Ets domain transcription factor PE1 suppresses human interstitial collagenase promoter activity by antagonizing protein-DNA interactions at a critical AP1 element

Identification of an anabolic selective androgen receptor modulator that actively induces death of androgen-independent prostate cancer cells

Prostate cancer (PCa) initially responds to inhibition of androgen receptor (AR) signaling, but inevitably progresses to hormone ablation-resistant disease. Much effort is focused on optimizing this androgen deprivation strategy by improving hormone depletion and AR antagonism. However we found that bicalutamide, a clinically used antiandrogen, actually resembles a selective AR modulator (SARM), as it partially regulates 24% of endogenously 5α-dihydrotestosterone (DHT)-responsive genes in AR(+) MDA-MB-453 breast cancer cells. These data suggested that passive blocking of all AR functions is not required for PCa therapy. Hence, we adopted an active strategy that calls for the development of novel SARMs, which induce a unique gene expression profile that is intolerable to PCa cells. Therefore, we screened 3000 SARMs for the ability to arrest the androgen-independent growth of AR(+) 22Rv1 and LNCaP PCa cells but not AR(-) PC3 or DU145 cells. We identified only one such compound; the 4-aza-steroid, MK-4541, a potent and selective SARM. MK-4541 induces caspase-3 activity and cell death in both androgen-independent, AR(+) PCa cell lines but spares AR(-) cells or AR(+) non-PCa cells. This activity correlates with its promoter context- and cell-type dependent transcriptional effects. In rats, MK-4541 inhibits the trophic effects of DHT on the prostate, but not the levator ani muscle, and triggers an anabolic response in the periosteal compartment of bone. Therefore, MK-4541 has the potential to effectively manage prostatic hypertrophic diseases owing to its antitumor SARM-like mechanism, while simultaneously maintaining the anabolic benefits of natural androgens.

STAT3 controls matrix metalloproteinase-1 expression in colon carcinoma cells by both direct and AP-1-mediated interaction with the MMP-1 promoter

Aberrant activation of STAT3 in colorectal carcinoma (CRC) tissue is correlated with elevated expression of matrix metalloproteinase-1 (MMP-1). We analyzed transcriptional regulation of the human MMP-1 promoter in CRC cells by tyrosine phosphorylated (pY-) STAT3. One of six putative STAT binding elements within a 4.3 kb MMP-1 trancriptional promoter fragment showed a particular high affinity for STAT3 in vitro. However, the most profound regulatory influence on MMP-1 promoter activity resides in a proximal region relative to the transcriptional start, bearing a pair of putative binding sites for STAT3 and AP-1. Mutational analysis of the combined STAT3/AP-1 recognition element revealed that the integrity of the STAT3 binding site is necessary, but not sufficient for both DNA interaction and transcriptional regulation by activated STAT3. Instead, the adjacent AP-1 site was essential for pY-STAT3-mediated transcription on the MMP-1 promoter. DNA-protein binding assays provided strong evidence for complex formation of STAT3 and c-Jun governed by protein-protein contacts. We observed striking coincidence for concerted aberrant activation of both STAT3 and AP-1 in human colon cancer specimens. This finding supports the notion that the combination of inappropriate STAT3 and AP-1 activities drives elevated MMP-1 expression and tissue invasion in colorectal cancer and is of clinical relevance.

Downregulation of Friend leukemia virus integration 1 as a feedback mechanism that restrains lipopolysaccharide induction of matrix metalloproteases and interleukin-10 in human macrophages

The E26 transformation-specific (Ets) proteins are a family of transcription factors with important roles in a variety of cellular processes ranging from proliferation and differentiation to transformation and metastasis. Tissue-specific expression of Ets proteins and their ability to interact with other families of transcription factors contribute to their versatility. In this study, we investigated the regulation of Ets factors in primary human monocytes and macrophages, and their role in matrix metalloprotease (MMP) and cytokine production. The macrophage-activating Toll-like receptor ligand, lipopolysaccharide (LPS), induced the expression of Ets family members epithelium-specific Ets factor 3 (ESE-3) and TEL-2 but rapidly suppressed Friend leukemia virus integration 1 (FLI-1) expression. Modulation of FLI-1 expression using either RNA interference or forced expression identified a positive role for FLI-1 in contributing to LPS-induced expression of MMP-1, MMP-3, MMP-10, and interleukin-10 (IL-10). Thus, the rapid downregulation of FLI-1 expression after LPS stimulation attenuates the induction of various MMPs and IL-10 under inflammatory conditions. In contrast, the expression of IL-6 and TNFα and the effects of interferon (IFN)γ on LPS responses were not dependent on FLI-1. Our results define a novel FLI-1-mediated self-regulatory feedback loop that limits MMP expression and thus may attenuate extent of tissue destruction associated with inflammatory responses.

Identification of anabolic selective androgen receptor modulators with reduced activities in reproductive tissues and sebaceous glands

Androgen replacement therapy is a promising strategy for the treatment of frailty; however, androgens pose risks for unwanted effects including virilization and hypertrophy of reproductive organs. Selective Androgen Receptor Modulators (SARMs) retain the anabolic properties of androgens in bone and muscle while having reduced effects in other tissues. We describe two structurally similar 4-aza-steroidal androgen receptor (AR) ligands, Cl-4AS-1, a full agonist, and TFM-4AS-1, which is a SARM. TFM-4AS-1 is a potent AR ligand (IC(50), 38 nm) that partially activates an AR-dependent MMTV promoter (55% of maximal response) while antagonizing the N-terminal/C-terminal interaction within AR that is required for full receptor activation. Microarray analyses of MDA-MB-453 cells show that whereas Cl-4AS-1 behaves like 5alpha-dihydrotestosterone (DHT), TFM-4AS-1 acts as a gene-selective agonist, inducing some genes as effectively as DHT and others to a lesser extent or not at all. This gene-selective agonism manifests as tissue-selectivity: in ovariectomized rats, Cl-4AS-1 mimics DHT while TFM-4AS-1 promotes the accrual of bone and muscle mass while having reduced effects on reproductive organs and sebaceous glands. Moreover, TFM-4AS-1 does not promote prostate growth and antagonizes DHT in seminal vesicles. To confirm that the biochemical properties of TFM-4AS-1 confer tissue selectivity, we identified a structurally unrelated compound, FTBU-1, with partial agonist activity coupled with antagonism of the N-terminal/C-terminal interaction and found that it also behaves as a SARM. TFM-4AS-1 and FTBU-1 represent two new classes of SARMs and will allow for comparative studies aimed at understanding the biophysical and physiological basis of tissue-selective effects of nuclear receptor ligands.

Lipopolysaccharide-induced expression of matrix metalloproteinases in human monocytes is suppressed by IFN-gamma via superinduction of ATF-3 and suppression of AP-1

Matrix metalloproteinases (MMPs) are induced during inflammatory responses and are important for immune regulation, angiogenesis, wound healing, and tissue remodeling. Expression of MMPs needs to be tightly controlled to avoid excessive tissue damage. In this study, we investigated the regulation of MMP expression by inflammatory factors in primary human monocytes and macrophages. IFN-gamma, which augments inflammatory cytokine production in response to macrophage-activating factors such as TLR ligands, instead broadly suppressed TLR-induced MMP expression. Inhibition of MMP expression was dependent on STAT1 and required de novo protein synthesis. IFN-gamma strongly enhanced TLR-induced expression of the transcriptional repressor activating transcription factor (ATF-3) in a STAT1-dependent manner, which correlated with recruitment of ATF-3 to the endogenous MMP-1 promoter as detected by chromatin immunoprecipitation assays. RNA interference experiments further supported a role for ATF-3 in suppression of MMP-1 expression. In addition, IFN-gamma suppressed DNA binding by AP-1 transcription factors that are known to promote MMP expression and a combination of supershift, RNA interference and overexpression experiments implicated AP-1 family member Fra-1 in the regulation of MMP-1 expression. These results define an IFN-gamma-mediated homeostatic loop that limits the potential for tissue damage associated with inflammation, and identify transcriptional factors that regulate MMP expression in myeloid cells in inflammatory settings.

Nucleolin binds specifically to an AP-1 DNA sequence and represses AP1-dependent transactivation of the matrix metalloproteinase-13 gene

Transcriptional regulation via activator protein-1 (AP-1) protein binding to AP-1 binding sites within gene promoter regions of AP-1 target genes plays a key role in controlling cellular invasion, proliferation, and oncogenesis, and is important to pathogenesis of arthritis and cardiovascular disease. To identify new proteins that interact with the AP-1 DNA binding site, we performed the DNA affinity chromatography-based Nucleotide Affinity Preincubation Specificity TEst of Recognition (NAPSTER) assay, and discovered a 97 kDa protein that binds in vitro to a minimal AP-1 DNA sequence element. Mass spectrometric fragmentation sequencing determined that p97 is nucleolin. Immunoblotting of DNA affinity-purified material with anti-nucleolin antibodies confirmed this identification. Nucleolin also binds the AP-1 site in gel shift assays. Nucleolin interacts in NAPSTER with the AP-1 site within the promoter sequence of the metalloproteinase-13 gene (MMP-13), and binds in vivo in chromatin immunoprecipitation assays in the vicinity of the AP-1 site in the MMP-13 promoter. Overexpression of nucleolin in human HeLa cervical carcinoma cells significantly represses AP-1 dependent gene transactivation of a minimal AP-1 reporter construct and of an MMP-13 promoter reporter sequence. This is the first report of nucleolin binding and transregulation at the AP-1 site.

Signal transducer and activator of transcription 3 activation promotes invasive growth of colon carcinomas through matrix metalloproteinase induction

Signal transducer and activator of transcription 3 (STAT3) is aberrantly activated in colorectal carcinomas (CRCs). Here, we define the relationship between STAT3 function and the malignant properties of colon carcinoma cells. Elevated activation of STAT3 enhances invasive growth of the CRC cell lines. To address mechanisms through which STAT3 influences invasiveness, the protease mRNA expression pattern of CRC biopsies was analyzed and correlated with the STAT3 activity status. These studies revealed a striking coincidence of STAT3 activation and strong expression of matrix metalloproteinases MMP-1, -3, -7, and -9. Immunohistological examination of CRC tumor specimens showed a clear colocalization of MMP-1 and activated STAT3. Experimentally induced STAT3 activity in CRC cell lines enhanced both the level of MMP-1 mRNA and secreted MMP-1 enzymatic activity. A direct connection of STAT3 activity and transcription from the MMP-1 promoter was shown by reporter gene experiments. Moreover, high-affinity binding of STAT3 to STAT recognition elements in both the MMP-1 and MMP-3 promoter was demonstrated. Xenograft tumors arising from implantation of CRC cells into nude mice showed simultaneous appearance and colocalization of p-Y-STAT3 and MMP-1 expression. Our results link aberrant activity of STAT3 in CRC to malignant tumor progression through upregulated expression of MMPs.

Absence of a Correlation between the Presence of a Single Nucleotide Polymorphism in the Matrix Metalloproteinase 1 Promoter and Outcome in Patients of Chondrosarcoma

PURPOSE

Increased levels of matrix metalloproteinase 1 (MMP-1) expression have been associated with poor outcome in chondrosarcoma. The existence of a single nucleotide polymorphism creating an Ets-binding site in the MMP-1 promoter may be one mechanism for elevated MMP-1 transcription. The aim of our study was to identify the prevalence of this single nucleotide polymorphism (SNP) in chondrosarcoma patients, to determine its correlation with disease outcome, and to discern whether it could serve as a prognostic marker in patients with chondrosarcoma.

EXPERIMENTAL DESIGN

Sixty-seven chondrosarcoma specimens were selected sequentially from an established tumor bank with a median duration of 47 months follow-up (range, 24 to 179 months). DNA was extracted, amplified with PCR, and sequenced to determine presence (GG) or absence of the Ets-binding site created by the SNP.

RESULTS

Eighteen (27%) samples were homozygous for the absence of the Ets site, 34 (51%) were heterozygous for the SNP, and 15 (22%) were homozygous for the SNP. The 5-year overall survival rate for patients was 78, 80, and 84%, respectively (P = 0.5527). The disease-free survival rate was 16, 63, and 76%, respectively (P = 0.0801). The 5-year disease-free survival rate for patients with the homozygous G/G genotype was 16%, compared with 71% for patients who were either homozygous or heterozygous for the GG allele (P = 0.0444).

CONCLUSIONS

Despite a statistical correlation between MMP-1 gene expression and outcome in chondrosarcoma, this study demonstrates an absence of a correlation between the presence of the SNP and prognosis in patients with chondrosarcoma.

PE-1/METS, an antiproliferative Ets repressor factor, is induced by CREB-1/CREM-1 during macrophage differentiation

The molecular mechanisms involved in regulating the balance between cellular proliferation and differentiation remain poorly understood. Members of the Ets-domain family of transcription factors are candidates for proteins that might differentially regulate cell cycle control and cell type-specific genes during the differentiation of myeloid progenitor cells. The Ets repressor PE-1/METS has been suggested to contribute to growth arrest during terminal macrophage differentiation by repressing Ets target genes involved in Ras-dependent proliferation. An important feature of this regulatory model is that PE-1/METS is itself induced by the program of macrophage differentiation elicited by M-CSF. Here, we present evidence that the PE-1/METS gene is a transcriptional target of the cyclic AMP response element-binding protein-1 (CREB-1). CREB-1 expression is dramatically up-regulated during macrophage differentiation and phosphorylation of CREB-1 and the related factor CREM-1 are stimulated by M-CSF in a SAPK2/p38-dependent manner. Chromatin immunoprecipitation experiments demonstrate that CREB-1/CREM-1 are recruited to the PE-1/METS promoter as well as to the promoters of other genes that are up-regulated during terminal macrophage differentiation. Overexpression of CREB-1 stimulates the activities of the PE-1/METS, and macrosialin promoters, while expression of a dominant negative form of CREB-1 during macrophage differentiation inhibits expression of the PE-1/METS and macrosialin genes. Inhibition of CREB function also results in reduced expression of CD54 and impaired cell adhesion. Taken together, these findings reveal new roles of CREB-1/CREM-1 as regulators of macrophage differentiation.

Regulation of the human leukemia inhibitory factor gene by ETS transcription factors

OBJECTIVES

Leukemia inhibitory factor (LIF) is a pleiotropic cytokine mainly produced by activated T lymphocytes. We previously demonstrated that human Jurkat T lymphoma cells represent a valid model of LIF gene expression. This study was designed to identify regions critical for LIF promoter activation in Jurkat cells.

METHODS

Luciferase constructs under the control of different portions of the human LIF promoter were transfected into Jurkat cells, and promoter activity was determined by luminometry. Similar experiments were performed with constructs bearing mutations in the putative ETS binding regions in the LIF promoter. RT-PCR, Western blot and gelshift experiments were performed to study expression and DNA binding of ETS factors in lymphoid cells.

RESULTS

With the exception of the shortest construct not including the putative ETS binding sites, all wildtype LIF promoter constructs were strongly inducible by phorbol ester/ionomycin. In contrast, the mutant constructs were significantly less inducible. Cotransfection of the wild-type constructs with ETS expression vectors resulted in significant enhancement of promoter activity. ets-1 and ets-2 mRNA and protein were shown to be expressed in Jurkat cells. Gelshift experiments revealed that proteins present in nuclear extracts from Jurkat cells specifically bind to both artificial ETS consensus sites and ETS binding sites present in the LIF promoter.

CONCLUSIONS

We conclude that binding of ETS transcription factors to the ETS binding sites in the human LIF promoter is critical for its inducibility in response to T cell activators. ETS transcription factors thus play an important functional role within the endocrine-immune network.

Osteopontin transcription in aortic vascular smooth muscle cells is controlled by glucose-regulated upstream stimulatory factor and activator protein-1 activities

The expression of the matrix cytokine osteopontin (OPN) is up-regulated in aortic vascular smooth muscle cells (VSMCs) by diabetes. OPN expression in cultured VSMCs is reciprocally regulated by glucose and 2-deoxyglucose (2-DG; inhibitor of cellular glucose metabolism). Systematic analyses of OPN promoter-luciferase reporter constructs identify a CCTCATGAC motif at nucleotides -80 to -72 relative to the initiation site that supports OPN transcription in VSMCs. The region -83 to -45 encompassing this motif confers basal and glucose- and 2-DG-dependent transcription on an unresponsive promoter. Competition and gel mobility supershift assays identify upstream stimulatory factor (USF; USF1:USF2) and activator protein-1 (AP1; c-Fos:c-Jun) in complexes binding the composite CCTCATGAC element. Glucose up-regulates both AP1 and USF binding activities 2-fold in A7r5 cells and selectively up-regulates USF1 protein levels. By contrast, USF (but not AP1) binding activity is suppressed by 2-DG and restored by glucose treatment. Expression of either USF or AP1 activates the proximal OPN promoter in A7r5 VSMCs in part via the CCTCATGAC element. Moreover, glucose stimulates the transactivation functions of c-Fos and USF1, but not c-Jun, in one-hybrid assays. Mannitol does not regulate binding, transactivation functions, USF1 protein accumulation, or OPN transcription. Thus, OPN gene transcription is regulated by USF and AP1 in aortic VSMCs, entrained to changes in cellular glucose metabolism.

Characterization of an osteoblast-specific enhancer element in the CBFA1 gene

Cbfa1 is a critical regulator of cell differentiation expressed only in the osteochondrogenic lineage. To define the molecular basis of this cell-specific expression we analyzed the murine Cbfa1 promoter. Here we show that the first 976 bp of this promoter are specifically active in osteoblastic cells. Within this region DNase I footprinting delineated a 40-bp area (CE1) protected differently by nuclear extracts from osteoblastic cells and from non-osteoblastic cells. When multimerized, CE1 conferred an osteoblast-specific activity to a heterologous promoter in DNA transfection experiments; this enhancing ability was conserved between mouse, rat, and human CE1 present in the respective Cbfa1 promoters. CE1 site-specific mutagenesis determined that it binds NF1- and AP1-like activities. Further analyses revealed that the NF1 site acts as a repressor in non-osteoblastic cells due to the binding of NF1-A, a NF1 isoform not expressed in osteoblastic cells. In contrast, the AP1 site mediates an osteoblast-specific activation caused by the preferential binding of FosB to CE1 in osteoblastic cells. In summary, this study identified an osteoblast-specific enhancer in the Cbfa1 promoter whose activity is achieved by the combination of an inhibitory and an activatory mechanism.

An induced Ets repressor complex regulates growth arrest during terminal macrophage differentiation

Defining the molecular mechanisms that coordinately regulate proliferation and differentiation is a central issue in development. Here, we describe a mechanism in which induction of the Ets repressor METS/PE1 links terminal differentiation to cell cycle arrest. Using macrophages as a model, we provide evidence that METS/PE1 blocks Ras-dependent proliferation without inhibiting Ras-dependent expression of cell type-specific genes by selectively replacing Ets activators on the promoters of cell cycle control genes. Antiproliferative effects of METS require its interaction with DP103, a DEAD box-containing protein that assembles a novel corepressor complex. Functional interactions between the METS/DP103 complex and E2F/ pRB family proteins are also necessary for inhibition of cellular proliferation, suggesting a combinatorial code that directs permanent cell cycle exit during terminal differentiation.

Repression of activator protein-1-mediated transcriptional activation by the Notch-1 intracellular domain

Developmental decisions that control cell fate are commonly regulated by the Notch signaling pathway. Activation of transmembrane Notch receptors results in proteolytic liberation of the intracellular domain of Notch, which translocates into the nucleus, binds a repressor (C promoter binding factor 1/RBP-Jkappa, Su(H), and Lag-1 (CSL)), and induces target genes. We found that the intracellular domain of human Notch-1 (NIC-1) represses activator protein-1 (AP-1)-mediated transactivation. Because numerous genes that control immune and inflammatory responses are AP-1-dependent and Notch regulates immune cell function, we investigated the underlying molecular mechanisms. Repression of AP-1 by NIC-1 did not represent a general inhibitory effect on transcription because nuclear factor kappaB-dependent transcription and transcription driven by a constitutive promoter and enhancer were not affected by NIC-1. The physiological relevance of the repression was supported by the facts that repression was apparent in multiple cell lines, endogenous AP-1 target genes were repressed, and similar concentrations of NIC-1 were required for CSL-dependent activation and AP-1 repression. The RBP-Jkappa-associated molecule domain of NIC-1 that mediates CSL binding and distinct sequences necessary for transactivation were required for repression. However, there was not a strict correlation between the sequence requirements for CSL-dependent activation and AP-1 repression. Repression correlated with predominant nuclear localization of NIC-1 and was not accompanied by disruption of c-Jun amino-terminal kinase-dependent signaling events required for AP-1 activation or by defective AP-1 DNA binding activity. These results provide evidence for negative cross-talk between Notch and AP-1, which may have important consequences for controlling diverse biological processes.