women by selectively altering the activity of the CREB1 promoter in glial cells exposed to 17 beta-estradiol. Furthermore, the exaggeration of this effect during a simulated stress condition may be relevant to reported gene-environment interactions that contribute to the emergence of MDD in clinical populations. The results of in silico analysis revealed four putative binding sites for transcription factors that are affected by the G to A transition at position -656, of which CP2 best fit the experimental observations.

Sp1 up-regulates cAMP-response-element-binding protein expression during retinoic acid-induced mucous differentiation of normal human bronchial epithelial cells

CREB [CRE (cAMP-response element)-binding protein] is an important transcription factor that is differentially regulated in cells of various types. We recently reported that RA (retinoic acid) rapidly activates CREB without using RARs (RA receptors) or RXRs (retinoid X receptors) in NHTBE cells (normal human tracheobronchial epithelial cells). However, little is known about the role of RA in the physiological regulation of CREB expression in the early mucous differentiation of NHTBE cells. In the present study, we report that RA up-regulates CREB gene expression and that, using 5'-serial deletion promoter analysis and mutagenesis analyses, two Sp1 (specificity protein 1)-binding sites located at nt -217 and -150, which flank the transcription initiation site, are essential for RA induction of CREB gene transcription. Furthermore, we found that CREs located at nt -119 and -98 contributed to basal promoter activity. Interestingly, RA also up-regulated Sp1 in a time- and dose-dependent manner. Knockdown of endogenous Sp1 using siRNA (small interfering RNA) decreased RA-induced CREB gene expression. However, the converse was not true: knockdown of CREB using CREB siRNA did not affect RA-induced Sp1 gene expression. We conclude that RA up-regulates CREB gene expression during the early stage of NHTBE cell differentiation and that RA-inducible Sp1 plays a major role in up-regulating human CREB gene expression. This result implies that co-operation of these two transcription factors plays a crucial role in mediating early events of normal mucous cell differentiation of bronchial epithelial cells.

Chronic CXCL10 alters the level of activated ERK1/2 and transcriptional factors CREB and NF-kappaB in hippocampal neuronal cell culture

Signal transduction pathways may be important targets of chemokines during neuroinflammation. In the current study, Western blot analyses show that in rat hippocampal neuronal/glial cell cultures chronic CXCL10 increases the level of protein for ERK1/2 as well as for the transcriptional factors CREB and NF-kappaB. Bcl-2, an anti-apoptotic protein whose expression can be regulated by a pathway involving ERK1/2, CREB and NF-kappaB, was also increased in the CXCL10 treated cultures. These results implicate a role for ERK1/2, CREB and NF-kappaB in effects of CXCL10 on hippocampal cells and suggest that chronic CXCL10 may have a protective role during certain neuroinflammatory conditions.

Dynamics of a minimal model of interlocked positive and negative feedback loops of transcriptional regulation by cAMP-response element binding proteins

cAMP-response element binding (CREB) proteins are involved in transcriptional regulation in a number of cellular processes (e.g., neural plasticity and circadian rhythms). The CREB family contains activators and repressors that may interact through positive and negative feedback loops. These loops can be generated by auto- and cross-regulation of expression of CREB proteins, via CRE elements in or near their genes. Experiments suggest that such feedback loops may operate in several systems (e.g., Aplysia and rat). To understand the functional implications of such feedback loops, which are interlocked via cross-regulation of transcription, a minimal model with a positive and negative loop was developed and investigated using bifurcation analysis. Bifurcation analysis revealed diverse nonlinear dynamics (e.g., bistability and oscillations). The stability of steady states or oscillations could be changed by time delays in the synthesis of the activator (CREB1) or the repressor (CREB2). Investigation of stochastic fluctuations due to small numbers of molecules of CREB1 and CREB2 revealed a bimodal distribution of CREB molecules in the bistability region. The robustness of the stable HIGH and LOW states of CREB expression to stochastic noise differs, and a critical number of molecules was required to sustain the HIGH state for days or longer. Increasing positive feedback or decreasing negative feedback also increased the lifetime of the HIGH state, and persistence of this state may correlate with long-term memory formation. A critical number of molecules was also required to sustain robust oscillations of CREB expression. If a steady state was near a deterministic Hopf bifurcation point, stochastic resonance could induce oscillations. This comparative analysis of deterministic and stochastic dynamics not only provides insights into the possible dynamics of CREB regulatory motifs, but also demonstrates a framework for understanding other regulatory processes with similar network architecture.

Role of the basic helix-loop-helix protein ITF2 in the hormonal regulation of Sertoli cell differentiation

Sertoli cells are a post-mitotic terminally differentiated cell population that forms the seminiferous tubules in the adult testis and provides the microenvironment and structural support for developing germ cells. During pubertal development, Sertoli cells are responsive to follicle-stimulating hormone (FSH) to promote the expression of differentiated gene products. The basic helix-loop-helix (bHLH) and inhibitors of differentiation (Id) transcription factors are involved in the differentiation of a variety of cell lineages during development. Both bHLH and Id transcription factors have been identified in Sertoli cells. A yeast two-hybrid screen was conducted using a rat Sertoli cell cDNA library to identify bHLH dimerization partners for the Id1 transcription factor. The ubiquitous bHLH protein ITF2 (i.e., E2-2) was identified as one of the interacting partners. The current study investigates the expression and function of ITF2 in Sertoli cells. ITF2 was found to be ubiquitously expressed in all testicular cell types including germ cells, peritubular myoid cells, and Sertoli cells. Stimulation of cultured Sertoli cells with FSH or dibutryl cAMP resulted in a transient decrease in expression of ITF2 mRNA levels followed by a rise in expression with FSH treatment. ITF2 expression was at its highest in mid-pubertal 20-day-old rat Sertoli cells. ITF2 was found to directly bind to negative acting Id HLH proteins and positive acting bHLH proteins such as scleraxis. Transient overexpression of ITF2 protein in cultured Sertoli cells stimulated transferrin promoter activity, which is a marker of Sertoli cell differentiation. Co-transfections of ITF2 and Id proteins sequestered the inhibitory effects of the Id family of proteins. Observations suggest ITF2 can enhance FSH actions through suppressing the inhibitory actions of the Id family of proteins and increasing the actions of stimulatory bHLH proteins (i.e., scleraxis) in Sertoli cells.

A multistep kinase-based sertoli cell autocrine-amplifying loop regulates prostaglandins, their receptors, and cytokines

In Sertoli epithelial cells, the IL-1beta induces prostaglandins (PG) PGE(2), PGF(2alpha) and PGI(2) (7-, 11-, and 2-fold, respectively), but not PGD(2), production. Cyclohexamide pretreatment inhibiting protein synthesis prevents IL-1beta increases in PG levels, indicating that induction requires de novo protein synthesis. IL-1beta-regulated PGE(2) and PGF(2alpha) production and cytokine expression require activation of cyclooxygenase-2 (COX-2) and c-Jun NH(2)-terminal kinase, as shown using specific enzyme inhibition. PGE(2) and PGF(2alpha) stimulate expression of IL-1alpha, -1beta, and -6, findings consistent with PG involvement in IL signaling within the seminiferous tubule. PGE(2) and PGF(2alpha) reverse COX-2-mediated inhibition of IL-1beta induction of cytokine expression and PG production. Sertoli PG receptor expression was determined; four known E-prostanoid receptor (EP) subtypes (1-4) and the F-prostanoid and prostacyclin prostanoid receptors were demonstrated using RNA and protein analyses. Pharmacological characterization of Sertoli PG receptors associated with cytokine regulation was ascertained by quantitative real-time RT-PCR analyses. IL-1beta regulates both EP(2) mRNA and protein levels, data consistent with a regulatory feedback loop. Butaprost (EP(2) agonist) and 11-deoxy PGE(1) (EP(2) and EP(4) agonist) treatments show that EP(2) receptor activation stimulates Sertoli cytokine expression. Consistent with EP(2)-cAMP signaling, protein kinase A inhibition blocks both IL-1beta- and PGE(2)-induced cytokines. Together, the data indicate an autocrine-amplifying loop involving IL-1beta-regulated Sertoli function mediated by COX-2-induced PGE(2) and PGF(2alpha) production. PGE(2) activates EP(2) and/or EP(4) receptor(s) and the protein kinase A-cAMP pathway; PGF(2alpha) activates F-prostanoid receptor-protein kinase C signaling. Further identification of the molecular mechanisms subserving these mediators may offer new insights into physiological events as well as proinflammatory-mediated pathogenesis in the testis.

Role of the basic helix-loop-helix transcription factor, scleraxis, in the regulation of Sertoli cell function and differentiation

Sertoli cells are a postmitotic terminally differentiated cell population in the adult testis that form the seminiferous tubules and provide the microenvironment and structural support for developing germ cells. The transcription factors that regulate Sertoli cell differentiation remain to be elucidated. The basic helix-loop-helix transcription factors are involved in the differentiation of a variety of cell lineages during development and are expressed in pubertal Sertoli cells. A yeast-two-hybrid procedure was used to screen a Sertoli cell library from 20-d-old pubertal rats to identify dimerization partners with the ubiquitous E47 basic helix-loop-helix transcription factor. Scleraxis was identified as one of the interacting partners. Among the cell types of the testis, scleraxis expression was found to be specific to Sertoli cells. Analysis of the expression pattern of scleraxis mRNA in developing Sertoli cells revealed an increase in scleraxis message at the onset of puberty. Sertoli cells respond to FSH to promote expression of differentiated gene products such as transferrin that aid in proper development of the germ cells. Analysis of the hormonal regulation of scleraxis expression revealed a 4-fold increase in scleraxis mRNA in response to the presence of FSH or dibutryl cAMP in cultured Sertoli cells. An antisense oligonucleotide procedure and overexpression analysis were used to determine whether scleraxis regulates the expression of Sertoli cell differentiated gene products. An antisense oligonucleotide to scleraxis down-regulated transferrin promoter activity in Sertoli cells. A transient overexpression of scleraxis in Sertoli cells stimulated transferrin and androgen binding protein promoter activities and the expression of a number of differentiated genes. Observations suggest scleraxis functions in a number of adult tissues and is involved in the regulation and maintenance of Sertoli cell function and differentiation. This is one of the first adult and nontendon/chondrocyte-associated functions described for scleraxis.

Identification, Characterization, and Functional Analysis of Sp1 Transcript Variants Expressed in Germ Cells During Mouse Spermatogenesis1

The SP family of zinc-finger transcription factors are important mediators of selective gene activation during embryonic development and cellular differentiation. SP-binding GC-box domains are common cis-regulatory elements present in the promoters of several genes expressed in a developmentally specific manner in differentiating mouse germ cells. Four Sp1 cDNAs were isolated from a mouse pachytene spermatocyte cDNA library and characterized by DNA sequence analysis. Northern blot studies revealed that these cDNAs corresponded to 3 full-length Sp1 transcripts (4.1, 3.7, and 3.2 kilobases [kb]) and an additional 1.4-kb 5'-truncated Sp1 transcript that are temporally expressed during spermatogenesis. Quantitative real-time polymerase chain reaction studies verified that the highest levels of Sp1 transcript expression of 4.1, 3.7, and 3.2 kb occur in the primary spermatocytes. The spatial and temporal expression patterns of these Sp1 transcripts and their encoded 60-kDa and 90-kDa SP1 proteins were demonstrated using in situ hybridization and immunohistochemical analyses. To assess the transcriptional properties of these SP1 transcription factors, SP-deficient Drosophila SL2 cells were stably transfected with the respective Sp1 cDNA expression vectors and cotransfected with either Ldh2, Ldh3, or Creb promoter/luciferase reporter constructs. The levels of SP-mediated luciferase expression observed depended on the structure of the glutamine-rich transactivation domains and the number of GC-box elements present in the respective promoters. The alterations observed in germ cells in the patterns of expression of the Sp1 transcripts encoding the 60-kDa and 90-kDa SP1 isoforms suggest that these SP1 factors may be involved in mediating stage-specific and cell type-specific gene expression during mouse spermatogenesis.

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.

Testosterone activates mitogen-activated protein kinase and the cAMP response element binding protein transcription factor in Sertoli cells

The androgen testosterone is essential for the Sertoli cell to support the maturation of male germ cells and the production of spermatozoa (spermatogenesis). In the classical view of androgen action, binding of androgen to the intracellular androgen receptor (AR) produces a conformational change in AR such that the receptor-steroid complex has high affinity for specific DNA regulatory elements and is able to stimulate gene transcription. Here, we demonstrate that testosterone can act by means of an alternative, rapid, and sustainable mechanism in Sertoli cells that is independent of AR-DNA interactions. Specifically, the addition of physiological levels of testosterone to Sertoli cells stimulates the mitogen-activated protein kinase signaling pathway and causes phosphorylation of the cAMP response element binding protein transcription factor on serine 133, a modification known to be required for Sertoli cells to support spermatogenesis. Androgen-mediated activation of mitogen-activated protein kinase and cAMP response element binding protein occurs within 1 min, extends for at least 12 h and requires AR. Furthermore, androgen induces endogenous cAMP response element binding protein-mediated transcription in Sertoli cells. These newly identified mechanisms of androgen action in Sertoli cells suggest new targets for developing male contraceptive agents.

The Id2 transcriptional repressor is induced by follicle-stimulating hormone and cAMP

Id (inhibitor of DNA binding/differentiation) proteins repress differentiation and promote cell division by dimerizing with and inhibiting the action of basic helix-loop-helix transcription factors including those that bind to E-box motifs. Of the four characterized Id proteins, only Id2 is found in the nucleus of Sertoli cells that support the development of spermatozoa in the testis. Differential display analysis of rat primary Sertoli cell mRNA identified Id2 as being inducible by forskolin, a stimulator of cAMP production. Northern blot analysis confirmed that Id2 mRNA expression peaked in Sertoli cells 6-12 h after stimulation with forskolin or follicle-stimulating hormone (FSH), the major physiological stimulator of cAMP in Sertoli cells. Similarly, Id2 promoter activity in Sertoli cells was induced after forskolin or FSH stimulation as well as by overexpression of protein kinase A. Forskolin induction of the Id2 promoter required sequences located between positions -122 and -82. Protein(s) of 40-45 kDa were found to bind two activated transcription factor/cAMP-response element-like sites and a GATA motif within the regulatory region. The induction of the Id2 gene by FSH corresponded with a decrease in protein binding to an E-box consensus motif and decreased E-box-mediated transcription. Together, these findings raise the possibility that FSH-mediated induction of Id2 and resultant inhibition of basic helix-loop-helix transcription factor-regulated genes in Sertoli cells may contribute to the regulation of spermatogenesis.

Regulation of cyclic adenosine 3',5'-monophosphate response element binding protein (CREB) expression by Sp1 in the mammalian testis

In the mammalian testis, the binding of FSH to Sertoli cells activates the cAMP-dependent protein kinase A signaling pathway, resulting in the phosphorylation of the cAMP response element binding protein (CREB). Previous studies have also shown that CREB gene expression is activated by cAMP in Sertoli cells and that 2 cAMP response elements (CREs) that bind CREB and a neighboring Sp1 binding site are required for basal and cAMP-inducible CREB promoter activity. In contrast, CREB expression has been less well characterized in testis germ cells. We demonstrated that CREB and Sp1 are expressed in early germ cells only through the midpachytene stage of spermatogenesis. Furthermore, CREB promoter activity was induced over 70-fold by transient overexpression of Sp1 in SL2 cells, suggesting that Sp1 is an important regulator of CREB expression. Further studies of the CREB promoter revealed an additional regulatory element in the -130 region between the Sp1 and CREB transcription factor binding sites that is necessary for full promoter activity. Proteins expressed in Sertoli cells and germ cells bind specifically to the newly identified regulatory region. These studies suggest that proteins binding to Sp1 motifs and the -130 region are required to activate the CREB promoter.

Activating transcription factor 1 and CREB are important for cell survival during early mouse development

Activating transcription factor 1 (ATF1), CREB, and the cyclic AMP (cAMP) response element modulatory protein (CREM), which constitute a subfamily of the basic leucine zipper transcription factors, activate gene expression by binding as homo- or heterodimers to the cAMP response element in regulatory regions of target genes. To investigate the function of ATF1 in vivo, we inactivated the corresponding gene by homologous recombination. In contrast to CREB-deficient mice, which suffer from perinatal lethality, mice lacking ATF1 do not exhibit any discernible phenotypic abnormalities. Since ATF1 and CREB but not CREM are strongly coexpressed during early mouse development, we generated mice deficient for both CREB and ATF1. ATF1(-/-) CREB(-/-) embryos die before implantation due to developmental arrest. ATF1(+/-) CREB(-/-) embryos display a phenotype of embryonic lethality around embryonic day 9.5 due to massive apoptosis. These results indicate that CREB and ATF1 act in concert to mediate signals essential for maintaining cell viability during early embryonic development.

Cyclic AMP regulates expression of the RI alpha subunit of cAMP-dependent protein kinase through an alternatively spliced 5' UTR

The present study examines novel mechanisms that regulate levels of the RI alpha subunit of cAMP-dependent protein kinase. We found that RI alpha protein is induced threefold by 8-(4-chlorophenyl)thio-cAMP in hormone responsive rat Sertoli cells, while total RI alpha mRNA is not correspondingly induced. Two RI alpha mRNA isoforms with different 5' untranslated sequences (RI alpha 1a and RI alpha 1b) are produced from the RI alpha gene in Sertoli cells. Deletion/mutation analysis of the cAMP-response-element-containing promoter upstream of the RI alpha exon 1b revealed that while mutation of the cAMP response element had no effects on cAMP-mediated induction, a 73-bp region of the RI alpha exon 1b itself conferred a fivefold to eightfold induction of reporter activity to homologous and heterologous promoters. The responsiveness of this region was dependent on a sense orientation downstream of the promoter start sites and had no effect on reporter mRNA, indicating that the cAMP-mediated induction occurs at the post-transcriptional level. Modeling of the RI alpha 1b 5' UTR secondary structure revealed a 5' CAP-proximal, strong stem-loop presenting an element similar to multiple start-site element downstream-1 (GCTCGG) in the loop region. RNA-EMSAs performed with the labeled RI alpha 1b 5' UTR showed stabilization of a protein/RNA complex in extracts from 8-(4-chlorophenyl)thio-cAMP stimulated Sertoli cells. This complex was abolished by mutation of the multiple start-site element downstream-1-like element. Our findings indicate that there is a cAMP-mediated induction of RI alpha expression at the post-transcriptional level, dependent on the 5' UTR of RI alpha 1b mRNA.

Role of the transcriptional coactivator CBP/p300 in linking basic helix-loop-helix and CREB responses for follicle-stimulating hormone-mediated activation of the transferrin promoter in Sertoli cells

Sertoli cells are the epithelial cells responsible for the onset of pubertal development and the maintenance of spermatogenesis in the adult. Transferrin is one of the major secretory products expressed by differentiated Sertoli cells. Investigation of the transcriptional control of transferrin gene expression provides insight regarding the regulation of Sertoli cell differentiation. The optimal activation of the mouse transferrin promoter (mTf) by FSH requires the synergistic actions of the cAMP response element-binding protein (CREB) binding to the cAMP response element-like proximal region II (PRII) and the basic helix-loop-helix (bHLH) binding to the E-box. Proximal region II alone is sufficient for cAMP-mediated activation. The proximity of the PRII and E-box (220 base pairs apart) suggests the possibility of interaction between CREB and bHLH proteins. Such an interaction can be mediated by transcriptional integrators such as CREB-binding protein (CBP) and/or p300 and may stabilize the binding of trans-acting factors to their respective cis-elements. Such an interaction may also provide a mechanism for cell-specific promoter activation. The hypothesis tested in this study was that CBP/p300 is required for the synergistic activation of the transferrin promoter involving PRII and E-box through the formation of a ternary complex. In the Sertoli cells, both CBP and p300 proteins are expressed. The effect of CBP/p300 on transferrin promoter activation and, hence, Sertoli cell function was studied by using antisense oligonucleotides (AS-oligo). In the presence of CBP/p300 AS-oligo, activity of the FSH-induced mTf-chloramphenicol acetyl transferase (CAT) was significantly lower as compared to the respective controls. Interestingly, AS-oligo had no effect on cAMP-induced activation of the transferrin promoter reporter construct (mTf-CAT). Mutations in the E-box (EB*) significantly reduced the FSH response. The presence of AS-oligo had no further effect on the FSH-mediated activation of the EB*-mTf-CAT construct but reduced cAMP-mediated activation. Mutations in the CRE-like PRII (PRII*) also significantly reduced the FSH response. Activation of the PRII*-mTf-CAT in response to cAMP was completely abolished. The presence of AS-oligo had no further effect on the FSH- or cAMP-mediated activation of the PRII*-mTf-CAT construct. In Sertoli cells, CBP/p300 was coimmunoprecipitated with CREB and the bHLH protein E47. These observations suggest that CBP/p300 appears to be involved in regulating FSH-mediated activation of the transferrin promoter by linking bHLH and CREB activities.

Functional properties of the rat phosphatase 1alpha promoter

The aim of this study was to investigate the functional properties of the promoter of the protein phosphatase 1alpha catalytic subunit. Luciferase plasmids with different fragments of the rat catalytic subunit of the protein phosphatase 1alpha promoter ranging from -3.7 kbp to -59 bp were transiently transfected into cells by the calcium-phosphate precipitation method. The promoter activity was determined in the absence and presence of inotropic agents which influencing the cAMP-depending pathway. The basal transcriptional activity decreased at fragment -124 bp and shorter fragments. To identify regions of regulatory importance we investigated the cAMP-dependent influence on the transcriptional activity. Stimulation of the complete promoter region with forskolin (1-100 microM) for 6 h led to a concentration-dependent decrease of transcriptional activity. Moreover, regions shorter than 3.7 kbp were inhibited by forskolin (10 microM). Short time stimulation (10 min) with forskolin (10 microM) increased the transcriptional activity of only the 3.7 kbp fragment. The effects were antagonized by Rp-cAMPS, a specific antagonist of protein kinase A, indicating cAMP-dependent effects. The results provide evidence for cAMP-dependent regulation of the protein phosphatase 1alpha promotor.

The role of cyclic AMP response element-binding protein in testosterone-induced differentiation of granular convoluted tubule cells in the rat submandibular gland

The postnatal development of granular convoluted tubules (GCT) in the duct system of the rodent submandibular gland is known to be androgen-dependent, but the underlying molecular mechanism is unclear. To test the possible role of the transcription factor, cyclic AMP response element-binding protein (CREB), in the androgen-induced differentiation of GCT, the effect of testosterone on the expression and localization of epidermal growth factor (EGF), a marker of GCT cells, and of CREB was examined in the submandibular glands of immature 3-week-old rats. Northern blotting demonstrated increases in both EGF and CREB mRNA 1-4 days after testosterone administration. Immunoprecipitation also indicated that CREB protein was increased in amount with testosterone administration, and that induced CREB was phosphorylated at the serine residue as in the active form of CREB. In situ hybridization demonstrated that cells with CREB mRNA signal first appeared in the distal portions of striated ducts at 1 day and had increased in number by 4 days after giving testosterone, when cells with EGF mRNA signal became evident in the same duct portions. Immunohistochemistry also showed the occurrence of CREB protein in the nuclei of duct epithelial cells before their differentiation into EGF-positive GCT cells. Finally, pieces of submandibular gland from immature rats were cultured in vitro and their expression of EGF mRNA analysed by the reverse transcriptase-polymerase chain reaction. Testosterone in the medium caused a marked enhancement of EGF expression in the gland in 1-4 days, which was attenuated by simultaneous administration of the antisense oligonucleotide for CREB as well as that for the androgen receptor. These results suggest the CREB is upregulated by androgen and has a crucial role in androgen-induced differentiation of GCT in the duct system of the rat submandibular gland.

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.

Depresssion--emerging insights from neurobiology

An emerging hypothesis suggests that the pathogenesis and treatment of depression is likely to involve a plasticity of neuronal pathways. The inability of neuronal systems to exhibit appropriate, adaptive plasticity could contribute to the pathogenesis of depression. Antidepressant treatments may exert their therapeutic effects by stimulating appropriate adaptive changes in neuronal systems. Recent studies have demonstrated that chronic antidepressant administration up-regulates the cAMP signal transduction cascade resulting in an increased expression and function of the transcription factor CREB. Enhanced CREB expression leads to an up-regulation of specific target genes, including the neurotrophin BDNF. Chronic antidepressant treatments enhance BDNF expression within hippocampal and cortical neurons and can prevent the stress-induced decrease in BDNF expression. Stress has been shown to: (i) induce neuronal atrophy/death; and (ii) decrease neurogenesis of hippocampal neurons. Clinical studies indicate significant hippocampal damage in cases of major, recurrent depression. It is possible that antidepressant treatments through enhanced expression of growth and survival promoting factors like BDNF may prevent or reverse the atrophy and damage of hippocampal neurons. Indeed, studies have indicated that chronic antidepressant treatments enhance hippocampal neurogenesis, promote neuronal sprouting and prevent atrophy. The molecular mechanisms underlying the effects of antidepressant treatments including adaptations in the cAMP transduction cascade, CREB and BDNF gene expression, and structural neuronal plasticity are discussed.