Regulation of expression of the early growth response gene-1 (EGR-1) in malignant and benign cells of the prostate

Identification, Characterization, and Regulatory Mechanisms of a Novel EGR1 Splicing Isoform

EGR1 is a transcription factor expressed in many cell types that regulates genes involved in different biological processes including growth, proliferation, and apoptosis. Dysregulation of EGR1 expression has been associated with many pathological conditions such as tumors and brain diseases. Known molecular mechanisms underlying the control of EGR1 function include regulation of transcription, mRNA and protein stability, and post-translational modifications. Here we describe the identification of a splicing isoform for the human EGR1 gene. The newly identified splicing transcript encodes a shorter protein compared to the canonical EGR1. This isoform lacks a region belonging to the N-terminal activation domain and although it is capable of entering the nucleus, it is unable to activate transcription fully relative to the canonical isoform.

Transcriptional Landscape of PARs in Epithelial Malignancies

G protein-coupled receptors (GPCRs), the largest family of cell receptors, act as important regulators of diverse signaling pathways. Our understanding of the impact of GPCRs in tumors is emerging, yet there is no therapeutic platform based on GPCR driver genes. As cancer progresses, it disrupts normal epithelial organization and maintains the cells outside their normal niche. The dynamic and flexible microenvironment of a tumor contains both soluble and matrix-immobilized proteases that contribute to the process of cancer advancement. An example is the activation of cell surface protease-activated receptors (PARs). Mammalian PARs are a subgroup of GPCRs that form a family of four members, PAR_1–4, which are uniquely activated by proteases found in the microenvironment. PAR₁ and PAR₂ play central roles in tumor biology, and PAR₃ acts as a coreceptor. The significance of PAR₄ in neoplasia is just beginning to emerge. PAR₁ has been shown to be overexpressed in malignant epithelia, in direct correlation with tumor aggressiveness, but there is no expression in normal epithelium. In this review, the involvement of key transcription factors such as Egr1, p53, Twist, AP2, and Sp1 that control PAR₁ expression levels specifically, as well as hormone transcriptional regulation by both estrogen receptors (ER) and androgen receptors (AR) are discussed. The cloning of the human protease-activated receptor 2; Par2 (hPar2) promoter region and transcriptional regulation of estrogen (E₂) via binding of the E₂–ER complex to estrogen response elements (ERE) are shown. In addition, evidence that TEA domain 4 (TEAD₄) motifs are present within the hPar2 promoter is presented since the YAP oncogene, which plays a central part in tumor etiology, acts via the TEAD₄ transcription factor. As of now, no information is available on regulation of the hPar3 promoter. With regard to hPar4, only data showing CpG methylation promoter regulation is available. Characterization of the PAR transcriptional landscape may identify powerful targets for cancer therapies.

Association and regulation of protein factors of field effect in prostate tissues

Field effect or field cancerization denotes the presence of molecular aberrations in structurally intact cells residing in histologically normal tissues adjacent to solid tumors. Currently, the etiology of prostate field‑effect formation is unknown and there is a prominent lack of knowledge of the underlying cellular and molecular pathways. We have previously identified an upregulated expression of several protein factors representative of prostate field effect, i.e., early growth response-1 (EGR‑1), platelet-derived growth factor‑A (PDGF‑A), macrophage inhibitory cytokine‑1 (MIC‑1), and fatty acid synthase (FASN) in tissues at a distance of 1 cm from the visible margin of intracapsule prostate adenocarcinomas. We have hypothesized that the transcription factor EGR‑1 could be a key regulator of prostate field‑effect formation by controlling the expression of PDGF‑A, MIC‑1, and FASN. Taking advantage of our extensive quantitative immunofluorescence data specific for EGR‑1, PDGF‑A, MIC‑1, and FASN generated in disease‑free, tumor‑adjacent, and cancerous human prostate tissues, we chose comprehensive correlation as our major approach to test this hypothesis. Despite the static nature and sample heterogeneity of association studies, we show here that sophisticated data generation, such as by spectral image acquisition, linear unmixing, and digital quantitative imaging, can provide meaningful indications of molecular regulations in a physiologically relevant in situ environment. Our data suggest that EGR‑1 acts as a key regulator of prostate field effect through induction of pro‑proliferative (PDGF‑A and FASN), and suppression of pro‑apoptotic (MIC‑1) factors. These findings were corroborated by computational promoter analyses and cell transfection experiments in non‑cancerous prostate epithelial cells with ectopically induced and suppressed EGR‑1 expression. Among several clinical applications, a detailed knowledge of pathways of field effect may lead to the development of targeted intervention strategies preventing progression from pre-malignancy to cancer.

Mechanisms by which the orexigen NPY regulates anorexigenic α-MSH and TRH

Protein posttranslational processing is a cellular mechanism fundamental to the generation of bioactive peptides, including the anorectic α-melanocyte-stimulating hormone (α-MSH) and thyrotropin-releasing hormone (TRH) peptides produced in the hypothalamic arcuate (ARC) and paraventricular (PVN) nuclei, respectively. Neuropeptide Y (NPY) promotes positive energy balance in part by suppressing α-MSH and TRH. The mechanism by which NPY regulates α-MSH output, however, is not well understood. Our results reveal that NPY inhibited the posttranslational processing of α-MSH's inactive precursor proopiomelanocortin (POMC) by decreasing the prohormone convertase-2 (PC2). We also found that early growth response protein-1 (Egr-1) and NPY-Y1 receptors mediated the NPY-induced decrease in PC2. NPY given intra-PVN also decreased PC2 in PVN samples, suggesting a reduction in PC2-mediated pro-TRH processing. In addition, NPY attenuated the α-MSH-induced increase in TRH production by two mechanisms. First, NPY decreased α-MSH-induced CREB phosphorylation, which normally enhances TRH transcription. Second, NPY decreased the amount of α-MSH in the PVN. Collectively, these results underscore the significance of the interaction between NPY and α-MSH in the central regulation of energy balance and indicate that posttranslational processing is a mechanism that plays a specific role in this interaction.

Early growth response 1 and fatty acid synthase expression is altered in tumor adjacent prostate tissue and indicates field cancerization

BACKGROUND

Field cancerization denotes the occurrence of molecular alterations in histologically normal tissues adjacent to tumors. In prostate cancer, identification of field cancerization has several potential clinical applications. However, prostate field cancerization remains ill defined. Our previous work has shown up-regulated mRNA of the transcription factor early growth response 1 (EGR-1) and the lipogenic enzyme fatty acid synthase (FAS) in tissues adjacent to prostate cancer.

METHODS

Immunofluorescence data were analyzed quantitatively by spectral imaging and linear unmixing to determine the protein expression levels of EGR-1 and FAS in human cancerous, histologically normal adjacent, and disease-free prostate tissues.

RESULTS

EGR-1 expression was elevated in both structurally intact tumor adjacent (1.6× on average) and in tumor (3.0× on average) tissues compared to disease-free tissues. In addition, the ratio of cytoplasmic versus nuclear EGR-1 expression was elevated in both tumor adjacent and tumor tissues. Similarly, FAS expression was elevated in both tumor adjacent (2.7× on average) and in tumor (2.5× on average) compared to disease-free tissues.

CONCLUSIONS

EGR-1 and FAS expression is similarly deregulated in tumor and structurally intact adjacent prostate tissues and defines field cancerization. In cases with high suspicion of prostate cancer but negative biopsy, identification of field cancerization could help clinicians target areas for repeat biopsy. Field cancerization at surgical margins on prostatectomy specimen should also be looked at as a predictor of cancer recurrence. EGR-1 and FAS could also serve as molecular targets for chemoprevention.

Induction of IGF-1R expression by EGR-1 facilitates the growth of prostate cancer cells

The transcription factor Early Growth Response-1 (EGR-1) is overexpressed in human prostate tumors and contributes to prostate cancer progression through an unknown mechanism. Here we report that EGR-1 transcriptionally regulates the expression of insulin-like growth factor-1 receptor (IGF-1R), which is highly expressed in primary prostate cancer. We find that ectopic expression of EGR-1 causes increase in IGF-1R expression, while knockdown of EGR-1 leads to dramatically decrease in IGF-1R expression. Results from chromatin immunoprecipitation (ChIP) and reporter assay show that the EGR-1 directly binds to the human IGF-1R gene and triggers the target gene expression. EGR-1 activates Erk and Akt pathway through regulation of IGF-1R, and thus promote prostate cancer cell growth. Taken together, these results suggest that EGR-1 may stimulate prostate cancer cell growth through up-regulation of IGF-1R and indicate that down-regulation of EGR-1 could be an effective therapeutic approach against prostate cancer.

Mature human neutrophils constitutively express the transcription factor EGR-1

The immediate early response gene, Early Growth Response 1 (EGR-1) has emerged as a central regulator of early inflammatory and immune processes by rapidly regulating the transcription of a wide array of downstream effector genes. Neutrophils, which are among the first circulating leukocytes to respond to inflammatory signals, exhibit a broad set of transcriptional changes immediately upon exposure to inflammatory and pathogenic stimuli. Such transcriptional changes are likely to be controlled by early gene transcription factors such as EGR-1. We therefore examined the regulation and role of EGR-1 in mature human neutrophils exposed to the inflammatory stimuli fMLP and IL-8. We report that human neutrophils rapidly and transiently up-regulate EGR-1 mRNA upon stimulation with fMLP or IL-8. However in contrast to that seen in other cells, EGR-1 mRNA expression profiles were not predictive of protein expression. Instead, we show that human neutrophils constitutively express EGR-1 protein. The cellular content of EGR-1 did not change over time or upon neutrophil activation. Confocal microscopy revealed that EGR-1 was present in both the cytoplasm and nuclei of un-stimulated neutrophils and that activation did not change this subcellular localization or promote nuclear translocation. Using chromatin immunoprecipitation, we demonstrate that EGR-1 is associated with the promoter regions of the immune regulatory genes IL-1 beta, TGFbeta-1 and MIF in both resting and activated neutrophils with increased promoter association observed upon cell activation. This novel pattern of EGR-1 protein expression may underlie the ability of the neutrophil to respond rapidly to inflammatory stimuli.

Targeted knockdown of EGR-1 inhibits IL-8 production and IL-8-mediated invasion of prostate cancer cells through suppressing EGR-1/NF-kappaB synergy

IL-8 produced by prostate cancer cells may be responsible for the androgen-independent growth of advanced prostate cancers. Accumulating evidence from microarray analyses and animal genetic models highlights the central involvement of the transcription factor early growth response-1 (EGR-1) in prostate carcinoma progression. It is unknown, however, whether knockdown of EGR-1 inhibits IL-8 production and IL-8-mediated tumor metastasis. Here we show that EGR-1 knockdown by a specific shRNA-Egr1 inhibited gene transcription and production of IL-8 by the human prostate cancer cell line DU145. Conversely, enforced expression of EGR-1 in EGR-1-lacking PC3 prostate cancer cells markedly enhanced IL-8 transcription and secretion. By using wild type and a series of mutant IL-8 promoter luciferase constructs, we found that the NF-kappaB binding site is important for EGR-1 regulation of IL-8. Furthermore, silencing EGR-1 suppressed a synergistically functional interaction between EGR-1 and NF-kappaB. Consequently, knockdown of EGR-1 inhibited IL-8-mediated tumor colony formation and invasion. Thus, targeted knockdown of EGR-1 could be an effective therapeutic approach against prostate cancer.

Convergence of biomarkers, bioinformatics and nanotechnology for individualized cancer treatment

Recent advances in biomarker discovery, biocomputing and nanotechnology have raised new opportunities in the emerging fields of personalized medicine (in which disease detection, diagnosis and therapy are tailored to each individual's molecular profile) and predictive medicine (in which genetic and molecular information is used to predict disease development, progression and clinical outcome). Here, we discuss advanced biocomputing tools for cancer biomarker discovery and multiplexed nanoparticle probes for cancer biomarker profiling, in addition to the prospects for and challenges involved in correlating biomolecular signatures with clinical outcome. This bio-nano-info convergence holds great promise for molecular diagnosis and individualized therapy of cancer and other human diseases.

Bioconjugated quantum dots for multiplexed and quantitative immunohistochemistry

Bioconjugated quantum dots (QDs) provide a new class of biological labels for evaluating biomolecular signatures (biomarkers) on intact cells and tissue specimens. In particular, the use of multicolor QD probes in immunohistochemistry is considered one of the most important and clinically relevant applications. At present, however, clinical applications of QD-based immunohistochemistry have achieved only limited success. A major bottleneck is the lack of robust protocols to define the key parameters and steps. Here, we describe our recent experience, preliminary results and detailed protocols for QD-antibody conjugation, tissue specimen preparation, multicolor QD staining, image processing and biomarker quantification. The results demonstrate that bioconjugated QDs can be used for multiplexed profiling of molecular biomarkers, and ultimately for correlation with disease progression and response to therapy. In general, QD bioconjugation is completed within 1 day, and multiplexed molecular profiling takes 1-3 days depending on the number of biomarkers and QD probes used.

Identification and characterization of the promoter region of the Nav1.7 voltage-gated sodium channel gene (SCN9A)

The Nav1.7 sodium channel plays an important role in pain and is also upregulated in prostate cancer. To investigate the mechanisms regulating physiological and pathophysiological Nav1.7 expression we identified the core promoter of this gene (SCN9A) in the human genome. In silico genomic analysis revealed a putative SCN9A 5' non-coding exon approximately 64,000 nucleotides from the translation start site, expression of which commenced at three very closely-positioned transcription initiation sites (TISs), as determined by 5' RACE experiments. The genomic region around these TISs possesses numerous core elements of a TATA-less promoter within a well-defined CpG island. Importantly, it acted as a promoter when inserted upstream of luciferase in a fusion construct. Moreover, the activity of the promoter-luciferase construct ostensibly paralleled endogenous Nav1.7 mRNA levels in vitro, with both increased in a quantitatively and qualitatively similar manner by numerous factors (including NGF, phorbol esters, retinoic acid, and Brn-3a transcription factor over-expression).

Transcriptional regulation of human protease-activated receptor 1: a role for the early growth response-1 protein in prostate cancer

Transcriptional regulation plays a central role in the molecular pathways underlying preferential cancer growth and metastasis. In the present study, we investigated the regulation of human protease-activated receptor 1 (hPar1) gene overexpression in the malignant androgen hormone-resistant phase. We found increased hPar1 RNA chain elongation and no change in message stability in cells with high levels of PAR1 expression, indicating that increased transcription is largely responsible for the overexpression of hPar1 in prostate tumor progression. Enforced expression of early growth response-1 (Egr-1) plasmid markedly enhanced luciferase activity driven by the hPar1 promoter. The neuroendocrine peptide bombesin significantly induced hPar1 expression and increased the ability of the cells to invade Matrigel, an effect abolished by expression of hPar1 small interfering RNA, showing the importance of hPAR1 in invasion. Bombesin also markedly enhanced Egr-1 binding to the hPar1 promoter in vivo and in vitro. These data suggest that bombesin enhances Egr-1 expression leading to increased hPar1 transcription, thereby increasing PAR1 expression and function. Immunohistostaining of prostate tissue biopsy specimens revealed a direct correlation between the degree of prostate cancer malignancy, PAR1 expression, and EGR-1 expression. Altogether, we show that transcriptional regulation of hPar1 in the aggressive hormone-resistant prostate cancer stage is controlled in part by the transcription factor Egr-1 and may play a central role in invasiveness, an important indicator of malignancy.

Nanotechnology applications in cancer

Cancer nanotechnology is an interdisciplinary area of research in science, engineering, and medicine with broad applications for molecular imaging, molecular diagnosis, and targeted therapy. The basic rationale is that nanometer-sized particles, such as semiconductor quantum dots and iron oxide nanocrystals, have optical, magnetic, or structural properties that are not available from molecules or bulk solids. When linked with tumor targeting ligands such as monoclonal antibodies, peptides, or small molecules, these nanoparticles can be used to target tumor antigens (biomarkers) as well as tumor vasculatures with high affinity and specificity. In the mesoscopic size range of 5-100 nm diameter, nanoparticles also have large surface areas and functional groups for conjugating to multiple diagnostic (e.g., optical, radioisotopic, or magnetic) and therapeutic (e.g., anticancer) agents. Recent advances have led to bioaffinity nanoparticle probes for molecular and cellular imaging, targeted nanoparticle drugs for cancer therapy, and integrated nanodevices for early cancer detection and screening. These developments raise exciting opportunities for personalized oncology in which genetic and protein biomarkers are used to diagnose and treat cancer based on the molecular profiles of individual patients.

Molecular profiling of single cancer cells and clinical tissue specimens with semiconductor quantum dots

Semiconductor quantum dots (QDs) are a new class of fluorescent labels with broad applications in biomedical imaging, disease diagnostics, and molecular and cell biology. In comparison with organic dyes and fluorescent proteins, quantum dots have unique optical and electronic properties such as size-tunable light emission, improved signal brightness, resistance against photobleaching, and simultaneous excitation of multiple fluorescence colors. Recent advances have led to multifunctional nanoparticle probes that are highly bright and stable under complex in vitro and in vivo conditions. New designs involve encapsulating luminescent QDs with amphiphilic block copolymers, and linking the polymer coating to tumor-targeting ligands and drug-delivery functionalities. These improved QDs have opened new possibilities for real-time imaging and tracking of molecular targets in living cells, for multiplexed analysis of biomolecular markers in clinical tissue specimens, and for ultrasensitive imaging of malignant tumors in living animal models. In this article, we briefly discuss recent developments in bioaffinity QD probes and their applications in molecular profiling of individual cancer cells and clinical tissue specimens.

Bombesin regulates cyclin D1 expression through the early growth response protein Egr-1 in prostate cancer cells

Our previous studies indicate that the activation of mitogen-activated protein kinase (MAPK) pathway is involved in bombesin-induced cell proliferation in prostate cancer cells. Cyclin D1 is a critical regulator involved in cell cycle progression through the G1 phase into the S phase, thereby contributing to cell proliferation. Mostly, mitogen-stimulated expression of cyclin D1 is attributed to the extracellular signal-regulated kinase (ERK) activation. Here, we found that bombesin induced human cyclin D1 expression on both mRNA and protein levels in DU-145 prostate cancer cells. Mutational analyses showed that bombesin-enhanced cyclin D1 transcription required the binding of nuclear proteins to the -143 to -105 region of the human cyclin D1 promoter, which contains binding sites for transcription factors Sp-1 and early growth response protein (Egr-1). Do novo protein synthesis was requisite for bombesin-induced cyclin D1 expression. Further studies showed Egr-1 was induced upon bombesin stimulation. The induction of Egr-1 expression and its binding to the cyclin D1 promoter were essential for bombesin-enhanced cyclin D1 transcription. Inhibition of MAPK pathway with either the MEK1 inhibitor PD98059 or a dominant-negative Ras mutant, RasN17, abolished bombesin-induced cyclin D1 activation. Taken together, bombesin-induced cyclin D1 expression in prostate cancer cells is mediated by Egr-1 activation and the interaction of Egr-1 with the Egr-1/Sp1 motif of the cyclin D1 promoter through the activation of MAPK pathway. These findings represent a novel mechanism of bombesin-dependent stimulation of mitogenesis by regulating directly the cell cycle in prostate cancer.