The Pit-1 homeodomain and beta-domain interact with Ets-1 and modulate synergistic activation of the rat prolactin promoter

Immunomodulatory role of decidual prolactin on the human fetal membranes and placenta

The close interaction between fetal and maternal cells during pregnancy requires multiple immune-endocrine mechanisms to provide the fetus with a tolerogenic environment and protection against any infectious challenge. The fetal membranes and placenta create a hyperprolactinemic milieu in which prolactin (PRL) synthesized by the maternal decidua is transported through the amnion-chorion and accumulated into the amniotic cavity, where the fetus is bedded in high concentrations during pregnancy. PRL is a pleiotropic immune-neuroendocrine hormone with multiple immunomodulatory functions mainly related to reproduction. However, the biological role of PRL at the maternal-fetal interface has yet to be fully elucidated. In this review, we have summarized the current information on the multiple effects of PRL, focusing on its immunological effects and biological significance for the immune privilege of the maternal-fetal interface.

Transcriptomic Profiles of Normal Pituitary Cells and Pituitary Neuroendocrine Tumor Cells

The pituitary gland is one of the most cellularly diverse regions of the brain. Recent advancements in transcriptomic biology, such as single-cell RNA sequencing, bring an unprecedented glimpse into the molecular composition of the pituitary, both in its normal physiological state and in disease. Deciphering the normal pituitary transcriptomic signatures provides a better insight into the ontological origin and development of five types of endocrine cells, a process involving complex cascades of transcription factors that are still being established. In parallel with these observations about normal pituitary development, recent transcriptomic findings on pituitary neuroendocrine tumors (PitNETs) demonstrate both preservations and changes in transcription factor expression patterns compared to those seen during gland development. Furthermore, recent studies also identify differentially expressed genes that drive various tumor behaviors, including hormone hypersecretion and tumor aggression. Understanding the comprehensive multiomic profiles of PitNETs is essential in developing molecular profile-based therapies for PitNETs not curable with current treatment modalities and could eventually help align PitNETs with the breakthroughs being made in applying precision medicine to other tumors.

POU1F1/Pou1f1 c.143-83A > G Variant Disrupts the Branch Site in Pre-mRNA and Leads to Dwarfism

POU Class 1 Homeobox1 (POU1F1/Pou1f1) is a well-established pituitary-specific transcription factor, and causes, when mutated, combined pituitary hormone deficiency in humans and mice. POU1F1/Pou1f1 has 2 isoforms: the alpha and beta isoforms. Recently, pathogenic variants in the unique coding region of the beta isoform (beta domain) and the intron near the exon-intron boundary for the beta domain were reported, although their functional consequences remain obscure. In this study, we generated mice carrying the Pou1f1 c.143-83A>G substitution that recapitulates the human intronic variant near the exon-intron boundary for the beta domain. Homozygous mice showed postnatal growth failure, with an average body weight that was 35% of wild-type littermates at 12 weeks, which was accompanied by anterior pituitary hypoplasia and deficiency of circulating insulin-like growth factor 1 and thyroxine. The results of RNA-seq analysis of the pituitary gland were consistent with reduction of somatotrophs, and this was confirmed immunohistochemically. Reverse transcription polymerase chain reaction of pituitary Pou1f1 mRNA showed abnormal splicing in homozygous mice, with a decrease in the alpha isoform, an increase in the beta isoform, and the emergence of the exon-skipped transcript. We further characterized artificial variants in or near the beta domain, which were candidate positions of the branch site in pre-mRNA, using cultured cell-basis analysis and found that only c.143-83A>G produced transcripts similar to the mice model. Our report is the first to show that the c.143-83A>G variant leads to splicing disruption and causes morphological and functional abnormalities in the pituitary gland. Furthermore, our mice will contribute understanding the role of POU1F1/Pou1f1 transcripts in pituitary development.

Identification of the binding domains and key amino acids for the interaction of the transcription factors BmPOUM2 and BmAbd-A in Bombyx mori

The transcription factor BmPOUM2 interacted with another transcription factor BmAbd-A to regulate the expression of the wing cuticle protein gene BmWCP4 in Bombyx mori. In this study, the binding domains and amino acids for the interaction between BmPOUM2 and BmAbd-A were reported. Two isoforms of BmPOUM2 were identified. The short isoform (BmPOUM2-S) lacks a 114-amino acid sequence containing a POU-homeodomain and a nuclear localization signal peptide (NLS), as compared to the full-length isoform (BmPOUM2). Both BmPOUM2 and BmPOUM2-S proteins bound to the BmAbd-A through the POU-specific domain. When the six amino acids (Lys166, Gly173, Gln176, Ser192, Glu200 and Asn208) that are highly conserved in POU family genes were mutated, BmPOUM2 did not bind to BmAbd-A. BmAbd-A interacted with BmPOUM2 by the homeobox domain or the LCR2 (low complexity region) domain. When seven amino acids (Phe156/248, His158/250, Ala175/263, Cys180/265, Glu190/268, Trp196/274 and Val214/289) that are shared in the homeobox and LCR2 domains were mutated, BmAbd-A did not bind to BmPOUM2. Overexpression of either BmPOUM2 or BmAbd-A or both increased the activity of BmWCP4 promoter in CHO cells. ChIP assay and EMSA showed that BmAbd-A protein bound to the Hox cis-regulatory element in the BmWCP4 promoter, while the BmPOUM2 bound to the nearby POU CRE. A model for the interaction and action of BmPOUM2 and BmAbd-A in regulation of the BmWCP4 expression is proposed.

The role of the transcription factor Ets1 in carcinoma

Ets1 belongs to the large family of the ETS domain family of transcription factors and is involved in cancer progression. In most carcinomas, Ets1 expression is linked to poor survival. In breast cancer, Ets1 is primarily expressed in the triple-negative subtype, which is associated with unfavorable prognosis. Ets1 contributes to the acquisition of cancer cell invasiveness, to EMT (epithelial-to-mesenchymal transition), to the development of drug resistance and neo-angiogenesis. The aim of this review is to summarize the current knowledge on the functions of Ets1 in carcinoma progression and on the mechanisms that regulate Ets1 activity in cancer.

Signaling pathways regulating pituitary lactotrope homeostasis and tumorigenesis

Dysregulation of the signaling pathways that govern lactotrope biology contributes to tumorigenesis of prolactin (PRL)-secreting adenomas, or prolactinomas, leading to a state of pathological hyperprolactinemia. Prolactinomas cause hypogonadism, infertility, osteoporosis, and tumor mass effects, and are the most common type of neuroendocrine tumor. In this review, we highlight signaling pathways involved in lactotrope development, homeostasis, and physiology of pregnancy, as well as implications for signaling pathways in pathophysiology of prolactinoma. We also review mutations found in human prolactinoma and briefly discuss animal models that are useful in studying pituitary adenoma, many of which emphasize the fact that alterations in signaling pathways are common in prolactinomas. Although individual mutations have been proposed as possible driving forces for prolactinoma tumorigenesis in humans, no single mutation has been clinically identified as a causative factor for the majority of prolactinomas. A better understanding of lactotrope-specific responses to intracellular signaling pathways is needed to explain the mechanism of tumorigenesis in prolactinoma.

The hidden but positive role for glucocorticoids in the regulation of growth hormone-producing cells

Growth hormone (GH) is a prominent metabolic factor that is targeted by glucocorticoids; however, their role in GH production remains controversial. This is explained in part by discrepancies between in vitro and in vivo, short-term versus long-term exposure and even species-specific effects. The prevailing view, however, is that glucocorticoids are negative modulators of growth and GH production. An examination of recent findings from elegant avian and gene ablation in mice studies as well as clinical case reports, suggests this is not the case. The evidence suggests that the effect of glucocorticoids on growth and GH production can be uncoupled, and reveals they play a crucial and positive role in maturation of functional somatotrophs, the GH-producing cells of the anterior pituitary. Here, we provide an overview and insights into the possible roles of glucocorticoids in the development of somatotrophs before birth as well as regulation of GH production in infancy (neonatal) and adulthood (postnatal). A fully functional glucocorticoid-signaling pathway appears to be required for establishment of somatotrophs before birth, and glucocorticoids continue to be required for maintenance of GH production in the newborn. There is evidence to suggest progenitor somatotrophs may persist after birth, and perhaps account for the ability of glucocorticoid therapy to correct some cases of GH deficiency as a result of compromised glucocorticoid signaling. Finally, there is support for positive regulation of avian, murine and human GH gene activation and/or expression by glucocorticoids, however, there appears to be no common mechanism and the contribution of direct versus indirect effects remains unclear. Thus, our observations reveal a largely hidden face of glucocorticoids, specifically, a positive role in somatotroph development and GH gene activation/expression, which may enable us to better understand the differential effect of glucocorticoids on growth and GH production in human studies.

Association of polymorphism in the prolactin promoter and egg quality traits in laying hens

Single strand conformation polymorphism analysis and DNA sequencing was performed in White Leghorn hens to explore the polymorphisms present in the promoter of the prolactin gene. The effects of different genotypes on egg production and quality traits were determined, and expression of the prolactin gene in different genotypes was quantified by real time-PCR. Five genotypes and four alleles at each of two Fragments of the promoter were found, of which the FG genotype in Fragment 1 and the PQ genotype in Fragment 2 were the most predominant genotypes. The genotypes of Fragment 1 had significant effects (P < 0·05) on Haugh unit, albumen weight, albumen percentage and shell percentage at 40 weeks of age; egg weight and yolk index at 52 weeks of age; and egg weight at 64 weeks of age. Prolactin expression in the genotypes of Fragment 1 differed significantly and GH genotyped birds had the highest level of expression. The genotypes of Fragment 2 did not show any significant differences of expression. It was concluded that the prolactin gene promoter was highly polymorphic, and had significant effects on egg quality traits in White Leghorn hens.

Identification of haplotypes in promoter of prolactin gene and their effect on egg production and quality traits in layer chicken

Expression of prolactin hormone is a crucial event in regulating egg production in chickens for which promoter plays the vital role in expressing the prolactin gene. The objective of the present study was to identify haplotypes in the prolactin promoter and their effects on egg production and egg quality traits in White Leghorn chicken. Single stranded conformation polymorphism followed by sequencing was conducted to explore polymorphism at 561 bp promoter of prolactin gene. The effect of haplotype combinations on egg production and quality traits were estimated following general linear model technique. The expression of prolactin by different haplogroups was quantified by qPCR. Total 28 haplotypes were found in White Leghorn chicken of which h1 haplotype possessed the highest frequency of 0.46 and h8, h14, h16, h25, h26, and h28 haplotypes had the lowest frequency (0.1%). The egg production up to 52 and 64 weeks of age were found to be significantly (p < 0.05) associated with haplotype combinations where the highest 52-w (52 weeks) egg production was found in animals with h1/h22 combination and the lowest production was observed in the birds with h1/h2 haplogroup. The haplotype combinations had the significant effect (p < 0.05) on Haugh Unit, yolk index and albumen weight at 40 weeks of age; Haugh Unit and albumen weight at 52 weeks of age and Haugh unit, yolk weight and yolk percentage at 64 weeks of age. The prolactin expression in h1/h22 birds was found to be the lowest and in h1/h5 birds to be the highest. The prolactin expression showed significant effect on 52-w egg production and albumin weight at 52 weeks age. In conclusion, it may be stated that the prolactin promoter was highly polymorphic and had the significant association with egg production and quality traits in White Leghorn chicken.

Associations between novel polymorphisms at the 5'-UTR region of the prolactin gene and egg production and quality in chickens

The objective was to characterize polymorphisms at the 5'-UTR region of the prolactin gene, and determine their association with egg production and egg quality traits in White Leghorn chickens. The study was conducted on four strains of White Leghorn chickens, namely IWH, IWI, IWK, and layer control. Overall, there were three alleles (designated A, B, and C) and five genotypes, with genotypic frequencies of 0.09, 0.75, 0.07, 0.02, and 0.07 for AA, AB, AC, BB, and BC, respectively. There were significant differences among genotypes for egg production up to 52 and 64 wk of age, with maximal egg yields for genotypes AA and AC (144.5 ± 5.06 and 143.2 ± 4.67 eggs, respectively). Furthermore, there were significant differences among genotypes for egg quality traits, including egg weight and Haugh unit at 40 wk of age, Haugh unit at 52 wk, and yolk color index and Haugh unit at 64 wk. Birds with AA or AC genotypes had the best egg quality traits. On the contrary, these genotypes had the lowest prolactin expression, whereas this expression was highest in birds with the BB genotype. In conclusion, polymorphisms at the 5'-UTR of prolactin gene were significantly associated with egg production and egg quality traits in White Leghorn chickens.

Appearance of the pituitary factor Pit-1 increases chromatin remodeling at hypersensitive site III in the human GH locus

Expression of pituitary and placental members of the human GH and chorionic somatomammotropin (CS) gene family is directed by an upstream remote locus control region (LCR). Pituitary-specific expression of GH requires direct binding of Pit-1 (listed as POU1F1 in the HUGO database) to sequences marked by a hypersensitive site (HS) region (HS I/II) 14.6 kb upstream of the GH-N gene (listed as GH1 in the HUGO database). We used human embryonic kidney 293 (HEK293) cells overexpressing wild-type and mutant Pit-1 proteins as a model system to gain insight into the mechanism by which Pit-1 gains access to the GH LCR. Addition of Pit-1 to these cells increased DNA accessibility at HS III, located 28 kb upstream of the human GH-N gene, in a POU homeodomain-dependent manner, as reflected by effects on histone hyperacetylation and RNA polymerase II activity. Direct binding of Pit-1 to HS III sequences is not supported. However, the potential for binding of ETS family members to this region has been demonstrated, and Pit-1 association with this ETS element in HS III sequences requires the POU homeodomain. Also, both ETS1 and ELK1 co-precipitate from human pituitary extracts using two independent sources of Pit-1 antibodies. Finally, overexpression of ELK1 or Pit-1 expression in HEK293 cells increased GH-N RNA levels. However, while ELK1 overexpression also stimulated placental CS RNA levels, the effect of Pit-1 appeared to correlate with ETS factor levels and target GH-N preferentially. These data are consistent with recruitment and an early role for Pit-1 in remodeling of the GH LCR at the constitutively open HS III through protein-protein interaction.

Ets-1/Elk-1 is a critical mediator of dipeptidyl-peptidase III transcription in human glioblastoma cells

Dipetidyl-peptidase III is a metallopeptidase involved in a number of physiological processes and its expression has been reported to increase with the histological aggressiveness of human ovarian primary carcinomas. Because no information regarding the regulation of its expression was available, experiments were designed to clone, define and characterize the promoter region of the human dipeptidyl-peptidase III (DPP-III) gene. In this study, we cloned a 1038 bp 5'-flanking DNA fragment of the human DPP-III gene for the first time and demonstrated strong promoter activity in this region. Deletion analysis revealed that as few as 45 nucleotides proximal to the transcription start site retained approximately 40% of the activity of the full-length promoter. This promoter lacked the TATA box but contained multiple GC boxes and a single CAAT box. Similarly, two Ets-1/Elk-1-binding motifs are present in the first 25 nucleotides from the transcription start site. Binding of Ets-1/Elk-1 proteins to these motifs was visualized by electrophoretic mobility shift and chromatin immunoprecipitation assays. Mutations of these binding sites abolished not only binding of the Ets protein, but also the intrinsic promoter activity. Increased DNA-binding activity of Ets-1/Elk-1 by v-Ha-ras also augmented the mRNA level and promoter activity of this gene. Similarly, co-transfection of DPP-III promoter-reporter constructs with Ets-1 expression vector led to a significant increase in promoter activity. From these results, we conclude that Ets-1/Elk-1 plays a critical role in transcription of the human DPP-III gene.

A Pit-1 threonine 220 phosphomimic reduces binding to monomeric DNA sites to inhibit Ras and estrogen stimulation of the prolactin gene promoter

Pit-1 is a POU-homeodomain transcription factor that dictates the ontogeny of pituitary somatotrophs, lactotrophs, and thyrotrophs through regulation of their respective protein hormone genes: GH, prolactin (PRL), and TSHbeta. Although Pit-1 threonine 220 (T220) and serine 115 are protein kinase phospho-acceptor sites, the transcriptional role of Pit-1 phosphorylation remains unclear. In the rat PRL promoter (rPRL), Ras-stimulated transcription is mediated by binding of Ets-1 and Pit-1 at a composite site (FPIV). Ets-1 and Pit-1 physically interact, and Pit-1 T220 is a major Ets-1 contact point. T220 was mutated to aspartic acid (D, to mimic phosphorylation) or a neutral alanine (A), and DNA binding and transcriptional activity were tested. The Pit-1 T220D mutation reduced binding at monomeric Pit-1 sites (FPIV, PRL-1d), but not dimeric Pit-1 sites (FPI). Pit-1 T220A bound all sites with wild-type (WT) affinity. In transfections of HeLa cells, each Pit-1 mutant transcriptionally activated the -425rPRL promoter and cooperated with Ets-1 to WT levels. In contrast, Pit-1-mediated Ras activation of the -425 rPRL promoter was significantly inhibited by T220D. Finally, Pit-1 synergistic activation of the 2500-bp rPRL promoter with estrogen receptor was reduced by T220D compared with T220A and WT Pit-1. Thus, phosphorylation of Pit-1 T220 reduces binding to monomeric sites blunting Ras and estrogen/estrogen receptor stimulation of the rPRL gene promoter. Consequently, T220 phosphorylation of Pit-1 by protein kinase A, protein kinase C, or cell cycle-dependent kinases appears to serve as a regulatory switch, inhibiting Ras and estrogen/estrogen receptor regulatory pathways, while enhancing the cAMP/protein kinase A response, thus allowing a more precise integration of pituitary responses to distinct signaling stimuli.

Molecular interaction of BMP-4, TGF-beta, and estrogens in lactotrophs: impact on the PRL promoter

The regulatory role of estrogen, bone morphogenetic protein-4 (BMP-4), and TGF-beta has a strong impact on hormone secretion, gene transcription, and cellular growth of prolactin (PRL)-producing cells. In contrast to TGF-beta, BMP-4 induces the secretion of PRL in GH3 cells. Therefore, we studied the mechanism of their transcriptional regulation. Both BMP-4 and TGF-beta inhibited the transcriptional activity of the estrogen receptor (ER). Estrogens had no effect on TGF-beta-specific Smad protein transcriptional activity but presented a stimulatory action on the transcriptional activity of the BMP-4-specific Smads. BMP-4/estrogen cross talk was observed both on PRL hormone secretion and on the PRL promoter. This cross talk was abolished by the expression of a dominant-negative form for Smad-1 and treatment with ICI 182780 but not by point mutagenesis of the estrogen response element site within the promoter, suggesting that Smad/ER interaction might be dependent on the ER and a Smad binding element. By serial deletions of the PRL promoter, we observed that indeed a region responsive to BMP-4 is located between -2000 and -1500 bp upstream of the transcriptional start site. Chromatin immunoprecipitation confirmed Smad-4 binding to this region, and by specific mutation and gel shift assay, a Smad binding element responsible site was characterized. These results demonstrate that the different transcriptional factors involved in the Smad/ER complexes regulate their transcriptional activity in differential ways and may account for the different regulatory roles of BMP-4, TGF-beta, and estrogens in PRL-producing cells.

Expression and localization of transcription factor Ets-1 in the rat ovary during the estrous cycle and pregnancy

OBJECTIVE

To examine the expression and localization of Ets-1 in the rat ovary during the estrous cycle and pregnancy, and to investigate its effects on ovarian function.

DESIGN

Prospective, randomized study.

SETTING

Department of Physiology at Harbin Medical University.

ANIMAL(S)

Pubertal female Wistar rats.

INTERVENTION(S)

Vaginal smears were taken daily from female rats to determine the stage of the estrous cycle. Pregnancies were achieved by caging female and male rats together overnight. Ovaries were collected from both cycling and pregnant rats for tissue sectioning and RNA and protein extractions.

MAIN OUTCOME MEASURE(S)

Real-time quantitative polymerase chain reaction, Western blot, in situ hybridization, and immunohistochemistry were performed to investigate the expression and localization of Ets-1 messenger RNA (mRNA) and protein in the rat ovary during the estrous cycle and pregnancy.

RESULT(S)

During the estrous cycle, the levels of Ets-1 mRNA and protein expression increased during the follicular phase, achieving their highest measurements at proestrus and lowest at metestrus. The expression of Ets-1 mRNA and protein fluctuated during pregnancy, increasing during early pregnancy, then decreasing during mid-pregnancy, and again increasing until parturition. Ets-1 mRNA and protein were present throughout the estrous cycle and pregnancy, principally localized in follicles of various sizes and in the corpus luteum.

CONCLUSION(S)

Ets-1 may participate and play an important role in the regulation of follicular development, corpus luteum formation, maintenance, and regression.

Differential Utilization of Transcription Activation Subdomains by Distinct Coactivators Regulates Pit-1 Basal and Ras Responsiveness

The POU-homeodomain transcription factor Pit-1 governs ontogeny and cell-specific gene expression of pituitary lactotropes, somatotropes, and thyrotropes. The splice isoform, Pit-1β, inserts a 26-amino acid (AA) repressor at AA48 in the Pit-1 transcription activation domain (TAD). The Pit-1 TAD contains a basal regulatory subregion, R1 (AA1–45), and a basal and Ras-responsive region, R2 (AA46–80). To precisely map these activities, we generated GAL4-Pit-1/Pit-1βTAD fusions and, in full-length HA-Pit-1, a series of substitution mutants of R2. Analysis in GH4 cells identified an activation domain at AA50–70, followed by an overlapping, dual-function, Ras-responsive-inhibitory domain, located from AA60–80. In contrast, GAL4-Pit-1βTAD repressed both basal and Ras-mediated TAD activity. To determine the functional interplay between TAD subregions and the β-domain, we inserted the β-domain every 10 AA across the 80-AA Pit-1 TAD. Like wild-type Pit-1β, each construct retained transcriptional activity in HeLa cells and repressed the Ras response in GH4 cells. However, β-domain insertion at AA61 and 71 resulted in greater repression of Ras responsiveness, defining a critical R2 TAD spanning AA61–71 of Pit-1. Furthermore, Ras activation is augmented by steroid receptor coactivator 1, whereas cAMP response element binding protein-binding protein is not a Ras mediator in this system. In summary, the Pit-1/Pit-1β TADs are composed of multiple, modular, and transferable subdomains, including a regulatory R1 domain, a basal activation region, a selective inhibitory-Ras-responsive segment, and a β-specific repressor domain. These data provide novel insights into the mechanisms by which the Pit-1 TAD integrates DNA binding, protein partner interactions, and distinct signaling pathways to fine-tune Pit-1 activity.

Pituitary transcription factors: from congenital deficiencies to gene therapy

Despite the existence of interspecies phenotypic variability, animal models have yielded valuable insights into human pituitary diseases. Studies on Snell and Jackson mice known to have growth hormone, prolactin and thyroid-stimulating hormone deficiencies involving the hypoplastic pituitary gland have led to identifying alterations of the pituitary specific POU homeodomain Pit-1 transcription factor gene. The human phenotype associated with rare mutations in this gene was found to be similar to that of these mice mutants. Terminal differentiation of lactotroph cells and direct regulation of the prolactin gene both require interactions between Pit-1 and cell type specific partners, including panpituitary transcriptional regulators such as Pitx1 and Pitx2. Synergistic activation of the prolactin promoter by Pitx factors and Pit-1 is involved not only in basal condition, but also in responsiveness to forskolin, thyrotrophin-releasing-hormone and epidermal growth factor. In corticotroph cells, Pitx1 interacts with Tpit. Tpit mutations have turned out to be the main molecular cause of neonatal isolated adrenocorticotrophin deficiency. This finding supports the idea that Tpit plays an essential role in the differentiation of the pro-opiomelanocortin pituitary lineage. The effects of Pit-1 are not restricted to hormone gene regulation because this factor also contributes to cell division and protects the cell from programmed cell death. Lentiviral vectors expressing a Pit-1 dominant negative mutant induced time- and dose-dependent cell death in somatotroph and lactotroph adenomas in vitro. Gene transfer by lentiviral vectors should provide a promising step towards developing an efficient specific therapeutic approach by which a gene therapy programme for treating human pituitary adenomas could be based.

Association of polymorphisms in the promoter region of chicken prolactin with egg production

Chicken prolactin (PRL) is a physiological candidate gene for egg production. The objective of the current research was to investigate the association of polymorphisms in the chicken PRL promoter region with egg production. Genotyping of 177 individuals from White Leghorn, Yangshan, Taihe Silkies, White Rock, and Nongdahe breeds for 6 single nucleotide polymorphisms (C-2402T, C-2161G, T-2101G, C-2062G, T-2054A, and G-2040A) and 1 24-bp indel (insertion-deletion) at the site of -358 of the chicken PRL gene revealed large breed differences in allelic frequencies for all but the T-2101G and T-2054A polymorphisms. An F2 population produced from Nongdahe x Taihe Silkies chickens consisted of 374 hens, which were recorded for egg production traits and genotyped for the above 7 polymorphisms. Marker-trait association analysis indicated that the 24-bp indel was associated with egg production (P < 0.01) and that H3 (C C T C T G) was the most advantageous haplotype for egg production.

MED220/thyroid receptor-associated protein 220 functions as a transcriptional coactivator with Pit-1 and GATA-2 on the thyrotropin-beta promoter in thyrotropes

Mediator (MED) 220/thyroid receptor-associated protein (TRAP) 220 is a transcriptional mediator that interacts with liganded thyroid/steroid hormone receptors. MED220 haploinsufficient heterozygotes exhibited hypothyroidism and reduced TSHbeta transcripts, suggesting a specific function for TSHbeta transcription. We previously demonstrated that Pit-1 and GATA-2 can bind to a composite element within the proximal TSHbeta promoter and synergistically activate transcription. We detected MED220 expression in TtT-97 thyrotropes by Northern and Western blot analysis. Cotransfections in CV-1 cells showed that Pit-1, GATA-2, or MED220 alone did not markedly stimulate the TSHbeta promoter. However, Pit-1 plus GATA-2 resulted in an 10-fold activation, demonstrating synergistic cooperativity. Titration of MED220 resulted in a further dose-dependent stimulation up to 25-fold that was promoter specific. Glutathione-S-transferase interaction studies showed that MED220 or GATA-2 each bound the homeodomain of Pit-1, whereas MED220 interacted independently with each zinc finger of GATA-2 but not with either terminus. MED220 interacted with GATA-2 and Pit-1 over a broad region of its N terminus. These regions of interaction were also important for maximal function. Coimmunoprecipitation confirmed that all three factors can interact in thyrotropes and chromatin immunoprecipitation demonstrated in vivo occupancy on the proximal TSHbeta promoter. Thus, the TSHbeta gene is maximally activated by a combination of three thyrotrope transcription factors that act via both protein-DNA and protein-protein interactions.

Structural and functional analysis of domains mediating interaction between NKX-3.1 and PDEF

NKX-3.1 is a suspected prostate tumor suppressor gene that encodes a homeodomain transcription factor. NKX-3.1 has been demonstrated to interact with prostate derived Ets factor (PDEF) and to suppress the ability of PDEF to transactivate the prostate specific antigen promoter. To dissect the molecular basis of the interaction between these transcription factors, deletion analyses were preformed using the yeast two-hybrid system. The interaction of NKX-3.1 with full-length PDEF requires part of the homeodomain and a tyrosine-rich 21 amino acid sequence that lies C-terminal to the homeodomain. The interaction of PDEF with full-length NKX-3.1 requires the Ets domain and a linker region that lies between the Ets and pointed domains. Deletion of the C-terminal 21 amino acids of NKX-3.1 completely disrupts the ability to suppress the transactivation function of PDEF in prostate tumor cells, demonstrating concordance between interaction in yeast and function in mammalian cells. These studies have identified novel protein-protein interaction domains within NKX-3.1 and PDEF that operate in concert with their respective DNA binding domains to mediate functional interactions between these growth regulatory transcription factors.

Identification of neuronal enhancers of the proopiomelanocortin gene by transgenic mouse analysis and phylogenetic footprinting

The proopiomelanocortin (POMC) gene is expressed in the pituitary and arcuate neurons of the hypothalamus. POMC arcuate neurons play a central role in the control of energy homeostasis, and rare loss-of-function mutations in POMC cause obesity. Moreover, POMC is the prime candidate gene within a highly significant quantitative trait locus on chromosome 2 associated with obesity traits in several human populations. Here, we identify two phylogenetically conserved neuronal POMC enhancers designated nPE1 (600 bp) and nPE2 (150 bp) located approximately 10 to 12 kb upstream of mammalian POMC transcriptional units. We show that mouse or human genomic regions containing these enhancers are able to direct reporter gene expression to POMC hypothalamic neurons, but not the pituitary of transgenic mice. Conversely, deletion of nPE1 and nPE2 in the context of the entire transcriptional unit of POMC abolishes transgene expression in the hypothalamus without affecting pituitary expression. Our results indicate that the nPEs are necessary and sufficient for hypothalamic POMC expression and that POMC expression in the brain and pituitary is controlled by independent sets of enhancers. Our study advances the understanding of the molecular nature of hypothalamic POMC neurons and will be useful to determine whether polymorphisms in POMC regulatory regions play a role in the predisposition to obesity.

Molecular Structure and Organization of Crustacean Hyperglycemic Hormone Genes of Penaeus monodon

The Crustacean hyperglycemic hormone (CHH) has been shown to exist as multiple molecular forms in several crustacean species. In Penaeus monodon, a gene encoding CHH (so-called Pem-CHH1) was recently described. In this study, the molecular structures of two other CHH genes (Pem-CHH2 and Pem-CHH3) are reported. Both the Pem-CHH2 and Pem-CHH3 genes contain three exons that are separated by two introns that are similar to the structure of other genes in the same family. An analysis of the upstream nucleotide sequences of each Pem-CHH gene has identified the putative promoter element (TATA box) and putative binding sites for several transcription factors. The binding sites for CREB, Pit-1, and AP-1 were found upstream of all three Pem-CHH genes. A Southern blot analysis showed that at least one copy of each Pem-CHH gene was located within the same 10 kb genomic DNA fragment. These results suggest that the CHH genes are arranged in a cluster in the genome of P. monodon, and that their expression may be modulated by similar mechanisms.

ESX induces transformation and functional epithelial to mesenchymal transition in MCF-12A mammary epithelial cells

ESX is an epithelial-restricted member of a large family of transcription factors known as the Ets family. ESX expression has been shown to be correlated with Her2/neu proto-oncogene amplification in highly aggressive breast cancers and induced by Her2/neu in breast cell lines, but its role in tumorigenesis is unknown. Previously, we have shown that ESX enhances breast cell survival in colony-formation assays. In order to determine whether ESX can act as a transforming gene, we stably transfected MCF-12A human mammary epithelial cells with the ESX expression vector, pCGN2-HA-ESX. The MCF-12A cell line is immortalized, but nontransformed, and importantly, these cells fail to express endogenous ESX protein. We used pCGN2-HA-Ets-2 and pSVRas expression vectors as positive controls for transformation. Like HA-Ets-2 and V12-Ras, stable expression of ESX induced EGF-independent proliferation, serum-independent MAPK phosphorylation and growth in soft agar. Additionally, stable ESX expression conferred increased cell adhesion, motility and invasion in two-dimensional and transwell filter assays, and an epithelial to mesenchymal morphological transition. In three-dimensional cultures, parental and vector control (pCGN2) cells formed highly organized duct-like structures with evidence of cell polarity, ECM adhesion-dependent proliferation and cell survival, and lack of cellular invasion into surrounding matrix. Remarkably, the ESX stable cells formed solid, disorganized structures, with lack of cell polarity, loss of adhesion junctions and cytokeratin staining and loss of dependence on ECM adhesion for cell proliferation and survival. In addition, ESX cells invaded the surrounding matrix, indicative of a transformed and metastatic phenotype. Taken together, these data show that ESX expression alone confers a transformed and in vitro metastatic phenotype to otherwise normal MCF-12A cells.

Inactivating Pit-1 mutations alter subnuclear dynamics suggesting a protein misfolding and nuclear stress response

Pit-1, a POU-class nuclear DNA-binding transcription factor, specifies three of the parenchymal cell types in anterior pituitary ontogeny. Using fluorescent fusions and live cell imaging, we have compared the dynamic behavior of wild-type and inactivating Pit-1 point mutations. Fluorescence recovery after photobleaching (FRAP) and real-time extraction data indicate that wild-type Pit-1 has a dynamic mobility profile, with t(1/2s) approximately 5-7 s when expressed from low to high amounts, respectively. Biochemically, Pit-1 is approximately 50% retained according to direct observation during extraction, indicating a dynamic interaction with nuclear structure. An analysis of transiently expressed Pit-1 carrying two different debilitating mutations reveals that they translocate normally to the nucleus, but exhibit two different levels of mobility, both clearly distinguishable from wild-type Pit-1. At low expression levels, the t(1/2s) of Pit(W261C) and Pit(A158P) are extremely rapid (0.3 and 0.6 s t(1/2s), respectively). At higher expression levels, unlike wild-type Pit-1, both mutant proteins become immobilized and insoluble, and fractionate completely with the insoluble nuclear matrix. Relative to wild-type, over expression of mutated Pit-1 elicits a nuclear stress response indicated by increased levels of heat shock inducible heat shock protein 70 (Hsp70), and reorganization of heat shock factor-1. The decreased mobility of Pit(A158P) relative to Pit(W261C) at low expression levels correlates with its ability to partially activate when expressed at low levels and its ability to bind cognate DNA. At high expression levels, lower Pit(A158P) activation correlates with its immobilization and insolubility. These data suggest a link between specific rates of intranuclear mobility and Pit-1 transcription function, perhaps to insure sufficient interactions with chromatin, or in the case of non-DNA binding Pit-1, interaction as a repressor. These data imply inactivating mutations can lead to an intranuclear sorting away from transcription related pathways, and at least in part to a misfolded protein pathway. Taken together, caution is suggested when interpreting point (or other) mutational analyses of transactivator function, as new compartmentation, especially in the context of expression levels, may cloud the distinction between defining functional molecular domains and intranuclear processing of misfolded proteins.

The de novo Q167K mutation in the POU1F1 gene leads to combined pituitary hormone deficiency in an Italian patient

The POU1F1 gene encodes a transcription factor that is important for the development and differentiation of the cells producing GH, prolactin, and TSH in the anterior pituitary gland. Patients with POU1F1 mutations show a combined pituitary hormone deficiency with low or absent levels of GH, prolactin, and TSH. Fourteen mutations have been reported in the POU1F1 gene up to now. These genetic lesions can be inherited either in an autosomal dominant or an autosomal recessive mode. We report on the first Italian patient, a girl, affected by combined pituitary hormone deficiency. The patient was found to be positive for congenital hypothyroidism (with low TSH levels) at neonatal screening. Substitutive therapy was started, but subsequent growth was very poor, although psychomotor development was substantially normal. Hospitalized at 10 mo she showed hypotonic crises, growth retardation, delayed bone age, and facial dysmorphism. In addition to congenital hypothyroidism, GH and prolactin deficiencies were found. Mutation DNA analysis of the patient's POU1F1 gene identified the novel Q167K amino acid change at the heterozygous level. The highly conserved Q167 residue is located in the POU-specific domain. No mutation was detected in the other allele. DNA analysis in the proband's parents did not identify this amino acid substitution, suggesting a de novo genetic lesion. From these data it can be hypothesized that the Q167K mutation has a dominant negative effect.

Ras signaling and transcriptional synergy at a flexible Ets-1/Pit-1 composite DNA element is defined by the assembly of selective activation domains

Pit-1 and Ets-1 binding to a composite element synergistically activates and targets Ras-mitogen-activated protein kinase signaling to the rat prolactin promoter. These transcriptional responses appear to depend on three molecular features: organization of the Ets-1/Pit-1 composite element, physical interaction of these two factors via the Pit-1 homeodomain (amino acids 199-291) and the Ets-1 regulatory III domain (amino acids 190-257), and assembly of their transcriptional activation domains (TADs). Here we show that the organization of the Ets-1/Pit-1 composite element tolerates significant flexibility with regard to Ras stimulation and synergy. Specifically, the putative monomeric Pit-1 binding site can be substituted with bona fide binding sites for either a Pit-1 monomer or dimer, and these sites tolerated a separation of 28 bp. Additionally, we show that the physical interaction of Ets-1 and Pit-1 is not required for Ras responsiveness or synergy because block mutations of the Pit-1 interaction surface in Ets-1, which reduced Ets-1/Pit-1 binding in vitro, did not significantly affect Ets-1 stimulation of Ras responsiveness or synergy. We also show differential use of distinct TAD subtypes and Pit-1 TAD subregions to mediate either synergy or Ras responsiveness. Specifically, TADs from Gal4, VP16, or Ets-2 regulatory III domain linked to Ets-1 DNA binding domain constructs restored synergy to these TAD/Ets-1 DNA binding domain fusions. Conversely, deletion of the defined Pit-1 TAD (amino acids 2-80) retained synergy, but not Ras responsiveness. Consequently, we further defined the Pit-1 amino-terminal TAD into region 1 (R1, amino acids 2-45) and region 2 (R2, amino acids 46-80). R1 appears to regulate basal and synergistic responses, whereas the Ras response was mapped to R2. In summary, Ras responsiveness and Pit-1/Ets-1 synergy are mediated through the assembly of distinct TADs at a flexible composite element, indicating that different mechanisms underlie these two transcriptional responses and that the Pit-1 R2 subregion represents a novel, tissue-specific Ras-responsive TAD.

The biology of the Ets1 proto-oncogene

The Ets1 proto-oncoprotein is a member of the Ets family of transcription factors that share a unique DNA binding domain, the Ets domain. The DNA binding activity of Ets1 is controlled by kinases and transcription factors. Some transcription factors, such as AML-1, regulate Ets1 by targeting its autoinhibitory module. Others, such as Pax-5, alter Ets1 DNA binding properties. Ets1 harbors two phosphorylation sites, threonine-38 and an array of serines within the exon VII domain. Phosphorylation of threonine-38 by ERK1/2 activates Ets1, whereas phosphorylation of the exon VII domain by CaMKII or MLCK inhibits Ets1 DNA binding activity. Ets1 is expressed by numerous cell types. In haemotopoietic cells, it contributes to the regulation of cellular differentiation. In a variety of other cells, including endothelial cells, vascular smooth muscle cells and epithelial cancer cells, Ets1 promotes invasive behavior. Regulation of MMP1, MMP3, MMP9 and uPA as well as of VEGF and VEGF receptor gene expression has been ascribed to Ets1. In tumors, Ets1 expression is indicative of poorer prognosis.

The epithelial-specific ETS transcription factor ESX/ESE-1/Elf-3 modulates breast cancer-associated gene expression

Several members of the ETS family of transcription factors contribute to tumorigenesis in many different tissues, including breast epithelium. The ESX gene is an epithelial-specific Ets member that is particularly relevant to breast cancer. ESX is amplified in early breast cancers, it is overexpressed in human breast ductal carcinoma in situ, and there may be a positive feedback loop between the HER2/neu proto-oncogene and ESX. Despite this progress in our understanding of ESX, its ability to regulate tumor-related gene expression and to modulate breast cell survival, remain unknown. Here we show that HA-ESX stimulates the collagenase and HER2/neu promoters, but fails to activate an intact stromelysin promoter. However, HA-ESX activates, in a dose-dependent manner, a heterologous promoter containing eight copies of the Ets binding site derived from the stromelysin gene (p8Xpal-CAT). Analysis of the ability of constructs encoding nine Ets family members to activate the HER2/neu promoter revealed three patterns of gene activation: (1) no effect or repressed promoter activity (Elk-1 and NET); (2) intermediate activity (ER81, GABP, ESX, and HA-Ets-2); and, (3) maximal activity (Ets-1, VP-16-Ets-1, and EHF). Based on these observations, we also determined whether ESX is capable of conferring a survival phenotype upon immortalized, but nontransformed and ESX negative MCF-12A human breast cells. Using a colony formation assay, we found that HA-ESX and HA-Ets-2, mediated MCF-12A cell survival rates that approached those generated by oncogenic V12 Ras, whereas empty vector resulted in negligible colony formation. By contrast, in immortalized and transformed T47D breast cancer cells, which express both HER2/neu and ESX, we found that antisense and dominant-negative HA-ESX inhibited T47D colony formation, whereas control vector allowed formation of many colonies. These results are significant because they show that HA-ESX is able to differentially activate several malignancy-associated gene promoters, and that ESX expression is required for cellular survival of nontransformed MCF-12A and transformed T47D human mammary cells.

A PIT-1 homeodomain mutant blocks the intranuclear recruitment of the CCAAT/enhancer binding protein alpha required for prolactin gene transcription

The pituitary-specific homeodomain protein Pit-1 cooperates with other transcription factors, including CCAAT/enhancer binding protein alpha (C/EBPalpha), in the regulation of pituitary lactotrope gene transcription. Here, we correlate cooperative activation of prolactin (PRL) gene transcription by Pit-1 and C/EBPalpha with changes in the subnuclear localization of these factors in living pituitary cells. Transiently expressed C/EBPalpha induced PRL gene transcription in pituitary GHFT1-5 cells, whereas the coexpression of Pit-1 and C/EBPalpha in HeLa cells demonstrated their cooperativity at the PRL promoter. Individually expressed Pit-1 or C/EBPalpha, fused to color variants of fluorescent proteins, occupied different subnuclear compartments in living pituitary cells. When coexpressed, Pit-1 recruited C/EBPalpha from regions of transcriptionally quiescent centromeric heterochromatin to the nuclear regions occupied by Pit-1. The homeodomain region of Pit-1 was necessary for the recruitment of C/EBPalpha. A point mutation in the Pit-1 homeodomain associated with the syndrome of combined pituitary hormone deficiency in humans also failed to recruit C/EBPalpha. This Pit-1 mutant functioned as a dominant inhibitor of PRL gene transcription and, instead of recruiting C/EBPalpha, was itself recruited by C/EBPalpha to centromeric heterochromatin. Together our results suggest that the intranuclear positioning of these factors determines whether they activate or silence PRL promoter activity.

Molecular biology of the Ets family of transcription factors

The Ets family of transcription factors characterized by an evolutionarily-conserved DNA-binding domain regulates expression of a variety of viral and cellular genes by binding to a purine-rich GGAA/T core sequence in cooperation with other transcriptional factors and co-factors. Most Ets family proteins are nuclear targets for activation of Ras-MAP kinase signaling pathway and some of them affect proliferation of cells by regulating the immediate early response genes and other growth-related genes. Some of them also regulate apoptosis-related genes. Several Ets family proteins are preferentially expressed in specific cell lineages and are involved in their development and differentiation by increasing the enhancer or promoter activities of the genes encoding growth factor receptors and integrin families specific for the cell lineages. Many Ets family proteins also modulate gene expression through protein-protein interactions with other cellular partners. Deregulated expression or formation of chimeric fusion proteins of Ets family due to proviral insertion or chromosome translocation is associated with leukemias and specific types of solid tumors. Several Ets family proteins also participate in malignancy of tumor cells including invasion and metastasis by activating the transcription of several protease genes and angiogenesis-related genes.

A central role for Ets-2 in the transcriptional regulation and cyclic adenosine 5'-monophosphate responsiveness of the human chorionic gonadotropin-beta subunit gene

Ets-2 has an important role in controlling the differentiation of the placenta. Here we show by truncation and mutational analysis that two closely spaced Ets-2 binding sites in the proximal promoter of the human chorionic gonadotropin beta5 (hCGbeta5) gene constitute a major enhancer for hCGbeta gene expression in JAr and JEG-3 human choriocarcinoma cells and in mouse NIH3T3 cells. Contrary to a previous report, we also demonstrate that the ability of Ets-2 to enhance transcription is subject to control by the Ras/MAPK pathway, although this relationship is less easily demonstrable in JAr and JEG-3 choriocarcinoma cells than in the 3T3 cells because the former already possess a fully activated MAPK pathway and contain Ets-2 phosphorylated at threonine residue at T72. Coexpression of Ets-2 and activated Ras in 3T3 cells led to activation of MAPK/ERK kinase 1/2, phosphorylation of Ets-2 at T72, and an approximately 120-fold up-regulation of reporter gene expression from a short (-175) hCGbeta promoter. Fold activation in JAr and JEG-3 cells was rather less (20- to 30-fold), but basal activity was much higher. These effects on promoter activity were largely reversed in presence of the MAPK inhibitor PD98059, which prevents ERK1/2 activation, and partially reversed by mutating T72 on Ets-2. We finally show that the ability of 8-bromoadenosine-cAMP to stimulate hCGbeta promoter activity in JAr and JEG-3 cells occurs with a short promoter lacking the upstream elements previously considered to be essential for cAMP activation of the gene and, through mutational analysis, confirm that the major cAMP effects on the hCGbeta promoter are mediated through the proximal Ets-2 enhancer. The data are consistent with the hypothesis that Ets-2 has a general and possibly essential role in controlling the activity of genes associated with trophectoderm differentiation.

Pitx factors are involved in basal and hormone-regulated activity of the human prolactin promoter

The pituitary-specific POU homeodomain factor Pit-1 likely interacts with other factors for cell-specific expression of prolactin. Here we identify the paired-like homeobox transcription factors Pitx1 and Pitx2 as factors functionally activating the proximal human prolactin promoter (hPRL-164luc). Using in vitro binding assays and a series of site-specific mutations of the proximal hPRL promoter, we mapped the B1 and B2 bicoid sites involved in Pitx-mediated transactivation of the hPRL-164luc construct. In somatolactotroph GH4C1 cells, basal proximal hPRL promoter activity was inhibited by a Pitx2 dominant-negative form in a dose-dependent manner, whereas binding disruptive mutations in the Pitx sites significantly reduced basal activity of the promoter. We also show that synergistic activation of hPRL-164luc by Pitx2 and Pit-1 requires the integrity of the B2 Pitx binding site, and at least one of the P1 and P2 Pit-1 response elements. In addition, mutation in the B2 Pitx site results in attenuation of the promoter's responsiveness to forskolin, thyrotropin-releasing hormone, and epidermal growth factor. Conversely, Pitx1 or Pitx2 overexpression in GH4C1 cells leads to an enhancement of the drugs stimulatory effects. Altogether, these results suggest that full responsiveness to several signaling pathways regulating the hPRL promoter requires the B2 Pitx binding site and that Pitx factors may be part of the proteic complex involved in these regulations. Finally, in situ hybridization analysis showing coexpression of the PRL and Pitx2 genes in rat and human lactotroph cells corroborates the physiological relevance of these results.

Domains of Pit-1 required for transcriptional synergy with GATA-2 on the TSH beta gene

Previous studies showed that Pit-1 functionally cooperates with GATA-2 to stimulate transcription of the TSH beta gene. Pit-1 and GATA-2 are uniquely coexpressed in pituitary thyrotropes and activate transcription by binding to a composite promoter element. To define the domains of Pit-1 important for functional cooperativity with GATA-2, we cotransfected a set of Pit-1 deletions with an mTSH beta-luciferase reporter. Plasmids were titrated to express equivalent amounts of protein. A mutant containing a deletion of the hinge region between the POU and homeodomains retained the ability to fully synergize with GATA-2. In contrast, mutants containing deletions of amino acids 2-80 or 72-125 demonstrated 56 or 34% of the synergy found with the full-length protein, suggesting that these regions contributed to cooperativity. Mutants with deletions of the POU-specific or homeodomain further reduced the effect signifying the requirement for DNA binding. GST interaction studies demonstrated that only the homeodomain of Pit-1 interacted with GATA-2. Finally, several mutations between the Pit-1 and GATA-2 sites on the TSH beta promoter reduced binding for each factor and greatly reduced ternary complex formation. Thus multiple domains of Pit-1 are required for full synergy with GATA-2 and sequences between the two binding sites contribute to co-occupancy with both factors on the proximal TSH beta promoter.

Structural characterization of the PIT-1/ETS-1 interaction: PIT-1 phosphorylation regulates PIT-1/ETS-1 binding

The POU-domain transcription factor Pit-1 and Ets-1, a member of the ETS family of transcription factors, can associate in solution and synergistically activate the prolactin promoter by binding to a composite response element in the prolactin promoter. We mapped the minimal region of Ets-1 required for the interaction with the Pit-1 POU-homeodomain. Here, we describe a detailed NMR study of the interaction between the POU-homeodomain of Pit-1 and the minimal interacting region of Ets-1. By using heteronuclear single quantum coherence titration experiments, we were able to map exact residues on the POU-homeodomain that are involved in the interaction with this minimal Ets-1 interaction domain. By using our NMR data, we generated point mutants in the POU-homeodomain and tested their effect on the interaction with Ets-1. Our results show that phosphorylation of Pit-1 can regulate the interaction with Ets-1.

Pituitary, pancreatic and gut neuroendocrine defects in protein tyrosine phosphatase-sigma-deficient mice

The expression of receptor protein tyrosine phosphatase sigma (PTPfinal sigma) is developmentally regulated in neuronal and neuroendocrine tissues. We have previously shown that mice deficient in PTPfinal sigma demonstrate nervous system abnormalities, pituitary hypoplasia, increased neonatal mortality (60%), and death from a wasting syndrome at 2-3 wk of age (38%). We have now examined the role of PTPfinal sigma on pituitary, pancreas and enteroendocrine cytodifferentiation, hormone production, and development. The adenohypophyses of PTPfinal sigma(-/-) mice were small and exhibited reduced GH and PRL immunoreactivity. Cells containing TSH, LH, FSH, ACTH, pituitary-specific POU homeodomain factor (Pit-1), ER, and steroidogenic factor 1 were found in normal proportions and distributions. The diminished expression of GH and PRL was not associated with apoptosis of somatotrophs or lactotrophs. Pit-1-positive TSH-negative cells were detected, suggesting that impaired GH and PRL synthesis was not attributable to Pit-1 deficiency. In the knockout mice, pancreatic islets were hypoplastic with reduced insulin immunoreactivity, and there was also variable expression of gut hormones. Functionally, the GH deficiency was associated with hypoglycemia and death in the PTPfinal sigma(-/-) neonate and accordingly, ip administration of GH rescued the PTPfinal sigma(-/-) neonate and normalized the blood glucose. These data indicate that PTPfinal sigma plays a major role in differentiation and development of the neuroendocrine system.

Signaling and transcriptional mechanisms in pituitary development

During the development of the pituitary gland, distinct hormone-producing cell types arise from a common population of ectodermal progenitors, providing an instructive model system for elucidating the molecular mechanisms of patterning and cell type specification in mammalian organogenesis. Recent studies have established that the development of the pituitary occurs through multiple sequential steps, allowing the coordinate control of the commitment, early patterning, proliferation, and positional determination of pituitary cell lineages in response to extrinsic and intrinsic signals. The early phases of pituitary development appear to be mediated through the activities of multiple signaling gradients emanating from key organizing centers that give rise to temporally and spatially distinct patterns of transcription factor expression. The induction of these transcriptional mediators in turn acts to positionally organize specific pituitary cell lineages within an apparently uniform field of ectodermal progenitors. Ultimately, pituitary cell types have proven to be both specified and maintained through the combinatorial interactions of a series of cell-type-restricted transcription factors that dictate the cell autonomous programs of differentiation in response to the transient signaling events.

Tight transcriptional control of the ETS domain factors Erm and Pea3 by Fgf signaling during early zebrafish development

Several molecules of the Fibroblast growth factor family have been implicated in the development of the vertebrate brain, but the effectors of these molecules remain largely unknown. Here we study Erm and Pea3, two ETS domain transcription factors, and show that their expression correlates closely with the domains of fgf8 and fgf3 expression. In situ hybridization analysis in wild-type and acerebellar (ace) mutant embryos defective for fgf8 demonstrates a requirement of Fgf8 for normal expression levels of erm and pea3 transcripts in and close to various domains of Fgf8 action, including the prospective midbrain-hindbrain region, the somites, the neural crest, the forebrain, and developing eyes. Morpholino-oligomer-assisted gene knock-down experiments targeted against fgf8 and fgf3 suggest that Fgf3 and Fgf8 are co-regulators of these genes in the early forebrain anlage. Furthermore, inhibition of Fgf signaling by overexpression of sprouty4 or application of the Fgf inhibitor SU5402 leads to a loss of all erm and pea3 expression domains. Conversely, ectopically provided fgf3 mRNA or implanted beads coated with Fgf8 elicit ectopic transcription of erm and pea3. Both activation and loss of transcripts can be observed within short time frames. We conclude that both the transcriptional onset and maintenance of these factors are tightly coupled to Fgf signaling and propose that erm and pea3 transcription is a direct readout of cells to Fgf levels. Given the knowledge that has accumulated on the posttranslational control of ETS domain factors and their combinatorial interactions with other transcription factors, we suggest that the close coupling of erm and pea3 transcription to Fgf signaling might serve to integrate Fgf signaling with other signals to establish refined patterns in embryonic development.

POU domain factors in the neuroendocrine system: lessons from developmental biology provide insights into human disease

POU domain factors are transcriptional regulators characterized by a highly conserved DNA-binding domain referred to as the POU domain. The structure of the POU domain has been solved, facilitating the understanding of how these proteins bind to DNA and regulate transcription via complex protein-protein interactions. Several members of the POU domain family have been implicated in the control of development and function of the neuroendocrine system. Such roles have been most clearly established for Pit-1, which is required for formation of somatotropes, lactotropes, and thyrotropes in the anterior pituitary gland, and for Brn-2, which is critical for formation of magnocellular and parvocellular neurons in the paraventricular and supraoptic nuclei of the hypothalamus. While genetic evidence is lacking, molecular biology experiments have implicated several other POU factors in the regulation of gene expression in the hypothalamus and pituitary gland. Pit-1 mutations in humans cause combined pituitary hormone deficiency similar to that found in mice deleted for the Pit-1 gene, providing a striking example of how basic developmental biology studies have provided important insights into human disease.

Regulation of Ets function by protein - protein interactions

Ets proteins are a family of transcription factors that share an 85 amino acid conserved DNA binding domain, the ETS domain. Over 25 mammalian Ets family members control important biological processes, including cellular proliferation, differentiation, lymphocyte development and activation, transformation and apoptosis by recognizing the GGA core motif in the promoter or enhancer of their target genes. Protein - protein interactions regulates DNA binding, subcellular localization, target gene selection and transcriptional activity of Ets proteins. Combinatorial control is a characteristic property of Ets family members, involving interaction between Ets and other key transcriptional factors such as AP-1, NFkappaB and Pax family members. Specific domains of Ets proteins interact with many protein motifs such as bHLH, bZipper and Paired domain. Such interactions coordinate cellular processes in response to diverse signals including cytokines, growth factors, antigen and cellular stresses.

Signal transduction and the Ets family of transcription factors

Cellular responses to environmental stimuli are controlled by a series of signaling cascades that transduce extracellular signals from ligand-activated cell surface receptors to the nucleus. Although most pathways were initially thought to be linear, it has become apparent that there is a dynamic interplay between signaling pathways that result in the complex pattern of cell-type specific responses required for proliferation, differentiation and survival. One group of nuclear effectors of these signaling pathways are the Ets family of transcription factors, directing cytoplasmic signals to the control of gene expression. This family is defined by a highly conserved DNA binding domain that binds the core consensus sequence GGAA/T. Signaling pathways such as the MAP kinases, Erk1 and 2, p38 and JNK, the PI3 kinases and Ca2+-specific signals activated by growth factors or cellular stresses, converge on the Ets family of factors, controlling their activity, protein partnerships and specification of downstream target genes. Interestingly, Ets family members can act as both upstream and downstream effectors of signaling pathways. As downstream effectors their activities are directly controlled by specific phosphorylations, resulting in their ability to activate or repress specific target genes. As upstream effectors they are responsible for the spacial and temporal expression or numerous growth factor receptors. This review provides a brief survey of what is known to date about how this family of transcription factors is regulated by cellular signaling with a special focus on Ras responsive elements (RREs), the MAP kinases (Erks, p38 and JNK) and Ca2+-specific pathways and includes a description of the multiple roles of Ets family members in the lymphoid system. Finally, we will discuss other potential mechanisms and pathways involved in the regulation of this important family of transcription factors.

The Pit-1beta domain dictates active repression and alteration of histone acetylation of the proximal prolactin promoter

A critical problem in current molecular biology is to gain a detailed understanding of the molecular mechanisms by which related transcription factor isoforms with identical DNA sequence specificity mediate distinct transcription responses. Pit-1 and Pit-1beta constitute such a pair of transcription factor isoforms. Pit-1 enhances the Ras signaling pathway to the prolactin promoter, and Pit-1beta represses basal prolactin promoter activity as well as Ras signaling to the prolactin promoter in pituitary cells. We have previously demonstrated that the beta-domain amino acid sequence dictates the transcriptional properties of Pit-1beta. Here, we show that five hydrophobic beta-domain residues are required for Pit-1 isoform-specific repression of Ras signaling, and we demonstrate that sodium butyrate and trichostatin A, pharmacological inhibitors of histone deacetylation, as well as viral Ski protein, a dominant-negative inhibitor of recruitment of N-CoR/mSin3 histone deacetylase complexes, specifically reverse beta isoform-specific repression of Ras signaling. Moreover, we directly demonstrate, with a chromatin immunoprecipitation assay, that the Pit-1beta isoform alters the histone acetylation state of the proximal prolactin promoter. This differential analysis of Pit-1/Pit-1beta isoform function provides significant insights into the structural determinants that govern how different transcription factors with identical DNA sequence specificity can display opposite effects on target gene activity.

Complex interactions between epidermal POU domain and activator protein 1 transcription factors regulate the expression of the profilaggrin gene in normal human epidermal keratinocytes

The human profilaggrin gene is expressed in the granular layer during the late stages of the epidermal differentiation. The proximal promoter region of the gene confers high levels of keratinocyte-specific transcription via interactions with c-Jun/c-Fos heterodimers. Here we provide evidence for another level of complexity in the regulation of the profilaggrin promoter activity. The POU domain proteins Oct1, Skn1a/i, and Oct6, which are abundantly expressed in the epidermal cells, act to both stimulate and repress transcription in a general and a cell type-specific mode. While binding to specific recognition elements within the promoter region, they exert their effects by either stimulating or antagonizing the c-Jun-dependent activity of the promoter. The response of the promoter to forced expression of the POU domain proteins reflects the effect of these transcription factors on the endogenous profilaggrin mRNA synthesis and suggests that the latter requires a fine balance in the amounts and the activities of the individual activator protein 1 and POU domain proteins.