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

Early growth response-1 is a new substrate of the GSK3β-FBXW7 axis

EGR1, a short-lived transcription factor, regulates several biological processes, including cell proliferation and tumor progression. Whether and how EGR1 is regulated by Cullin-RING ligases (CRLs) remains elusive. Here, we report that MLN4924, a small molecule inhibitor of neddylation, causes EGR1 accumulation by inactivating SCFFBXW7 (CRL1), which is a new E3 ligase for EGR1. Specifically, FBXW7 binds to EGR1 via its consensus binding motif/degron, whereas cancer-derived FBXW7 mutants showed a much reduced EGR1 binding. SiRNA-mediated FBXW7 knockdown caused EGR1 accumulation, whereas FBXW7 overexpression reduced EGR1 levels. Likewise, FBXW7 knockdown significantly extended EGR1 protein half-life, while FBXW7 overexpression promotes polyubiquitylation of wild-type EGR1, but not EGR1-S2A mutant with the binding site abrogated. GSK3β kinase is required for the FBXW7-EGR1 binding, and for enhanced EGR1 degradation by wild type FBXW7, but not by FBXW7 mutants. Likewise, GSK3β knockdown or treatment with GSK3β inhibitor significantly increased the EGR1 levels and extended EGR1 protein half-life, while reducing EGR1 polyubiquitylation. Hypoxia exposure reduces the EGR1 levels via enhancing the FBXW7-EGR1 binding, and FBXW7-induced EGR1 polyubiquitylation. Biologically, EGR1 knockdown suppressed cancer cell growth, whereas growth stimulation by FBXW7 knockdown is partially rescued by EGR1 knockdown. Thus, EGR1 is a new substrate of the GSK3β-FBXW7 axis, and the FBXW7-EGR1 axis coordinately regulates growth of cancer cells.

Early Growth Response Factor 1 in Aging Hematopoietic Stem Cells and Leukemia

Aging is associated with various hematological disorders and a higher risk of myeloproliferative disorders. An aged hematopoietic system can be characterized by decreased immune function and increased myeloid cell production. Hematopoietic stem cells (HSCs) regulate the production of blood cells throughout life. The self-renewal and regenerative potential of HSCs determine the quality and quantity of the peripheral blood cells. External signals from the microenvironment under different conditions determine the fate of the HSCs to proliferate, self-renew, differentiate, or remain quiescent. HSCs respond impromptu to a vast array of extracellular signaling cascades such as cytokines, growth factors, or nutrients, which are crucial in the regulation of HSCs. Early growth response factor 1 (EGR1) is one of the key transcription factors controlling HSC proliferation and their localization in the bone marrow (BM) niche. Downregulation of Egr1 activates and recruits HSCs for their proliferation and differentiation to produce mature blood cells. Increased expression of Egr1 is implicated in immuno-aging of HSCs. However, dysregulation of Egr1 is associated with hematological malignancies such as acute myeloid leukemia (AML), acute lymphoblastic leukemia (ALL), and chronic myelogenous leukemia (CML). Here, we summarize the current understanding of the role of EGR1 in the regulation of HSC functionality and the manifestation of leukemia. We also discuss the alternative strategies to rejuvenate the aged HSCs by targeting EGR1 in different settings.

The Role of the Transcription Factor EGR1 in Cancer

Early growth response factor 1 (EGR1) is a transcription factor that is mainly involved in the processes of tissue injury, immune responses, and fibrosis. Recent studies have shown that EGR1 is closely related to the initiation and progression of cancer and may participate in tumor cell proliferation, invasion, and metastasis and in tumor angiogenesis. Nonetheless, the specific mechanism whereby EGR1 modulates these processes remains to be elucidated. This review article summarizes possible mechanisms of action of EGR1 in tumorigenesis and tumor progression and may serve as a reference for clinical efficacy predictions and for the discovery of new therapeutic targets.

Silencing ARAF Suppresses the Malignant Phenotypes of Gallbladder Cancer Cells

ARAF is a member of the RAF kinase family that is necessary for mitogen-activated protein kinase (MAPK) activation in various malignancies, including lung, colorectal, pancreatic, and breast cancers. As the most common biliary tract tumor, gallbladder cancer (GBC) seriously harms human health while the function of ARAF in GBC remains elusive. Here, we found that ARAF expression was upregulated in gallbladder cancer tissues. In vitro, ARAF silencing mediated by RNA interference effectively inhibited cell proliferation, colony formation, migration, and invasion of GBC cells. Moreover, knocking down ARAF suppressed tumor growth in vivo. Our results indicated that ARAF functions as an oncogene in GBC and, thus, could be a potential therapeutic target for GBC.

Friend or foe, the role of EGR-1 in cancer

Early growth response-1 (EGR-1), also termed NEFI-A and Krox-24, as a multi-domain protein is implicated in several vital physiological processes, including development, metabolism, cell growth and proliferation. Previous studies have implied that EGR-1 was producing in response to the tissue injury, immune response and fibrosis. Meanwhile, emerging studies stressed the pronounced correlation of EGR-1 and human cancers. Nevertheless, the intricate mechanisms of cancer-reduce EGR-1 alteration still poorly characterized. In the review, we evaluated the effects of EGR-1 in tumor cell proliferation, apoptosis, migration, invasion and tumor microenvironment, and then, we dwell on the intricate signaling pathways that EGR-1 involved in. The aberrantly expressed of EGR-1 in cancers are expected to provide a new cancer therapy strategy or a new marker for assessing treatment efficacy.

VEGFC/VEGFR3 Signaling Regulates Mouse Spermatogonial Cell Proliferation via the Activation of AKT/MAPK and Cyclin D1 Pathway and Mediates the Apoptosis by affecting Caspase 3/9 and Bcl-2

We have previously shown that the transcript levels of Vegfc and its receptor Vegfr3 were high in spermatogonia and extremely low in spermatocytes and spermatids. However, it remains unknown about the functions and the mechanisms of VEGFC/VEGFR3 signaling in regulating the fate determinations of spermatogonia. To this end, here we explored the role and signaling pathways of VEGFC/VEGFR3 by using a cell line derived from immortalized mouse spermatogonia retaining markers of mitotic germ cells, namely GC-1 cells. VEGFR3 was expressed in mouse primary spermatogonia and GC-1 cells. VEGFC stimulated the proliferation and DNA synthesis of GC-1 cells and enhanced the phosphorylation of PI3K-AKT and MAPK, whereas LY294002 (an inhibitor for AKT) and CI-1040 (an inhibitor for MAPK) blocked the effect of VEGFC on GC-1 cell proliferation. Furthermore, VEGFC increased the transcripts of c-fos and Egr1 and protein levels of cyclin D1, PCNA and Bcl-2. Conversely, the blocking of VEGFC/VEGFR3 signaling by VEGFR3 knockdown reduced the phosphorylation of AKT/MAPK and decreased the levels of cyclin D1 and PCNA. Additionally, VEGFR3 knockdown not only resulted in more apoptosis of GC-1 cells but also led to a decrease of Bcl-2 and promoted the cleavage of Caspase-3/9 and PARP. Collectively, these data suggested that VEGFC/VEGFR3 signaling promotes the proliferation of GC-1 cells via the AKT /MAPK and cyclin D1 pathway and it inhibits the cell apoptosis through Caspase-3/9, PARP and Bcl-2. Thus, this study sheds a novel insight to the molecular mechanisms underlying the fate decisions of mammalian spermatogonia.

Role of early growth response 1 in arteriogenesis: Impact on vascular cell proliferation and leukocyte recruitment in vivo

Based on previous findings that early growth response 1 (Egr-1) participates in leukocyte recruitment and cell proliferation in vitro, this study was designed to investigate its mode of action during arteriogenesis in vivo. In a model of peripheral arteriogenesis, Egr-1 was significantly upregulated in growing collaterals of wild-type (WT) mice, both on mRNA and protein level. Egr-1−/− mice demonstrated delayed arteriogenesis after femoral artery ligation. They further showed increased levels of monocytes and granulocytes in the circulation, but reduced levels in adductor muscles under baseline conditions. After femoral artery ligation, elevated numbers of macrophages were detected in the perivascular zone of collaterals in Egr-1−/− mice and mRNA of leukocyte recruitment mediators was upregulated. Other Egr family members (Egr-2 to -4) were significantly upregulated only in Egr-1−/− mice, suggesting a mechanism of counterbalancing Egr-1 deficiency. Moreover, splicing factor-1, downregulated in WT mice after femoral artery ligation in the process of increased vascular cell proliferation, was upregulated in Egr-1−/− mice. αSM-actin on the other hand, significantly downregulated in WT mice, showed no differential expression in Egr-1−/− mice. While cell cycle regulator cyclin E and cdc20 were upregulated in Egr-1−/− mice, cyclin D1 expression decreased below the detection limit in collaterals, and the proliferation marker ki67 was not differentially expressed. In conclusion, compensation for deficiency in Egr-1 function in leukocyte recruitment can presumably be mediated by other transcription factors; however, Egr-1 is indispensable for effective vascular cell cycle progression in arteriogenesis.

Binding and inhibition of the ternary complex factor Elk-4/Sap1 by the adapter protein Dok-4

The adapter protein Dok-4 (downstream of kinase-4) has been reported as both an activator and inhibitor of Erk and Elk-1, but lack of knowledge about the identity of its partner molecules has precluded any mechanistic insight into these seemingly conflicting properties. We report that Dok-4 interacts with the transactivation domain of Elk-4 through an atypical phosphotyrosine-binding domain-mediated interaction. Dok-4 possesses a nuclear export signal and can relocalize Elk-4 from nucleus to cytosol, whereas Elk-4 possesses two nuclear localization signals that restrict interaction with Dok-4. The Elk-4 protein, unlike Elk-1, is highly unstable in the presence of Dok-4, through both an interaction-dependent mechanism and a pleckstrin homology domain-dependent but interaction-independent mechanism. This is reversed by proteasome inhibition, depletion of endogenous Dok-4 or lysine-to-arginine mutation of putative Elk-4 ubiquitination sites. Finally, Elk-4 transactivation is potently inhibited by Dok-4 overexpression but enhanced by Dok-4 knockdown in MDCK renal tubular cells, which correlates with increased basal and EGF-induced expression of Egr-1, Fos and cylcinD1 mRNA, and cell proliferation despite reduced Erk activation. Thus, Dok-4 can target Elk-4 activity through multiple mechanisms, including binding of the transactivation domain, nuclear exclusion and protein destabilization, without a requirement for inhibition of Erk.

Oxytocin: its role in benign prostatic hyperplasia via the ERK pathway

The aim of the present study was to evaluate oxytocin and benign prostatic hyperplasia (BPH), and study the cell signalling mechanism. Investigation was performed in patients about the correlation between oxytocin level and BPH. Mice were injected with oxytocin or oxytocin antagonist for 2 weeks and the prostate morphology was studied after their sacrifice. Furthermore, in vitro experiments were performed to evaluate the oxytocin effect through the MEK/ERK/RSK pathway. Oxytocin was significantly elevated in the serum and prostate tissue of patients with BPH, and a positive correlation with prostate volume indicated. In the animal experiments, prostate enlargement was observed in the oxytocin-treated group, whereas oxytocin antagonist reduced prostate hyperplasia. The in vitro study confirmed this result and also revealed activation of the MEK/ERK/RSK pathway. Oxytocin is highly expressed in the serum and prostate tissue of patients with BPH. In addition, oxytocin aggravates BPH and the oxytocin-induced proliferative effect on prostatic cells is mediated through the MEK/ERK/RSK pathway, at least partly. Thus, the hypothalamic regulation may be involved in development of BPH, which may open a new door to more medications for BPH in the future.

Regulation of mice liver regeneration by early growth response-1 through the GGPPS/RAS/MAPK pathway

BACKGROUND & AIMS

Liver regeneration (LR) consists of a series of complicated processes in which several transcription factors play important roles. Among them, the early growth response 1 gene (EGR-1) is rapidly induced in response to liver resection. Previous studies have shown that EGR-1-/- mice exhibit delayed hepatocellular mitotic progression after partial hepatectomy (PH). The mechanism underlying the EGR-1 regulated LR is still unknown. Our aim is to elucidate the underlying mechanism.

METHODS

Mice infected with adenoviral vectors expressing GFP, EGR-1 or dominant negative EGR-1 (dnEGR-1) were subjected to 2/3 PH. The serum starvation recovery cell model was chosen to mimic the regeneration process for the in vitro studies. Cell proliferation and signaling pathways downstream of geranylgeranyl diphosphate synthase (GGPPS) were examined in the regenerating liver and serum starvation recovery cell model.

RESULTS

Loss of function of EGR-1 significantly inhibited liver recovery and the expression of cyclin D1, cyclin E, and proliferating cell nuclear antigen (PCNA). The expression of GGPPS and the activity of the downstream RAS/MAPK pathway were inhibited in dnEGR-1-infected liver, which was consistent with the serum-induced cell model. In addition, loss of function of EGR-1 aggravated liver damage with increased serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels.

CONCLUSIONS

EGR-1-induced GGPPS plays a vital role in the LR after PH through the RAS/MAPK signaling.

ERK activation is required for CCK-mediated pancreatic adaptive growth in mice

High levels of cholecystokinin (CCK) can stimulate pancreatic adaptive growth in which mature acinar cells divide, leading to enhanced pancreatic mass with parallel increases in protein, DNA, RNA, and digestive enzyme content. Prolonged release of CCK can be induced by feeding trypsin inhibitor (TI) to disrupt normal feedback control. This leads to exocrine growth in a CCK-dependent manner. The extracellular signal-related kinase (ERK) pathway regulates many proliferative processes in various tissues and disease models. The aim of this study was to evaluate the role of ERK signaling in pancreatic adaptive growth using the MEK inhibitors PD-0325901 and trametinib (GSK-1120212). It was determined that PD-0325901 given two times daily by gavage or mixed into powdered chow was an effective and specific inhibitor of ERK signaling in vivo. TI-containing chow led to a robust increase in pancreatic mass, protein, DNA, and RNA content. This pancreatic adaptive growth was blocked in mice fed chow containing the MEK inhibitors. PD-0325901 blocked TI-induced ERK-regulated early response genes, cell-cycle proteins, and mitogenesis by acinar cells. It was determined that ERK signaling is necessary for the initiation of pancreatic adaptive growth but not necessary to maintain it. PD-0325901 blocked adaptive growth when given before cell-cycle initiation but not after mitogenesis had been established. Furthermore, GSK-1120212, a chemically distinct inhibitor of the ERK pathway that is now approved for clinical use, inhibited growth similar to PD-0325901. These data demonstrate that the ERK pathway is required for CCK-stimulated pancreatic adaptive growth.

Mechanisms of RAS/β-catenin interactions

Signaling through the WNT/β-catenin and the RAS (rat sarcoma)/MAPK (mitogen-activated protein kinase) pathways plays a key role in the regulation of various physiological cellular processes including proliferation, differentiation, and cell death. Aberrant mutational activation of these signaling pathways is closely linked to the development of cancer in many organs, in humans as well as in laboratory animals. Over the past years, more and more evidence for a close linkage of the two oncogenic signaling cascades has accumulated. Using different experimental approaches, model systems, and experimental conditions, a variety of molecular mechanisms have been identified by which signal transduction through WNT/β-catenin and RAS interact, either in a synergistic or an antagonistic manner. Mechanisms of interaction comprise an upstream crosstalk at the level of pathway-activating ligands and their receptors, interrelations of cytosolic kinases involved in either pathways, as well as interaction in the nucleus related to the joint regulation of target gene transcription. Here, we present a comprehensive review of the current knowledge on the interaction of RAS/MAPK- and WNT/β-catenin-driven signal transduction in mammalian cells.

Phosphorylation of histone H3 at serine 10 has an essential role in arsenite-induced expression of FOS, EGR1 and IL8 mRNA in cultured human cell lines

Trivalent inorganic arsenite [iAs(III)] is known to alter the expression of a number of genes associated with transcription and cell proliferation, which was thought to be one of the possible mechanisms of arsenical carcinogenesis. However, the detailed mechanisms underlying iAs(III) induction of changes in gene expression are not fully understood. Here we examine the role of histone H3 phosphorylation at serine 10 (Ser(10) ) in gene regulation when the cells were treated with iAs(III). Among the 34 genes tested, iAs(III) induced mRNA expression of JUN, FOS, EGR1, HMOX1, HSPA1A, IL8, GADD45A, GADD45B and GADD153. Phosphorylation of histone H3 Ser(10) was induced by iAs(III) in interphase cells, and was effectively blocked by the ERKs pathway inhibitor (U0126). U0126 treatment significantly reduced constitutive mRNA expression of FOS and EGR1, and dramatically suppressed the induction of FOS, EGR1 and IL8 mRNA in iAs(III)-treated cells. The other genes, which were induced by iAs(III), were not affected by U0126 treatment. When the histone H3 nonphosphorylatable mutant of serine 10 (S10A) was overexpressed in cells, iAs(III) induction of FOS, EGR1and IL8 expression was significantly decreased as compared with wild-type cells. The other genes induced by iAs(III) were not changed in S10A cells nor by U0126 treatment. In addition, S10A cells were more resistant to iAs(III) cytotoxicity. These results indicated that the phosphorylation of histone H3 at Ser(10) through the ERKs pathway in interphase cells is an important regulatory event for iAs(III)-mediated gene expression. Aberrant gene expression seems to be an important cause of cytotoxicity and may have some relation to iAs(III) carcinogenicity.

Profiling gastrin-releasing peptide receptor in prostate tissues: clinical implications and molecular correlates

BACKGROUND

The gastrin-releasing peptide receptor (GRPR) has emerged as an attractive target for both therapeutic and diagnostic appliances, but has only insufficiently been characterized in the human prostate so far. The aim of this study is to profile GRPR in a large cohort and correlate it with clinicopathologic and molecular parameters.

METHODS

Benign and malignant (primary carcinoma, metastases, and castration-resistant prostate cancer) prostate samples from 530 patients were analyzed immunohistochemically for GRPR, androgen receptor and Cyclin D1 expression. Staining intensity was assessed assigning a semiquantitative score to each sample.

RESULTS

Normal prostate tissues were mostly GRPR negative, significantly higher expression rates were seen in primary carcinomas and metastases. Significant inverse correlations were found for GRPR and increasing Gleason score, PSA value, and tumor size. A stratified Kaplan-Meyer analysis for GRPR and high AR expression shows a significant prognostic advantage for high GRPR expression, whereas GRPR expression alone shows no independent prognostic value. Highly significant correlations for GRPR, AR, and Cyclin D1 were found.

CONCLUSIONS

Our data show that GRPR is overexpressed in prostate cancer, particularly of lower grade and smaller size. These findings constitute a caveat for the use of GRPR as a target for diagnostic or therapeutic approaches to high grade or progressed prostate cancer.

GPER mediates the Egr-1 expression induced by 17β-estradiol and 4-hydroxitamoxifen in breast and endometrial cancer cells

Early growth response-1 (Egr-1) is an immediate early gene involved in relevant biological events including the proliferation of diverse types of cell tumors. In a microarray analysis performed in breast cancer cells, 17β-estradiol (E2) and the estrogen receptor antagonist 4-hydroxitamoxifen (OHT) up-regulated Egr-1 through the G protein-coupled receptor named GPR30/GPER. Hence, in this study, we aimed to provide evidence regarding the ability of E2, OHT and the selective GPER ligand G-1 to regulate Egr-1 expression and function through the GPER/EGFR/ERK transduction pathway in both Ishikawa (endometrial) and SkBr3 (breast) cancer cells. Interestingly, we demonstrate that Egr-1 is involved in the transcription of genes regulating cell proliferation like CTGF and cyclin D1 and required for the proliferative effects induced by E2, OHT, and G-1 in both Ishikawa and SkBr3 cells. In addition, we show that GPER mediates the expression of Egr-1 also in carcinoma-associated fibroblasts (CAFs). Our data suggest that Egr-1 may represent an important mediator of the biological effects induced by E2 and OHT through GPER/EGFR/ERK signaling in breast and endometrial cancer cells. The results obtained in CAFs provide further evidence regarding the potential role exerted by the GPER-dependent Egr-1 up-regulation in tumor development and progression. Therefore, Egr-1 may be included among the bio-markers of estrogen and antiestrogen actions and may be considered as a further therapeutic target in both breast and endometrial tumors.

Neuroendocrine tumor cells in prostate cancer: evaluation of the neurosecretory products serotonin, bombesin, and gastrin - impact on angiogenesis and clinical follow-up

BACKGROUND

Neuroendocrine differentiated tumor cells (NETC) can be found in a large portion of prostate carcinoma (PCa) specimens. This is the first study to systematically quantify and analyze the influence of the NETC distribution and of their secretory products, serotonin, bombesin, and gastrin, on angiogenesis and in the clinical follow-up of PCa patients.

METHODS

175 PCa specimens were included in this study. NETC were displayed using the marker CgA. Specimens showing a high expression of CgA were analyzed for serotonin, bombesin, and gastrin. Blood vessels were stained with the epitope CD34. Data was analyzed for inter-correlation and its correlation to clinical-pathological parameters and the results of a mid-term follow-up.

RESULTS

The number of NETC was correlated with the pT-status and the Gleason score. Specimens with high NETC expression had an increased microvessel density (MVD). No correlation between the neurosecretory products and the clinical-pathological parameters was found. High NETC expression, high bombesin expression and increased MVD were associated with early treatment failure in the follow-up.

CONCLUSION

NETC have an influence on angiogenesis and are correlated with the clinical-pathological parameters. A high expression of NETC is associated with an early failure of treatment. Our study underlines the importance of NETC in prostate cancer.

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.

Early growth response (EGR)-1 is required for timely cell-cycle entry and progression in hepatocytes after acute carbon tetrachloride exposure in mice

Cell-cycle induction in hepatocytes protects from prolonged tissue damage after toxic liver injury. Early growth response (Egr)-1(-/-) mice exhibit increased liver injury after carbon tetrachloride (CCl(4)) exposure and reduced TNF-α production. Because TNF-α is required for prompt cell-cycle induction after liver injury, here, we tested the hypothesis that Egr-1 is required for timely hepatocyte entry into the cell cycle after CCl(4)-induced liver injury. Acute liver injury was induced by a single injection of CCl(4). Assays were employed to assess indices of the cell cycle in liver after CCl(4) exposure. Bromodeoxyuridine incorporation peaked in wild-type mice at 48 h after CCl(4) but was reduced by 80% in Egr-1(-/-) mice. Proliferating-cell nuclear-antigen immunohistochemistry revealed blocks in cell-cycle entry and progression to DNA synthesis in Egr-1-deficient mice 48 h after CCl(4). Cyclin D, important for G0/G1 progression, was reduced at baseline and 36 h after CCl(4). Cyclin E1, required for G1/S-phase transition, was reduced in Egr-1(-/-) mice 24 and 48 h after CCl(4) exposure and was associated with reduced phosphorylation of the retinoblastoma protein. Proliferation in Egr-1(-/-) mice was delayed, rather than blocked, because indices of cell-cycle progression were restored 72 h after CCl(4) exposure. We concluded that Egr-1 was required for prompt cell-cycle entry (G0- to G1-phase) and G1/S-phase transition after toxic liver injury. These data support the hypothesis that Egr-1 provides hepatoprotection in the CCl(4)-injured liver, attributable, in part, to timely cell-cycle induction and progression.

Inhibition of cell proliferation by CD44: Akt is inactivated and EGR-1 is down-regulated

OBJECTIVE

CD44 is a transmembrane glycoprotein and can facilitate signal transduction by serving as a platform for molecular recruitment and assembly. A number of studies have suggested that CD44 can either positively or negatively regulate cell proliferation. The purpose of this study was to investigate how CD44 can inhibit cell proliferation.

MATERIALS AND METHODS

We engineered E6.1 Jurkat cells to express CD44. Importantly, these cells lack endogenous CD44 expression. Molecular pathways involved with cell proliferation were studied using RT(2)-PCR array, siRNA, Western blotting and by employing pharmacological inhibitors of ERK1/2, p38 and the PI3K/Akt pathways.

RESULTS

We found that CD44 expression significantly inhibited cell proliferation and down-regulated EGR-1 expression and EGR-1 targets cyclin D1 and cyclin D2. Transfection of control E6.1 Jurkat cells with EGR-1 siRNA also inhibited cell proliferation, confirming its role. Disruption of the PI3K/Akt pathway with pharmacological inhibitors reduced both EGR-1 expression and cell proliferation, recapitulating the properties of CD44 expressing cells. Akt was hypophosphorylated in cells expressing CD44 showing its potential role in negatively regulating Akt activation. Strikingly, constitutively active Akt rescued the proliferation defect showing requirement for active Akt, in our system.

CONCLUSION

Our results suggest a novel pathway by which CD44 inactivates Akt, down-regulates EGR-1 expression and inhibits cell proliferation.

Potential-dependent studies on the interaction between phenylalanine-substituted bombesin fragments and roughened Ag, Au, and Cu electrode surfaces

In this work, we report systematic surface-enhanced Raman spectroscopy (SERS) and generalized two-dimensional correlation analysis (G2DCA) studies of the structures of five specifically modified phenylalanine-substituted C-terminal bombesin 6-14 fragments (BN(6-14)). The fragments studied have all been tested as chemotherapeutic agents in cancer therapy, and they form amino acid sequences in bombesin: cyclo[d-Phe(6),His(7),Leu(14)]BN(6-14), [D-Phe(6),Leu-NHEt(13),des-Met(14)]BN(6-14), [D-Phe(6),Leu(13)-((R))-p-Cl-Phe(14)]BN(6-14), [D-Phe(6),beta-Ala(11),Phe(13),Nle(14)]BN(6-14), and [D-Tyr(6),beta-Ala(11),Phe(13),Nle(14)]BN(6-14). We adsorbed these fragments onto roughened Ag, Au, and Cu electrode surfaces, using a potential range from -1.200 to 0.400 V, at physiological pH. We compared the adsorption mechanism of each fragment on these substrates, as well any changes observed with varying electrode potential, to determine the relationship between adsorption strength and geometry of each of the peptides wherever it was possible. For example, we showed that none of these fragments directly interact with the Ag, Au, and Cu surfaces via residues of Phe (phenylalanine) and Trp(8) (L-tryptophane at position 8 of the BN amino acid sequence) or by an amide bond, due to a very small shift in wavenumber of their characteristic vibrations. Specific interactions were recognized from the broadening, wavenumber shift, and increase in intensity of the W18 Trp(8) mode near 759 cm(-1) and decrease in nu(12) vibration frequency of the Phe residue. In general, more intense SERS bands were observed due to the Phe ring, compared with the Trp(8) ring, which suggested a preferential adsorption of phenylalanine over tryptophane. For [D-Tyr(6),beta-Ala(11),Phe(13),Nle(14)]BN(6-14), the data also suggest some interaction of a D-Tyr(6) residue (D-tyrosine at position 6). Finally, only slight rearrangements of these moieties on the substrates are observed with changes in electrode potential.

Is EGR1 a potential target for prostate cancer therapy?

Prostate cancer is a major cause of cancer-related death in American men, for which finding new therapeutic strategies remains a challenge. Early growth response-1 (EGR1) is a transcription factor involved in cell proliferation and in the regulation of apoptosis. Although it has long been considered a tumor suppressor, a wealth of new evidence shows that EGR1 promotes the progression of prostate cancer. This review addresses the paradoxes of EGR1 function. While EGR1 mediates apoptosis in response to stress and DNA damage by regulating a tumor suppressor network, it also promotes the proliferation of prostate cancer cells by a mechanism that is not fully understood. Thus, EGR1 might be targeted for prostate cancer therapy either by ectopic expression in combination with radiotherapy or chemotherapy, or by direct inhibition for systemic treatment. Possible strategies to antagonize EGR1 function in a therapeutic setting are discussed.

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.

Regulation and signaling of human bombesin receptors and their biological effects

PURPOSE OF REVIEW

This review will highlight recent advances in the understanding of molecular mechanisms by which mammalian bombesin receptors are regulated and which intracellular signaling pathways have been characterized to mediate agonist-dependent receptor biological effects.

RECENT FINDINGS

Mammalian bombesin receptors have been demonstrated to be involved in a larger array of physiological and pathophysiological conditions than previously reported. Pharmacological experiments in vitro and in vivo as well as utilization of animals genetically deficient of the gastrin-releasing peptide receptor demonstrated roles in memory and fear behavior, lung development and injury, small intestinal cell repair, autocrine tumor growth, and mediating signals for pruritus and penile reflexes. Intracellular signaling studies predominantly of the gastrin-releasing peptide receptor owing to its frequent overexpression in some human malignancies showed that PI3 kinase activation is an important mechanism of cell proliferation. Tumor cell treatment including gastrin-releasing peptide receptor antagonists combined with inhibition of epidermal growth factor receptor resulted in an additive effect on blocking cell proliferation. Novel molecular mechanisms of the orphan bombesin receptor subtype-3 and gastrin-releasing peptide receptor gene regulation have been elucidated.

SUMMARY

Inhibition of gastrin-releasing peptide receptor signaling in human malignancies represents an attractive target for pharmacological treatment. Novel functions of bombesin related peptides have been identified including processes in the central nervous system, lung and intestinal tract.

Structures and bonding on a colloidal silver surface of the various length carboxyl terminal fragments of bombesin

Raman (RS) and surface-enhanced Raman scattering spectra (SERS) were measured for various length carboxyl terminal fragments (X-14 of amino acid sequence) of bombesin ( BN): BN13-14, BN12-14, BN11-14, BN10-14, BN9-14, and BN8-14 in silver colloidal solutions. Density functional theory (DFT) calculations of Raman wavenumbers and intensities with extended basis sets (B3LYP/6-31++G**) were performed with the aim of providing the definitive band allocations to the normal coordinates. The proposed band assignment is consistent with the assignment for similar compounds reported in the literature. The nonadsorbed and adsorbed molecular structures were deducted by detailed spectral analysis of the RS and SERS spectra, respectively. This analysis also allowed us to propose the particular surface geometry and orientation of these peptides on silver surface, and their specific interaction with the surface. For example, a SERS spectrum of BN8-14 indicates that the interaction of a thioether atom and Trp8 with the silver surface is favorable and may dictate the orientation and conformation of adsorbed peptide. One of the most prominent and common features in all of the fragments' SERS spectra is a approximately 692 cm (-1) band due to nu(C-S) accompanied by two or three bands of different C-S conformers for all, except BN8-14, which suggests that all of the above-mentioned compounds adsorb on the silver surface through the thioether atom and that the attachment of Trp8 produces limitation in a number of possible C-S conformers adopted on this surface. Our results also show clearly that His12 and CO do not interact with the colloid surface, which supports our earlier results.

International Union of Pharmacology. LXVIII. Mammalian bombesin receptors: nomenclature, distribution, pharmacology, signaling, and functions in normal and disease states

The mammalian bombesin receptor family comprises three G protein-coupled heptahelical receptors: the neuromedin B (NMB) receptor (BB(1)), the gastrin-releasing peptide (GRP) receptor (BB(2)), and the orphan receptor bombesin receptor subtype 3 (BRS-3) (BB(3)). Each receptor is widely distributed, especially in the gastrointestinal (GI) tract and central nervous system (CNS), and the receptors have a large range of effects in both normal physiology and pathophysiological conditions. The mammalian bombesin peptides, GRP and NMB, demonstrate a broad spectrum of pharmacological/biological responses. GRP stimulates smooth muscle contraction and GI motility, release of numerous GI hormones/neurotransmitters, and secretion and/or hormone release from the pancreas, stomach, colon, and numerous endocrine organs and has potent effects on immune cells, potent growth effects on both normal tissues and tumors, potent CNS effects, including regulation of circadian rhythm, thermoregulation; anxiety/fear responses, food intake, and numerous CNS effects on the GI tract as well as the spinal transmission of chronic pruritus. NMB causes contraction of smooth muscle, has growth effects in various tissues, has CNS effects, including effects on feeding and thermoregulation, regulates thyroid-stimulating hormone release, stimulates various CNS neurons, has behavioral effects, and has effects on spinal sensory transmission. GRP, and to a lesser extent NMB, affects growth and/or differentiation of various human tumors, including colon, prostate, lung, and some gynecologic cancers. Knockout studies show that BB(3) has important effects in energy balance, glucose homeostasis, control of body weight, lung development and response to injury, tumor growth, and perhaps GI motility. This review summarizes advances in our understanding of the biology/pharmacology of these receptors, including their classification, structure, pharmacology, physiology, and role in pathophysiological conditions.

Novel pro-survival functions of the Kruppel-like transcription factor Egr2 in promotion of macrophage colony-stimulating factor-mediated osteoclast survival downstream of the MEK/ERK pathway

Determining the underlying mechanisms of macrophage colony-stimulating factor (M-CSF)-mediated osteoclast survival may be important in identifying novel approaches for treating excessive bone loss. This study investigates M-CSF-mediated MEK/ERK activation and identifies a downstream effector of this pathway. M-CSF activates MEK/ERK and induces MEK-dependent expression of the immediate early gene Egr2. Inhibition of either MEK1/2 or inhibition of Egr2 increases osteoclast apoptosis. In contrast, wild-type Egr2 or an Egr2 point mutant unable to bind the endogenous repressors Nab1/2 (caEgr2) suppresses basal osteoclast apoptosis and rescues osteoclasts from apoptosis induced by MEK1/2 or Egr2 inhibition. Mechanistically, Egr2 induces pro-survival Blc2 family member Mcl1 while stimulating proteasome-mediated degradation of pro-apoptotic Bim. In addition, Egr2 increased the expression of c-Cbl, the E3 ubiquitin ligase that catalyzes Bim ubiquitination. M-CSF, therefore, promotes osteoclast survival through MEK/ERK-dependent induction of Egr2 to control the Mcl1/Bim ratio, documenting a novel function of Egr2 in promoting survival.

Mitogenic signaling pathways induced by G protein-coupled receptors

G protein-coupled receptor (GPCR) agonists, including neurotransmitters, hormones, chemokines, and bioactive lipids, act as potent cellular growth factors and have been implicated in a variety of normal and abnormal processes, including development, inflammation, and malignant transformation. Typically, the binding of an agonistic ligand to its cognate GPCR triggers the activation of multiple signal transduction pathways that act in a synergistic and combinatorial fashion to relay the mitogenic signal to the nucleus and promote cell proliferation. A rapid increase in the activity of phospholipases C, D, and A2 leading to the synthesis of lipid-derived second messengers, Ca2+ fluxes and subsequent activation of protein phosphorylation cascades, including PKC/PKD, Raf/MEK/ERK, and Akt/mTOR/p70S6K is an important early response to mitogenic GPCR agonists. The EGF receptor (EGFR) tyrosine kinase has emerged as a transducer in the signaling by GPCRs, a process termed transactivation. GPCR signal transduction also induces striking morphological changes and rapid tyrosine phosphorylation of multiple cellular proteins, including the non-receptor tyrosine kinases Src, focal adhesion kinase (FAK), and the adaptor proteins CAS and paxillin. The pathways stimulated by GPCRs are extensively interconnected by synergistic and antagonistic crosstalks that play a critical role in signal transmission, integration, and dissemination. The purpose of this article is to review recent advances in defining the pathways that play a role in transducing mitogenic responses induced by GPCR agonists.

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.

FP prostanoid receptor-mediated induction of the expression of early growth response factor-1 by activation of a Ras/Raf/mitogen-activated protein kinase signaling cascade

FP prostanoid receptors are G-protein-coupled receptors whose physiological activator is prostaglandin-F(2alpha) (PGF(2alpha)). PGF(2alpha) has been implicated in wound healing and cardiac hypertrophy, which are both known to involve the induction of the immediate-early response gene, early growth response factor-1 (EGR-1). We hypothesized that activation of the human FP receptor by PGF(2alpha) could induce the expression of EGR-1 and found that 1 muM PGF(2alpha) produced a time-dependent induction of both mRNA and protein expression for EGR-1. This FP receptor-mediated induction of EGR-1 expression involved activation of the small GTPase Ras followed by activation of C-Raf and the mitogen-activated protein (MAP) kinase kinases 1 and 2 (MEK1/2). Thus, induction of EGR-1 expression by PGF(2alpha) was blocked using dominant-negative constructs of Ras and C-Raf and the Raf kinase inhibitor 4-(4-(3-(4-chloro-3-trifluoromethylphenyl)ureido)phenoxy)-pyridine-2-carboxyllic acid methyamide-4-methylbenzenesulfonate (BAY43-9006). Likewise, the MEK1/2 inhibitor 2'-amino-3'-methoxyflavone (PD98059) blocked the induction of EGR-1 expression by PGF(2alpha). FP receptor stimulation by PGF(2alpha) induced the phosphorylation of C-Raf, MEK1/2, and extracellular signal-regulated kinases 1 and 2, consistent with the activation of a MAP kinase signaling cascade. PGF(2alpha) was also found to induce the expression of EGR-1 in rat cardiomyocytes through the activation of endogenous FP receptors. This induction of EGR-1 expression in cardiomyocytes also involved the activation of Raf and MAP kinase signaling and was dependent on the activation of protein kinase C. This is the first report to show the regulation of EGR-1 expression after PGF(2alpha) activation of FP receptors and suggests that this could be an early event involved in wound healing and cardiac hypertrophy.

Modulation of transcription factors by curcumin

Curcumin is the active ingredient of turmeric that has been consumed as a dietary spice for ages. Turmeric is widely used in traditional Indian medicine to cure biliary disorders, anorexia, cough, diabetic wounds, hepatic disorders, rheumatism, and sinusitis. Extensive investigation over the last five decades has indicated that curcumin reduces blood cholesterol, prevents low-density lipoprotein oxidation, inhibits platelet aggregation, suppresses thrombosis and myocardial infarction, suppresses symptoms associated with type II diabetes, rheumatoid arthritis, multiple sclerosis, and Alzheimer's disease, inhibits HIV replication, enhances wound healing, protects from liver injury, increases bile secretion, protects from cataract formation, and protects from pulmonary toxicity and fibrosis. Evidence indicates that the divergent effects of curcumin are dependent on its pleiotropic molecular effects. These include the regulation of signal transduction pathways and direct modulation of several enzymatic activities. Most of these signaling cascades lead to the activation of transcription factors. Curcumin has been found to modulate the activity of several key transcription factors and, in turn, the cellular expression profiles. Curcumin has been shown to elicit vital cellular responses such as cell cycle arrest, apoptosis, and differentiation by activating a cascade of molecular events. In this chapter, we briefly review the effects of curcumin on transcription factors NF-KB, AP-1, Egr-1, STATs, PPAR-gamma, beta-catenin, nrf2, EpRE, p53, CBP, and androgen receptor (AR) and AR-related cofactors giving major emphasis to the molecular mechanisms of its action.

The EP4 receptor antagonist, L-161,982, blocks prostaglandin E2-induced signal transduction and cell proliferation in HCA-7 colon cancer cells

Accumulating evidence indicates that elevated levels of prostaglandin E(2) (PGE(2)) can increase intestinal epithelial cell proliferation, and thus play a role in colorectal tumorigenesis. PGE(2) exerts its effects through four G-protein-coupled PGE receptor (EP) subtypes, named the EP1, EP2, EP3, and EP4. Increased phosphorylation of extracellular regulated kinases (ERK1/2) is required for PGE(2) to stimulate cell proliferation of human colon cancer cells. However, the EP receptor(s) that are involved in this process remain unknown. We provide evidence that L-161,982, a selective EP4 receptor antagonist, completely blocks PGE(2)-induced ERK phosphorylation and cell proliferation of HCA-7 cells. In order to identify downstream target genes of ERK1/2 signaling, we found that PGE(2) induces expression of early growth response gene-1 (EGR-1) downstream of ERK1/2 and regulates its expression at the level of transcription. PGE(2) treatment induces phosphorylation of cyclic AMP response element binding protein (CREB) at Ser133 residue and CRE-mediated luciferase activity in HCA-7 cells. Studies with dominant-negative CREB mutant (ACREB) provide clear evidence for the involvement of CREB in PGE(2) driven egr-1 transcription in HCA-7 cells. In conclusion, this study reveals that egr-1 is a target gene of PGE(2) in HCA-7 cells and is regulated via the newly identified EP4/ERK/CREB pathway. Finally our results support the notion that antagonizing EP4 receptors may provide a novel therapeutic approach to the treatment of colon cancer.

ErbB-2 induces the cyclin D1 gene in prostate epithelial cells in vitro and in vivo

The receptor tyrosine kinase ErbB-2 plays an important role in the regulation of growth factor-induced signal transduction cascades in the epithelium, and ErbB-2 is frequently overexpressed in epithelial tumors. Our previous studies on clinical prostate cancer specimens indicated that ErbB-2 expression was increased in patients undergoing hormone ablation therapy. We had also shown that the critical cell cycle regulatory gene cyclin D1 and its promoter were targets of proliferative signaling in prostate cancer cell lines, and that cyclin D1 was required for ErbB-2-induced mammary tumorigenesis. In the current studies, we found that increased ErbB-2 membrane expression correlated with increased nuclear cyclin D1 staining in clinical prostate cancer specimens, and that expression of ErbB-2 was capable of inducing cell cycle progression in human prostate cancer cell lines. We further showed that ErbB-2 induced the cyclin D1 promoter in DU145 cells, and that small interfering RNA knockdown of cyclin D1 protein levels blocked a significant proportion of the heregulin-induced cell cycle progression in LNCaP cells. Probasin promoter-targeted expression of an activated ErbB-2 isoform induced cyclin D1 expression in the mouse prostate, commensurate with prostate intraepithelial neoplasia. Together, these in vitro and in vivo studies identify cyclin D1 as a critical downstream target of ErbB-2 in the prostate epithelium, both of which are possible therapeutic targets for cancer intervention. Furthermore, our novel mouse model provides a useful platform for ongoing in vivo investigations of ErbB-2 signaling in the prostate epithelium.

Loss of mitochondrial membrane potential is inhibited by bombesin in etoposide-induced apoptosis in PC-3 prostate carcinoma cells

Neuroendocrine secretory products and their interactions with epithelial prostate cells are currently under investigation in order to understand their significance in the pathogenesis, prognosis, and therapy of prostate carcinoma. These neuropeptides have the potential to disrupt the balance between cell death and cell growth in the tumor. Our research was based on the role of bombesin in modulating the mitochondrial membrane potential (Delta psi(m)) in cell death induced by etoposide on PC-3 cells. Cells were cultured and stained with 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolylcarbocyanine iodide (JC-1). At low membrane potentials, JC-1 produces a green fluorescence, and at high membrane potentials, it forms "J aggregates" with red fluorescence. Cells were examined in a confocal microscope. For quantitative analyses, regions of interest were selected. The size, number of pixels, and ratios between fluorescence intensity in the red and green channels in each region of interest were calculated. The loss of Delta psi(m) in etoposide-treated PC-3 cells was prevented by bombesin. The quantitative analysis of JC-1-stained cells revealed a significant decrease in the red (high Delta psi(m)) to green (low Delta psi(m)) ratio in etoposide-treated cells when compared with control cells, which was restored in the presence of bombesin (P < 0.00001). The interaction between treatments and area (P = 0.0002) was highly significant, and confirms that PC-3 cells keep their apoptosis machinery, showing an apoptotic volume decrease in response to etoposide. The protection by bombesin occurs by inhibition of apoptosis and maintenance of mitochondrial integrity. New therapeutic protocols and trials need to be developed to test drugs acting through the neutralization of antiapoptotic intracellular pathways mediated by neuroendocrine hormones.

Bombesin induces angiogenesis and neuroblastoma growth

Gastrin-releasing peptide (GRP), the mammalian equivalent of bombesin (BBS), is a trophic factor for highly vascular neuroblastomas; its mechanisms of action in vivo are unknown. We sought to determine the effects of BBS on the growth of neuroblastoma xenografts and on angiogenesis. BBS significantly increased the growth of SK-N-SH and BE(2)-C human neuroblastomas; tumors demonstrated increased expression of angiogenic markers, PECAM-1 and VEGF, as well as phosphorylated (p)-Akt levels. RC-3095, a BBS/GRP antagonist, attenuated BBS-stimulated tumor growth and angiogenesis in vivo. GRP or GRPR silencing significantly inhibited VEGF as well as p-Akt and p-mTOR expression in vitro. Our findings demonstrate that BBS stimulates neuroblastoma growth and the expression of angiogenic markers. Importantly, these findings suggest that novel therapeutic agents, targeting BBS-mediated angiogenesis, may be useful adjuncts in patients with advanced-stage neuroblastomas.

Non-genomic effects of 17beta-estradiol in activation of the ERK1/ERK2 pathway induces cell proliferation through upregulation of cyclin D1 expression in bovine artery endothelial cells

OBJECTIVE

Growing evidence indicates that estrogen's non-genomic effects play important roles in cellular functions and backs up the hypothesis of the existence of a membrane estrogen receptor (mER) in a number of cell types, but little is known about the complementary effects between traditional genomic and novel non-genomic effects of estrogen. The aim of the present study was to explore the non-genomic activation of ERK1/2 mitogen-activated protein kinase (MAPK) by 17beta-estradiol (E(2)) through mER and its role in cell proliferation.

METHODS

On cultured bovine artery endothelial cells (BAECs) we used the [(3)H]thymidine incorporation assay to evaluate the influence of E(2) on cell proliferation and fluorescence microscopy to show the presence of mER on the cell membrane. Scatchard analysis was performed to identify and characterize the mER on a purified membrane fraction of BAECs.

RESULTS

E(2) upregulated cyclin D1 protein expression and enhanced cell proliferation. Inhibition of the MAPK cascade with PD98059 or of G protein with pertussis toxin (PTX) completely abolished the above effects, while the estrogen receptor antagonist tamoxifen attenuated E(2)-dependent upregulation of cyclin D1 and cell proliferation. Accordingly, E(2) rapidly led to ERK1/ERK2 activation, which was prevented by tamoxifen or PTX and was entirely reproduced by membrane-impermeable estradiol-bovine serum albumin conjugate (E(2)coBSA). Immunofluorescent staining with E(2)coBSA-fluorescein isothiocyanate resulted in a punctuate staining pattern of the plasma membrane and Scatchard analysis of the E(2)-binding protein in a purified membrane fraction of BAECs showed that E(2) binds to the membrane fraction with a dissociation constant of 0.2394 nmol/l.

CONCLUSION

Our findings showed that E(2) induces cell proliferation through upregulation of cyclin D1 via non-genomic activation of the ERK1/ERK2 pathway mediated by mER and G protein.

Inhibition of macrophage migration inhibitory factor or its receptor (CD74) attenuates growth and invasion of DU-145 prostate cancer cells

Macrophage migration inhibitory factor (MIF), a proinflammatory cytokine, is overexpressed in prostate cancer, but the mechanism by which MIF exerts effects on tumor cells remains undetermined. MIF interacts with its identified membrane receptor, CD74, in association with CD44, resulting in ERK 1/2 activation. Therefore, we hypothesized that increased expression or surface localization of CD74 and MIF overexpression by prostate cancer cells regulated tumor cell viability. Prostate cancer cell lines (LNCaP and DU-145) had increased MIF gene expression and protein levels compared with normal human prostate or benign prostate epithelial cells (p < 0.01). Although MIF, CD74, and CD44 variant 9 expression were increased in both androgen-dependent (LNCaP) and androgen-independent (DU-145) prostate cancer cells, cell surface of CD74 was only detected in androgen-independent (DU-145) prostate cancer cells. Therefore, treatments aimed at blocking CD74 and/or MIF (e.g., inhibition of MIF or CD74 expression by RNA interference or treatment with anti-MIF- or anti-CD74- neutralizing Abs or MIF-specific inhibitor, ISO-1) were only effective in androgen-independent prostate cancer cells (DU-145), resulting in decreased cell proliferation, MIF protein secretion, and invasion. In DU-145 xenografts, ISO-1 significantly decreased tumor volume and tumor angiogenesis. Our results showed greater cell surface CD74 in DU-145 prostate cancer cells that bind to MIF and, thus, mediate MIF-activated signal transduction. DU-145 prostate cancer cell growth and invasion required MIF activated signal transduction pathways that were not necessary for growth or viability of androgen-dependent prostate cells. Thus, blocking MIF either at the ligand (MIF) or receptor (CD74) may provide new, targeted specific therapies for androgen-independent prostate cancer.

Proximal cyclic AMP response element is essential for exendin-4 induction of rat EGR-1 gene

Glucagon-like peptide-1 and its potent agonist exendin-4 induce several immediate early response genes (IEGs) that code for transcription factors implicated in cell proliferation, differentiation, and apoptosis. We recently observed that early growth response factor-1 (EGR-1), an IEG product, was required for transcriptional activation of Ccnd1 (cyclin D1) gene by exendin-4. Herein, the regulatory mechanism whereby exendin-4 activates the transcription of EGR-1 gene was investigated in the pancreatic beta-cell line INS-1. Deletion analysis of rat EGR-1 promoter identified a critical region between -73 and -46 for the activation of EGR-1 in response to exendin-4. Mutation of the proximal putative cAMP response element (CRE, 5'-GTACGTCA-3') located at -69 resulted in a significant decrease in the EGR-1 transcription, whereas the mutation of the distal putative CRE at -139 was without such an effect. In immune supershift assays using exendin-4-treated cells, binding of cAMP response element-binding protein (CREB) phosphorylated on Ser(133) to the proximal CRE was increased. Employment of a CREB mutant containing Ala substitution at Ser(133) or a dominant negative CREB mutant that inhibits the binding of endogenous CREB to DNA significantly decreased the exendin-4-induced EGR-1 transcription. In experiments using specific protein kinase inhibitors, the effect of H-89 was more prominent than PD-98059, indicating the predominance of the PKA signaling over the MEK/ERK in induction of EGR-1. Therefore, it appears that the proximal CRE site is critical and the binding with CREB phosphorylated on Ser(133) is necessary for induction of the EGR-1 transcription by exendin-4.

Gastrin - active participant or bystander in gastric carcinogenesis?

Gastrin is a pro-proliferative, anti-apoptotic hormone with a central role in acid secretion in the gastric mucosa and a long-standing association with malignant progression in transgenic mouse models. However, its exact role in human gastric malignancy requires further validation. Gastrin expression is tightly regulated by two closely associated hormones, somatostatin and gastrin-releasing peptide, and aspects of their interaction may be deregulated during progression to gastric adenocarcinoma. Furthermore, agonists and antagonists of the receptors for all three hormones have shown modest clinical efficacy against gastric adenocarcinoma, which might provide useful information on the future combined use of these agents.