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

Single-Cell Evolutionary Analysis Reveals Drivers of Plasticity and Mediators of Chemoresistance in Small Cell Lung Cancer

Small cell lung cancer (SCLC) is often a heterogeneous tumor, where dynamic regulation of key transcription factors can drive multiple populations of phenotypically different cells which contribute differentially to tumor dynamics. This tumor is characterized by a very low 2-year survival rate, high rates of metastasis, and rapid acquisition of chemoresistance. The heterogeneous nature of this tumor makes it difficult to study and to treat, as it is not clear how or when this heterogeneity arises. Here we describe temporal, single-cell analysis of SCLC to investigate tumor initiation and chemoresistance in both SCLC xenografts and an autochthonous SCLC model. We identify an early population of tumor cells with high expression of AP-1 network genes that are critical for tumor growth. Furthermore, we have identified and validated the cancer testis antigens (CTA) PAGE5 and GAGE2A as mediators of chemoresistance in human SCLC. CTAs have been successfully targeted in other tumor types and may be a promising avenue for targeted therapy in SCLC.

IMPLICATIONS

Understanding the evolutionary dynamics of SCLC can shed light on key mechanisms such as cellular plasticity, heterogeneity, and chemoresistance.

Targeting c-Jun Is a Potential Therapy for Luminal Breast Cancer Bone Metastasis

Luminal breast cancer has the highest bone metastasis frequency among all breast cancer subtypes; however, its metastatic mechanism has not been elucidated because of a lack of appropriate models. We have previously developed useful bone metastatic cell lines of luminal breast cancer using MCF7 cells. In this study, we characterized bone metastatic MCF7-BM cell lines and identified c-Jun as a novel bone metastasis marker of luminal breast cancer. The protein level of c-Jun was upregulated in MCF7-BM cells compared with that in parental cells, and its deficiency resulted in the suppression of tumor cell migration, transformation, and reduced osteolytic ability. In vivo, dominant-negative c-Jun exhibited smaller bone metastatic lesions and a lower metastatic frequency. Histologic analysis revealed that c-Jun expression was heterogeneous in bone metastatic lesions, whereas c-Jun overexpression mediated a vicious cycle between MCF7-BM cells and osteoclasts by enhancing calcium-induced migration and releasing the osteoclast activator BMP5. Pharmacological inhibition of c-Jun by the Jun amino-terminal kinase (JNK) inhibitor JNK-IN-8 effectively suppressed tumorigenesis and bone metastasis in MCF7-BM cells. Furthermore, c-Jun downstream signals were specifically correlated with the clinical prognosis of patients with the luminal subtype of breast cancer. Our results illustrate the potential benefits of a therapy that targets c-Jun to prevent bone metastasis in luminal breast cancer.

IMPLICATIONS

c-Jun expression mediates bone metastasis in luminal breast cancer by forming a vicious cycle in the bone microenvironment, which reveals potential strategies for subtype-specific bone metastasis therapy.

Regulatory networks driving expression of genes critical for glioblastoma are controlled by the transcription factor c-Jun and the pre-existing epigenetic modifications

BACKGROUND

Glioblastoma (GBM, WHO grade IV) is an aggressive, primary brain tumor. Despite extensive tumor resection followed by radio- and chemotherapy, life expectancy of GBM patients did not improve over decades. Several studies reported transcription deregulation in GBMs, but regulatory mechanisms driving overexpression of GBM-specific genes remain largely unknown. Transcription in open chromatin regions is directed by transcription factors (TFs) that bind to specific motifs, recruit co-activators/repressors and the transcriptional machinery. Identification of GBM-related TFs-gene regulatory networks may reveal new and targetable mechanisms of gliomagenesis.

RESULTS

We predicted TFs-regulated networks in GBMs in silico and intersected them with putative TF binding sites identified in the accessible chromatin in human glioma cells and GBM patient samples. The Cancer Genome Atlas and Glioma Atlas datasets (DNA methylation, H3K27 acetylation, transcriptomic profiles) were explored to elucidate TFs-gene regulatory networks and effects of the epigenetic background. In contrast to the majority of tumors, c-Jun expression was higher in GBMs than in normal brain and c-Jun binding sites were found in multiple genes overexpressed in GBMs, including VIM, FOSL2 or UPP1. Binding of c-Jun to the VIM gene promoter was stronger in GBM-derived cells than in cells derived from benign glioma as evidenced by gel shift and supershift assays. Regulatory regions of the majority of c-Jun targets have distinct DNA methylation patterns in GBMs as compared to benign gliomas, suggesting the contribution of DNA methylation to the c-Jun-dependent gene expression.

CONCLUSIONS

GBM-specific TFs-gene networks identified in GBMs differ from regulatory pathways attributed to benign brain tumors and imply a decisive role of c-Jun in controlling genes that drive glioma growth and invasion as well as a modulatory role of DNA methylation.

Snail Upregulates Transcription of FN, LEF, COX2, and COL1A1 in Hepatocellular Carcinoma: A General Model Established for Snail to Transactivate Mesenchymal Genes

SNA is one of the essential EMT transcriptional factors capable of suppressing epithelial maker while upregulating mesenchymal markers. However, the mechanisms for SNA to transactivate mesenchymal markers was not well elucidated. Recently, we demonstrated that SNA collaborates with EGR1 and SP1 to directly upregulate MMP9 and ZEB1. Remarkably, a SNA-binding motif (TCACA) upstream of EGR/SP1 overlapping region on promoters was identified. Herein, we examined whether four other mesenchymal markers, lymphoid enhancer-binding factor (LEF), fibronectin (FN), cyclooxygenase 2 (COX2), and collagen type alpha I (COL1A1) are upregulated by SNA in a similar fashion. Expectedly, SNA is essential for expression of these mesenchymal genes. By deletion mapping and site directed mutagenesis coupled with dual luciferase promoter assay, SNA-binding motif and EGR1/SP1 overlapping region are required for TPA-induced transcription of LEF, FN, COX2 and COL1A1. Consistently, TPA induced binding of SNA and EGR1/SP1 on relevant promoter regions of these mesenchymal genes using ChIP and EMSA. Thus far, we found six of the mesenchymal genes are transcriptionally upregulated by SNA in the same fashion. Moreover, comprehensive screening revealed similar sequence architectures on promoter regions of other SNA-upregulated mesenchymal markers, suggesting that a general model for SNA-upregulated mesenchymal genes can be established.

miR-4721, Induced by EBV-miR-BART22, Targets GSK3β to Enhance the Tumorigenic Capacity of NPC through the WNT/β-catenin Pathway

Nasopharyngeal carcinoma (NPC) is prevalent in East and Southeast Asia. In a previous study, Epstein-Barr virus (EBV)-miR-BART22 induces tumor metastasis and stemness and is significantly involved in NPC progression. In the present study, we observed that miR-4721 is induced by EBV-miR-BART22 through phosphatidylinositol 3-kinase (PI3K)/AKT/c-JUN/Sp1 signaling to promote its transcription. In a subsequent study, we observed that miR-4721 serves as a potential oncogenic factor promoting NPC cell cycle progression and cell proliferation in vitro and in vivo. Mechanism analysis indicated that miR-4721 directly targetes GSK3β and reduces its expression, which therefore elevates β-catenin intra-nuclear aggregation and activates its downstream cell cycle factors, including CCND1 and c-MYC. In clinical samples, miR-4721 and GSK3β are respectively observed to be upregulated and downregulated in NPC progression. Elevated expression of miR-4721 is positively associated with clinical progression and poor prognosis. Our study first demonstrated that miR-4721 as an oncogene is induced by EBV-miR-BART22 via modulating PI3K/AKT/c-JUN/Sp1 signaling to target GSK3β, which thus activates the WNT/β-catenin-stimulated cell cycle signal and enhances the tumorigenic capacity in NPC. miR-4721 may be a potential biomarker or therapeutic target in NPC treatment in the future.

Timeless-Stimulated miR-5188-FOXO1/β-Catenin-c-Jun Feedback Loop Promotes Stemness via Ubiquitination of β-Catenin in Breast Cancer

MicroRNAs (miRNAs) play an essential role in the self-renewal of breast cancer stem cells (BCCs). Our study aimed to clarify the role of proto-oncogene c-Jun-regulated miR-5188 in breast cancer progression and its association with Timeless-mediated cancer stemness. In the present study, we showed that miR-5188 exerted an oncogenic effect by inducing breast cancer stemness, proliferation, metastasis, and chemoresistance in vitro and in vivo. The mechanistic analysis demonstrated that miR-5188 directly targeted FOXO1, which interacted with β-catenin in the cytoplasm, facilitated β-catenin degradation, and impaired the nuclear accumulation of β-catenin, thus stimulating the activation of known Wnt targets, epithelial-mesenchymal transition (EMT) markers, and key regulators of cancer stemness. Moreover, miR-5188 potentiated Wnt/β-catenin/c-Jun signaling to promote breast cancer progression. Interestingly, c-Jun enhanced miR-5188 transcription to form a positive regulatory loop, and Timeless interacted with Sp1/c-Jun to induce miR-5188 expression by promoting c-Jun-mediated transcription, which further activated miR-5188-FOXO1/β-catenin-c-Jun loop and facilitated breast cancer progression. Importantly, miR-5188 was upregulated in breast cancer and was positively correlated with poor patient prognosis. This study identifies miR-5188 as a novel oncomiR and provides a new theoretical basis for the clinical use of miR-5188 antagonists in the treatment of breast cancer.

Long noncoding RNA LINC01111 suppresses pancreatic cancer aggressiveness by regulating DUSP1 expression via microRNA-3924

Dysfunction in long noncoding RNAs (lncRNAs) is reported to participate in the initiation and progression of human cancer; however, the biological functions and molecular mechanisms through which lncRNAs affect pancreatic cancer (PC) are largely unknown. Here, we report a novel lncRNA, LINC01111, that is clearly downregulated in PC tissues and plasma of PC patients and acts as a tumor suppressor. We found that the LINC01111 level was negatively correlated with the TNM stage but positively correlated with the survival of PC patients. The overexpression of LINC01111 significantly inhibited cell proliferation, the cell cycle, and cell invasion and migration in vitro, as well as tumorigenesis and metastasis in vivo. Conversely, the knockdown of LINC01111 enhanced cell proliferation, the cell cycle, and cell invasion and migration in vitro, as well as tumorigenesis and metastasis in vivo. Furthermore, we found that high expression levels of LINC01111 upregulated DUSP1 levels by sequestering miR-3924, resulting in the blockage of SAPK phosphorylation and the inactivation of the SAPK/JNK signaling pathway in PC cells and thus inhibiting PC aggressiveness. Overall, these data reveal that LINC01111 is a potential diagnostic biomarker for PC patients, and the newly identified LINC01111/miR-3924/DUSP1 axis can modulate PC initiation and development.

MiR-124-3p suppresses glioma aggressiveness via targeting of Fra-2

Malignant glioma is the most common and deadly primary brain tumor in adults. However, the mechanisms underlying the malignancy of glioma remain unclear. In the present study, we found that Fos-related antigen-2 (Fra-2) was overexpressed in most glioma cells, and knockdown of Fra-2 prevented cell proliferation, migration, and invasion. Mechanistically, Fra-2 silencing led to a significant reduction in cell-cycle drivers (Cyclin D1 and Cyclin E1), one invasion-associated gene (MMP9), the mesenchymal marker (Vimentin), and induction of the epithelial marker (E-cadherin). Further study confirmed that miR-124-3p decreased the expression of Fra-2 via directly targeting the 3'-UTR, and transfection with miR-124-3p in glioma cells inhibited expression of the above cell-cycle and EMT promoters. Phenotypic experiments also showed that overexpression of Fra-2 weakened the inhibitory effects of miR-124-3p on the proliferation, migration, and invasion of glioma cells. In addition, Fra-2 knockdown impaired the malignant phenotypes enhanced by miR-124-3p inhibition, which suggested a crucial role for the miR-124-3p/Fra-2 pathway in glioma development. Consistently, high expression of Fra-2 was closely associated with low miR-124-3p level and indicated a poor prognosis in patients with glioma. In conclusion, this study indicates the existence of an aberrant miR-124-3p/Fra-2 pathway that results in glioma aggressiveness, which suggests novel therapeutic opportunities for this fatal disease.

Cigarette smoke upregulates SPRR3 by favoring c-Jun/Fra1 heterodimerization in human bronchial epithelial cells

AIM

The airway epithelium of smokers exhibits upregulated SPRR3, an indicator of pathogenic keratinization. The mechanisms underlying this phenomenon require investigation.

PATIENTS & METHODS

Human bronchial epithelial (HBE) SPRR3 expression was analyzed by smoking status. Primary HBE cells were exposed to cigarette smoke (CS). SPRR3 expression, SPRR3 promoter activity, AP-1 factor binding and AP-1 factors' effects were analyzed.

RESULTS

Current smokers display SPRR3 upregulation relative to never smokers. CS upregulates SPRR3 transcription in an exposure-dependent manner. CS promotes c-Jun and Fra1 binding to the SPRR3-AP-1/TRE site. Wild-type c-Jun and Fra1 upregulate, whereas c-Jun and Fra1, dominant-negative mutants, suppress SPRR3 promoter activity.

CONCLUSION

CS induces SPRR3 upregulation in HBE cells by promoting aberrant c-Jun/Fra1 dimerization.

Molecular Mechanisms Underlying the Regulation of the MFG-E8 Gene Promoter Activity in Physiological and Inflammatory Conditions

Milk fat globule-EGF factor 8 (MFG-E8) is expressed by macrophages and plays an important role in attenuating inflammation and maintaining tissue homeostasis. Previously, we and others found that lipopolysaccharide (LPS) inhibits MFG-E8 gene expression in macrophages. Here, we characterized the 5'-flanking region of the mouse MFG-E8 gene. To functionally analyze the upstream regulatory region of the MFG-E8 gene, a series of luciferase reporter gene constructs containing deleted or mutated regulatory elements were prepared. Using the luciferase assay, we revealed that Sp1 binding motifs within the proximal promoter region were necessary for full activity of the MFG-E8 promoter, whereas AP-1 like binding sequence at -372 played a role in governing the promoter activity at a homeostatic level. With chromatin immunoprecipitation assay, we showed that Sp1 and c-Jun physically interact with the MFG-E8 promoter region in vivo. In addition, Sp1 was found to regulate the MFG-E8 promoter activity positively and c-Jun negatively. Furthermore, we demonstrated that LPS inhibited MFG-E8 promoter activity via targeting Sp1 and AP-1-like motifs in the 5'-flanking region. Collectively, our data indicate that Sp1 and AP-1-related factors are involved in the regulation of MFG-E8 gene transcription by targeting their binding sites in the 5'-flanking region under physiological and inflammatory states.

Inhibitor of Differentiation/DNA Binding 1 (ID1) Inhibits Etoposide-induced Apoptosis in a c-Jun/c-Fos-dependent Manner

ID1 (inhibitor of differentiation/DNA binding 1) acts an important role in metastasis, tumorigenesis, and maintenance of cell viability. It has been shown that the up-regulation of ID1 is correlated with poor prognosis and the resistance to chemotherapy of human cancers. However, the underlying molecular mechanism remains elusive. Here, we determined for the first time that up-regulating ID1 upon etoposide activation was mediated through AP-1 binding sites within theID1promoter and confirmed that ID1 enhanced cell resistance to DNA damage-induced apoptosis in esophageal squamous cell carcinoma cells. Ablation of c-Jun/c-Fos or ID1 expression enhanced etoposide-mediated apoptosis through increasing activity of caspase 3 and PARP cleavage. Moreover, c-Jun/c-Fos and ID1 were positively correlated in human cancers. More importantly, simultaneous high expression of ID1 and c-Jun or c-Fos was correlated with poor survival in cancer patients. Collectively, we demonstrate the importance of c-Jun/c-Fos-ID1 signaling pathway in chemoresistance of esophageal cancer cells and provide considerable insight into understanding the underlying molecular mechanisms in esophageal squamous cell carcinoma cell biology.

Dual Action of miR-125b As a Tumor Suppressor and OncomiR-22 Promotes Prostate Cancer Tumorigenesis

MicroRNAs (miRs) are a novel class of small RNA molecules, the dysregulation of which can contribute to cancer. A combinatorial approach was used to identify miRs that promote prostate cancer progression in a unique set of prostate cancer cell lines, which originate from the parental p69 cell line and extend to a highly tumorigenic/metastatic M12 subline. Together, these cell lines are thought to mimic prostate cancer progression in vivo. Previous network analysis and miR arrays suggested that the loss of hsa-miR-125b together with the overexpression of hsa-miR-22 could contribute to prostate tumorigenesis. The dysregulation of these two miRs was confirmed in human prostate tumor samples as compared to adjacent benign glandular epithelium collected through laser capture microdissection from radical prostatectomies. In fact, alterations in hsa-miR-125b expression appeared to be an early event in tumorigenesis. Reverse phase microarray proteomic analysis revealed ErbB2/3 and downstream members of the PI3K/AKT and MAPK/ERK pathways as well as PTEN to be protein targets differentially expressed in the M12 tumor cell compared to its parental p69 cell. Relevant luciferase+3’-UTR expression studies confirmed a direct interaction between hsa-miR-125b and ErbB2 and between hsa-miR-22 and PTEN. Restoration of hsa-miR-125b or inhibition of hsa-miR-22 expression via an antagomiR resulted in an alteration of M12 tumor cell behavior in vitro. Thus, the dual action of hsa-miR-125b as a tumor suppressor and hsa-miR-22 as an oncomiR contributed to prostate tumorigenesis by modulations in PI3K/AKT and MAPK/ERK signaling pathways, key pathways known to influence prostate cancer progression.

Combined phosphoproteomics and bioinformatics strategy in deciphering drug resistant related pathways in triple negative breast cancer

Because of the absence of a clear therapeutic target for triple negative breast cancer (TNBC), conventional chemotherapy is the only available systemic treatment option for these patients. Despite chemotherapy treatment, TNBC patients still have worse prognosis when compared with other breast cancer patients. The study is to investigate unique phosphorylated proteins expressed in chemoresistant TNBC cell lines. In the current study, twelve TNBC cell lines were subjected to drug sensitivity assays against chemotherapy drugs docetaxel, doxorubicin, gemcitabine, and cisplatin. Based on their half maximal inhibitory concentrations, four resistant and two sensitive cell lines were selected for further analysis. The phosphopeptides from these cells were enriched with TiO2 beads and fractionated using strong cation exchange. 1,645 phosphoprotein groups and 9,585 unique phosphopeptides were identified by a high throughput LC-MS/MS system LTQ-Orbitrap. The phosphopeptides were further filtered with Ascore system and 1,340 phosphoprotein groups, 2,760 unique phosphopeptides, and 4,549 unique phosphosites were identified. Our study suggested that differentially phosphorylated Cdk5, PML, AP-1, and HSF-1 might work together to promote vimentin induced epithelial to mesenchymal transition (EMT) in the drug resistant cells. EGFR and HGF were also shown to be involved in this process.

Crucial role of c-Jun phosphorylation at Ser63/73 mediated by PHLPP protein degradation in the cheliensisin a inhibition of cell transformation

Cheliensisin A (Chel A), as a novel styryl-lactone isolated from Goniothalamus cheliensis Hu, has been demonstrated to have an inhibition of EGF-induced Cl41 cell transformation via stabilizing p53 protein in a Chk1-dependent manner, suggesting its chemopreventive activity in our previous studies. However, its underlying molecular mechanisms have not been fully characterized yet. In the current study, we found that Chel A treatment could increase c-Jun protein phosphorylation and activation, whereas the inhibition of c-Jun phosphorylation, by ectopic expression of a dominant-negative mutant of c-Jun, TAM67, reversed the Chel A inhibition of EGF-induced cell transformation and impaired Chel A induction of p53 protein and apoptosis. Moreover, our results indicated that Chel A treatment led to a PHLPP downregulation by promoting PHLPP protein degradation. We also found that PHLPP could interact with and bind to c-Jun protein, whereas ectopic PHLPP expression blocked c-Jun activation, p53 protein and apoptotic induction by Chel A, and further reversed the Chel A inhibition of EGF-induced cell transformation. With the findings, we have demonstrated that Chel A treatment promotes a PHLPP protein degradation, which can bind to c-Jun and mediates c-Jun phosphorylation, and further leading to p53 protein induction, apoptotic responses, subsequently resulting in cell transformation inhibition and chemopreventive activity of Chel A.

Propolis augments apoptosis induced by butyrate via targeting cell survival pathways

Diet is one of the major lifestyle factors affecting incidence of colorectal cancer (CC), and despite accumulating evidence that numerous diet-derived compounds modulate CC incidence, definitive dietary recommendations are not available. We propose a strategy that could facilitate the design of dietary supplements with CC-preventive properties. Thus, nutrient combinations that are a source of apoptosis-inducers and inhibitors of compensatory cell proliferation pathways (e.g., AKT signaling) may produce high levels of programmed death in CC cells. Here we report the combined effect of butyrate, an apoptosis inducer that is produced through fermentation of fiber in the colon, and propolis, a honeybee product, on CC cells. We established that propolis increases the apoptosis of CC cells exposed to butyrate through suppression of cell survival pathways such as the AKT signaling. The programmed death of CC cells by combined exposure to butyrate and propolis is further augmented by inhibition of the JNK signaling pathway. Analyses on the contribution of the downstream targets of JNK signaling, c-JUN and JAK/STAT, to the apoptosis of butyrate/propolis-treated CC cells ascertained that JAK/STAT signaling has an anti-apoptotic role; whereas, the role of cJUN might be dependent upon regulatory cell factors. Thus, our studies ascertained that propolis augments apoptosis of butyrate-sensitive CC cells and re-sensitizes butyrate-resistant CC cells to apoptosis by suppressing AKT signaling and downregulating the JAK/STAT pathway. Future in vivo studies should evaluate the CC-preventive potential of a dietary supplement that produces high levels of colonic butyrate, propolis, and diet-derived JAK/STAT inhibitors.

AP1 transcription factors in epidermal differentiation and skin cancer

AP1 (jun/fos) transcription factors (c-jun, junB, junD, c-fos, FosB, Fra-1, and Fra-2) are key regulators of epidermal keratinocyte survival and differentiation and important drivers of cancer development. Understanding the role of these factors in epidermis is complicated by the fact that each protein is expressed, at different levels, in multiple cells layers in differentiating epidermis, and because AP1 transcription factors regulate competing processes (i.e., proliferation, apoptosis, and differentiation). Various in vivo genetic approaches have been used to study these proteins including targeted and conditional knockdown, overexpression, and expression of dominant-negative inactivating AP1 transcription factors in epidermis. Taken together, these studies suggest that individual AP1 transcription factors have different functions in the epidermis and in cancer development and that altering AP1 transcription factor function in the basal versus suprabasal layers differentially influences the epidermal differentiation response and disease and cancer development.

Human T-cell leukemia virus type 1 (HTLV-1) bZIP factor requires cellular transcription factor JunD to upregulate HTLV-1 antisense transcription from the 3' long terminal repeat

Infection with the human T-cell leukemia virus type 1 (HTLV-1) results in a variety of diseases including adult T-cell leukemia (ATL), a fatal malignancy characterized by the uncontrolled proliferation of virally infected CD4(+) T cells. The HTLV-1 basic leucine zipper factor (HBZ) is believed to contribute to development and maintenance of ATL. Unlike the other HTLV-1 genes, the hbz gene is encoded on the complementary strand of the provirus and therefore is not under direct control of the promoter within the 5' long terminal repeat (LTR) of the provirus. This promoter can undergo inactivating genetic or epigenetic changes during the course of ATL that eliminates expression of all viral genes except that of hbz. In contrast, repressive modifications are not known to occur on the hbz promoter located in the 3' LTR, and hbz expression has been consistently detected in all ATL patient samples. Although Sp1 regulates basal transcription from the HBZ promoter, other factors that activate transcription remain undefined. In this study, we used a proviral reporter construct deleted of the 5' LTR to show that HBZ upregulates its own expression through cooperation with JunD. Activation of antisense transcription was apparent in serum-deprived cells in which the level of JunD was elevated, and elimination of JunD expression by gene knockout or shRNA-mediated knockdown abrogated this effect. Activation through HBZ and JunD additionally required Sp1 binding at the hbz promoter. These data favor a model in which JunD is recruited to the promoter through Sp1, where it heterodimerizes with HBZ thereby enhancing its activity. Separately, hbz gene expression led to an increase in JunD abundance, and this effect correlated with emergence of features of transformed cells in immortalized fibroblasts. Overall, our results suggest that JunD represents a novel therapeutic target for the treatment of ATL.

Sp1 transcription factor interaction with accumulated prelamin a impairs adipose lineage differentiation in human mesenchymal stem cells: essential role of sp1 in the integrity of lipid vesicles

Lamin A (LMNA)-linked lipodystrophies may be either genetic (associated with LMNA mutations) or acquired (associated with the use of human immunodeficiency virus protease inhibitors [PIs]), and in both cases they share clinical features such as anomalous distribution of body fat or generalized loss of adipose tissue, metabolic alterations, and early cardiovascular complications. Both LMNA-linked lipodystrophies are characterized by the accumulation of the lamin A precursor prelamin A. The pathological mechanism by which prelamin A accumulation induces the lipodystrophy associated phenotypes remains unclear. Since the affected tissues in these disorders are of mesenchymal origin, we have generated an LMNA-linked experimental model using human mesenchymal stem cells treated with a PI, which recapitulates the phenotypes observed in patient biopsies. This model has been demonstrated to be a useful tool to unravel the pathological mechanism of the LMNA-linked lipodystrophies, providing an ideal system to identify potential targets to generate new therapies for drug discovery screening. We report for the first time that impaired adipogenesis is a consequence of the interaction between accumulated prelamin A and Sp1 transcription factor, sequestration of which results in altered extracellular matrix gene expression. In fact, our study shows a novel, essential, and finely tuned role for Sp1 in adipose lineage differentiation in human mesenchymal stem cells. These findings define a new physiological experimental model to elucidate the pathological mechanisms LMNA-linked lipodystrophies, creating new opportunities for research and treatment not only of LMNA-linked lipodystrophies but also of other adipogenesis-associated metabolic diseases.

Induction of group IVC phospholipase A2 in allergic asthma: transcriptional regulation by TNFα in bronchoepithelial cells

Airway inflammation in allergen-induced asthma is associated with eicosanoid release. These bioactive lipids exhibit anti- and pro-inflammatory activities with relevance to pulmonary pathophysiology. We hypothesized that sensitization/challenge using an extract from the ubiquitous fungus Aspergillus fumigatus in a mouse model of allergic asthma would result in altered phospholipase gene expression, thus modulating the downstream eicosanoid pathway. We observed the most significant induction in the group IVC PLA2 (phospholipase A2) [also known as cPLA2γ (cytosolic PLA2γ) or PLA2G4C]. Our results infer that A. fumigatus extract can induce cPLA2γ levels directly in eosinophils, whereas induction in lung epithelial cells is most likely to be a consequence of TNFα (tumour necrosis factor α) secretion by A. fumigatus-activated macrophages. The mechanism of TNFα-dependent induction of cPLA2γ gene expression was elucidated through a combination of promoter deletions, ChIP (chromatin immunoprecipitation) and overexpression studies in human bronchoepithelial cells, leading to the identification of functionally relevant CRE (cAMP-response element), NF-κB (nuclear factor κB) and E-box promoter elements. ChIP analysis demonstrated that RNA polymerase II, ATF-2 (activating transcription factor 2)-c-Jun, p65-p65 and USF (upstream stimulating factor) 1-USF2 complexes are recruited to the cPLA2γ enhancer/promoter in response to TNFα, with overexpression and dominant-negative studies implying a strong level of co-operation and interplay between these factors. Overall, our results link cytokine-mediated alterations in cPLA2γ gene expression with allergic asthma and outline a complex regulatory mechanism.

Menin and JunD regulate gastrin gene expression through proximal DNA elements

Mutations in the MEN1 gene correlate with multiple endocrine neoplasia I (MEN1). Gastrinomas are the most malignant of the neuroendocrine tumors associated with MEN1. Because menin and JunD proteins interact, we examined whether JunD binds to and regulates the gastrin gene promoter. Both menin and JunD are ubiquitous nuclear proteins that we showed colocalize in the gastrin-expressing G cells of the mouse antrum. Transfection with a JunD expression vector alone induced endogenous gastrin mRNA in AGS human gastric cells, and the induction was blocked by menin overexpression. We mapped repression by menin to both a nonconsensus AP-1 site and proximal GC-rich elements within the human gastrin promoter. Chromatin immunoprecipitation assays, EMSAs, and DNA affinity precipitation assays documented that JunD and Sp1 proteins bind these two elements and are both targets for menin regulation. Consistent with menin forming a complex with histone deacetylases, we found that repression of gastrin gene expression by menin was reversed by trichostatin A. In conclusion, proximal DNA elements within the human gastrin gene promoter mediate interactions between JunD, which induces gastrin gene expression and menin, which suppresses JunD-mediated activation.

Transcriptional activity of TAp63 promoter is regulated by c-jun

The transcription factor p63 belongs to the p53 protein family and plays an important role in epithelial development. Recent studies showed that p63 is over-expressed in some human squamous cell carcinomas of the head and neck, suggesting a role in carcinogenesis. The p63 gene contains two promoters and alternative promoter usage generates two groups of proteins with (TAp63) or without (ΔNp63) the transactivation domain. Although the roles of TAp63 in epithelial development have been described in numerous recent studies, the regulation of its expression has not been elucidated. In this study, we showed that the transcriptional activity of the TAp63 promoter and TAp63 protein level were both up-regulated by an increased c-jun activity in Hep3B human hepatocellular carcinoma cell. Moreover, the elevated TAp63 expression was coincided with an increased binding of c-jun to the TAp63 promoter. Point mutation of the sp1 binding site within the TAp63 promoter region attenuated the effect of c-jun on TAp63 expression. Knockdown of TAp63 expression by shRNA led to increased proliferation of Hep3B cell compared to that of the mock cell, suggesting a growth suppressive effect of TAp63.

Suppression of the androgen receptor function by quercetin through protein-protein interactions of Sp1, c-Jun, and the androgen receptor in human prostate cancer cells

We have previously reported that the increase in c-Jun expression induced by quercetin inhibited androgen receptor (AR) transactivation, and Sp1 was involved in quercetin-mediated downregulation of AR activity. Transient transfection assays in this work revealed that co-expression of c-Jun quenched Sp1-induced production of luciferase activity driven by AR promoter or three copies of Sp1 binding elements in the AR promoter. Moreover, c-Jun repressed AR-mediated luciferase activity via androgen-response elements (AREs) of the hK2 gene, while this suppression could be restored partially by cotransfection of Sp1 expression plasmid. The physical associations of c-Jun, Sp1, and AR induced by quercetin were further demonstrated by co-immunoprecipitation experiments. In addition, quercetin-mediated repression of AR expression and activity was partially reversed by blocking of JNK signaling pathway. These results suggested that c-Jun might play an important role in the suppression of AR expression and activity in the presence of quercetin, and association of a c-Jun/Sp1/AR protein complex induced by quercetin represented a novel mechanism that was involved in down-regulation of the AR function in prostate cancer cells.

Review article: pulmonary sarcomatoid carcinomas: a practical overview

Pulmonary sarcomatoid carcinomas (PSCs) are currently defined as poorly differentiated non-small-cell carcinomas containing a component with sarcoma or sarcoma-like (spindle and/or giant cell) features. They consist of 5 major histological variants, namely pleomorphic carcinoma, spindle cell carcinoma, giant cell carcinoma, carcinosarcoma, and pulmonary blastoma. The segregation of PSCs into a distinct clinicopathologic entity seems justified on the basis of morphologic, behavioral, and genotypic/phenotypic attributes. As a group, PSCs generally run an aggressive clinical course and may cause major difficulties in the differential diagnosis with other primary and secondary malignancies of the lung. At present, PSCs are believed to represent a family of carcinomas "in transition," in which diverse pathways of clonal evolution account for histological differences of a common ancestor lesion. The sarcomatous or sarcomatoid component of these tumors is thought to derive from carcinoma cells during the progression of carcinogenesis through the activation of an epithelial-mesenchymal transition program leading to sarcomatous transformation or metaplasia (conversion paradigm). Conceivably, targeting the epithelial-mesenchymal transition program could become a valid therapeutic strategy for these life-threatening tumors, whose sensitivity to current medical manipulation is disappointing.

Structural changes in TAF4b-TFIID correlate with promoter selectivity

Proper ovarian development requires the cell type-specific transcription factor TAF4b, a subunit of the core promoter recognition complex TFIID. We present the 35 A structure of a cell type-specific core promoter recognition complex containing TAF4b and TAF4 (4b/4-IID), which is responsible for directing transcriptional synergy between c-Jun and Sp1 at a TAF4b target promoter. As a first step toward correlating potential structure/function relationships of the prototypic TFIID versus 4b/4-IID, we have compared their 3D structures by electron microscopy and single-particle reconstruction. These studies reveal that TAF4b incorporation into TFIID induces an open conformation at the lobe involved in TFIIA and putative activator interactions. Importantly, this open conformation correlates with differential activator-dependent transcription and promoter recognition by 4b/4-IID. By combining functional and structural analysis, we find that distinct localized structural changes in a megadalton macromolecular assembly can significantly alter its activity and lead to a TAF4b-induced reprogramming of promoter specificity.

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.

Poly(ADP-ribose) polymerase-1 regulates vimentin expression in lung cancer cells

Vimentin is one of the mammalian intermediate filament proteins. It is expressed in cells of mesenchymal origin and is characteristic of proliferating cells at the fetal stage. During malignancy, vimentin expression is activated in certain lung epithelial cells. Examination of a group of lung cancer cells showed a marked difference in their vimentin expression. The difference in vimentin expression among lung cancer cells is due to differential regulation at the transcriptional level. Analysis of the vimentin promoter revealed a 102-bp promoter sequence that is important for promoter activity in a lung cancer cell line in which vimentin is strongly expressed. This promoter region interacts with poly(ADP-ribose) polymerase-1 (PARP-1), which is also a transcription regulator. Exogenous expression of PARP-1 increased vimentin promoter activity. A shortened PARP-1 without the COOH-terminal catalytic domain showed the same promoter activation effect. Treatment of cells with H(2)O(2) reduced PARP-1 and vimentin expression at the protein level. H(2)O(2) also dose dependently suppressed vimentin promoter activity in cells overexpressing PARP-1. These results demonstrate that vimentin expression in lung cancer cells is regulated at the transcriptional level and that PARP-1 binds and activates the vimentin promoter independent of its catalytic domain and may play a role in H(2)O(2)-induced inhibition of vimentin expression.

The zinc finger repressor, ZBP-89, recruits histone deacetylase 1 to repress vimentin gene expression

Vimentin, a member of the intermediate filament (IF) protein family, exhibits a complex pattern of tissue- and developmental-specific expression. Although vimentin is widely expressed in the embryo, its expression becomes restricted during terminal differentiation. Moreover, it is often expressed in tissue culture cells despite their embryological origin and is a marker for the metastatic tumor cell. Previously, the vimentin promoter has been shown to contain several positive- and negative-acting cis-elements. The negative elements bind the transcription factor ZBP-89. Interestingly, ZBP-89 can be either an activator or a repressor of gene expression. For instance, ZBP-89 has been shown to activate p21(waf1/cip1) expression by recruiting p300 to the p21 promoter. Here, we have investigated the mechanism of ZBP-89 repression. The histone deacetylase (HDAC) inhibitor TSA enhances vimentin gene expression requiring the proximal promoter region including GC-box 1, a known Sp1/Sp3 binding site. Chromatin immunoprecipitation (ChIP) assays document an increase in the acetylation status of histone H3 on the endogenous vimentin gene concomitant with TSA treatment. However, EMSAs, DNA precipitation, co-immunoprecipitation and ChIP data show that it is not Sp1, but rather ZBP-89, which recruits HDAC1. From these studies we conclude that ZBP-89 functions as a repressor by recruiting HDAC1 to the vimentin promoter.

Structure of the human 5-HT7 receptor gene and characterization of its promoter region

The molecular mechanism regulating serotonin 5-HT(7) receptor expression is still unclear. In this study we provide evidence that transcription of the 5-HT(7) gene is at least partly regulated by Sp1 and Sp3. We isolated and sequenced >3000 bp of the upstream sequences and identified by RACE a number of transcriptional initiation sites over a region of 300 bp upstream of the coding region. This region has a high GC content, but contains no obvious TATA or a CAAT box. Besides a Sp1/Sp3 consensus motif, regulatory elements for AP2, Egr-1 and MAZ are also present. Transient transfection assays using deletion variants indicated that the GC-rich region is essential for full promoter activity. The role of Sp1 in this was confirmed by transient overexpression of both wild type Sp1 or dominant-negative forms. By gel shift and supershift analyses, targeting the Sp1 consensus sequence and the GC-rich region just upstream of the transcription initiation sites, binding of Sp1 and Sp3 was demonstrated. Both in vitro as well as in vivo experiments, using a cell line which endogenously expresses the 5-HT(7) receptor, indicated that mithramycin A, an inhibitor of Sp1/3 transcription factor binding, was able to inhibit 5-HT(7) promoter activity. Taken together these results support the essential role of Sp factors in regulating 5-HT(7) promoter activity.

PP2B-mediated dephosphorylation of c-Jun C terminus regulates phorbol ester-induced c-Jun/Sp1 interaction in A431 cells

The c-Jun/Sp1 interaction is essential for growth factor- and phorbol 12-myristate 13-acetate (PMA)-induced genes expression, including human 12(S)-lipoxygenase, keratin 16, cytosolic phospholipase A2, p21(WAF1/CIP1), and neuronal nicotinic acetylcholine receptor beta4. Here, we examined the mechanism underlying the PMA-induced regulation on the interaction between c-Jun and Sp1. We found that treatment of cells with PMA induced a dephosphorylation at the C terminus of c-Jun at Ser-243 and a concomitant inhibition of PP2B by using PP2B small interfering RNA, resulting in reduction of PMA-induced gene expression as well as the c-Jun/Sp1 interaction. The c-Jun mutant TAM-67-3A, which contains three substitute alanines at Thr-231, Ser-243, and Ser-249 compared with TAM-67, binds more efficaciously with Sp1 and is about twice as efficacious as TAM-67 in inhibiting the PMA-induced activation of the 12(S)-lipoxygenase promoter. Importantly, PP2B not only dephosphorylates the c-Jun at Ser-243 but also interacts with c-Jun in PMA-treated cells. PMA stimulates the association of the PP2B/c-Jun/Sp1 complex with the promoter. These findings indicate the dephosphorylation of c-Jun C terminus is required for the c-Jun/Sp1 interaction and reveal that PP2B plays an important role in regulating c-Jun/Sp1 interaction in PMA-induced gene expression.

TGFbeta1 regulation of vimentin gene expression during differentiation of the C2C12 skeletal myogenic cell line requires Smads, AP-1 and Sp1 family members

Vimentin exhibits a complex pattern of developmental and tissue-specific expression regulated by such growth factors as TGFbeta1, PDGF, FGF, EGF and cytokines. Vimentin is expressed in the more migratory, mesenchymal cell and its expression is often down-regulated to make way for tissue-specific intermediate filaments proteins such as desmin in muscle. Here, we suggest a mechanism to explain how TGFbeta1 contributes to the up-regulation of vimentin expression while blocking myogenesis. TGFbeta1 binds to serine/threonine kinase receptors resulting in the phosphorylation of Smad2 and Smad3, followed by formation of a heteromeric complex with Smad4. The translocation of this complex to the nucleus modulates transcription of selected genes such as vimentin. However, the vimentin gene lacks a consensus TGFbeta1 response element. By transient transfection analysis of vimentin's various promoter elements fused to the CAT reporter gene, we have determined that tandem AP-1 sites surrounded by GC-boxes are required for TGFbeta1 induction. Mutations within this region eliminated the ability of Smad3 to induce reporter gene expression. DNA precipitation and ChIP assays suggest that c-Jun, c-Fos, Smad3 and Sp1/Sp3 interact over this region, but this interaction changes during myogenesis with TGFbeta1 induction.

Sarcomatoid carcinomas of the lung—are these histogenetically heterogeneous tumors?

Sarcomatoid carcinomas (SC) of the lung are a heterogeneous group of nonsmall cell lung carcinomas (NSCLC) containing a sarcoma or sarcoma-like component. SC may represent an epithelial neoplasm undergoing divergent tissue differentiation originating from a single clone. Epithelial-mesenchymal transition (EMT) best describes the origin of the spindle and giant cells. We aimed to define chromosomal aberrations within the subgroups of SC and if EMT does play a role in SC. Twenty-two SC were investigated by chromosomal comparative genomic hybridization (CGH). Immunohistochemical staining was performed with antibodies for E-cadherin, Vimentin, c-Fos, c-Jun, Snail, TGFbeta1, Notch1, beta-catenin, Glycogen synthase kinase 3beta (GSK3beta), and Fascin. Gains occurred more frequently than losses (70.5 vs 29.5%). The shortest regions of overlap were gains on chromosomes 8q and 7 followed by 1q, 3q, and 19, supporting the common origin of the different subtypes of SC. The immunohistochemical staining suggests that the sarcomatoid components of SC might have undergone EMT, not triggered by the signaling pathways Notch1, Snail, and TGFbeta1, but probably initiated by an upregulation of c-Jun and a consecutive overexpression of Vimentin and Fascin. The Wnt-pathway was not deregulated because combined membrane and cytoplasmic reactivity for beta-catenin and GSK3beta was observed.

An intronic enhancer regulates cyclooxygenase-1 gene expression

To identify cis-elements regulating PMA-induced prostaglandin H synthase-1 (PGHS-1) gene expression in the human megakaryoblast cell line, MEG-01, we performed promoter reporter assays with a luciferase reporter vector containing the -2030/-22 region of the human PGHS-1 gene. PMA treatment for 24 h increased PGHS-1 promoter activity by twofold. Mutagenesis studies of the promoter revealed a single Sp1 site essential for PMA-inducible transcription. Insertion of a highly conserved 100 bp sequence cloned from intron 8 into the -2030/-22 reporter plasmid enhanced PMA-dependent transcription 10-fold. Mutation of either a consensus AP-1 site within intron 8 or the Sp1 site in the promoter reduced PMA-induced activity by 80-100%. Gel shift assays using the intron 8 AP-1 sequence demonstrated the formation of an AP-1-specific DNA-protein complex. Our results suggest that inducible PGHS-1 gene expression involves the coordinate functioning of a Sp1 site in the promoter and an AP-1 site in intron 8.

Regulation of KiSS-1 metastasis suppressor gene expression in breast cancer cells by direct interaction of transcription factors activator protein-2alpha and specificity protein-1

KiSS-1 has been shown to function as a tumor metastasis suppressor gene and reduce the number of metastases in different cancers. The expression of KiSS-1 or KiSS1, like other tumor suppressor, is commonly reduced or completely ablated in a variety of cancers via an unknown mechanism. Here we show that the loss of KiSS-1 expression in highly metastatic breast cancer cell lines correlates directly with the expression levels of two transcription factors, activator protein-2alpha (AP-2alpha) and specificity protein 1 (Sp1), which synergistically activate the transcriptional regulation of KiSS-1 in breast cancer cells. Although the KiSS-1 promoter contains multiple AP-2alpha binding elements, AP-2alpha-mediated regulation occurs indirectly through Sp1 sites, as determined by deletion and mutation analysis. Overexpression of AP-2alpha into highly metastatic breast cell lines did not alter KiSS-1 promoter-driven luciferase gene activity. However, co-transfection of AP-2alpha wild-type or the dominant negative form of AP-2 lacking its C-terminal DNA-binding domain, AP-2B, together with Sp1, increased KiSS-1 promoter activity dramatically, suggesting that AP-2alpha regulation of KiSS-1 transcription does not require direct binding to the KiSS-1 promoter. Furthermore, we demonstrated that AP-2alpha directly interacted with Sp1 to form transcription complexes at two tandem Sp1-binding sites of the promoter to activate KiSS-1 transcription. Together, our results indicate that AP-2alpha and Sp1 are strong transcriptional regulators of KiSS-1 and that loss or decreased expression of AP-2alpha in breast cancer may account for the loss of tumor metastasis suppressor KiSS-1 expression and thus increased cancer metastasis.

Two transactivation mechanisms cooperate for the bulk of HIF-1-responsive gene expression

The C-terminal activation domain (C-TAD) of the hypoxia-inducible transcription factors HIF-1alpha and HIF-2alpha binds the CH1 domains of the related transcriptional coactivators CREB-binding protein (CBP) and p300, an oxygen-regulated interaction thought to be highly essential for hypoxia-responsive transcription. The role of the CH1 domain in vivo is unknown, however. We created mutant mice bearing deletions in the CH1 domains (DeltaCH1) of CBP and p300 that abrogate their interactions with the C-TAD, revealing that the CH1 domains of CBP and p300 are genetically non-redundant and indispensable for C-TAD transactivation function. Surprisingly, the CH1 domain was only required for an average of approximately 35-50% of global HIF-1-responsive gene expression, whereas another HIF transactivation mechanism that is sensitive to the histone deacetylase inhibitor trichostatin A (TSA(S)) accounts for approximately 70%. Both pathways are required for greater than 90% of the response for some target genes. Our findings suggest that a novel functional interaction between the protein acetylases CBP and p300, and deacetylases, is essential for nearly all HIF-responsive transcription.

Activation of extracellular signal-regulated kinase signaling by epidermal growth factor mediates c-Jun activation and p300 recruitment in keratin 16 gene expression

In studies of gene regulation of keratin 16, we reported previously that simian virus 40 promoter factor 1 shows a functional cooperation with c-Jun and coactivators p300/CBP in driving the transcriptional regulation of epidermal growth factor (EGF)-induced keratin 16 gene expression. In the present study, we found that the stimulated expression of keratin 16 by EGF was mediated mainly through the mitogen-activated protein kinase kinase-extracellular signal-regulated kinases 1 and 2 (ERK1/2) signaling pathway. Ser63 and Ser73 on the c-Jun NH(2)-terminal transactivation domain could be phosphorylated in cells treated with EGF; nevertheless, we found that the c-Jun COOH terminus played a pivotal role in EGF-induced expression of keratin 16. The activation of keratin 16 by EGF treatment could not be enhanced by the overexpression of myc-c-JunK3R, in which three putative acetylation lysine residues on the c-Jun COOH terminus were all mutated into arginines, suggesting that c-Jun acetylation on the COOH terminus might partially play a functional role in this system. In addition, by using a chromatin immunoprecipitation assay and a DNA affinity precipitation assay, EGF treatment up-regulated the p300 recruitment through ERK signaling to the promoter region in regulating keratin 16 transcriptional activity. Furthermore, the enhancement of acetyl-histone H3 to the keratin 16 chromatin promoter induced by EGF was also mediated via ERK activation. In conclusion, these results strongly suggest that both c-Jun induction and p300 recruitment to gene promoter, mediated through ERK activation, played an essential role in regulating keratin 16 gene expression by EGF. p300 mediated and regulated EGF-induced keratin 16 gene expression, at least in part, through multiple mechanisms, including a selective acetylation of c-Jun and histone H3.

Hsp90α Recruited by Sp1 Is Important for Transcription of 12(S)-Lipoxygenase in A431 Cells

Sp1 is a basic transcriptional factor that binds to the GC-rich region in the promoter of the target gene. It is involved in transcription of numerous genes by recruiting transcriptional factors to the promoters of target genes. In this study, we found in vivo and in vitro that Hsp90alpha was recruited to the GC-rich region of the 12(S)-lipoxygenase promoter through interaction with Sp1 in A431 cells by employing DNA affinity immunoprecipitation assay and chromatin immunoprecipitation assay. When Hsp90alpha was inhibited by geldanamycin (GA, a specific inhibitor of the Hsp90 family) or by siRNA of Hsp90alpha (to block its activity or to knockdown protein levels), respectively, luciferase activity (driven by the 12(S)-lipoxygenase promoter) and both mRNA and protein levels of 12(S)-lipoxygenase were reduced significantly in cells. In addition, the effect of GA was abolished when the Sp1 binding sites of 12(S)-lipoxygenase were mutated in A431 cells. Interestingly, binding of Sp1 to the 12(S)-lipoxygenase promoter was also decreased upon GA treatment in cells. In conclusion, our results indicate that Sp1 interacts with Hsp90alpha to recruit it to the promoter of 12(S)-lipoxygenase and then to regulate gene transcription by modulating the binding ability of Sp1 to promoters.

Calorie restriction protects against age-related rat aorta sclerosis

Many theories have been advanced to account for the ageing process, among which the free radical theory deserves much attention. Numerous studies have also shown an association between tissue fibrosis and oxidative stress. Of note, fibrosis may be considered a significant index of tissue ageing. Calorie restriction (CR) has been demonstrated to maintain many physiological processes in a youthful state until a very advanced age. However the anti-ageing mechanisms of CR are still not fully understood. We thus evaluated the effect of CR on oxidative damage and its relationship with fibrosis during ageing. We found a significant increase of both oxidative stress and fibrosis parameters in the aortae from aged vs. young rats. CR reversed both phenomena. CR also protected against the age-associated increase of Jun-N-terminal kinase and p-38 activities, involved in TGFbeta1 expression and signaling. On the contrary, extracellular regulated kinases did not show any age-related change. CR similarly reversed the age-related increase of AP-1 DNA binding activity and the AP-1-dependent increase of vimentin gene expression. In parallel, CR reversed the age-related morphological alterations of the aorta wall cell composition. These data further support the relationship between oxidative stress and fibrosis in different diseases and during ageing. The protection exerted by CR against fibrosclerosis might be due to a decrease of oxidative stress, with consequent decreased MAPK activity and down-regulation of AP-1 activation and of TGFbeta1 expression and signaling.

Transcription factor Sp1 functions as an anchor protein in gene transcription of human 12(S)-lipoxygenase

The signal transduction of human 12(S)-lipoxygenase and the regulation of gene activation, induced by epidermal growth factor (EGF), are discussed in this review article. Treatment of human epidermoid carcinoma A431 cells with EGF induces the gene expression of human 12(S)-lipoxygenase, and two Sp1 binding sites residing at -158 to -150 bp and -123 to -114 bp are essential in the mediation of EGF induction of the 12(S)-lipoxygenase gene. EGF induces MAPK activation in cells, followed by the activation of AP1. Thus, the biosynthesis of c-Jun is enhanced, which subsequently interacts with Sp1. c-Jun on Sp1/c-Jun complex is then recruited to gene promoter through the binding of Sp1 to Sp1-binding sites on gene promoter. Subsequent transactivation of the promoter activation of the human 12(S)-lipoxygenase gene is induced. In addition to the functional role of Sp1 in gene regulation of 12(S)-lipoxygenase, recent studies have also demonstrated that Sp1 acting as an anchor protein to recruit transcription factor c-Jun is essential for growth factor and/or phorbol ester-induced expression of several genes.

Hypothesis: Cell plasticity, linking embryonal stem cells to adult stem cell reservoirs and metastatic cancer cells?

Embryonal stem (ES) cells are the earliest ontogenetically identifiable stem cells of the embryo proper for all subsequent mesenchymal stem cells and for highly specialized differentiated cells. This review characterizes, in a working hypothesis, the role of reversible EMT/MET (epithelialmesenchymal transition) as a manifestation of cell plasticity 1) in the development of ES cells to adult stem cells (hematopoietic stem cells) and 2) in metastasizing cancer cells. Animal studies support the concept that EMT/MET is a key manifestation of cell plasticity in the development of ES cells to adult stem cells, and in conversion of localized to metastasizing cancer cells. In fact, ES cells may persist to postnatal life, in cytologically verifiable form and/or within the frame of EMT/MET, as ultimate reservoir for adult stem cells. Furthermore, EMT could possibly serve as a conceptional link between physiologic and pathologic signaling pathways. Clonal confirmation in humans is necessary.

Cyclin A is a c-Jun target gene and is necessary for c-Jun-induced anchorage-independent growth in RAT1a cells

Overexpression of c-Jun enables Rat1a cells to grow in an anchorage-independent manner. We used an inducible c-Jun system under the regulation of doxycycline in Rat1a cells to identify potential c-Jun target genes necessary for c-Jun-induced anchorage-independent growth. Induction of c-Jun results in sustained expression of cyclin A in the nonadherent state with only minimal expression in the absence of c-Jun. The promoter activity of cyclin A2 was 4-fold higher in Rat1a cells in which c-Jun expression was induced compared with the control cells. Chromatin immunoprecipitation demonstrated that c-Jun bound directly to the cyclin A2 promoter. Mutation analysis of the cyclin A2 promoter mapped the c-Jun regulatory site to an ATF site at position -80. c-Jun was able to bind to this site both in vitro and in vivo, and mutation of this site completely abolished promoter activity. Cyclin A1 was also elevated in c-Jun-overexpressing Rat1a cells; however, c-Jun did not regulate this gene directly, since it did not bind directly to the cyclin A1 promoter. Suppression of cyclin A expression via the introduction of a cyclin A antisense sequences significantly reduced the ability of c-Jun-overexpressing Rat1a cells to grow in an anchorage-independent fashion. Taken together, these results suggest that cyclin A is a target of c-Jun and is necessary but not sufficient for c-Jun-induced anchorage-independent growth. In addition, we demonstrated that the cytoplasmic oncogenes Ras and Src transcriptionally activated the cyclin A2 promoter via the ATF site at position -80. Using a dominant negative c-Jun mutant, TAM67, we showed that this transcriptional activation of cyclin A2 requires c-Jun. Thus, our results suggest that c-Jun is a mediator of the aberrant cyclin A2 expression associated with Ras/Src-induced transformation.

v-Jun downregulates the alpha 2 (I) collagen target gene indirectly through Sp1/3

Transformation of chick embryo fibroblasts (CEFs) by the v-Jun oncoprotein correlates with a downregulation of the alpha 2 (I) collagen gene. To investigate whether this gene constitutes a direct target of v-Jun, an analysis of a large proximal fragment of the promoter, extending from position -1080 to +109, was performed. Transient transfections with -1080/+109 and deleted derivatives revealed that a short proximal fragment, -433/+11, is the target for repression by v-Jun. Extensive analysis, conducted in CEFs and in Sp1/3-deficient Drosophila SL2 cells, further showed that (i) high constitutive activity of -433/+11 requires a direct binding of the ubiquitous Sp1 and/or Sp3 transcription factors acting on two distinct motifs, that is, a proximal TCC-rich region and an upstream GC box, and that (ii) repression by v-Jun does not require any direct binding of the oncoprotein to the DNA, but an indirect binding within a v-Jun-Sp1/3-DNA chromatin-associated complex. This situation is reminiscent of a situation previously reported with the tata-less, SPARC (secreted protein, acidic, and rich in cysteine) target promoter that regulates the expression of another extracellular matrix component in the same model of cell transformation. Taken together, these data reinforce the view that, at least in CEFs, v-Jun downregulates a family of direct target genes by binding to the DNA indirectly through Sp1/3.

Regulation of Involucrin Gene Expression

The epidermis is a dynamic renewing structure that provides life-sustaining protection from the environment. The major cell type of the epidermis, the epidermal keratinocyte, undergoes a carefully choreographed program of differentiation. Alteration of these events results in a variety of debilitating and life-threatening diseases. Understanding how this process is regulated is an important current goal in biology. In this review, we summarize the literature regarding regulation of involucrin, an important marker gene that serves as a model for understanding the mechanisms that regulate the differentiation process. Current knowledge describing the role of transcription factors and signaling cascades in regulating involucrin gene expression are presented. These studies describe a signaling cascade that includes the novel protein kinase C isoforms, Ras, MEKK1, MEK3, and a p38delta-extracellular signal regulated kinase 1/2 complex. This cascade regulates activator protein one, Sp1, and CCATT/enhancer-binding protein transcription factor DNA binding to two discrete involucrin promoter regions, the distal- and proximal-regulatory regions, to regulate involucrin gene expression.

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.