Serum, AP-1 and Ets-1 stimulate the human ets-1 promoter

Syndecan-1 Promotes Hepatocyte-Like Differentiation of Hepatoma Cells Targeting Ets-1 and AP-1

Syndecan-1 is a transmembrane heparan sulfate proteoglycan which is indispensable in the structural and functional integrity of epithelia. Normal hepatocytes display strong cell surface expression of syndecan-1; however, upon malignant transformation, they may lose it from their cell surfaces. In this study, we demonstrate that re-expression of full-length or ectodomain-deleted syndecan-1 in hepatocellular carcinoma cells downregulates phosphorylation of ERK1/2 and p38, with the truncated form exerting an even stronger effect than the full-length protein. Furthermore, overexpression of syndecan-1 in hepatoma cells is associated with a shift of heparan sulfate structure toward a highly sulfated type specific for normal liver. As a result, cell proliferation and proteolytic shedding of syndecan-1 from the cell surface are restrained, which facilitates redifferentiation of hepatoma cells to a more hepatocyte-like phenotype. Our results highlight the importance of syndecan-1 in the formation and maintenance of differentiated epithelial characteristics in hepatocytes partly via the HGF/ERK/Ets-1 signal transduction pathway. Downregulation of Ets-1 expression alone, however, was not sufficient to replicate the phenotype of syndecan-1 overexpressing cells, indicating the need for additional molecular mechanisms. Accordingly, a reporter gene assay revealed the inhibition of Ets-1 as well as AP-1 transcription factor-induced promoter activation, presumably an effect of the heparan sulfate switch.

TERT expression is susceptible to BRAF and ETS-factor inhibition in BRAFV600E/TERT promoter double-mutated glioma

The BRAF gene and the TERT promoter are among the most frequently altered genomic loci in low-grade (LGG) and high-grade-glioma (HGG), respectively. The coexistence of BRAF and TERT promoter aberrations characterizes a subset of aggressive glioma. Therefore, we investigated interactions between those alterations in malignant glioma. We analyzed co-occurrence of BRAFV600E and TERT promoter mutations in our clinical data (n = 8) in addition to published datasets (n = 103) and established a BRAFV600E-positive glioma cell panel (n = 9) for in vitro analyses. We investigated altered gene expression, signaling events and TERT promoter activity upon BRAF- and E-twenty-six (ETS)-factor inhibition by qRT-PCR, chromatin immunoprecipitation (ChIP), Western blots and luciferase reporter assays. TERT promoter mutations were significantly enriched in BRAFV600E-mutated HGG as compared to BRAFV600E-mutated LGG. In vitro, BRAFV600E/TERT promoter double-mutant glioma cells showed exceptional sensitivity towards BRAF-targeting agents. Remarkably, BRAF-inhibition attenuated TERT expression and TERT promoter activity exclusively in double-mutant models, while TERT expression was undetectable in BRAFV600E-only cells. Various ETS-factors were broadly expressed, however, only ETS1 expression and phosphorylation were consistently downregulated following BRAF-inhibition. Knock-down experiments and ChIP corroborated the notion of a functional role for ETS1 and, accordingly, all double-mutant tumor cells were highly sensitive towards the ETS-factor inhibitor YK-4-279. In conclusion, our data suggest that concomitant BRAFV600E and TERT promoter mutations synergistically support cancer cell proliferation and immortalization. ETS1 links these two driver alterations functionally and may represent a promising therapeutic target in this aggressive glioma subgroup.

Upregulation of Ets1 expression by NFATc2 and NFKB1/RELA promotes breast cancer cell invasiveness

Breast cancer is highly aggressive and is the leading cause of cancer-related mortality in women in developed countries. The ETS proto-oncogene 1 (Ets1) has versatile roles during the cellular processes of cancer development. It is often highly expressed in breast cancers and mediates migration and invasion of human breast cancer cells. However, underlying mechanisms of Ets1 gene expression is still ambiguous. Here, we identified a core-regulatory element (CRE) located in the Ets1 promoter region (−540/−80 bp from TSS) that contains elements responsible for associating with NFATs and NF-κBs. Compared with the less metastatic breast cancer cells, metastatic breast cancer cells (MDA-MB-231) show open chromatin configurations in the CRE, which facilitates direct binding of NFATc2 and/or NFKB1/RELA complex to trans-activate Ets1 transcription. Moreover, enhanced level of Nfatc2 and Nfkb1 positively correlated with Ets1 expression in the human breast cancer specimens. Deletion of the CRE region by CRISPR/Cas9 system resulted in significant reduction in Ets1 expression, which led to alterations of Ets1-mediated transcription programs including tumor invasiveness-related genes. Proper regulation of Ets1 gene expression by targeting the NFATc2 and NFKB1/RELA interaction could be a potential therapeutic target for Ets1-mediated metastatic breast cancer.

The two functionally distinct amino termini of chicken c-ets-1 products arise from alternative promoter usage

The chicken c-ets-1 locus gives rise to two distinct transcription factors differing by structurally and functionally unrelated N-termini. p54c-ets-1 shows a striking phylogenetic conservation from Xenopus to humans, while p68c-ets-1, the cellular counterpart of the E26-derived v-ets oncogene, is apparently restricted to avian and reptilian species. In the chick embryo, both mRNAs are expressed in a wide array of tissues of mesodermal origin; however, in the embryo and after hatching, p68c-ets-1 is excluded from lymphoid cells where p54c-ets-1 accumulates. In this report, we define the basis of the differential expression of the chicken c-ets-1 products to assess their different potentials as transcription factors. We demonstrate that the two distinct N-termini arise from alternative promoter usage within the chicken c-ets-1 locus. Examination of both promoters reveals that transcription initiates from multiple sites, consistent with the absence of TATA and CAAT elements. Of these two regulatory regions, only the one that initiates the p54c-ets-1 mRNA synthesis is of the G + C-rich type, and its organization is conserved in humans. The avian-specific p68c-ets-1 promoter activity was enhanced by its own product. In addition, we identify numerous potential binding sites for lymphoid-specific transcription factors that might contribute to a tight repressor effect in lymphoid tissues.

ETV4 transcription factor and MMP13 metalloprotease are interplaying actors of breast tumorigenesis

BACKGROUND

The ETS transcription factor ETV4 is involved in the main steps of organogenesis and is also a significant mediator of tumorigenesis and metastasis, such as in breast cancer. Indeed, ETV4 is overexpressed in breast tumors and is associated with distant metastasis and poor prognosis. However, the cellular and molecular events regulated by this factor are still misunderstood. In mammary epithelial cells, ETV4 controls the expression of many genes, MMP13 among them. The aim of this study was to understand the function of MMP13 during ETV4-driven tumorigenesis.

METHODS

Different constructs of the MMP13 gene promoter were used to study the direct regulation of MMP13 by ETV4. Moreover, cell proliferation, migration, invasion, anchorage-independent growth, and in vivo tumorigenicity were assayed using models of mammary epithelial and cancer cells in which the expression of MMP13 and/or ETV4 is modulated. Importantly, the expression of MMP13 and ETV4 messenger RNA was characterized in 456 breast cancer samples.

RESULTS

Our results revealed that ETV4 promotes proliferation, migration, invasion, and anchorage-independent growth of the MMT mouse mammary tumorigenic cell line. By investigating molecular events downstream of ETV4, we found that MMP13, an extracellular metalloprotease, was an ETV4 target gene. By overexpressing or repressing MMP13, we showed that this metalloprotease contributes to proliferation, migration, and anchorage-independent clonogenicity. Furthermore, we demonstrated that MMP13 inhibition disturbs proliferation, migration, and invasion induced by ETV4 and participates to ETV4-induced tumor formation in immunodeficient mice. Finally, ETV4 and MMP13 co-overexpression is associated with poor prognosis in breast cancer.

CONCLUSION

MMP13 potentiates the effects of the ETV4 oncogene during breast cancer genesis and progression.

ETS-targeted therapy: can it substitute for MEK inhibitors?

BACKGROUND

The RAS/MAPK pathway has been intensively studied in cancer. Constitutive activation of ERK1 and ERK2 is frequently found in cancer cells from a variety of tissues. In clinical practice and clinical trials, small molecules targeting receptor tyrosine kinases or components in the MAPK cascade are used for treatment. MEK1 and MEK2 are ideal targets because these enzymes are physiologically important and have narrow substrate specificities and distinctive structural characteristics. Despite success in pre-clinical testing, only two MEK inhibitors, trametinib and cobimetinib, have been approved, both for treatment of BRAF-mutant melanoma. Surprisingly, the efficacy of MEK inhibitors in other tumors has been disappointing. These facts suggest the need for a different approach. We here consider transcription factor ETS1 and ETS2 as alternate therapeutic targets because they are major MAPK downstream effectors.

MAIN TEXT

The lack of clinical efficacy of MEK inhibitors is attributed mostly to a subsequent loss of negative feedback regulation in the MAPK pathway. To overcome this obstacle, second-generation MEK inhibitors, so-called "feedback busters," have been developed. However, their efficacy is still unsatisfactory in the majority of cancers. To substitute ETS-targeted therapy, therapeutic strategies to modulate the transcription factor in cancer must be considered. Chemical targeting of ETS1 for proteolysis is a promising strategy; Src and USP9X inhibitors might achieve this by accelerating ETS1 protein turnover. Targeting the ETS1 interface might have great therapeutic value because ETS1 dimerizes itself or with other transcription factors to regulate target genes. In addition, transcriptional cofactors, including CBP/p300 and BRD4, represent intriguing targets for both ETS1 and ETS2.

CONCLUSIONS

ETS-targeted therapy appears to be promising. However, it may have a potential problem. It might inhibit autoregulatory negative feedback loops in the MAPK pathway, with consequent resistance to cell death by ERK1 and ERK2 activation. Further research is warranted to explore clinically applicable ways to inhibit ETS1 and ETS2.

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.

EGFR inhibition evokes innate drug resistance in lung cancer cells by preventing Akt activity and thus inactivating Ets-1 function

Nonsmall cell lung cancer (NSCLC) is the leading cause of cancer death worldwide. About 14% of NSCLCs harbor mutations in epidermal growth factor receptor (EGFR). Despite remarkable progress in treatment with tyrosine kinase inhibitors (TKIs), only 5% of patients achieve tumor reduction >90%. The limited primary responses are attributed partly to drug resistance inherent in the tumor cells before therapy begins. Recent reports showed that activation of receptor tyrosine kinases (RTKs) is an important determinant of this innate drug resistance. In contrast, we demonstrate that EGFR inhibition promotes innate drug resistance despite blockade of RTK activity in NSCLC cells. EGFR TKIs decrease both the mitogen-activated protein kinase (MAPK) and Akt protein kinase pathways for a short time, after which the Ras/MAPK pathway becomes reactivated. Akt inhibition selectively blocks the transcriptional activation of Ets-1, which inhibits its target gene, dual specificity phosphatase 6 (DUSP6), a negative regulator specific for ERK1/2. As a result, ERK1/2 is activated. Furthermore, elevated c-Src stimulates Ras GTP-loading and activates Raf and MEK kinases. These observations suggest that not only ERK1/2 but also Akt activity is essential to maintain Ets-1 in an active state. Therefore, despite high levels of ERK1/2, Ets-1 target genes including DUSP6 and cyclins D1, D3, and E2 remain suppressed by Akt inhibition. Reduction of DUSP6 in combination with elevated c-Src renews activation of the Ras/MAPK pathway, which enhances cell survival by accelerating Bim protein turnover. Thus, EGFR TKIs evoke innate drug resistance by preventing Akt activity and inactivating Ets-1 function in NSCLC cells.

Suppressive effect of SATB1 on hepatic stellate cell activation and liver fibrosis in rats

Liver fibrosis is a worldwide clinical issue. Activation of hepatic stellate cells (HSCs) is the central event during liver fibrosis. We investigated the role of SATB1 in HSC activation and liver fibrogenesis. The results show that SATB1 expression is reduced during HSC activation. Additionally, SATB1 inhibits HSC activation, proliferation, migration, and collagen synthesis. Furthermore, CTGF, a pro-fibrotic agent, is also significantly inhibited by SATB1 through the Ras/Raf-1/MEK/ERK/Ets-1 pathway. In vivo, SATB1 deactivates HSCs and attenuates fibrosis in TAA-induced fibrotic rat livers. These data indicate that SATB1 plays an important role in HSC activation and liver fibrosis.

c-ETS1 facilitates G1/S-phase transition by up-regulating cyclin E and CDK2 genes and cooperates with hepatitis B virus X protein for their deregulation

Recent studies on the molecular mechanisms responsible for cell cycle deregulation in cancer have puzzled out the role of oncogenes in mediating unscheduled cellular proliferation. This is reminiscence of their activity as proto-oncogenes that drives scheduled cell cycle progression under physiological conditions. Working on the cell cycle regulatory activity of proto-oncogene, we observed that c-ETS1 transcriptionally up-regulated both cyclin E and CDK2 genes, the master regulators of G(1)/S-phase transition. The process was mediated by kinetic coherence of c-ETS1 expression and its recruitment to both promoters during G(1)/S-phase transition. Furthermore, enforced expression of c-ETS1 helped G(0)-arrested cells to progress into G(1)/S-phases apparently due to the activation of cyclin E/CDK2 genes. Physiological induction of c-ETS1 by EGF showed the remodeling of mononucleosomes bound to the c-ETS1 binding site on both promoters during their activation. The exchange of HDAC1 with histone acetyltransferase-p300 was contemporaneous to the chromatin remodeling with consequent increase in histone H3K9 acetylation. Furthermore, the ATP-dependent chromatin remodeler hBRM1 recruitment was also associated with nucleosome remodeling and promoter occupancy of phospho-Ser5 RNA polymerase II. Intriguingly, the activity of the HBx viral oncoprotein was dependent on c-ETS1 in a hepatotropic manner, which led to the activation of cyclin E/CDK2 genes. Thus, cyclin E and CDK2 genes are key physiological effectors of the c-ETS1 proto-oncogene. Furthermore, c-ETS1 is indispensable for the hepatotropic action of HBx in cell cycle deregulation.

Ets-1 mediates upregulation of Mcl-1 downstream of XBP-1 in human melanoma cells upon ER stress

Past studies have shown that upregulation of the anti-apoptotic Bcl-2 family protein Mcl-1 is a major adaptive mechanism of melanoma cells to endoplasmic reticulum (ER) stress, and has an important role in resistance of the cells to apoptosis. In this study, we show that the increase in transcription of Mcl-1 in melanoma cells triggered by pharmacological ER stress inducers is mediated by the transcription factor Ets-1. By incremental deletion analysis of the Mcl-1 promoter, we identified a DNA fragment containing an Ets-1 binding site that is transcriptionally responsive to ER stress. Mutations in the Ets-1 binding site or knockdown of Ets-1 inhibited the increase in Mcl-1, indicating that Ets-1 has a critical role in transcriptional upregulation of Mcl-1. Similar to Mcl-1, Ets-1 was transcriptionally upregulated by ER stress. This was mediated by the IRE1α/XBP-1 branch of the unfolded protein response, as upregulation of Ets-1 was inhibited in melanoma cell lines deficient in IRE1α or XBP-1 established by short hairpin RNA knockdown. Activation of the PI3k/Akt pathway downstream of XBP-1 was also involved, in that inhibition of the pathway blocked upregulation of Ets-1. Inhibition of Ets-1 enhanced ER stress-induced apoptosis in melanoma cell lines and in fresh melanoma isolates, recapitulating the effect of inhibition of Mcl-1. These results reveal a key mechanism by which Mcl-1 is transcriptionally upregulated in melanoma cells by ER stress, and identify Ets-1 as a potential target for inhibition to sensitize melanoma cells to apoptosis.

c-Jun regulates phosphoinositide-dependent kinase 1 transcription: implication for Akt and protein kinase C activities and melanoma tumorigenesis

Mutations in N-RAS and B-RAF, which commonly occur in melanomas, result in constitutive activation of the mitogen-activated protein kinase (MAPK)/extracellular signal-regulated protein kinase (ERK) signaling. Active ERK increases expression and activity of the c-Jun transcription factor, linking ERK and Jun N-terminal kinase (JNK) cascades. Here, we show that c-Jun regulates transcription of phosphoinositide-dependent kinase 1 (PDK1) with a concomitant impact on Akt and protein kinase C (PKC) activity and related substrates. Inhibition of c-Jun reduces PDK1 expression and attenuates Akt and PKC activity, which can be restored by exogenous PDK1. c-Jun regulation of PDK1 in melanoma contributes to growth rate and the ability to form tumors in mice. Correspondingly, increased levels of c-Jun in melanoma cell lines coincide with up-regulation of PDK1 and phosphorylation of PKC and Akt. The identification of c-Jun as a transcriptional regulator of PDK1 expression highlights key mechanisms underlying c-Jun oncogenic activity, and provides new insight into the nature of up-regulated Akt and PKC in melanoma.

Shear stress-induced Ets-1 modulates protease inhibitor expression in microvascular endothelial cells

Elevated shear stress within the skeletal muscle microvasculature is implicated in the induction of a longitudinal splitting form of angiogenesis, which is characterized by the lack of basement membrane breakage. We investigated whether the transcriptional regulator, Ets-1, is responsive to changes in hemodynamic forces and if so, whether Ets-1 controls microvascular endothelial cell integrity by inducing the expression of inhibitors of matrix degrading proteases. Rats were treated with prazosin for 2, 4, and 7 days to increase in microvascular shear stress in hindlimb skeletal muscles. In complimentary in vitro experiments, rat microvascular skeletal muscle endothelial cells were exposed to laminar shear stress (15 dyne/cm(2)) for 0.5, 2, and 24 h. TaqMan PCR analysis of laser microdissected capillaries isolated from EDL muscles demonstrated transient (after 2 days) induction of Ets-1 gene expression. In cultured cells, a transient up-regulation of Ets-1 mRNA was observed after 2 h shear stimulation, accompanied by increased phosphorylation of Ets-1 and enhanced Ets-1 DNA binding activity. This response was modulated by ERK1/2 and p38 MAP kinases, but was not dependent on NOS or COX-2 activity. PAI-1, TIMP-1 and TIMP-3 mRNA were elevated significantly in prazosin treated EDL, and in response to shear stimulation in vitro. In cultured endothelial cells, Ets-1 RNA interference abolished the shear-induced increases in Ets-1, PAI-1, TIMP-1, and TIMP-3 mRNA expression. These results suggest that enhanced laminar shear stress may act to preserve the integrity of microvascular walls in part through Ets-1-dependent induction of protease inhibitors.

Stromelysin-1 expression is activated in vivo by Ets-1 through palindromic head-to-head Ets binding sites present in the promoter

Regulation of the gene expression of Stromelysin-1 (matrix metalloproteinase-3), a member of the matrix metalloproteinase family, is critical for tissue homeostasis. The Stromelysin-1 promoter is known to be transactivated by Ets proteins through palindromic head-to-head Ets binding sites (EBS), an unusual configuration among metalloproteinase promoters. Patterns of increased co-expression of Stromelysin-1 and Ets-1 genes have been observed in pathological processes such as rheumatoid arthritis, glomerulonephritis and tumor invasion. In this context, we show in a synovial fibroblastic model cell line (HIG-82), which is able to co-express Stromelysin-1 and Ets-1, that the EBS palindrome is essential for the expression of Stromelysin-1. More precisely, using electrophoretic mobility shift assays, DNA affinity purification and chromatin immunoprecipitation, we demonstrate that endogenous Ets-1, but not Ets-2, is present on this palindrome. The use of a dominant-negative form of Ets-1 and the decrease of Ets-1 amount either by fumagillin, an antiangiogenic compound, or by short interfering RNA show that the activation rate of the promoter and the expression of Stromelysin-1 correlate with the level of endogenous Ets-1. Thus, it is the first demonstration, using this cellular model, that endogenously expressed Ets-1 is actually a main activator of the Stromelysin-1 promoter through its effective binding to the EBS palindrome.

Effect of staurosporine on N-glycosylation and cell adhesion to fibronectin of SW480 human colorectal adenocarcinoma cells

As N-glycosylation of tumor cell surface proteins affects metastasis of the cells, it was considered that the suppression of metastasis by staurosporine, a protein kinase C inhibitor, is partly caused by changes in N-glycosylation. To examine this possibility, we studied the glycosylation of membrane proteins of SW480 human colorectal adenocarcinoma cells before and after treatment with staurosporine by lectin blot analysis. The results showed that the reactivity of leuko-agglutinating phytohemagglutinin and Datura stramonium agglutinin, both of which bind to highly branched N-linked oligosaccharides characteristic of cancer cells, decreases significantly in the staurosporine-treated cells. In accordance with this, the gene expression of the N-acetylglucosaminyltransferase V, which synthesizes the GlcNAcbeta1-->6 branch of highly branched N-linked oligosaccharides decreased by 30-40% in the drug-treated cells. Since a decrease in the lectin binding was found in several glycoproteins including fibronectin (FN)-receptor, effect of the changes in N-glycosylation of the cells on cell adhesion to FN-matrix was examined. The results showed that the number of cells attached to FN-matrix increases upon treatment of the cells with staurosporine, indicating that the change of N-glycosylation of the FN-receptor promotes cell adhesion to the extracellular matrix, which may lead to the suppression of metastasis of cancer cells.

Integrin α5 expression by the ARPE-19 cell line: comparison with primary RPE cultures and effect of growth medium on the α5 gene promoter strength

Primary cultures of human retinal pigment epithelium (RPE) requires young human donors with short post-mortem time and no known retinal diseases. The use of an established human RPE cell line, like ARPE-19, would be a welcomed alternative to primary cultures. This cell line retains many of the characteristics of RPE cells, including cell morphology, functional tight junctions and expression of CRALBP and RPE65. This study was conducted in order to investigate integrin alpha5 expression at both the gene and protein level in the ARPE-19 cell line and compare the results with those obtained with primary cultures of RPE cells. The potential use of this cell line as a substitute for primary cultures of RPE cells was also considered. Integrin alpha5 protein was detected on RPE and ARPE-19 cultures at different confluencies by immunofluorescence and immunoprecipitation analyses. Semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) was used to study alpha5 mRNA levels. Transient transfections were performed in order to compare alpha5 promoter strength in both types of cells. Immunofluorescence studies showed that both primary RPE and ARPE-19 cells yielded similar alpha5 staining patterns at all cell confluencies. Both immunoprecipitation and RT-PCR analyses provided evidence that sub-confluent and confluent RPE and ARPE-19 cells have similar cell surface alpha5 protein and mRNA levels whereas post-confluent cells had a marked decrease in both protein and transcript levels. ARPE-19 cells show a large increase in promoter strength compared to primary cultures. When compared to primary cultures, the cell line exhibited major differences in the way the alpha5 promoter is regulated, even if both cell types are cultured under identical conditions. This study demonstrates that primary cultures of human RPE and ARPE-19 cells show reductions in both the alpha5 protein and the mRNA when cells reach post-confluency. However, major differences have been observed in the strength of the alpha5 promoter between both cell types. We also show that culturing ARPE-19 cells in a different growth medium alters the transcriptional activity directed by the alpha5 promoter.

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.

A 27 bp cis-acting sequence is essential for L-type calcium channel alpha(1C) subunit expression in vascular smooth muscle cells

Expression of L-type calcium channels in cardiac myocytes and vascular smooth muscle cells (VSMC) critically regulates the contractile state of these cells. In order to discover the elements in the promoter region of the Ca(v)1.2 gene encoding the vascular/cardiac calcium channel alpha(1C) subunit that are important for the basal gene expression, approximately 2 kb of the 5'-flanking sequence of the Ca(v)1.2 gene has been cloned in our lab. In this study, using various lengths of the 5'-flanking DNA fused with a luciferase gene as a reporter, we have defined a 493-bp fragment of the cis-regulatory DNA which carries the majority of promoter activity in pulmonary artery smooth muscle (PAC1) cells. DNase I footprinting analysis of this 493-bp DNA using nuclear extracts from PAC1 cells revealed a 27-bp DNA sequence that contains a c-Ets like motif (CAGGATGC). Mutation of the Ets-like site and the respective flanking sequence within the DNase I footprinting protection region induced a marked change in the promoter activity in PAC1 cells. Electrophoretic mobility shift assays (EMSA) confirmed the presence of specific binding factor(s) in PAC1 cells' nuclear extracts for this 27-bp DNA. Competition studies with the wild-type and mutated DNA fragments established the importance of the 27 bp DNA sequence for high-affinity binding of the nuclear proteins to the promoter. We conclude that there is a 27 bp region in the promoter of the Ca(v)1.2 gene to which nuclear proteins from VSMC bind and strongly regulate the basal promoter activity.

Transforming growth factor beta regulates parathyroid hormone-related protein expression in MDA-MB-231 breast cancer cells through a novel Smad/Ets synergism

The majority of breast cancers metastasizing to bone secrete parathyroid hormone-related protein (PTHrP). PTHrP induces local osteolysis that leads to activation of bone matrix-borne transforming growth factor beta (TGF beta). In turn, TGF beta stimulates PTHrP expression and, thereby, accelerates bone destruction. We studied the mechanism by which TGF beta activates PTHrP in invasive MDA-MB-231 breast cancer cells. We demonstrate that TGF beta 1 up-regulates specifically the level of PTHrP P3 promoter-derived RNA in an actinomycin D-sensitive fashion. Transient transfection studies revealed that TGF beta 1 and its effector Smad3 are able to activate the P3 promoter. This effect depended upon an AGAC box and a previously described Ets binding site. Addition of Ets1 greatly enhanced the Smad3/TGF beta-mediated activation. Ets2 had also some effect, whereas other Ets proteins, Elf-1, Ese-1, and Erf-1, failed to cooperate with Smad3. In comparison, Ets1 did not increase Smad3/TGF beta-induced stimulation of the TGF beta-responsive plasminogen activator inhibitor 1 (PAI-1) promoter. Smad3 and Smad4 were able to specifically interact with the PTHrP P3-AGAC box and to bind to the P3 promoter together with Ets1. Inhibition of endogenous Ets1 expression by calphostin C abrogated TGF beta-induced up-regulation of the P3 transcript, whereas it did not affect the TGF beta effect on PAI expression. In TGF beta receptor II- and Ets1-deficient, noninvasive MCF-7 breast cancer cells, TGF beta 1 neither influenced endogenous PTHrP expression nor stimulated the PTHrP P3 promoter. These data suggest that TGF beta activates PTHrP expression by specifically up-regulating transcription from the PTHrP P3 promoter through a novel Smad3/Ets1 synergism.

Transcriptional coordination of the genes encoding catalytic (CK2alpha) and regulatory (CK2beta) subunits of human protein kinase CK2

Little is known of how protein kinase CK2 genes are regulated, and it is unclear whether there are mechanisms of transcriptional coordination. Response elements present in the promoter sequences of the human catalytic (CK2alpha) and regulatory (CK2beta) subunit genes have been examined for the significance in transcriptional control using reporter gene assays, electrophoretic mobility shift assays, site-directed mutagenesis, ectopic protein expressions, and transcript assessments. Most strikingly, in both promoters the regions of highest transcriptional activity contain two adjoining, completely identical and conserved Ets1 response elements, and both the mutation of motifs and the overexpression of Ets1 affect significantly transcriptional activity. Also in common are Sp1 response elements that cooperate with Ets1, and Sp1 is phosphorylatable by CK2 holoenzyme but not by individual CK2alpha, the phosphorylation negatively affecting DNA binding. CK2alpha and CK2beta transcript levels and stoichiometries of mRNA species turned out quite constant in cultured cells despite progressing through various stages of proliferation and differentiation. The data seem to indicate transcriptional coordination of the human genes encoding CK2alpha and CK2beta based on an Ets1 double motif common to both genes cooperating with Sp1 motifs and amenable to negative feedback control by the gene products which, following complexation into CK2 holoenzyme, could phosphorylate Sp1 (and Ets1?) and thus downregulate transcription and contribute to the observed constant cellular CK2alpha and CK2beta transcripts situation.

Ets1 is a common element in directing transcription of the alpha and beta genes of human protein kinase CK2

Protein kinase CK2 is a conserved and vital Ser/Thr phosphotransferase with various links to malignant diseases, occurring as a tetramer composed of two catalytically active (CK2alpha and/or CK2alpha') and two regulatory subunits (CK2beta). There is balanced availability of CK2alpha and CK2beta transcripts in proliferating and differentiating cultured cells. Examination of the human CK2beta gene for transcriptionally active regions by systematic deletions and reporter gene assays indicates strong promoter activity at positions -42 to 14 and 12 to 72 containing transcription start sites 1 and 2 of the gene (positions +1 and 33), respectively, an upstream and a downstream enhancer activity at positions -241 to -168 and 123 to 677, respectively, and silencer activity at positions -241 to -261. Of the various transcription factor binding motifs present in those regions, Ets1 and CAAT-related motifs turned out to be of particular importance, Ets1 for promoter activation and CAAT-related motifs for enhancer activation. In addition, there are contributions by Sp1. Most strikingly, the Ets1 region representing two adjoining consensus motifs also occurs with complete identity in the recently characterized promoter of the CK2alpha gene [Krehan, A., Ansuini, H., Böcher, O., Grein, S., Wirkner, U. & Pyerin, W. (2001) J. Biol. Chem. 275, 18327-18336], and affects comparably, when assayed in parallel, the promoters of both CK2 genes, both by motif mutations and by Ets1 overexpression. The data strongly support the hypothesis that Ets1 acts as a common regulatory element of the CK2alpha and CK2beta genes involved in directing coordinate transcription and contributing to the balanced availability of transcripts.

Natural biology of polyomavirus middle T antigen

"It has been commented by someone that 'polyoma' is an adjective composed of a prefix and suffix, with no root between--a meatless linguistic sandwich" (C. J. Dawe). The very name "polyomavirus" is a vague mantel: a name given before our understanding of these viral agents was clear but implying a clear tumor life-style, as noted by the late C. J. Dawe. However, polyomavirus are not by nature tumor-inducing agents. Since it is the purpose of this review to consider the natural function of middle T antigen (MT), encoded by one of the seemingly crucial transforming genes of polyomavirus, we will reconsider and redefine the virus and its MT gene in the context of its natural biology and function. This review was motivated by our recent in vivo analysis of MT function. Using intranasal inoculation of adult SCID mice, we have shown that polyomavirus can replicate with an MT lacking all functions associated with transformation to similar levels to wild-type virus. These observations, along with an almost indistinguishable replication of all MT mutants with respect to wild-type viruses in adult competent mice, illustrate that MT can have a play subtle role in acute replication and persistence. The most notable effect of MT mutants was in infections of newborns, indicating that polyomavirus may be highly adapted to replication in newborn lungs. It is from this context that our current understanding of this well-studied virus and gene is presented.

The Ets1 proto-oncogene is upregulated by retinoic acid: characterization of a functional retinoic acid response element in the Ets1 promoter

The v-ets oncoprotein and its progenitor Ets1 belong to a family of transcription factors that are related by an 85 amino acid conserved DNA binding domain, the ets domain. Ets1 plays important role(s) in control of cell proliferation, differentiation and apoptosis. Abnormal expression of Ets1 could lead to disruption of these processes and contribute to development of malignancy. Retinoic acid (RA) inhibits proliferation, induces differentiation and regulates apoptosis in many different cell types. Here, we demonstrate that RA treatment increases the expression of Ets1 mRNA, but not that of Ets2, Elk1 or Fli1 in MC3T3-E1 cells. Ets1 induction is detectable after 4 h, can be maintained for at least 14 days, and is inhibited by Actinomycin D, which suggests that RA regulation of Ets1 occurs at the transcriptional level. The promoter region of Ets1 contains four retinoic acid response element (RARE) half sites located at -94, -152, -1765 and -2252 from the translation start site. We show that RARbeta is expressed by MC3T3-E1 cells in the presence of RA and demonstrate that it binds to the -94 RARE half site. Furthermore, RA induces transcription of Ets1 promoter-reporter constructs containing this RARE half site.

The human NAD+-dependent 15-hydroxyprostaglandin dehydrogenase gene promoter is controlled by Ets and activating protein-1 transcription factors and progesterone

NAD+-dependent 15-hydroxyprostaglandin dehydrogenase (PGDH) is a key catabolic enzyme in the inactivation of PGF2alpha and PGE2 and therefore serves as an important determinant in regulating their local concentrations. To gain insights into the transcriptional regulation of this enzyme, we have isolated 3.5 kb of the 5'-flanking sequence of the human PGDH promoter and characterized its control in hemopoietic cells and cells of myometrial and placental origin. Several potential binding sites for cAMP-responsive element-binding protein (CREB), Ets, and activating protein-1 (AP-1) transcription factors are present within 2368 bp of the 5'-flanking region. This region and deletions thereof were fused to the luciferase reporter gene and used for transient transfection experiments. In Jurkat leukemic T cells, which express PGDH endogenously, the transfected PGDH promoter was strongly induced by phorbol ester. Induction was reversed by coexpression of A-Fos, a dominant negative to AP-1. In primary cultures of myometrial smooth muscle cells (SMC), the Ets family members Ets-1, Ets-2, and PEA3 potently stimulated transcriptional activity of the PGDH promoter. PEA3-mediated activation was partially repressed by A-Fos, suggesting an involvement of AP-1 proteins, which might be conferred by a distal and a proximal Ets/ AP-1 composite element. The distal Ets/AP-1 element is flanked by two CRE-like sequences. Cotransfection of A-CREB, a dominant negative to CREB, inhibited stimulation of PGDH-2368/luc3 by PEA3 in myometrial SMC, whereas treatment with 8-bromo-cAMP moderately enhanced promoter activity. Progesterone is believed to be an important stimulus for PGDH expression in the utero-placental unit, thus contributing to the maintenance of a quiescent uterus during pregnancy. In myometrial SMC, both isoforms of the progesterone receptor, PR-B and PR-A, caused a ligand-dependent activation of PGDH-2368/luc3. Transcriptional activity of PR-B, but not PR-A, was further enhanced by the addition of 8-bromo-cAMP. We could not confirm a recently proposed transcriptional control of PGDH by mineralocorticoid receptor. No effect of mineralocorticoid receptor, in the absence or presence of aldosterone, with or without 8-bromo-cAMP, was observed on PGDH-2368/luc3. Taken together, these findings demonstrate control of the PGDH promoter by multiple pathways and provide evidence for cross-talk among Ets, AP-1, cAMP, and PR-mediated signaling, suggesting complex regulatory mechanisms for the expression of PGDH.

The GATA-1 and Spi-1 transcriptional factors bind to a GATA/EBS dual element in the Fli-1 exon 1

Fli-1 is a proto-oncogene which is rearranged in tumors induced by three different retroviruses, Cas-Br-E, F-MuLV, and 10A1. This gene is a member of the Ets gene family, a class of transcription factors that recognize and bind to a DNA motif known as the Ets binding site (EBS). Our laboratory has previously cloned and characterized the promoter region of both human and mouse Fli-1 genes. We had then identified several regulatory elements conserved between the two species. Two of them, an exon 1 GATA/EBS dual element and an EBS element located in the 5' end of intron 1, were analysed in the present study. EMSA analysis performed with nuclear extracts from different cell lines showed that the EBS element in intron 1 (EBSi) was bound by one potential Ets-related ubiquitous factor. The GATA/EBS element was bound by several factors that seemed Ets-related, one of which was found to be specifically expressed in hematopoietic cells. the GATA/EBS dual element was thus chosen for further analysis. A human Fli-1-derived genomic fragment containing the GATA/EBS led to enhanced transcription when positioned upstream of the SV40 promoter in the erythroleukemic HEL cell line. In addition, an increasing number of GATA/EBS oligonucleotides upstream of this same promoter resulted in a copy number-dependent increase in luciferase activity which was greatly reduced when the EBS consensus sequence was mutated. One of the factors binding to the GATA/EBS region was identified to be Spi-1 by supershift analysis and was also shown to bind to the EBS element of the human Ets-2 gene. Supershift analysis also demonstrated the binding of the GATA-1 factor to the GATA/EBS dual element. Our results suggest that Spi-1 and GATA-1 might play a key role in the regulation of Fli-1.

Roles of extracellular signal-regulated kinase 1/2 and p38 mitogen-activated protein kinase in the signal transduction of basic fibroblast growth factor in endothelial cells during angiogenesis

We examined the role of mitogen-activated protein (MAP) kinases in the signal transduction of basic fibroblast growth factor (bFGF)-mediated effects in endothelial cells (ECs). When MSS31 murine endothelial cells were stimulated with bFGF, three MAP kinase homologs, extracellular signal-regulated kinase (ERK) 1/2, c-Jun N-terminal kinase (JNK) 1, and p38 MAP kinase were activated. The inhibition of the ERK1/2 pathway with PD98059, a specific inhibitor of MEK1, or of the p38 MAP kinase pathway with SB203580, a specific inhibitor of p38 MAP kinase, abrogated bFGF-mediated tube formation by MSS31 cells in type I collagen gel. Tube formation in type I collagen gel requires proliferation and migration of these cells, and degradation of the extracellular matrix by these cells. Both PD98059 and SB203580 inhibited bFGF-stimulated DNA synthesis as well as migration of MSS31 cells. Cell migration requires cytoskeleton reorganization and cell adhesion. bFGF induced actin reorganization and vinculin assembly in the focal adhesion plaque, both of which were inhibited by SB203580 but not by PD98059. bFGF induced the expression of the transcription factor ETS-1 in MSS31 cells. ETS-1 is responsible for the expression of proteases as well as integrin beta 3 subunit in ECs, and converts ECs to invasive phenotype. PD98059 inhibited this induction of ETS-1, whereas SB203580 did not. These results indicate that ERK1/2 and p38 MAP kinase are requisite for the signal transduction of bFGF in ECs. The roles of these two MAP kinase homologs are not identical, but these kinases work in a coordinated fashion.

Regulation of the human interleukin-5 promoter by Ets transcription factors. Ets1 and Ets2, but not Elf-1, cooperate with GATA3 and HTLV-I Tax1

Interleukin-5 (IL-5), expressed primarily by type-2 T helper (Th2) cells, plays an important role in the development of allergic diseases, such as allergic asthma. Studying the regulation of IL-5 gene expression by Ets transcription factors, we found that Ets1 and Ets2, but not Elf-1, were able to activate the human IL-5 promoter in Jurkat T-cells. This required the presence of either phorbol 12-myristate acetate (PMA) plus ionomycin or PMA plus the viral protein HTLV-I Tax1. By mutation studies, it could be shown that Ets1 and Ets2 exerted their effects on the IL-5 promoter through a GGAA motif within the Cle0 element. In myeloid Kasumi cells, Ets1 and Ets2 failed to stimulate IL-5 promoter activity, unless the T-cell specific transcription factor GATA3 was added. These results show, for the first time, that Ets1 and Ets2 are able to cooperate with GATA3. Both ionomycin and Tax1 increased the combined effect of GATA3 with Ets1 and Ets2 in the presence of PMA. The data further demonstrate that, in addition to Ets1, Ets2 is also able to functionally cooperate with Tax1. The synergism of GATA3 with either Ets1 or Ets2 may play an important role in calcium- or Tax1-dependent regulation of IL-5 expression in Th2 cells or in HTLV-I transformed adult T-cell leukemia cells, respectively.

Autoregulation of eukaryotic transcription factors

The structures of several promoters regulating the expression of eukaryotic transcription factors have in recent years been examined. In many cases there is good evidence for autoregulation, in which a given factor binds to its own promoter and either activates or represses transcription. Autoregulation occurs in all eukaryotes and is an important component in controlling expression of basal, cell cycle specific, inducible response and cell type-specific factors. The basal factors are autoregulatory, being strictly necessary for their own expression, and as such must be epigenetically inherited. Autoregulation of stimulus response factors typically serves to amplify cellular signals transiently and also to attenuate the response whether or not a given inducer remains. Cell cycle-specific transcription factors are positively and negatively autoregulatory, but this frequently depends on interlocking circuits among family members. Autoregulation of cell type-specific factors results in a form of cellular memory that can contribute, or define, a determined state. Autoregulation of transcription factors provides a simple circuitry, useful in many cellular circumstances, that does not require the involvement of additional factors, which, in turn, would need to be subject to another hierarchy of regulation. Autoregulation additionally can provide a direct means to sense and control the cellular conce]ntration of a given factor. However, autoregulatory loops are often dependent on cellular pathways that create the circumstances under which autoregulation occurs.

CCAAT/enhancer-binding protein delta gene expression is mediated by autoregulation through downstream binding sites

CCAAT/enhancer-binding protein delta (C/EBP delta) transcription factor is sharply induced at the early stage of the acute phase response. We previously reported that the C/EBP delta gene expression is induced by the acute-phase response factor/signal transducers and activators of transcription 3 (APRF/STAT3). However, the expression level of the C/EBP delta gene is relatively high up to several hours after the stimulation, whereas APRF/STAT3 is inactivated within one hour. In this report, we identified the two C/EBP delta binding sites at the downstream region of this gene. The binding analysis revealed that both of these sites bound recombinant C/EBP delta protein. A cotransfection analysis identified these sites as the cis-elements for the autoregulation. We conclude that the C/EBP delta gene is activated by APRF/STAT3, and the expression level is then maintained by an autoregulation mechanism.

Regulated expression of the ets-1 transcription factor in vascular smooth muscle cells in vivo and in vitro

Ets-1 regulates the transcription of several genes encoding extracellular matrix proteins (ie, osteopontin and tenascin) as well as enzymes involved in degradation and remodeling of the extracellular matrix (ie, stromelysin and urokinase plasminogen activator). In the present study, we investigated the regulation of c-ets-1 in cultured rat vascular smooth muscle cells as well as in the arterial wall after balloon injury in vivo. Serum-starved smooth muscle cells exposed to serum for various time points express a major c-ets-1 mRNA transcript of 5.3 kb and minor bands of 4.0 and 2.5 kb with a peak at 2 hours after stimulation. These effects were concentration dependent. Western blotting revealed an increase in 55- and 40-kD immunoreactive ets-1 proteins in cells treated with serum for 2 hours, and binding to an oligonucleotide containing the ets-1 consensus cis-acting motif was demonstrated by electrophoretic mobility shift assay. Ets-1 mRNA abundance was induced with a peak at 2 hours after stimulation with platelet-derived growth factor-BB and with angiotensin II. There was a distinct increase of ets-1 immunoreactivity in the inner layer of the media 2 hours after balloon catheter injury of rat arteries, which declined after 6 hours and returned to the basal level 1 day after vessel wall damage. Arterial c-ets-1 mRNA content was induced with an identical time course. These findings suggest that c-ets-1 may be of importance in the mitogenic signaling pathway of smooth muscle cells grown in culture. In addition, ets-1 may play a role in the activation of smooth muscle cells in vivo after mechanical injury of the vessel wall. Because the ets-1 transcription factor activates the gene expression of a number of mRNA species involved in matrix deposition and degradation, these data are compatible with a role for ets-1 in vascular remodeling and/or cell migration.

Anti-immunoglobulin M activates nuclear calcium/calmodulin-dependent protein kinase II in human B lymphocytes

We and others have previously shown that the nuclear protein, Ets-1, is phosphorylated in a calcium-dependent manner after ligation of immunoglobulin (Ig) M on B lymphocytes. As this phosphorylation was independent of protein kinase C activity, we tested whether a calcium/calmodulin-dependent protein kinase (CaM kinase) might phosphorylate the Ets-1 protein after elevation of intracellular free calcium concentrations. The dephosphorylated form of Ets-1 has been shown to bind to chromatin, suggesting that the operative kinase should be detectable in the nucleus. We prepared nuclear extracts from two human B cell lines in which increased intracellular free calcium levels correlated with increased phosphorylation of the Ets-1 protein. Activity of the CaM kinases was determined using a synthetic peptide substrate both in the absence and presence of an inhibitor specific for the CaM kinase family, KN-62. Stimulation of cells with anti-IgM led to increased activity of a nuclear kinase that could phosphorylate the peptide, and this activity was reduced by 10 microM KN-62. Kinase activity was reduced in lysates preadsorbed using an antibody specific for CaM kinase II. Two-dimensional phosphopeptide maps of the Ets-1 protein from cells incubated with ionomycin or anti-IgM contained two unique phosphopeptides that were absent in untreated cells. Incubation of isolated Ets-1 protein with purified CaM kinase II produced phosphorylation of peptides that migrated identically to those found in cells incubated with either anti-IgM or ionomycin. These data suggest a model of signal transduction by the antigen receptor on B lymphocytes in which increased intracellular free calcium can rapidly activate nuclear CaM kinase II, potentially resulting in phosphorylation and regulation of DNA-binding proteins.

A direct physical association between ETS and AP-1 transcription factors in normal human T cells

The Ets and AP-1 families of transcription factors bind distinct DNA elements and subserve diverse functions in multiple lymphoid and nonlymphoid cell types. Functionally important Ets and AP-1 binding sites have been identified in a large number of enhancer elements, suggesting important cooperative interactions between these two families of transcription factors. In this report, we have demonstrated a direct physical interaction between Ets and AP-1 proteins both in vitro and in activated human T cells. This interaction is mediated by the binding of the basic domain of Jun to the Ets domain of Ets proteins. Jun, in association with Ets, is capable of interacting with Fos family members to form a trimolecular protein complex. The physical association between Ets-1 and AP-1 proteins is required for the transcriptional activity of enhancer elements containing adjacent Ets and AP-1 binding sites. We conclude that direct physical interactions between Ets and AP-1 transcription factors play an important role in regulating mammalian gene expression.

Regulation of gene expression by transcription factors Ets-1 and Ets-2

The ETS family of transcription factors have a DNA-binding domain in common that binds a core GGA(A/T) DNA sequence. A large number of proteins have now been identified that contain an ETS DNA-binding domain (see review by Wasylyk et al., 1993). Ets-1 was first described as the cellular homolog of v-ets. which is translated as a 135-kDa gag-myb-ets fusion protein from the replication-deficient retrovirus E26 in chickens. Ets-2 was subsequently described as a closely related protein that contains the highly conserved ETS DNA-binding domain. This paper considers the manner by which the two closely related genes, Ets-1 and Ets-2, apparently play distinct roles in embryo development and in the immune system of adult mice. Although both Ets-1 and Ets-2 transform fibroblasts (Seth et al., 1989), the temporal and tissue-specific expression patterns suggest that these two proteins play distinct biological roles and consequently transactivate different downstream cellular target genes.

Identification of a killer cell-specific regulatory element of the mouse perforin gene: an Ets-binding site-homologous motif that interacts with Ets-related proteins

The gene encoding the cytolytic protein perforin is selectively expressed by activated killer lymphocytes. To understand the mechanisms underlying the cell-type-specific expression of this gene, we have characterized the regulatory functions and the DNA-protein interactions of the 5'-flanking region of the mouse perforin gene (Pfp). A region extending from residues +62 through -141, which possesses the essential promoter activity, and regions further upstream, which are able to either enhance or suppress gene expression, were identified. The region between residues -411 and -566 was chosen for further characterization, since it contains an enhancer-like activity. We have identified a 32-mer sequence (residues -491 to -522) which appeared to be capable of enhancing gene expression in a killer cell-specific manner. Within this segment, a 9-mer motif (5'-ACAGGAAGT-3', residues -505 to -497; designated NF-P motif), which is highly homologous to the Ets proto-oncoprotein-binding site, was found to interact with two proteins, NF-P1 and NF-P2. NF-P2 appears to be induced by reagents known to up-regulate the perforin message level and is present exclusively in killer cells. Electrophoretic mobility shift assay and UV cross-linking experiments revealed that NF-P1 and NF-P2 may possess common DNA-binding subunits. However, the larger native molecular mass of NF-P1 suggests that NF-P1 contains an additional non-DNA-binding subunit(s). In view of the homology between the NF-P motif and other Ets proto-oncoprotein-binding sites, it is postulated that NF-P1 and NF-P2 belong to the Ets protein family. Results obtained from the binding competition assay, nevertheless, suggest that NF-P1 and NF-P2 are related to but distinct from Ets proteins, e.g., Ets-1, Ets-2, and NF-AT/Elf-1, known to be expressed in T cells.

Identification of a killer cell-specific regulatory element of the mouse perforin gene: an Ets-binding site-homologous motif that interacts with Ets-related proteins

The gene encoding the cytolytic protein perforin is selectively expressed by activated killer lymphocytes. To understand the mechanisms underlying the cell-type-specific expression of this gene, we have characterized the regulatory functions and the DNA-protein interactions of the 5'-flanking region of the mouse perforin gene (Pfp). A region extending from residues +62 through -141, which possesses the essential promoter activity, and regions further upstream, which are able to either enhance or suppress gene expression, were identified. The region between residues -411 and -566 was chosen for further characterization, since it contains an enhancer-like activity. We have identified a 32-mer sequence (residues -491 to -522) which appeared to be capable of enhancing gene expression in a killer cell-specific manner. Within this segment, a 9-mer motif (5'-ACAGGAAGT-3', residues -505 to -497; designated NF-P motif), which is highly homologous to the Ets proto-oncoprotein-binding site, was found to interact with two proteins, NF-P1 and NF-P2. NF-P2 appears to be induced by reagents known to up-regulate the perforin message level and is present exclusively in killer cells. Electrophoretic mobility shift assay and UV cross-linking experiments revealed that NF-P1 and NF-P2 may possess common DNA-binding subunits. However, the larger native molecular mass of NF-P1 suggests that NF-P1 contains an additional non-DNA-binding subunit(s). In view of the homology between the NF-P motif and other Ets proto-oncoprotein-binding sites, it is postulated that NF-P1 and NF-P2 belong to the Ets protein family. Results obtained from the binding competition assay, nevertheless, suggest that NF-P1 and NF-P2 are related to but distinct from Ets proteins, e.g., Ets-1, Ets-2, and NF-AT/Elf-1, known to be expressed in T cells.

The ets multigene family is conserved throughout the Metazoa

This study provides the first empirical evidence for the conservation of the ets proto-oncogene transcription factor family throughout the Metazoa. Using the polymerase chain reaction with degenerate primers corresponding to conserved sequences within the ETS DNA-binding domain, we have detected ets genes in a range of lower metazoans, including sponges, ctenophores, anemones, flatworms and nematodes, and in several higher invertebrate metazoans. Many of these sequences are significantly divergent from the original v-ets-1 oncogene, although most can be aligned with recently defined groups within the ets gene family. Multiple ETS domain sequences were detected in a number of the lower metazoan species, providing evidence for the existence of an ets multigene family at the earliest stages of metazoan evolution. In contrast, we were unable to detect any ETS sequences in fungal, plant or several protozoan DNAs. Our findings suggest that the duplication and divergence of ets proto-oncogenes responsible for generating the multigene family occurred concomitantly with the development of metazoan animals. In addition, these data corroborate other recent molecular evidence in providing strong support for the monophyletic origin of all multicellular animals, including sponges.

The Ets family of transcription factors

Interest in the Ets proteins has grown enormously over the last decade. The v-ets oncogene was originally discovered as part of a fusion protein expressed by a transforming retrovirus (avian E26), and later shown to be transduced from a cellular gene. About 30 related proteins have now been found in species ranging from flies to humans, that resemble the vEts protein in the so-called 'ets domain'. The ets domain has been shown to be a DNA-binding domain, that specifically interacts with sequences containing the common core trinucleotide GGA. Furthermore, it is involved in protein-protein interactions with co-factors that help determine its biological activity. Many of the Ets-related proteins have been shown to be transcription activators, like other nuclear oncoproteins and anti-oncoproteins (Jun, Fos, Myb, Myc, Rel, p53, etc.). However, Ets-like proteins may have other functions, such as in DNA replication and a general role in transcription activation. Ets proteins have been implicated in regulation of gene expression during a variety of biological processes, including growth control, transformation, T-cell activation, and developmental programs in many organisms. Signals regulating cell growth are transmitted from outside the cell to the nucleus by growth factors and their receptors. G-proteins, kinases and transcription factors. We will discuss how several Ets-related proteins fit into this scheme, and how their activity is regulated both post- and pre-translationally. Loss of normal control is often associated with conversion to an oncoprotein. vEts has been shown to have different properties from its progenitor, which might explain how it has become oncogenic. Oncogene-related products have been implicated in the control of various developmental processes. Evidence is accumulating for a role for Ets family members in Drosophila development, Xenopus oocyte maturation, lymphocyte differentiation, and viral infectious cycles. An ultimate hope in studying transformation by oncoproteins is to understand how cells become cancerous in humans, which would lead to more effective treatments. vEts induces erythroblastosis in chicken. Cellular Ets-family proteins can be activated by proviral insertion in mice and, most interestingly, by chromosome translocation in humans. We are at the beginning of understanding the multiple facets of regulation of Ets activity. Future work on the Ets family promises to provide important insights into both normal control of growth and differentiation, and deregulation in illness.