Alteration of Egr-1 mRNA during multistage carcinogenesis in mouse skin

Putative Tumor Suppressor Genes EGR1 and BRSK1 Are Mutated in Gastric and Colorectal Cancers

OBJECTIVE

The transcription factor-encoding EGR1 and the kinase-encoding BRSK1 are considered putative tumor suppressor genes (TSGs). However, EGR1 and BRSK1 mutations that could inactivate their functions are not reported in colorectal (CRC) and gastric (GC) cancers.

METHODS

There are mononucleotide repeats in EGR1 and BRSK1, which could be mutated in cancers with defects in mismatch repair, resulting in microsatellite instability (MSI). We analyzed 124 CRCs and 79 GCs for mutations and their intratumoral heterogeneities (ITHs).

RESULTS

Twenty-one out of 79 CRCs (26.6%) and 5 out of 34 GCs (14.7%) carrying high MSI (MSI-H) exhibited frameshift mutations. However, we found no such mutations in cancers with microsatellite stability. In addition, we studied ITH for these mutations in 16 cases of CRCs and observed that EGR1 and BRSK1 mutations exhibited ITH in 3 (18.8%) and 2 (12.5%) cases, respectively.

CONCLUSION

Our data in this study reveal that the TSG genes EGR1 and BRSK1 carry mutational ITH as well as frameshift mutations in MSI-H CRC and GC, which together may be features of GC and CRC with MSI-H. These results suggest that frameshift mutations of EGR1 and BRSK1 might play a role in tumorigenesis through TSG inactivation in CRC and GC.

Effect of Combined Treatment with Ursolic Acid and Resveratrol on Skin Tumor Promotion by 12-O-Tetradecanoylphorbol-13-Acetate

In this study, the effects of combining ursolic acid + resveratrol, for possible combined inhibitory effects on skin tumor promotion, were evaluated. Ursolic acid, resveratrol, and the combination of ursolic acid + resveratrol were applied topically prior to 12-O-tetracanoylphorbol-13-acetate (TPA) treatment on mouse skin to examine their effect on TPA-induced signaling pathways, epidermal hyperproliferation, skin inflammation, inflammatory gene expression, and skin tumor promotion. The combination of ursolic acid + resveratrol produced a greater inhibition of TPA-induced epidermal hyperproliferation. The combination of ursolic acid + resveratrol inhibited TPA-induced signaling pathways, including EGFR, STAT3, Src, Akt, Cox-2, Fas, NF-κB, p38 MAPK, c-Jun, and JNK1/2 while increasing levels of tumor suppressors, such as p21 and PDCD4, to a greater extent compared with the groups treated with the individual compounds. Ursolic acid + resveratrol also induced a dramatic increase of p-AMPK-α(Thr172). Combined treatment with ursolic acid + resveratrol resulted in a greater inhibition of expression of proinflammatory cytokines, including Il1a, Il1b, and Il22. Furthermore, NF-κB, Egr-1, and AP-1 DNA binding activities after TPA treatment were dramatically decreased by the combination of ursolic acid + resveratrol. Treatment with ursolic acid + resveratrol during skin tumor promotion with TPA produced greater inhibition of tumor multiplicity and tumor size than with either agent alone. Collectively, the greater ability of the combination of ursolic acid + resveratrol to inhibit skin tumor promotion was due to the greater inhibitory effects on growth factor and inflammatory signaling, skin inflammation, and epidermal hyperproliferation induced by TPA treatment.

Expression of early growth response-1 in colorectal cancer and its relation to tumor cell proliferation and apoptosis

Early growth response-1 (Egr-1) is implicated in the regulation of cell growth, proliferation, differentiation and apoptosis. Egr-1 is considered tobe either a tumor-suppressor or tumor-promoter, depending on the cell type and environment. The aim of the present study was to evaluate the expression of Egr-1 in colorectal cancer and its correlation with tumor cell proliferation, apoptosis and clinicopathological features. The expression of Egr-1 in colorectal cancer tissues was investigated by reverse transcription-polymerase chain reaction (RT-PCR), western blotting and immunohistochemistry. Apoptosis was detected by terminal deoxynucleotidyl transferase (TdT)-mediated deoxyuridine triphosphate (dUTP) nick end labeling (TUNEL), and cellular proliferative activity was evaluated by immunohistochemical staining with the Ki-67 antibody. Egr-1 expression was significantly elevated in colorectal cancer tissues, when compared to that in the paired normal mucosa at the mRNA and protein levels. In addition, Egr-1 expression was significantly increased in the metastatic lymph node tissues, when compared to that in the non‑metastatic lymph node tissues at the protein level. The mean Ki-67 labeling index (KI) and apoptotic index (AI) values for 158 tumors were 53.6±15.4 and 9.0±1.0, respectively. Higher KI values were significantly associated with distant metastasis. Lower AI values were significantly associated with lymph node metastasis. However, KI or AI values were not associated with patient survival. The mean KI value of Egr-1-positive tumors was significantly higher than that of Egr-1-negative tumors. However, there was no significant difference between Egr-1 expression and AI value. Positive expression of Egr-1 was significantly associated with age, lymphovascular invasion, lymph node and distant metastasis, tumor stage and poor survival. These results indicate that Egr-1 may be associated with colorectal cancer progression via tumor cell proliferation.

LPA-induced suppression of periostin in human osteosarcoma cells is mediated by the LPA(1)/Egr-1 axis

Lysophosphatidic acid (LPA), a naturally occurring bioactive phospholipid, mediates a multitude of (patho)physiological events including activation of mitogen-activated protein kinases (MAPKs). As LPA may induce cellular reponses in human osteosarcoma, the present study aimed at investigating expression of various LPA receptors, LPA-mediated activation of MAPK via G-protein coupling, and expression of early response genes in a cellular model for human osteosarcoma. We show that MG-63 cells express three members of the endothelial differentiation gene (Edg) family of G-protein coupled receptor transcripts (LPA(1-3)) but only two (LPA(4/5)) out of three members of the non-Edg family LPA receptor transcripts. Stimulation of MG-63 cells with LPA or synthetic LPA receptor agonists resulted in p42/44 MAPK phosphorylation via LPA(1)-LPA(3) receptors. Using pharmacological inhibitors, we show that LPA-mediated phosphorylation of p42/44 MAPK by LPA receptor engagement is transmitted by G(αi)-dependent pathways through the Src family of tyrosine kinases. As a consequence, a rapid and transient upregulation of the zinc finger transcription factor early growth response-1 (Egr-1) was observed. Egr-1 expression was strictly mediated via G(αi)/Src/p42/44 MAPK pathway; no involvement of the G(αq/11)/PLC/PKC or the PLD/PI3 kinase/Akt pathways was found. LPA-induced expression of functional Egr-1 in MG-63 cells could be confirmed by electrophoretic mobility shift assay. LPA-induced Egr-1 upregulation was accompanied by a time-dependent decrease of periostin (previously called osteoblast-specific factor 2), a cell adhesion protein for pre-osteoblasts. Silencing of LPA(1) and/or Egr-1 in MG-63 cells reversed LPA-mediated suppression of periostin. We here demonstrate a crosslink between Egr-1 and periostin in cancer cells, in particular in human osteosarcoma.

Early growth response-1 is a regulator of DR5-induced apoptosis in colon cancer cells

Background:

Tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) induces tumour cell apoptosis by binding to death receptor 4 (DR4) and DR5. DR4 and DR5 activation however can also induce inflammatory and pro-survival signalling. It is not known how these different cellular responses are regulated and what the individual role of DR4 vs DR5 is in these processes.

Methods:

DNA microarray study was carried out to identify genes differentially expressed after DR4 and DR5 activation. RT–PCR and western blotting was used to examine the expression of early growth response gene-1 (Egr-1) and the proteins of the TRAIL signalling pathway. The function of Egr-1 was studied by siRNA-mediated knockdown and overexpression of a dominant-negative version of Egr-1.

Results:

We show that the immediate early gene, Egr-1, regulates TRAIL sensitivity. Egr-1 is constitutively expressed in colon cancer cells and further induced upon activation of DR4 or DR5. Our results also show that DR4 mediates a type II, mitochondrion-dependent apoptotic pathway, whereas DR5 induces a mitochondrion-independent, type I apoptosis in HCT15 colon carcinoma cells. Egr-1 drives c-FLIP expression and the short splice variant of c-FLIP (c-FLIP_S) specifically inhibits DR5 activation.

Conclusion:

Selective knockdown of c-FLIP_S sensitises cells to DR5-induced but not DR4-induced apoptosis and Egr-1 exerts an effect as an inhibitor of the DR5-induced apoptotic pathway, possibly by regulating the expression of c-FLIP_S.

ESE-1/EGR-1 pathway plays a role in tolfenamic acid-induced apoptosis in colorectal cancer cells

Nonsteroidal anti-inflammatory drugs (NSAIDs) are known to prevent colorectal tumorigenesis. Although antitumor effects of NSAIDs are mainly due to inhibition of cyclooxygenase activity, there is increasing evidence that cyclooxygenase-independent mechanisms may also play an important role. The early growth response-1 (EGR-1) gene is a member of the immediate-early gene family and has been identified as a tumor suppressor gene. Tolfenamic acid is a NSAID that exhibits anticancer activity in a pancreatic cancer model. In the present study, we investigated the anticancer activity of tolfenamic acid in human colorectal cancer cells. Tolfenamic acid treatment inhibited cell growth and induced apoptosis as measured by caspase activity and bioelectric impedance. Tolfenamic acid induced EGR-1 expression at the transcription level, and analysis of the EGR-1 promoter showed that a putative ETS-binding site, located at -400 and -394 bp, was required for activation by tolfenamic acid. The electrophoretic mobility shift assay and chromatin immunoprecipitation assay confirmed that this sequence specifically bound to the ETS family protein epithelial-specific ETS-1 (ESE-1) transcription factor. Tolfenamic acid also facilitated translocation of endogenous and exogenous ESE-1 to the nucleus in colorectal cancer cells, and gene silencing using ESE-1 small interfering RNA attenuated tolfenamic acid-induced EGR-1 expression and apoptosis. Overexpression of EGR-1 increased apoptosis and decreased bioelectrical impedance, and silencing of endogenous EGR-1 prevented tolfenamic acid-induced apoptosis. These results show that activation of ESE-1 via enhanced nuclear translocation mediates tolfenamic acid-induced EGR-1 expression, which plays a critical role in the activation of apoptosis.

Egr-1 and serum response factor are involved in growth factors- and serum-mediated induction of E2-EPF UCP expression that regulates the VHL-HIF pathway

E2-EPF ubiquitin carrier protein (UCP) has been shown to be highly expressed in common human cancers and target von Hippel-Lindau (VHL) for proteosomal degradation in cells, thereby stabilizing hypoxia-inducible factor (HIF)-1alpha. Here, we investigated cellular factors that regulate the expression of UCP gene. Promoter deletion assay identified binding sites for early growth response-1 (Egr-1) and serum response factor (SRF) in the UCP promoter. Hepatocyte or epidermal growth factor (EGF), or phorbol 12-myristate 13-acetate induced UCP expression following early induction of Egr-1 expression in HeLa cells. Serum increased mRNA and protein levels of SRF and UCP in the cell. By electrophoretic mobility shift and chromatin immunoprecipitation assays, sequence-specific DNA-binding of Egr-1 and SRF to the UCP promoter was detected in nuclear extracts from HeLa cells treated with EGF and serum, respectively. Overexpression of Egr-1 or SRF increased UCP expression. RNA interference-mediated depletion of endogenous Egr-1 or SRF impaired EGF- or serum-mediated induction of UCP expression, which was required for cancer cell proliferation. Systemic delivery of EGF into mice also increased UCP expression following early induction of Egr-1 expression in mouse liver. The induced UCP expression by the growth factors or serum increased HIF-1alpha protein level under non-hypoxic conditions, suggesting that the Egr-1/SRF-UCP-VHL pathway is in part responsible for the increased HIF-1alpha protein level in vitro and in vivo. Thus, growth factors and serum induce expression of Egr-1 and SRF, respectively, which in turn induces UCP expression that positively regulates cancer cell growth.

Evidence of EGR1 as a differentially expressed gene among proliferative skin diseases

Hyperproliferative epidermal disorders range from benign hyperplasias such as psoriasis to basal cell carcinoma (BCC) and squamous cell carcinoma (SCC), the two most common cancers in the US. While they all arise from the epidermis, these diseases differ dramatically in biological behavior and their underlying gene expression patterns have not been compared. We thus examined mRNA transcript levels in these disorders to identify and further characterize differentially expressed genes. Transcript expression patterns distinguish these disorders and identify EGR1, among other genes, whose epidermal expression is decreased in BCC and SCC but is elevated in psoriasis. Egr-1 inhibits growth of benign and malignant epidermal cells in vitro and appears to suppress both Cdc25A expression and Cdk2 dephosphorylation. These data indicate that gene expression profiling can differentiate epidermal hyperproliferative diseases and suggest that Egr-1 may play a role in preventing uncontrolled epidermal growth.

Hepatocyte growth factor induces cell scattering through MAPK/Egr-1-mediated upregulation of Snail

Hepatocyte growth factor/scatter factor (HGF) exerts several functions in physiological and pathological processes, among them the induction of epithelial cell scattering and motility. Its pivotal role in angiogenesis, tumor progression, and metastasis is evident; however, the underlying molecular mechanisms are still poorly understood. Here, we demonstrate that HGF induces scattering of epithelial cells by upregulating the expression of Snail, a transcriptional repressor involved in epithelial-mesenchymal transition (EMT). Snail is required for HGF-induced cell scattering, since shRNA-mediated ablation of Snail expression prevents this process. HGF-induced upregulation of Snail transcription involves activation of the mitogen-activated protein kinase (MAPK) pathway and requires the activity of early growth response factor-1 (Egr-1). Upon induction by Egr-1, Snail represses the expression of E-cadherin and claudin-3 genes. It also binds to the Egr-1 promoter and represses Egr-1 transcription, thereby establishing a negative regulatory feedback loop. These findings indicate that Snail upregulation by HGF is mediated via the MAPK/Egr-1 signaling pathway and that both Snail and Egr-1 play a critical role in HGF-induced cell scattering, migration, and invasion.

Transcriptional activation of the Egr-1 gene mediated by tetradecanoylphorbol acetate and extracellular signal-regulated protein kinase

Activation of extracellular signal-regulated protein kinase (ERK) triggers the biosynthesis of Egr-1, a zinc finger transcription factor. Likewise, the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) strongly upregulates Egr-1 biosynthesis. Here, we have analyzed the genetic elements involved in the regulation of Egr-1 gene transcription by ERK and TPA in human hepatoma cells. Expression experiments using mitogen-activated protein kinase phosphatase-1 or a dominant-negative mutant of the ternary complex factor Elk-1 revealed that the distal cluster of serum response elements is essential in the TPA-induced enhancement of Egr-1 promoter activity, encompassing two independent TPA-responsive elements. The CRE in the proximal Egr-1 promoter plays, if anything, only a marginal role in TPA-induced stimulus-transcription coupling of the Egr-1 gene. The fact that Egr-1 promoter/reporter gene transcription is upregulated by a constitutively active CREB mutant indicates that the CRE couples other signaling cascades via CREB to the Egr-1 gene.

NF-kappaB/Egr-1/Gadd45 are sequentially activated upon UVB irradiation to mediate epidermal cell death

Chronic sun exposure can lead to severe skin disorders such as carcinogenesis. The cell death process triggered by ultraviolet B (UVB) irradiation is crucial because it protects the surrounding tissue from the emergence and the accumulation of cells that bear the risk of becoming transformed. Here, we show that repression of NF-kappaB and Egr-1 expression drastically inhibits UVB-mediated cell death. Furthermore, we demonstrate that Egr-1 is induced upon UVB irradiation through NF-kappaB activation and the binding of p65/RelA within the Egr-1 promoter. We show that Egr-1 contributes to the regulation of the Gadd45a and Gadd45b genes, which are involved in the control of cell cycle, DNA repair and apoptosis, by direct binding to their promoter. Our study demonstrates for the first time a signaling cascade involving sequential activation of NF-kappaB, Egr-1 and Gadd45 to induce UVB-mediated cell death. Failure in the induction of each protagonist of this pathway alters the UVB-mediated cell death process. Therefore, impairment of the cascade could be at the onset of skin carcinogenesis mediated by genotoxic stress.

Brain-derived neurotrophic factor-, epidermal growth factor-, or A-Raf-induced growth of HaCaT keratinocytes requires extracellular signal-regulated kinase

The epidermal growth factor (EGF) receptor plays an important role in epithelial cells by controlling cell proliferation and survival. Keratinocytes also express another class of receptor tyrosine kinases, the neurotrophin receptors. To analyze the biological role of the neurotrophin brain-derived neurotrophic factor (BDNF) in keratinocytes, we expressed the BDNF receptor TrkB in immortalized human HaCaT keratinocytes. Stimulation of HaCaT-TrkB cells with BDNF induced DNA synthesis and increased mitochondrial reduction capacities, both indications of proliferating cells. An analysis of the signal transduction cascade revealed that the activated TrkB receptor effectively utilized components of the EGF receptor signaling pathway to control cell proliferation. Mitogenic signaling induced by BDNF or EGF was completely abrogated by the MAP kinase kinase inhibitor PD-98059, whereas inhibition of phosphatidylinositol 3-kinase by wortmannin only delayed the proliferative response. The importance of the extracellular signal-regulated kinase signaling pathway for growth of HaCaT keratinocytes was further demonstrated with HaCaT cells engineered to express an inducible A-Raf-estrogen receptor fusion protein (ΔA-Raf:ER). Despite differences in the amplitude and duration of extracellular signal-regulated kinase activation, HaCaT cells expressing ΔA-Raf:ER proliferated after activation of mutant A-Raf protein kinase. Proliferation was completely inhibited by PD-98059. Proliferation of HaCaT cells induced by EGF, BDNF, or ΔA-Raf:ER was also accompanied by biosynthesis of the transcription factors Egr-1 and c-Jun, suggesting that these proteins may be part of the mitogenic signaling cascade.

Antisense to the early growth response-1 gene (Egr-1) inhibits prostate tumor development in TRAMP mice

Egr-1 is a transcription factor induced by stress or injury, mitogens, and differentiation factors. Egr-1 regulates the expression of genes involved in growth control or survival. Expression of Egr-1 results in either promotion or regression of cell proliferation, depending on cell type and environment. Egr-1 acts as a tumor suppressor in many cell types and loss of Egr-1 has been proposed to contribute to cancer progression. There is strong new evidence however suggesting that Egr-1 overexpression is involved in prostate cancer progression. For example, Egr-1 expression levels are elevated in human prostate carcinomas in proportion to grade and stage. Furthermore, prostate cancer progression was significantly delayed in two models of prostate cancer mice lacking Egr-1. Our objective in the present study is to test whether inhibition of Egr-1 function would block cell proliferation and inhibit the transformed phenotype of prostate cancer cells in vitro and in vivo. We describe the development of high affinity and high specificity antisense oligonucleotides that efficiently inhibit Egr-1 expression. We show that inhibition of Egr-1 expression in mouse or human prostate cancer cells decreased proliferation and reduced the capacity of these cells to form colonies and to grow in soft agar. Conversely, stable expression of Egr-1 in normal human prostate epithelial 267B1 cells promoted transformation. In TRAMP mice, treatment with Egr-1 antisense oligonucleotides delayed the occurrence of prostate tumors. Importantly, Egr-1 antisense showed little or no toxicity when injected into animals. Finally, we identified a few genes such as cyclin D2, p19ink4d, and Fas that are directly regulated by Egr-1 in prostate cancer cells and that control cell cycle and survival.

Gene expression profile of tissue engineered skin subjected to acute barrier disruption

The main function of the skin is to protect the body from infection, dehydration, and other environmental insults by creating an impermeable barrier of cornified cell layers, the stratum corneum. In contrast to cells in culture, tissue-engineered skin equivalents contain well-developed basal, spinous, granular, and cornified cell layers providing an excellent model to study the tissue response to barrier disruption. After 7 d of culture at the air-liquid interface the barrier of the tissues was disrupted by short exposure to acetone and the global gene expression profile of the tissues was evaluated using DNA microarrays. We found that tissue-engineered skin responds to barrier disruption by a two-wave dynamic response. Early on, the cells upregulate signal transducing, stress, proliferation, and inflammation genes to protect the tissue and possibly to communicate the damage to the immune system and neighboring tissues. At later times, pro-inflammatory cytokines and some growth-related genes are significantly reduced but enzymes that participate in lipid synthesis increase, suggesting that the epidermal cells attempt to restore the lost barrier. Quantitative immunostaining for the proliferation antigen Ki67 revealed that barrier disruption by acetone increased proliferation by 4-fold in agreement with the microarray data and previous in vivo studies. Our work suggests that functional genomics may be used in tissue engineering to understand tissue development, wound regeneration, and response to environmental stimuli. A better understanding of engineered tissues at the molecular level may facilitate their application in the clinic and as biosensors for toxicologic testing.

Role of INK4a/Arf locus-encoded senescent checkpoints activated in normal and psoriatic keratinocytes

During malignant transformation in skin, epidermal keratinocytes (KCs) frequently acquire the capacity to by-pass cellular senescence, a response that normally limits their unrestricted proliferation. Despite growing interest in the role for senescence during aging of skin and cutaneous carcinogenesis, little is known regarding regulation of three proteins encoded by the INK4a/ARF locus (p12, p14(ARF), p16) in KCs. In this study, several molecular pathways are explored using cultured KCs and KCs freshly isolated from psoriatic plaques. p16 and p14(ARF) are predominantly expressed spontaneously when foreskin-derived early-passage KCs undergo confluency-induced premature senescence. Induction of p14(ARF) on confluency occurred with low E2F-1 levels. Suspension of KCs in methylcellulose induced p12 expression. Addition of various cytokines (interferon-gamma, tumor necrosis factor-alpha) or a phorbol ester [12-O-tetradecanoylphorbol-13-acetate (TPA)] only induced p16, but not p14(ARF). Confluent KCs up-regulated Ras activity and the downstream signaling involving ERK. Addition of MAPK inhibitor blocked cytokine and TPA-induced p16 expression. Confluency and interferon-gamma induced premature senescence and p16 expression was linked to induction of the transcription factor Egr-1. KCs derived from chronic psoriatic plaques were characterized by enhanced p16, p14(ARF), and p12 expression accompanied by elevated Egr-1 levels. These results demonstrate that multiple and highly divergent stimuli can trigger the senescent checkpoint in human KCs with differential regulation of p16, p14(ARF), and p12. Although abnormal mitogenic signaling by oncogenic Ras is generally cited as being responsible for induction of premature senescence, our findings indicate that a broader perspective is warranted, to include confluency and cytokine-/TPA-induced pathways for KCs.

Regulation of life and death by the zinc finger transcription factor Egr-1

The biosynthesis of the zinc finger transcription factor Egr-1 is stimulated by many extracellular signaling molecules including hormones, neurotransmitters, growth and differentiation factors, and cytotoxic metabolites. The 5'-flanking region of the Egr-1 gene contains genetic elements that are essential in connecting stimulation of the cells with enhanced transcription of the Egr-1 gene, and subsequently, transcription of Egr-1-responsive genes. Thus, Egr-1 links cellular signaling cascades with changes in the gene expression pattern. Many biological functions have been attributed to Egr-1. Here, we discuss evidence for Egr-1 control of cellular proliferation and programmed cell death.

Epidermal growth factor and thrombin induced proliferation of immortalized human keratinocytes is coupled to the synthesis of Egr-1, a zinc finger transcriptional regulator

The epidermal growth factor (EGF) receptor is highly expressed in HaCaT keratinocytes as shown by Western blotting. Stimulation of HaCaT cells with EGF, and also with the serine protease thrombin, induced DNA synthesis, measured by incorporation of 5-bromo-2'-deoxyuridine into the DNA of proliferating cells. Using antibodies directed against the active form of the EGF receptor, we show that in HaCaT cells EGF and thrombin triggered a rapid activation of the EGF receptor, followed by the phosphorylation and activation of the extracellular signal-regulated protein kinase (ERK). Moreover, EGF and thrombin induced a transient synthesis of the zinc finger transcriptional regulator Egr-1. Proliferation, activation of ERK, and biosynthesis of Egr-1 was completely inhibited in EGF or thrombin-treated HaCaT cells by the MAP kinase kinase inhibitor PD98059 and by AG1487, an EGF receptor-specific tyrosine kinase inhibitor. These data indicate that phosphorylation and activation of both the EGF receptor and ERK are essential for mitogenic signaling via EGF and thrombin. The synthesis of Egr-1 in HaCaT cells as a result of EGF or thrombin stimulation suggests that Egr-1 may be an important "late" part of the EGF and thrombin-initiated signaling cascades. We postulate that Egr-1 may function as a "third messenger" in keratinocytes connecting mitogenic stimulation with changes in gene transcription.

Differential Display and Suppressive Subtractive Hybridization Used to Identify Granulosa Cell Messenger RNA Associated with Bovine Oocyte Developmental Competence1

The main objective of this study was to identify mRNA expressed in the granulosa cells characterizing differentiated follicles bearing developmentally competent bovine oocytes. Analytical comparisons were made on mRNA pools of granulosa cells using differential display reverse transcription polymerase chain reaction (DDRT) analysis and suppressive subtractive hybridization (SSH). With DDRT, mRNA patterns of granulosa cells from small (< 4 mm) and large (> 8 mm) follicles cultured in the presence or absence of LH were compared to identify mRNA associated with follicular size or with the LH response. Nine clones were sequenced, and two were identified. One of the clones, DRAK 1, was associated with the presence of LH in the medium. Other comparisons directed toward the identification of mRNA associated with the presence of a competent oocyte were done on granulosa cells collected in vivo from superstimulated heifers. With the DDRT analysis, four clones associated with the oocyte developmental competence status were identified. With the SSH analysis, four clones specific to the presence of an incompetent oocyte were sequenced and none were identified, whereas 49 clones specific to the presence of a competent oocyte were sequenced and 18 were identified. Among these clones, early growth response 1, sprouty 2, cytochrome C oxidase, matrix metalloproteinase inducer, matrix metalloproteinase, epiregulin, prostaglandin receptor, and progesterone receptor were the most relevant to the ovarian physiology being examined.

Impaired prostate tumorigenesis in Egr1-deficient mice

The transcription factor early growth response protein 1 (EGR1) is overexpressed in a majority of human prostate cancers and is implicated in the regulation of several genes important for prostate tumor progression. Here we have assessed the effect of Egr1 deficiency on tumor development in two transgenic mouse models of prostate cancer (CR2-T-Ag and TRAMP). Using a combination of high-resolution magnetic resonance imaging and histopathological and survival analyses, we show that tumor progression was significantly impaired in Egr1-/- mice. Tumor initiation and tumor growth rate were not affected by the lack of Egr1; however, Egr1 deficiency significantly delayed the progression from prostatic intra-epithelial neoplasia to invasive carcinoma. These results indicate a unique role for Egr1 in regulating the transition from localized, carcinoma in situ to invasive carcinoma.