Alterations in the gene expression profile of MCF-7 breast tumor cells in response to c-Jun

Transcription factor Runx2 changes the expression of some matricellular proteins in metastatic breast cancer cells

BACKGROUND

Runx2 is one of the runt-related genes that are overexpressed in human cancers and contribute to metastasis. The cancer cell metastasis requires modifications of the extracellular matrix (ECM) and reduction in ECM-cell interaction. This process is performed by various enzymes and proteins secreted by cancer and surrounding cells. This study aimed to investigate the effect of the Runx2 transcription factor on the expression of matricellular proteins such as HPA1, LOX, SPARC, and OPN, which have important roles in ECM modification and ECM-cell interaction in human breast cancer. Also, the changes in their associated oncogenic pathways including Akt, Erk, FAK activities, and c-jun protein expression were investigated.

METHODS AND RESULTS

Runx2 knockdown model was created using runx2 siRNA in MDA-MB-231 human metastatic breast cancer cells. The changes in the mRNA and protein expressions of ECM proteins were shown by the qPCR and Western blotting, respectively. The results showed that there was a decrease in both mRNA and protein expressions of HPA1, SPARC, and LOX, whereas there was no change in those of OPN. Phosphorylated Akt, Erk, FAK levels, and protein expression of c-jun, however, decreased in the cells.

CONCLUSION

Our results revealed that Runx2 affected matricellular protein expression, which is important for metastasis and invasion of breast cancer. Hence, we have concluded that runx2 appears to be efficient for regulating breast cancer metastasis through an expression of matricellular proteins.

Effect of Dickkopf-1 (Dkk-1) and SP600125, a JNK Inhibitor, on Wnt Signaling in Canine Prostate Cancer Growth and Bone Metastases

Human Dickkopf-1 (Dkk-1) upregulates a noncanonical Wnt/JNK pathway, resulting in osteoclast stimulation, cell proliferation, and epithelial-to-mesenchymal transition (EMT) of cancer cells. Ace-1-Dkk-1, a canine prostate cancer (PCa) cell line overexpressing Dkk-1, was used to investigate Wnt signaling pathways in PCa tumor growth. SP600125, a JNK inhibitor, was used to examine whether it would decrease tumor growth and bone tumor phenotype in canine PCa cells in vitro and in vivo. Ace-1-Vector^YFP-Luc and Ace-1-Dkk-1^YFP-Luc cells were transplanted subcutaneously, while Ace-1-Dkk-1^YFP-Luc was transplanted intratibially into nude mice. The effects of Dkk-1 and SP600125 on cell proliferation, in vivo tumor growth, and bone tumor phenotype were investigated. The mRNA expression levels of Wnt/JNK-related genes were measured using RT-qPCR. Dkk-1 significantly increased the mRNA expression of Wnt/JNK-signaling-related genes. SP600125 significantly upregulated the mRNA expression of osteoblast differentiation genes and downregulated osteoclastic-bone-lysis-related genes in vitro. SP600125 significantly decreased tumor volume and induced spindle-shaped tumor cells in vivo. Mice bearing intratibial tumors had increased radiographic density of the intramedullary new bone, large foci of osteolysis, and increased cortical lysis with abundant periosteal new bone formation. Finally, SP600125 has the potential to serve as an alternative adjuvant therapy in some early-stage PCa patients, especially those with high Dkk-1 expression.

Ubiquitin ligase COP1 coordinates transcriptional programs that control cell type specification in the developing mouse brain

The ubiquitin ligase CRL4^COP1/DET1 modifies specific transcription factor substrates with polyubiquitin so that they are degraded. However, the Ras–MEK–ERK signaling pathway can inactivate CRL4^COP1/DET1 and thereby promote the rapid accumulation of these transcription factors. Here we show that constitutive photomorphogenesis 1 (COP1) has a critical role in mouse brain development because its deletion from neural stem cells stabilizes the transcription factors c-JUN, ETV1, ETV4, and ETV5, leading to perturbation of normal gene expression patterns; anatomic anomalies in cerebral cortex, hippocampus, and cerebellum; and perinatal lethality.

The E3 ubiquitin ligase CRL4^COP1/DET1 is active in the absence of ERK signaling, modifying the transcription factors ETV1, ETV4, ETV5, and c-JUN with polyubiquitin that targets them for proteasomal degradation. Here we show that this posttranslational regulatory mechanism is active in neurons, with ETV5 and c-JUN accumulating within minutes of ERK activation. Mice with constitutive photomorphogenesis 1 (Cop1) deleted in neural stem cells showed abnormally elevated expression of ETV1, ETV4, ETV5, and c-JUN in the developing brain and spinal cord. Expression of c-JUN target genes Vimentin and Gfap was increased, whereas ETV5 and c-JUN both contributed to an expanded number of cells expressing genes associated with gliogenesis, including Olig1, Olig2, and Sox10. The mice had subtle morphological abnormalities in the cerebral cortex, hippocampus, and cerebellum by embryonic day 18 and died soon after birth. Elevated c-JUN, ETV5, and ETV1 contributed to the perinatal lethality, as several Cop1-deficient mice also lacking c-Jun and Etv5, or lacking Etv5 and heterozygous for Etv1, were viable.

Mechanistic regulation of epithelial-to-mesenchymal transition through RAS signaling pathway and therapeutic implications in human cancer

RAS effector signaling instead of being simple, unidirectional and linear cascade, is actually recognized as highly complex and dynamic signaling network. RAF-MEK-ERK cascade, being at the center of complex signaling network, links to multiple scaffold proteins through feed forward and feedback mechanisms and dynamically regulate tumor initiation and progression. Three isoforms of Ras harbor mutations in a cell and tissue specific manner. Besides mutations, their epigenetic silencing also attributes them to exhibit oncogenic activities. Recent evidences support the functions of RAS oncoproteins in the acquisition of tumor cells with Epithelial-to-mesenchymal transition (EMT) features/ epithelial plasticity, enhanced metastatic potential and poor patient survival. Google Scholar electronic databases and PubMed were searched for original papers and reviews available till date to collect information on stimulation of EMT core inducers in a Ras driven cancer and their regulation in metastatic spread. Improved understanding of the mechanistic basis of regulatory interactions of microRNAs (miRs) and EMT by reprogramming the expression of targets in Ras activated cancer, may help in designing effective anticancer therapies. Apparent lack of adverse events associated with the delivery of miRs and tissue response make 'drug target miRNA' an ideal therapeutic tool to achieve progression free clinical response.

Modulation of oncogenic transcription factors by bioactive natural products in breast cancer

Carcinogenesis, a multi-step phenomenon, characterized by alterations at genetic level and affecting the main intracellular pathways controlling cell growth and development. There are growing number of evidences linking oncogenes to the induction of malignancies, especially breast cancer. Modulations of oncogenes lead to gain-of-function signals in the cells and contribute to the tumorigenic phenotype. These signals yield a large number of proteins that cause cell growth and inhibit apoptosis. Transcription factors such as STAT, p53, NF-κB, c-JUN and FOXM1, are proteins that are conserved among species, accumulate in the nucleus, bind to DNA and regulate the specific genes targets. Oncogenic transcription factors resulting from the mutation or overexpression following aberrant gene expression relay the signals in the nucleus and disrupt the transcription pattern. Activation of oncogenic transcription factors is associated with control of cell cycle, apoptosis, migration and cell differentiation. Among different cancer types, breast cancer is one of top ten cancers worldwide. There are different subtypes of breast cancer cell-lines such as non-aggressive MCF-7 and aggressive and metastatic MDA-MB-231 cells, which are identified with distinct molecular profile and different levels of oncogenic transcription factor. For instance, MDA-MB-231 carries mutated and overexpressed p53 with its abnormal, uncontrolled downstream signalling pathway that account for resistance to several anticancer drugs compared to MCF-7 cells with wild-type p53. Appropriate enough, inhibition of oncogenic transcription factors has become a potential target in discovery and development of anti-tumour drugs against breast cancer. Plants produce diverse amount of organic metabolites. Universally, these metabolites with biological activities are known as "natural products". The chemical structure and function of natural products have been studied since 1850s. Investigating these properties leaded to recognition of their molecular effects as anticancer drugs. Numerous natural products extracted from plants, fruits, mushrooms and mycelia, show potential inhibitory effects against several oncogenic transcription factors in breast cancer. Natural compounds that target oncogenic transcription factors have increased the number of candidate therapeutic agents. This review summarizes the current findings of natural products in targeting specific oncogenic transcription factors in breast cancer.

Alternative Polyadenylation in Triple-Negative Breast Tumors Allows NRAS and c-JUN to Bypass PUMILIO Posttranscriptional Regulation

Alternative polyadenylation (APA) is a process that changes the posttranscriptional regulation and translation potential of mRNAs via addition or deletion of 3' untranslated region (3' UTR) sequences. To identify posttranscriptional-regulatory events affected by APA in breast tumors, tumor datasets were analyzed for recurrent APA events. Motif mapping of the changed 3' UTR regions found that APA-mediated removal of Pumilio regulatory elements (PRE) was unusually common. Breast tumor subtype-specific APA profiling identified triple-negative breast tumors as having the highest levels of APA. To determine the frequency of these events, an independent cohort of triple-negative breast tumors and normal breast tissue was analyzed for APA. APA-mediated shortening of NRAS and c-JUN was seen frequently, and this correlated with changes in the expression of downstream targets. mRNA stability and luciferase assays demonstrated APA-dependent alterations in RNA and protein levels of affected candidate genes. Examination of clinical parameters of these tumors found those with APA of NRAS and c-JUN to be smaller and less proliferative, but more invasive than non-APA tumors. RT-PCR profiling identified elevated levels of polyadenylation factor CSTF3 in tumors with APA. Overexpression of CSTF3 was common in triple-negative breast cancer cell lines, and elevated CSTF3 levels were sufficient to induce APA of NRAS and c-JUN. Our results support the hypothesis that PRE-containing mRNAs are disproportionately affected by APA, primarily due to high sequence similarity in the motifs utilized by polyadenylation machinery and the PUM complex. Cancer Res; 76(24); 7231-41. ©2016 AACR.

Regulation of the C/EBPα signaling pathway in acute myeloid leukemia (Review)

The transcription factor CCAAT/enhancer binding protein α (C/EBPα), as a critical regulator of myeloid development, directs granulocyte and monocyte differentiation. Various mechanisms have been identified to explain how C/EBPα functions in patients with acute myeloid leukemia (AML). C/EBPα expression is suppressed as a result of common leukemia-associated genetic and epigenetic alterations such as AML1-ETO, RARα-PLZF or gene promoter methylation. Recent data have shown that ubiquitination modification also contributes to its downregulation. In addition, 10-15% of patients with AML in an intermediate cytogenetic risk subgroup were characterized by mutations of the C/EBPα gene. As a transcription factor, C/EBPα can translocate into the nucleus and further regulate a variety of genes directly or indirectly, which are all key factors for cell differentiation. This review summarizes recent reports concerning the dysregulation of C/EBPα expression at various levels in human AML. The currently available data are persuasive evidence suggesting that impaired abnormal C/EBPα expression contributes to the development of AML, and restoration of C/EBPα expression as well as its function represents a promising target for novel therapeutic strategies in AML.

Discoidin domain receptor 1 contributes to tumorigenesis through modulation of TGFBI expression

Discoidin domain receptor 1 (DDR1) is a member of the receptor tyrosine kinase family. The receptor is activated upon binding to its ligand, collagen, and plays a crucial role in many fundamental processes such as cell differentiation, adhesion, migration and invasion. Although DDR1 is expressed in many normal tissues, upregulated expression of DDR1 in a variety of human cancers such as lung, colon and brain cancers is known to be associated with poor prognosis. Using shRNA silencing, we assessed the oncogenic potential of DDR1. DDR1 knockdown impaired tumor cell proliferation and migration in vitro and tumor growth in vivo. Microarray analysis of tumor cells demonstrated upregulation of TGFBI expression upon DDR1 knockdown, which was subsequently confirmed at the protein level. TGFBI is a TGFβ-induced extracellular matrix protein secreted by the tumor cells and is known to act either as a tumor promoter or tumor suppressor, depending on the tumor environment. Here, we show that exogenous addition of recombinant TGFBI to BXPC3 tumor cells inhibited clonogenic growth and migration, thus recapitulating the phenotypic effect observed from DDR1 silencing. BXPC3 tumor xenografts demonstrated reduced growth with DDR1 knockdown, and the same xenograft tumors exhibited an increase in TGFBI expression level. Together, these data suggest that DDR1 expression level influences tumor growth in part via modulation of TGFBI expression. The reciprocal expression of DDR1 and TGFBI may help to elucidate the contribution of DDR1 in tumorigenesis and TGFBI may also be used as a biomarker for the therapeutic development of DDR1 specific inhibitors.

p21-activated kinase 3 (PAK3) is an AP-1 regulated gene contributing to actin organisation and migration of transformed fibroblasts

Activating Protein 1 (AP-1) plays a vital role in cell proliferation, differentiation and apoptosis. While de-regulation of AP-1 has been linked to many cancers, little is known regarding its downstream transcriptional targets that associate with cellular transformation. Previous studies identified PAK3, a serine/threonine kinase, as a potential AP-1 target gene. PAK3 has been implicated in a variety of pathological disorders and over-expression of other PAK-family members has been linked to cancer. In this study, we investigate AP-1 regulation of PAK3 expression and the role of PAK3 in cJun/AP-1-associated cellular transformation. Our results showed elevated PAK3 expression at both the mRNA and protein level in cJun-over-expressing Rat1a fibroblasts, as well as in transformed human fibroblasts. Elevated PAK3 expression in cJun/AP-1 over-expressing cells associated with a significant increase in PAK3 promoter activation. This increased promoter activity was lost when a single putative Jun binding site, which can bind AP-1 directly both in vitro and in vivo, was mutated. Further, inhibition of PAK3 using siRNA showed a regression in the cell morphology, migratory potential and actin organisation associated with AP-1 transformed cells. Our study is a first to describe a role for AP-1 in regulating PAK3 expression and suggest that PAK3 is an AP-1 target required for actin organization and migration observed in transformed cells.

Elevated PIN1 expression by C/EBPalpha-p30 blocks C/EBPalpha-induced granulocytic differentiation through c-Jun in AML

The transcription factor CCAAT enhancer-binding protein alpha (C/EBPalpha) has an important role in granulopoiesis. The tumor suppressor function of C/EBPalpha is shown by the findings that loss of expression or function of C/EBPalpha in leukemic blasts contributes to a block in myeloid cell differentiation and to leukemia. C/EBPalpha mutations are found in around 9% of acute myeloid leukemia (AML) patients. The mechanism by which the mutant form of C/EBPalpha (C/EBPalpha-p30) exerts a differentiation block is not well understood. By using a proteomic screen, we have recently reported PIN1 as a target of C/EBPalpha-p30 in AML. In the present study, we show that C/EBPalpha-p30 induces PIN1 expression. We observed elevated PIN1 expression in leukemic patient samples. Induction of C/EBPalpha-p30 results in recruitment of E2F1 in the PIN1 promoter. We show that the inhibition of PIN1 leads to myeloid differentiation in primary AML blasts with C/EBPalpha mutations. Overexpression of PIN1 in myeloid cells leads to block of granulocyte differentiation. We also show that PIN1 increases the stability of the c-Jun protein by inhibiting c-Jun ubiquitination, and c-Jun blocks granulocyte differentiation mediated by C/EBPalpha. Our data suggest that the inhibition of PIN1 could be a potential strategy of treating AML patients with C/EBPalpha mutation.

Oleic acid induces ERK1/2 activation and AP-1 DNA binding activity through a mechanism involving Src kinase and EGFR transactivation in breast cancer cells

GPR40 and GPR120 are G-protein-coupled receptors that can be activated by medium- and long-chain fatty acids. GPR40 is expressed in several breast cancer cell lines and its stimulation with oleic acid (OA) induces cell proliferation. However, the signal transduction pathways activated by OA have not been studied in detail. Our results demonstrate that both GPR40 and GPR120 are expressed in MCF-7 cells. Stimulation of MCF-7 and MDA-MB-231 cells with OA promoted the phosphorylation of ERK1/2 at Thr-202 and Tyr-204 and the formation of AP-1-DNA complex in a fashion dependent of Src kinase activity and EGFR transactivation. Furthermore, proliferation induced by OA is restricted to breast cancer cells in a fashion dependent of ERK1/2 activation and matrix metalloproteinases. In summary, our data indicate that proliferation induced by OA is restricted to breast cancer cells, and that ERK1/2 activation and AP-1-DNA complex formation are mediated by Src family kinases and transactivation of EGFR.

TATA box-binding protein-associated factor 12 is important for RAS-induced transformation properties of colorectal cancer cells

Activating mutations in the RAS proto-oncogene result in constant stimulation of its downstream pathways, further leading to tumorigenesis. Transcription factor IID (TFIID) can be regulated by cellular signals to specifically alter transcription of particular subsets of genes. To investigate potential links between the regulation of TFIID function and the RAS-induced carcinogenesis, we monitored the expression of the TATA box-binding protein and its associated factors (TAF) in human colon carcinoma cells. We primarily identified TAF12 levels as being up-regulated in cell lines bearing natural RAS mutations or stably overexpressing a mutated RAS isoform via a mitogen-activated protein kinase/extracellular signal-regulated kinase kinase-dependent pathway. We further showed by electrophoretic mobility shift assays and chromatin immunoprecipitation that the ETS1 protein was interacting with an ETS-binding site on the TAF12 promoter and was regulating TAF12 expression. The binding was enhanced in extracts from oncogenic RAS-transformed cells, pointing to a role in the RAS-mediated regulation of TAF12 expression. Reduction of TAF12 levels by small interfering RNA treatment induced a destabilization of the TFIID complex, enhanced E-cadherin mRNA and protein levels, and reduced migration and adhesion properties of RAS-transformed cells with epithelial to mesenchymal transition. Overall, our study indicates the importance of TAF12 in the process of RAS-induced transformation properties of human colon cells and epithelial to mesenchymal transition, most notably those related to increased motility, by regulating specifically expression of genes such as E-cadherin.

New paradigms for the function of JNKK1/MKK4 in controlling growth of disseminated cancer cells

Much work has been done in the 20 years since the discovery of the first metastasis suppressor gene to investigate the diverse biochemical functions of the proteins these genes encode. The function of metastasis suppressors cannot be solely predicted from correlative clinical data or in vitro studies. Instead, careful design of in vivo experiments to test broader hypotheses is necessary to pinpoint the mechanism of action of these novel proteins. Our laboratory identified c-Jun NH2-terminal kinase activating kinase 1 (JNKK1)/Mitogen-activated protein kinase (MAPK) kinase 4 (JNKK1/MKK4) as a metastasis suppressor in prostate and ovarian cancer. JNKK1/MKK4 is a stress activated protein kinase (SAPK) involved in a variety of signaling events, ranging from the regulation of hepatoblast survival during mammalian development to metastasis suppression in adult ovarian and prostate cancers. JNKK1/MKK4 function has typically been associated with the c-Jun NH2-terminal kinase (JNK) signaling pathway, particularly in the immune system where JNK plays a role in inflammatory signaling and apoptosis. However, evidence continues to accumulate that JNKK1/MKK4 is also a physiologic activator of p38 under certain conditions, and that activation of p38 arrests cell cycle progression. This review will provide a historical perspective on the role of JNKK1/MKK4 in SAPK signaling, including some recent findings from our own laboratory that shed light on the complicated role for JNKK1/MKK4 in metastatic colonization.

Using metastasis suppressor proteins to dissect interactions among cancer cells and their microenvironment

Cancer metastasis is a complex, dynamic process that begins with dissemination of cells from the primary tumor and culminates in the formation of clinically detectable, overt metastases at one or more discontinuous secondary sites. Evidence from in vivo video microscopy as well as PCR and immunohistochemical studies suggest that cancer cell dissemination is an early event in tumor progression and that cells may persist in a potentially dormant state for a prolonged period. Similarly, the mechanisms by which these disseminated cells initiate growth and complete the process of metastatic colonization remain largely unknown. Understanding signal transduction pathways regulating this final step of metastasis is therefore critical for successful clinical management. While genetic mutations or epigenetic changes may be required for a cell or group of cells to separate and survive distant from the primary tumor, the microenvironment within secondary tissues plays a substantial role in influencing whether disseminated cells survive and proliferate. Our work is focused on using metastasis suppressor proteins to gain insight into why the majority of disseminated cells, which should be fully malignant, do not proliferate immediately at secondary sites. The translational goal of this work is to identify targets for inhibiting metastatic growth and prolonging disease-free survival.

Fra-1 regulates vimentin during Ha-RAS-induced epithelial mesenchymal transition in human colon carcinoma cells

The process of epithelial mesenchymal transition, whereby cells acquire molecular alterations and fibroblastic features, is a fundamental process of embryogenesis and cancer invasion/metastasis. The mechanisms responsible for epithelial mesenchymal transition remain elusive. Human tumors frequently establish constitutively activated RAS signaling, which contributes to the malignant phenotype. In an effort to dissect distinct RAS isoform specific functions, we previously established human colon cell lines stably overexpressing activated Harvey-RAS (Ha-RAS) and Kirsten-RAS (Ki-RAS). Using these, we observed that only oncogenic Ha-RAS overexpression resulted in morphologic and molecular changes suggestive of epithelial to mesenchymal transition. We showed that vimentin, a key molecule of epithelial mesenchymal transition, was differentially regulated between Ha-RAS and Ki-RAS leading to a Ha-RAS specific induction of a migratory phenotype and eventually epithelial to mesenchymal transition. We demonstrated that the AP-1 sites in vimentin promoter could be involved in this regulation. A potential role of FRA-1 was suggested in the regulation of vimentin during the Ha-RAS-induced epithelial to mesenchymal transition, in association with colon cell migration. Our results therefore propose that in colon cells, the induction of epithelial mesenchymal transition by oncogenic Ha-RAS could occur through the overexpression of proteins like FRA-1 and vimentin.

Protein kinase Cepsilon mediates polymeric fibronectin assembly on the surface of blood-borne rat breast cancer cells to promote pulmonary metastasis

Malignant breast cancer cells that have entered the blood circulation from primary mammary fat pad tumors or are grown in end-over-end suspension culture assemble a characteristic, multi-globular polymeric fibronectin (polyFn) coat on their surfaces. Surface polyFn is critical for pulmonary metastasis, presumably by facilitating lung vascular arrest via endothelial dipeptidylpeptidase IV (CD26). Here, we show that cell-surface polyFn assembly is initiated by the state of suspension, is dependent upon the synthesis and secretion of cellular Fn, and is augmented in a dose- and time-dependent manner by plasma Fn. PolyFn assembly is regulated by protein kinase Cepsilon (PKCepsilon), which translocates rapidly and in increasing amounts from the cytosol to the plasma membrane and is phosphorylated. PolyFn assembly is impeded by select inhibitors of this kinase, i.e. bisindolylmaleimide I, Ro-32-0432, Gö6983, and Rottlerin, by the phorbol 12-myristate 13-acetate-mediated and time-dependent loss of PKCepsilon protein and decreased plasma membrane translocation, and more specifically, by stable transfection of lung-metastatic MTF7L breast cancer cells with small interfering RNA-PKCepsilon and dominant-negative PKCepsilon constructs (e.g. RD-PKCepsilon). The inability to assemble a cell surface-associated polyFn coat by knockdown of endogenous Fn or PKCepsilon impedes cancer cells from metastasis to the lungs. The present studies identify a novel regulatory mechanism for polyFn assembly on blood-borne breast cancer cells and depict its effect on pulmonary metastasis.

Critical role of c-Jun overexpression in liver metastasis of human breast cancer xenograft model

Background

c-Jun/AP-1 has been linked to invasive properties of aggressive breast cancer. Recently, it has been reported that overexpression of c-Jun in breast cancer cell line MCF-7 resulted in increased AP-1 activity, motility and invasiveness of the cells in vitro and tumor formation in nude mice. However, the role of c-Jun in metastasis of human breast cancer in vivo is currently unknown.

Methods

To further investigate the direct involvement of c-Jun in tumorigenesis and metastasis, in the present study, the effects of c-Jun overexpression were studied in both in vitro and in nude mice.

Results

Ectopic overexpression of c-Jun promoted the growth of MCF-7 cells and resulted in a significant increase in the percentage of cells in S phase and increased motility and invasiveness. Introduction of c-Jun gene alone into weakly invasive MCF-7 cells resulted in the transfected cells capable of metastasizing to the nude mouse liver following tail vein injection.

Conclusion

The present study confirms that overexpression of c-Jun contributes to a more invasive phenotype in MCF-7 cells. It indicates an interesting relationship between c-Jun expression and increased property of adhesion, migration and in vivo liver metastasis of MCF-7/c-Jun cells. The results provide further evidence that c-Jun is involved in the metastasis of breast cancer. The finding also opens an opportunity for development of anti-c-Jun strategies in breast cancer therapy.

bZIPDB: a database of regulatory information for human bZIP transcription factors

Background

Basic region-leucine zipper (bZIP) proteins are a class of transcription factors (TFs) that play diverse roles in eukaryotes. Malfunctions in these proteins lead to cancer and various other diseases. For detailed characterization of these TFs, further public resources are required.

Description

We constructed a database, designated bZIPDB, containing information on 49 human bZIP TFs, by means of automated literature collection and manual curation. bZIPDB aims to provide public data required for deciphering the gene regulatory network of the human bZIP family, e.g., evaluation or reference information for the identification of regulatory modules. The resources provided by bZIPDB include (1) protein interaction data including direct binding, phosphorylation and functional associations between bZIP TFs and other cellular proteins, along with other types of interactions, (2) bZIP TF-target gene relationships, (3) the cellular network of bZIP TFs in particular cell lines, and (4) gene information and ontology. In the current version of the database, 721 protein interactions and 560 TF-target gene relationships are recorded. bZIPDB is annually updated for the newly discovered information.

Conclusion

bZIPDB is a repository of detailed regulatory information for human bZIP TFs that is collected and processed from the literature, designed to facilitate analysis of this protein family. bZIPDB is available for public use at .

A splice variant of CD99 increases motility and MMP-9 expression of human breast cancer cells through the AKT-, ERK-, and JNK-dependent AP-1 activation signaling pathways

The CD99 gene encodes two distinct transmembrane proteins by alternative splicing of its transcript. To examine the effects of two CD99 isoforms on the invasive phenotypes of breast cancer cells, MDA-MB-231 and MCF-7 human breast cancer cell lines were stably transfected with CD99 cDNAs encoding the major wild-type form (type I) or a minor splice variant (type II). As a result, expression of CD99 type II, but not type I, markedly elevated the motility, binding to fibronectin, MMP-9 expression, and invasiveness of MDA-MB-231 and MCF-7 breast cancer cells. In MDA-MB-435 breast cancer cells expressing both CD99 type I and type II, invasion-related cellular activities were inhibited by the transfection of small interfering RNA (siRNA) targeted to CD99 type II. Meanwhile, CD99 type II-induced MMP-9 expression in MDA-MB-231 cells was shown to be mediated by the binding of AP-1 factors to the MMP-9 gene promoter. Gel shift assay revealed that ligation of CD99 type II with antibody resulted in the binding of JunD to the AP-1 site of the MMP-9 promoter region. Initiation of CD99 type II signaling by antibody ligation increased expression of JunD and FosB AP-1 factors, along with phosphorylation of Src, Akt, p38 MAPK, ERK, and JNK. Knockdown of JunD and FosB by siRNA transfection abolished the positive effects of CD99 type II on the motility and MMP-9 expression of MDA-MB-231 cells. Increased expression of JunD and FosB as well as elevated cell motility and MMP-9 expression by CD99 type II ligation were also abrogated by inhibitors, dominant-negative forms, and siRNAs for Akt1, ERK1/2, and JNK1 but not for p38 MAPK. These results suggest that expression of a splice variant of CD99 contributes to the invasive ability of human breast cancer cells by up-regulating AP-1-mediated gene expression through the Akt-dependent ERK and JNK signaling pathways.

Transcription factors control invasion: AP-1 the first among equals

Metastasis, the aggressive spread of a malignant tumor to distant organs, is a major cause of death in cancer patients. Despite this critical role in cancer outcomes, the molecular mechanisms that control this process are just beginning to be understood. Metastasis is largely dependent upon the ability of tumor cells to invade the barrier formed by the basement membrane and to migrate through neighboring tissues. This review will summarize the evidence that tumor cell invasion is the result of oncogene-mediated signal transduction pathways that control the expression of a specific set of genes that together mediate tumor cell invasion. We focus on the role of the transcription factor AP-1 to both induce the expression of genes that function as invasion effectors and repress other genes that function as invasion suppressors. This identifies AP-1 as a critical regulator of a complex program of gene expression that defines the invasive phenotype.

Homophilic interactions of Tetraspanin CD151 up-regulate motility and matrix metalloproteinase-9 expression of human melanoma cells through adhesion-dependent c-Jun activation signaling pathways

The tetraspanin membrane protein CD151 has been suggested to regulate cancer invasion and metastasis by initiating signaling events. The CD151-mediated signaling pathways involved in this regulation remain to be revealed. In this study, we found that stable transfection of CD151 into MelJuSo human melanoma cells lacking CD151 expression significantly increased cell motility, matrix metalloproteinase-9 (MMP-9) expression, and invasiveness. The enhancement of cell motility and MMP-9 expression by CD151 overexpression was abrogated by inhibitors and small interfering RNAs targeted to focal adhesion kinase (FAK), Src, p38 MAPK, and JNK, suggesting an essential role of these signaling components in CD151 signaling pathways. Also, CD151-induced MMP-9 expression was shown to be mediated by c-Jun binding to AP-1 sites in the MMP-9 gene promoter, indicating AP-1 activation by CD151 signaling pathways. Meanwhile, CD151 was found to be associated with alpha(3)beta(1) and alpha(6)beta(1) integrins in MelJuSo cells, and activation of associated integrins was a prerequisite for CD151-stimulated MMP-9 expression and activation of FAK, Src, p38 MAPK, JNK, and c-Jun. Furthermore, CD151 on one cell was shown to bind to neighboring cells expressing CD151, suggesting that CD151 is a homophilic interacting protein. The homophilic interactions of CD151 increased motility and MMP-9 expression of CD151-transfected MelJuSo cells, along with FAK-, Src-, p38 MAPK-, and JNK-mediated activation of c-Jun in an adhesion-dependent manner. Furthermore, C8161 melanoma cells with endogenous CD151 were also shown to respond to homophilic CD151 interactions for the induction of adhesion-dependent activation of FAK, Src, and c-Jun. These results suggest that homophilic interactions of CD151 stimulate integrin-dependent signaling to c-Jun through FAK-Src-MAPKs pathways in human melanoma cells, leading to enhanced cell motility and MMP-9 expression.

Identification of promoters bound by c-Jun/ATF2 during rapid large-scale gene activation following genotoxic stress

The NH2-terminal Jun kinases (JNKs) function in diverse roles through phosphorylation and activation of AP-1 components including ATF2 and c-Jun. However, the genes that mediate these processes are poorly understood. A model phenotype characterized by rapid activation of Jun kinase and enhanced DNA repair following cisplatin treatment was examined using chromatin immunoprecipitation with antibodies against ATF2 and c-Jun or their phosphorylated forms and hybridization to promoter arrays. Following genotoxic stress, we identified 269 genes whose promoters are bound upon phosphorylation of ATF2 and c-Jun. Binding did not occur following treatment with transplatin or the JNK inhibitor SP600125 or JNK-specific siRNA. Of 89 known DNA repair genes represented on the array, 23 are specifically activated by cisplatin treatment within 3-6 hr. Thus, the genotoxic stress response occurs at least partly via activation of ATF2 and c-Jun, leading to large-scale coordinate gene expression dominated by genes of DNA repair.

The role of the AP-1 transcription factors c-Fos, FosB, Fra-1 and Fra-2 in the invasion process of mammary carcinomas

Members of the Fos family of AP-1 transcription factors (c-Fos, FosB, FosB2, Fra-1 and Fra-2) are able to form dimers with Jun proteins which bind to the regulatory sequences of target genes. As many proteases involved in tumor invasion are AP-1-regulated, we assumed that Fos family members might be important for invasion of mammary carcinomas. Therefore, we performed transient transfections with expression vectors for c-Fos, FosB, FosB2, Fra-1 and Fra-2, followed by matrigel invasion assays. Fra-1 transfection resulted in a 2-4-fold increase of invasive cells in both cell lines. In a less degree, the invasive potential of MDA-MB231 cells was stimulated by Fra-2, whereas MCF7 invasion was enhanced by c-Fos and FosB. By double-labelling immunocytochemistry, PAI-1 up-regulation was observed in cells transfected with c-Fos, Fra-1 and Fra-2 expression vectors, whereas MMP1 and MMP9 expression was not affected. Results of cotransfection with a MMP9 promoter construct and AP-1 expression vectors do not indicate a direct up-regulation of MMP9 expression by Fos proteins except a positive effect of c-Fos in MCF7 cells. In parallel, expression of Fos family members as determined by Western Blot analysis in 75 mammary carcinomas was correlated with MMP1, MMP9, PAI-1 and uPAR protein levels in the tumors. Interestingly, high FosB levels were significantly associated with MMP1 overexpression, whereas expression of c-Fos and phosphorylated Fra-1 correlated with MMP9 protein levels. Strong Fra-2 expression correlated with high levels of MMP9, PAI-1, the uPA/PAI-1 complex and early recurrence. These data indicate that Fos proteins, especially Fra-1, c-Fos and Fra-2, might be involved in invasion of breast cancer cells.

Multiple kinase cascades mediate prolactin signals to activating protein-1 in breast cancer cells

The importance of prolactin (PRL) in physiological proliferation and differentiation of the mammary gland, together with high levels of PRL receptors in breast tumors, the association of circulating PRL with incidence of breast cancer, and the recognition of locally produced PRL, point to the need for greater understanding of PRL actions in mammary disease. Although PRL has been shown to activate multiple kinase cascades in various target cells, relatively little is known of its signaling pathways in the mammary gland apart from the Janus kinase 2/ signal transducer and activator of transcription 5 pathway, particularly in tumor cells. Another potential effector is activating protein-1 (AP-1), a transcription complex that regulates processes essential for neoplastic progression, including proliferation, survival and invasion. We demonstrate that PRL activates AP-1 in MCF-7 cells, detectable at 4 h and sustained for at least 24 h. Although Janus kinase 2 and ERK1/2 are the primary mediators of PRL-induced signals, c-Src, phosphatidylinositol 3'-kinase, protein kinase C, and other MAPKs contribute to maximal activity. PRL activation of these pathways leads to increased c-Jun protein and phosphorylation, JunB protein, and phosphorylation of c-Fos, elevating the levels of AP-1 complexes able to bind DNA. These active AP-1 dimers may direct expression of multiple target genes, mediating some of PRL's actions in mammary disease.

Stat3 enhances vimentin gene expression by binding to the antisilencer element and interacting with the repressor protein, ZBP-89

Vimentin exhibits a complex pattern of developmental- and tissue-specific expression and is aberrantly expressed in most metastatic tumors. The human vimentin promoter contains multiple DNA elements, some of which enhance gene expression and one that inhibits. A silencer element (at -319) binds the repressor ZBP-89. Further upstream (at -757) is an element, which acts positively in the presence of the silencer element and, thus, is referred to as an antisilencer (ASE). Previously, we showed that Stat1alpha binds to this element upon induction by IFN-gamma. However, substantial binding and reporter gene activity was still present in nontreated cells. Here, we have found that Stat3 binds to the ASE element in vitro. Transfection experiments in COS-1 cells with various vimentin promoter--reporter constructs show that gene activity is dependent upon the cotransfection and activation of Stat3. Moreover, activated Stat3 can overcome ZBP-89 repression. Coimmunoprecipitation studies demonstrate that Stat3 and ZBP-89 can interact and confocal microscopy detects these factors to be colocalized in the nucleus. Moreover, a correlation exists between the presence of activated Stat3 and vimentin expression in MDA-MB-231 cells, which is lacking in MCF7 cells where vimentin is not expressed. In the light of these results, we propose that the interaction of Stat3 and ZBP-89 may be crucial for overcoming the effects of the repressor ZBP-89, which suggests a novel mode for Stat3 gene activation.

c-Jun and the dominant-negative mutant, TAM67, induce vimentin gene expression by interacting with the activator Sp1

Vimentin exhibits a complex pattern of developmental- and tissue-specific expression. Since it is aberrantly expressed in metastatic tumors, which have progressed through the epithelial-mesenchymal transition, it has been cited as a marker for tumor progression. Previous studies have indicated that the transcription factor activator protein (AP1) is important in tumor progression. The stable transformation of the MCF7 cell line with the oncogene c-Jun resulted in a cell line (MCF7Jun), which displayed a change in morphology, enhanced migratory and invasive properties, and metastatic behavior. Of the 21 genes whose expression levels were altered in the MCF7Jun cell line, the greatest change in expression occurred for the vimentin gene. Previously, tandem AP1 sites in the promoter were reported to be important for the serum and TPA inducibility of the vimentin gene. However, we find that the AP1 elements only contribute in part to c-Jun activation. Moreover, this activation can be duplicated in COS-1 or S2 cells by expression of c-Jun or TAM67, and is dependent only on the leucine-zipper region of c-Jun. Transient transfection analyses, electrophoretic mobility shift assays, DNA precipitation assays, and coimmunoprecipitation studies suggest that c-Jun is able to synergize with the activator protein Sp1 in binding to GC-box1 to enhance vimentin gene expression.

v-Jun downregulates the SPARC target gene by binding to the proximal promoter indirectly through Sp1/3

Transformation of chick embryo fibroblasts by the v-Jun oncoprotein correlates with a downregulation of the extracellular matrix protein SPARC and repression of the corresponding mRNA. Repression of SPARC contributes to the oncogenic process by facilitating tumor development in vivo. A proximal promoter fragment, designated -124/+16, is responsible for high constitutive activity of the SPARC gene and is the target of repression by v-Jun. In this paper, using electrophoretic mobility shift and pull-down assays in vitro, and transient transfections and chromatin immunoprecipitation assays in Sp1/3-deficient Drosophila SL2 cells and in chick embryo fibroblasts, we show that (i) Sp1 and/or Sp3 is required for constitutive activation of SPARC transcription, by binding directly to the GGA-rich -92/-57 fragment; and (ii) v-Jun does not bind -124/+16 directly, but binds to the GGA-rich fragment indirectly, most likely through a physical interaction with Sp1/3. Moreover, a transactivation-proficient v-Jun derivative, designated v-Jun/cebp/glz, which cannot bind Jun DNA motifs anymore and cannot heterodimerize, is still capable of downregulating SPARC efficiently. Taken together, these data strongly suggest that v-Jun downregulates SPARC through the formation of a DNA-Sp1/3-v-Jun, chromatin-associated complex.

FosB is highly expressed in normal mammary epithelia, but down-regulated in poorly differentiated breast carcinomas

FosB is a member of the AP-1 family of transcription factors which represent important regulators of cell proliferation and differentiation. Based on prior results which indicated a role of FosB in breast cancer, we studied FosB protein and mRNA expression by immunohistochemistry and, partly, in situ hybridization in 68 mammary carcinomas and normal breast tissues. We found strong nuclear FosB immunoreactivity in epithelial cells of normal lobules and ducts, whereas carcinomas frequently showed loss of FosB expression (n = 8) or weak immunostaining (n = 24). Reduced FosB protein expression in tumors correlated with high grading (p = 0.005), negative estrogen and progesterone receptor status (p < 0.001), and strong HER2/neu expression (p = 0.025). Comparison with expression of seven cell-cycle regulators revealed an association of low/absent FosB staining with p16MTS1 overexpression (p = 0.005). RT-PCR showed expression of full-length FosB and the smaller splice variant FosB2 in most carcinomas and cell lines with and without FosB protein expression, indicating that both proteins are differentially regulated mainly at a post-transcriptional level. By sequence analysis of the coding region in four cell lines and 17 carcinomas we detected a mutation in HBL-100 cells. Our results indicate that high FosB expression might be necessary for normal proliferation and differentiation of mammary epithelial cells, and reduced FosB protein levels might be involved in dedifferentiation during breast tumorigenesis.

Transcriptional upregulation of SPARC, in response to c-Jun overexpression, contributes to increased motility and invasion of MCF7 breast cancer cells

Overexpression of the c-Jun proto-oncogene in MCF7 breast cancer cells results in a variety of phenotype changes related to malignant progression including increased motility and invasion. Concurrent with these phenotypic effects are changes in the expression of multiple gene targets. We previously demonstrated that expression of the SPARC/osteonectin gene, while undetectable in the MCF7 cell line, is highly induced in response to stable c-Jun overexpression (c-Jun/MCF7). Because the SPARC gene product is associated with tumor cell invasion in a variety of different cancers, we have examined its role in mediating the phenotypic changes induced by c-Jun in MCF7 cells. We found that antisense mediated suppression of SPARC dramatically inhibits both motility and invasion in this c-Jun/MCF7 model. In contrast, stable overexpression of SPARC in the parental MCF7 cell line is not sufficient to stimulate cell motility or invasion. Examination of the promoter region of the human SPARC gene reveals three non-canonical AP-1 sites. We demonstrate that one of these sites binds c-Jun/Fra1 heterodimers in vitro, but that this and the other AP-1 like sites are dispensable with respect to c-Jun stimulated SPARC promoter activation. Deletion analysis identified a region between -120 and -70 as a c-Jun responsive element sufficient to induce maximal promoter activation. This region does not contain any AP-1 sites but does mediate binding by SP1 'like' complexes. Furthermore, this region is necessary for SP1/SP3 responsiveness in Drosophila SL2 cells. These results demonstrate that SPARC plays an important role in stimulating motility and the invasive behavior of c-Jun/MCF7 cells and that SPARC promoter activation by c-Jun appears to occur through an indirect mechanism.

JAC, a direct target of oncogenic transcription factor Jun, is involved in cell transformation and tumorigenesis

Using subtractive hybridization techniques, we have isolated a gene termed JAC that is strongly and specifically activated in avian fibroblasts transformed by the v-jun oncogene of avian sarcoma virus 17 (ASV17), but not in cells transformed by other oncogenic agents. Furthermore, JAC is highly expressed in cell lines derived from jun-induced avian fibrosarcomas. Kinetic analysis using a doxycycline-controlled conditional cell transformation system showed that expression of the 0.8-kb JAC mRNA is induced rapidly upon activation of the oncogenic v-jun allele. Nucleotide sequence analysis and transcriptional mapping revealed that the JAC gene contains two exons, with the longest ORF confined to exon 2. The deduced 68-amino acid chicken JAC protein is rich in cysteine residues and displays 37% sequence identity to mammalian high-sulfur keratin-associated proteins. The promoter region of JAC contains a consensus (5'-TGACTCA-3') and a nonconsensus (5'-TGAGTAA-3') AP-1 binding site in tandem, which are both specifically bound by the Gag-Jun hybrid protein encoded by ASV17. Mutational analysis revealed that the two AP-1 sites confer strong transcriptional activation by Gag-Jun in a synergistic manner. Ectopic expression of JAC in avian fibroblasts leads to anchorage-independent growth, strongly suggesting that deregulation of JAC is an essential event in jun-induced cell transformation and tumorigenesis.

TOJ3, a target of the v-Jun transcription factor, encodes a protein with transforming activity related to human microspherule protein 1 (MCRS1)

Using the established quail cell line Q/d3 conditionally transformed by the v-jun oncogene, cDNA clones (TOJ2, TOJ3, TOJ5, TOJ6) were isolated by representational difference analysis (RDA) that correspond to genes which were induced immediately upon conditional activation of v-jun. One of these genes, TOJ3, is immediately and specifically activated after doxycycline-mediated v-jun induction, with kinetics similar to the induction of well characterized direct AP-1 target genes. TOJ3 is neither activated upon conditional activation of v-myc, nor in cells or cell lines non-conditionally transformed by oncogenes other than v-jun. Sequence analysis revealed that the TOJ3-specific cDNA encodes a 530-amino acid protein with significant sequence similarities to the murine or human microspherule protein 1 (MCRS1, MSP58), a nucleolar protein that directly interacts with the ICP22 regulatory protein from herpes simplex virus 1 or with p120, a proliferation-related protein expressed at high levels in most human malignant tumor cells. Similar to its mammalian counterparts, the TOJ3 protein contains a bipartite nuclear localization motif and a forkhead associated domain (FHA). Using polyclonal antibodies directed against a recombinant amino-terminal TOJ3 protein segment, the activation of TOJ3 in jun-transformed fibroblasts was also demonstrated at the protein level by specific detection of a polypeptide with an apparent M(r) of 65 000. Retroviral expression of the TOJ3 gene in quail or chicken embryo fibroblasts induces anchorage-independent growth, indicating that the immediate activation of TOJ3 in fibroblasts transformed by the v-jun oncogene contributes to cell transformation.

Jun, the oncoprotein

Cellular Jun (c-Jun) and viral Jun (v-Jun) can induce oncogenic transformation. For this activity, c-Jun requires an upstream signal, delivered by the Jun N-terminal kinase (JNK). v-Jun does not interact with JNK; it is autonomous and constitutively active. v-Jun and c-Jun address overlapping but not identical sets of genes. Whether all genes essential for transformation reside within the overlap of the v-Jun and c-Jun target spectra remains to be determined. The search for transformation-relevant targets of Jun is moving into a new stage with the application of DNA microarrays technology. Genetic screens and functional tests remain a necessity for the identification of genes that control the oncogenic phenotype.