Oct-1 potentiates CREB-driven cyclin D1 promoter activation via a phospho-CREB- and CREB binding protein-independent mechanism

Multi-faceted regulation of CREB family transcription factors

cAMP response element-binding protein (CREB) is a ubiquitously expressed nuclear transcription factor, which can be constitutively activated regardless of external stimuli or be inducibly activated by external factors such as stressors, hormones, neurotransmitters, and growth factors. However, CREB controls diverse biological processes including cell growth, differentiation, proliferation, survival, apoptosis in a cell-type-specific manner. The diverse functions of CREB appear to be due to CREB-mediated differential gene expression that depends on cAMP response elements and multi-faceted regulation of CREB activity. Indeed, the transcriptional activity of CREB is controlled at several levels including alternative splicing, post-translational modification, dimerization, specific transcriptional co-activators, non-coding small RNAs, and epigenetic regulation. In this review, we present versatile regulatory modes of CREB family transcription factors and discuss their functional consequences.

CREB1 contributes colorectal cancer cell plasticity by regulating lncRNA CCAT1 and NF-κB pathways

The CREB1 gene encodes an exceptionally pleiotropic transcription factor that frequently dysregulated in human cancers. CREB1 can regulate tumor cell status of proliferation and/or migration; however, the molecular basis for this switch involvement in cell plasticity has not fully been understood yet. Here, we first show that knocking out CREB1 triggers a remarkable effect of epithelial-mesenchymal transition (EMT) and leads to the occurrence of inhibited proliferation and enhanced motility in HCT116 colorectal cancer cells. By monitoring 45 cellular signaling pathway activities, we find that multiple growth-related pathways decline significantly while inflammatory pathways including NF-κB are largely upregulated in comparing between the CREB1 wild-type and knocked out cells. Mechanistically, cells with CREB1 knocked out show downregulation of MYC as a result of impaired CREB1-dependent transcription of the oncogenic lncRNA CCAT1. Interestingly, the unbalanced competition between the coactivator CBP/p300 for CREB1 and p65 leads to the activation of the NF-κB pathway in cells with CREB1 disrupted, which induces an obvious EMT phenotype of the cancer cells. Taken together, these studies identify previously unknown mechanisms of CREB1 in CRC cell plasticity via regulating lncRNA CCAT1 and NF-κB pathways, providing a critical insight into a combined strategy for CREB1-targeted tumor therapies.

Type IIB PKA is highly expressed in β cells and controls cell proliferation via regulating Cyclin D1 expression

β cell number is maintained mainly by cell proliferation and cell apoptosis. Protein kinase A (PKA) pathway is an important intracellular signalling-mediating β cell proliferation. However, the precise roles of PKA isoforms are not well-defined. We found that the RIIB subunit of PKA is expressed specifically by β cells of mouse and human islets. Sixty percent pancreatectomy caused increased β cell proliferation. Deletion of type IIB PKA by disruption of RIIB expression further promoted β cell proliferation, leading to enhanced β cell mass expansion. RIIB KO mice also showed increased insulin levels and improved glucose tolerance. Mechanistically, activation of type IIB PKA decreased Cyclin D1 levels and inhibition of RIIB expression increased Cyclin D1 levels. Consistently, activation of type IIB PKA inhibited cell cycle entry. These results suggest that type IIB PKA plays a pivotal role in β cell proliferation via regulating Cyclin D1 expression.

OCT1 Is a Poor Prognostic Factor for Breast Cancer Patients and Promotes Cell Proliferation via Inducing NCAPH

Octamer transcription factor 1 (OCT1) is a transcriptional factor reported to be a poor prognostic factor in various cancers. However, the clinical value of OCT1 in breast cancer is not fully understood. In the present study, an immunohistochemical study of OCT1 protein was performed using estrogen receptor (ER)-positive breast cancer tissues from 108 patients. Positive OCT1 immunoreactivity (IR) was associated with the shorter disease-free survival (DFS) of patients (p = 0.019). Knockdown of OCT1 inhibited cell proliferation in MCF-7 breast cancer cells as well as its derivative long-term estrogen-deprived (LTED) cells. On the other hand, the overexpression of OCT1 promoted cell proliferation in MCF-7 cells. Using microarray analysis, we identified the non-structural maintenance of chromosomes condensin I complex subunit H (NCAPH) as a novel OCT1-taget gene in MCF-7 cells. Immunohistochemical analysis showed that NCAPH IR was significantly positively associated with OCT1 IR (p < 0.001) and that positive NCAPH IR was significantly related to the poor DFS rate of patients (p = 0.041). The knockdown of NCAPH inhibited cell proliferation in MCF-7 and LTED cells. These results demonstrate that OCT1 and its target gene NCAPH are poor prognostic factors and potential therapeutic targets for patients with ER-positive breast cancer.

PDGF-BB-mediated activation of CREB in vascular smooth muscle cells alters cell cycling via Rb, FoxO1 and p27kip1

INTRODUCTION & AIM

The vascular response to injury leads to the secretion of several factors, including platelet-derived growth factor (PDGF-BB). PDGF-BB stimulates smooth muscle cell (SMC) conversion to the synthetic phenotype, thereby enhancing proliferation and migration, and contributing to neointimal hyperplasia. Likewise, the cAMP response element binding protein (CREB) transcription factor has been shown to mediate SMC proliferation in response to various mitogens. We therefore investigated the contribution of CREB to PDGF-BB-dependent proliferation of SMCs with the intention of identifying signaling pathways involved both up and downstream of CREB activation.

METHODS & RESULTS

Treatments were performed on vascular SMCs from a porcine coronary artery explant model. The role of CREB was examined via adenoviral expression of a dominant-negative CREB mutant (kCREB) as well as inhibition of CREB binding protein (CBP). Involvement of the p27^kip1 pathway was determined using a constitutively expressing p27^kip1 adenoviral vector. PDGF-BB stimulated transient CREB phosphorylation on Ser-133 via ERK1/2-, PI3-kinase- and Src-dependent pathways. Expression of kCREB decreased PDGF-BB-dependent cell proliferation. PCNA expression and Rb phosphorylation were also inhibited by kCREB. These cell cycle proteins are controlled via p27^kip1 expression in response to CREB-dependent post-translational modification of FoxO1. kCREB had no effect on Cyclin D1 expression, but did prevent PDGF-BB-induced Cyclin D1 nuclear translocation. An interaction inhibitor of CBP confirmed that Cyclin D1 is downstream of PDGF-BB and CREB.

CONCLUSION

CREB phosphorylation is required for SMC proliferation in response to PDGF-BB. This phenotypic change requires CBP and is mediated by Cyclin D1 and p27^kip as a result of changes in FoxO1 activity.

Pathological matrix stiffness promotes cardiac fibroblast differentiation through the POU2F1 signaling pathway

Cardiac fibroblast (CF) differentiation into myofibroblasts is a crucial cause of cardiac fibrosis, which increases in the extracellular matrix (ECM) stiffness. The increased stiffness further promotes CF differentiation and fibrosis. However, the molecular mechanism is still unclear. We used bioinformatics analysis to find new candidates that regulate the genes involved in stiffness-induced CF differentiation, and found that there were binding sites for the POU-domain transcription factor, POU2F1 (also known as Oct-1), in the promoters of 50 differentially expressed genes (DEGs) in CFs on the stiffer substrate. Immunofluorescent staining and Western blotting revealed that pathological stiffness upregulated POU2F1 expression and increased CF differentiation on polyacrylamide hydrogel substrates and in mouse myocardial infarction tissue. A chromatin immunoprecipitation assay showed that POU2F1 bound to the promoters of fibrosis repressors IL1R2, CD69, and TGIF2. The expression of these fibrosis repressors was inhibited on pathological substrate stiffness. Knockdown of POU2F1 upregulated these repressors and attenuated CF differentiation on pathological substrate stiffness (35 kPa). Whereas, overexpression of POU2F1 downregulated these repressors and enhanced CF differentiation. In conclusion, pathological stiffness upregulates the transcription factor POU2F1 to promote CF differentiation by inhibiting fibrosis repressors. Our work elucidated the crosstalk between CF differentiation and the ECM and provided a potential target for cardiac fibrosis treatment.

RUNX2 Promotes Malignant Progression in Glioma

Glioblastoma (GBM) is the most aggressive and lethal form of brain tumor. However, therapeutic strategies against malignant gliomas have not been completely established. Runt-related transcription factor 2 (Runx2) is an essential gene for skeletal development but its regulatory role in the malignant progression of glioma remains unclear. Here we investigated expression levels of RUNX2 in glioma tissues and its regulatory effects on aberrant growth of glioma cells. RUNX2 mRNA levels were higher in GBM tissues than that of normal brains or low-grade gliomas. RUNX2 protein was detected in five out of seven human GBM cell lines and its level was positively correlated with proliferative capacity. Stable transduction of dominant-negative Runx2 in rat-derived C6 glioma cells not only inhibited the promoter activity containing Runx2 response element, but also decreased mRNA expression levels of Runx2 target genes, such as Mmp13 and Spp1, as well as the proliferative capacity. Furthermore, transient introduction of Runx2-targeted siRNAs into C6 glioma cells significantly decreased mRNA expression levels of Mmp13 and Spp1 and the proliferative capacity. Furthermore, Runx2 knockdown suppressed both Ccnd1 mRNA expression and activation of the Ccnd1 promoter by forskolin, a PKA-activating reagent, in C6 glioma cells. Our results demonstrate that cross-talk between cAMP/PKA signaling and RUNX2 promotes a malignant phenotype of glioma cells.

POU2F1 over-expression correlates with poor prognoses and promotes cell growth and epithelial-to-mesenchymal transition in hepatocellular carcinoma

Despite recent efforts to understand activities of POU domain class 2 transcription factor 1 (POU2F1), little is known about the roles of POU2F1 in hepatocellular carcinoma (HCC) tumorigenesis and its correlation with any clinicopathological feature of HCC. In this study, we found that POU2F1 was significantly up-regulated in HCC specimens compared with adjacent non-cancerous liver specimens. The high POU2F1 protein expression level positively correlated with large tumor size, high histological grade, tumor metastasis and advanced clinical stage, and HCC patients with high POU2F1 levels exhibited poor prognoses. We further demonstrated that POU2F1 over-expression promoted HCC cell proliferation, colony formation, epithelial-to-mesenchymal transition (EMT), migration and invasion, while silencing of POU2F1 inhibited these malignant phenotypes. POU2F1 induced the expression of Twist1, Snai1, Snai2 and ZEB1 genes which are involved in the regulation of EMT. Furthermore, POU2F1 was up-regulated by AKT pathway in HCC, and POU2F1 over-expression reversed the inhibition of malignant phenotypes induced by AKT knock-down, indicating POU2F1 is a key down-stream effector of AKT pathway. Collectively, our results indicate that POU2F1 over-expression is positively associated with aggressive phenotypes and poor survival in patients with HCC, and POU2F1 regulated by AKT pathway promotes HCC aggressive phenotypes by regulating the transcription of EMT genes. POU2F1 may be employed as a new prognostic factor and therapeutic target for HCC.

Role of A-Kinase anchor protein (AKAP4) in growth and survival of ovarian cancer cells

Ovarian cancer represents one of the most common malignancies among women with very high mortality rate worldwide. A-kinase anchor protein 4 (AKAP4), a unique cancer testis (CT) antigen has been shown to be associated with various malignant properties of cancer cells. However, its involvement in various molecular pathways in ovarian cancer remains unknown. In present investigation, employing gene silencing approach, we examined the role of AKAP4 in cell cycle, apoptosis and epithelial-mesenchymal transition (EMT). Further, we also investigated the effect of ablation of AKAP4 on tumor growth in SCID mice ovarian cancer xenograft mouse model. Our results showed that ablation of AKAP4 resulted in increased reactive oxygen species (ROS) generation, DNA damage, cell cycle arrest and apoptosis in ovarian cancer cells. AKAP4 knockdown lead to degradation of protien kinase A (PKA) which was rescued by proteosome inhibitor MG-132. ROS quencher N-acetyl cysteine (NAC) treatment rescued cell cycle arrest and resumed cell division. Subsequently, increased expression of pro-apoptotic molecules and decreased expression of pro-survival/anti-apoptotic factors was observed. As a result of AKAP4 depletion, DNA damage response proteins p-γH2AX, p-ATM and p21 were upregulated. Also, knockdown of CREB resulted in similar findings. Further, PKA inhibitor (H89) and oxidative stress resulted in similar phenotype of ovarian cancer cells as observed in AKAP4 ablated cells. Collectively, for the first time our data showed the involvement of AKAP4 in PKA degradation and perturbed signaling through PKA-CREB axis in AKAP4 ablated ovarian cancer cells.

Human leucine zipper protein promotes hepatic steatosis via induction of apolipoprotein A-IV

The molecular mechanism of stress-induced hepatic steatosis is not well known. Human leucine zipper protein (LZIP) regulates the expression of genes involved in inflammation, cell migration, and stress response. The aim of this study was to determine the regulatory role of LZIP in stress-induced hepatic steatosis. We used a microarray analysis to identify LZIP-induced genes involved in hepatic lipid metabolism. LZIP increased the expression of apolipoprotein A-IV (APOA4) mRNA. In the presence of stress inducer, APOA4 promoter analysis was performed, and LZIP-induced lipid accumulation was monitored in mouse primary cells and human tissues. Under Golgi stress conditions, LZIP underwent proteolytic cleavage and was phosphorylated by AKT to protect against proteasome degradation. The stabilized N-terminal LZIP was translocated to the nucleus, where it directly bound to the APOA4 promoter, leading to APOA4 induction. LZIP-induced APOA4 expression resulted in increased absorption of surrounding free fatty acids. LZIP also promoted hepatic steatosis in mouse liver. Both LZIP and APOA4 were highly expressed in human steatosis samples. Our findings indicate that LZIP is a novel modulator of APOA4 expression and hepatic lipid metabolism. LZIP might be a therapeutic target for developing treatment strategies for hepatic steatosis and related metabolic diseases.-Kang, M., Kim, J., An, H.-T., Ko, J. Human leucine zipper protein promotes hepatic steatosis via induction of apolipoprotein A-IV.

The Oct1 transcription factor and epithelial malignancies: Old protein learns new tricks

The metazoan-specific POU domain transcription factor family comprises activities underpinning developmental processes such as embryonic pluripotency and neuronal specification. Some POU family proteins efficiently bind an 8-bp DNA element known as the octamer motif. These proteins are known as Oct transcription factors. Oct1/POU2F1 is the only widely expressed POU factor. Unlike other POU factors it controls no specific developmental or organ system. Oct1 was originally described to operate at target genes associated with proliferation and immune modulation, but more recent results additionally identify targets associated with oxidative and cytotoxic stress resistance, metabolic regulation, stem cell function and other unexpected processes. Oct1 is pro-oncogenic in multiple contexts, and several recent reports provide broad evidence that Oct1 has prognostic and therapeutic value in multiple epithelial tumor settings. This review focuses on established and emerging roles of Oct1 in epithelial tumors, with an emphasis on mechanisms of transcription regulation by Oct1 that may underpin these findings. This article is part of a Special Issue entitled: The Oct Transcription Factor Family, edited by Dr. Dean Tantin.

Small molecule inhibition of cAMP response element binding protein in human acute myeloid leukemia cells

The transcription factor CREB (cAMP Response-Element Binding Protein) is overexpressed in the majority of acute myeloid leukemia (AML) patients, and this is associated with a worse prognosis. Previous work revealed that CREB overexpression augmented AML cell growth, while CREB knockdown disrupted key AML cell functions in vitro. In contrast, CREB knockdown had no effect on long-term hematopoietic stem cell activity in mouse transduction/transplantation assays. Together, these studies position CREB as a promising drug target for AML. To test this concept, a small molecule inhibitor of CREB, XX-650-23, was developed. This molecule blocks a critical interaction between CREB and its required co-activator CBP (CREB Binding Protein), leading to disruption of CREB-driven gene expression. Inhibition of CBP-CREB interaction induced apoptosis and cell-cycle arrest in AML cells, and prolonged survival in vivo in mice injected with human AML cells. XX-650-23 had little toxicity on normal human hematopoietic cells and tissues in mice. To understand the mechanism of XX-650-23, we performed RNA-seq, ChIP-seq and Cytometry Time of Flight with human AML cells. Our results demonstrate that small molecule inhibition of CBP-CREB interaction mostly affects apoptotic, cell-cycle and survival pathways, which may represent a novel approach for AML therapy.

Selective CREB-dependent cyclin expression mediated by the PI3K and MAPK pathways supports glioma cell proliferation

The cyclic-AMP response element binding (CREB) protein has been shown to have a pivotal role in cell survival and cell proliferation. Transgenic rodent models have revealed a role for CREB in higher-order brain functions, such as memory and drug addiction behaviors. CREB overexpression in transgenic animals imparts oncogenic properties on cells in various tissues, and aberrant CREB expression is associated with tumours. It is the central position of CREB, downstream from key developmental and growth signalling pathways, which gives CREB this ability to influence a spectrum of cellular activities, such as cell survival, growth and differentiation, in both normal and cancer cells. We show that CREB is highly expressed and constitutively activated in patient glioma tissue and that this activation closely correlates with tumour grade. The mechanism by which CREB regulates glioblastoma (GBM) tumour cell proliferation involves activities downstream from both the mitogen-activated protein kinase and phosphoinositide 3-kinase (PI3K) pathways that then modulate the expression of three key cell cycle factors, cyclin B, D and proliferating cell nuclear antigen (PCNA). Cyclin D1 is highly CREB-dependent, whereas cyclin B1 and PCNA are co-regulated by both CREB-dependent and -independent mechanisms. The precise regulatory network involved appears to differ depending on the tumour-suppressor phosphatase and tensin homolog status of the GBM cells, which in turn allows CREB to regulate the activity of the PI3K itself. Given that CREB sits at the hub of key cancer cell signalling pathways, understanding the role of glioma-specific CREB function may lead to improved novel combinatorial anti-tumour therapies, which can complement existing PI3K-specific drugs undergoing early phase clinical trials.

YB-1 promotes transcription of cyclin D1 in human non-small-cell lung cancers

Cyclin D1, an oncogenic G1 cyclin, and YB-1, a transcription factor involved in cell growth, are both over-expressed in several human cancers. In human lung cancer, the functional association between YB-1 and cyclin D1 has never been elucidated. In this study, we show YB-1 is involved in the transcription of cyclin D1 in human lung cancer. Depletion of endogenous YB-1 by siRNA inhibited progression of G1 phase and down-regulated both the protein and mRNA levels of cyclin D1 in human lung cancer cells. Forced over-expression of YB-1 with a cyclin D1 reporter plasmid increased luciferase activity, and ChIP assay results showed YB-1 bound to the cyclin D1 promoter. Moreover, the amount of YB-1 mRNA positively correlated with cyclin D1 mRNA levels in clinical non-small-cell lung cancer (NSCLC) specimens. Immunohistochemical analysis also indicated YB-1 expression correlated with cyclin D1 expression in NSCLC specimens. In addition, most of the cases expressing both cyclin D1 and CDC6, another molecule controlled by YB-1, had co-existing YB-1 over-expression. Together, our results suggest that aberrant expression of both cyclin D1 and CDC6 by YB-1 over-expression may collaboratively participate in lung carcinogenesis.

T3 enhances thyroid cancer cell proliferation through TRβ1/Oct-1-mediated cyclin D1 activation

Several studies have demonstrated that thyroid hormone T3 promotes cancer cell growth, even though the molecular mechanism involved in such processes still needs to be elucidated. In this study we demonstrated that T3 induced proliferation in papillary thyroid carcinoma cell lines concomitantly with an up-regulation of cyclin D1 expression, that is a critical mitogen-regulated cell-cycle control element. Our data revealed that T3 enhanced the recruitment of the TRβ1/Oct-1 complex on Octamer-transcription factor-1 site within cyclin D1 promoter, leading to its transactivation. In addition, silencing of TRβ1 or Oct-1 expression by RNA interference reversed both increased cell proliferation and up-regulation of cyclin D1, underlying the important role of both transcriptional factors in mediating these effects. Finally, T3-induced increase in cell growth was abrogated after knocking down cyclin D1 expression. All these findings highlight a new molecular mechanism by which T3 promotes thyroid cancer cell growth.

H2A.Z-dependent crosstalk between enhancer and promoter regulates cyclin D1 expression

H2A.Z association with specific genomic loci is thought to contribute to a chromatin structure that promotes transcription activation. Acetylation of H2A.Z at promoters of oncogenes has been linked to tumorigenesis. The mechanism is unknown. Here, we show that in triple negative breast cancer cells, H2A.Z bound to the promoter of the constitutively, weakly expressed cyclin D1 oncogene (CCND1), a key regulator of cellular proliferation. Depleting the pool of H2A.Z stimulated transcription of CCND1 in the absence of its cognate transcription factor, the estrogen receptor (ER). During activation of CCND1, H2A.Z was released from the transcription start site (TSS) and downstream enhancer (enh2) sequences. Concurrently, acetylation of H2A.Z, H3 and H4 at the TSS was increased but only H2A.Z was acetylated at enh2. Acetylation of H2A.Z required the Tip60 acetyltransferase to be associated with the activated CCND1 on both TSS and enh2 sites. Depletion of Tip60 prevented CCND1 activation. Chromosome conformation capture experiments (3C) revealed specific contacts between the TSS and enh2 chromatin regions. These results suggest that release of a histone H2A.Z-mediated repression loop activates CCND1 for transcription. Our findings open new avenues for controlling and understanding aberrant gene expression associated with tumorigenesis.

STAT3-driven upregulation of TLR2 promotes gastric tumorigenesis independent of tumor inflammation

Gastric cancer (GC) is associated with chronic inflammation; however, the molecular mechanisms promoting tumorigenesis remain ill defined. Using a GC mouse model driven by hyperactivation of the signal transducer and activator of transcription (STAT)3 oncogene, we show that STAT3 directly upregulates the epithelial expression of the inflammatory mediator Toll-like receptor (TLR)2 in gastric tumors. Genetic and therapeutic targeting of TLR2 inhibited gastric tumorigenesis, but not inflammation, characterized by reduced proliferation and increased apoptosis of the gastric epithelium. Increased STAT3 pathway activation and TLR2 expression were also associated with poor GC patient survival. Collectively, our data reveal an unexpected role for TLR2 in the oncogenic function of STAT3 that may represent a therapeutic target in GC.

CD44 proteolysis increases CREB phosphorylation and sustains proliferation of thyroid cancer cells

CD44 is a marker of cancer stem-like cells and epithelial-mesenchymal transition that is overexpressed in many cancer types, including thyroid carcinoma. At extracellular and intramembranous domains, CD44 undergoes sequential metalloprotease- and γ-secretase-mediated proteolytic cleavage, releasing the intracellular protein fragment CD44-ICD, which translocates to the nucleus and activates gene transcription. Here, we show that CD44-ICD binds to the transcription factor CREB, increasing S133 phosphorylation and CREB-mediated gene transcription. CD44-ICD enhanced CREB recruitment to the cyclin D1 promoter, promoting cyclin D1 transcription and cell proliferation. Thyroid carcinoma cells harboring activated RET/PTC, RAS, or BRAF oncogenes exhibited CD44 cleavage and CD44-ICD accumulation. Chemical blockade of RET/PTC, BRAF, metalloprotease, or γ-secretase were each sufficient to blunt CD44 processing. Furthermore, thyroid cancer cell proliferation was obstructed by RNA interference-mediated knockdown of CD44 or inhibition of γ-secretase and adoptive CD44-ICD overexpression rescued cell proliferation. Together, these findings reveal a CD44-CREB signaling pathway that is needed to sustain cancer cell proliferation, potentially offering new molecular targets for therapeutic intervention in thyroid carcinoma.

Sp1 phosphorylation by cyclin-dependent kinase 1/cyclin B1 represses its DNA-binding activity during mitosis in cancer cells

Sp1 is important for the transcription of many genes. Our previous studies have shown that Sp1 is degraded in normal cell, but it is preserved in cancer cells during mitosis and exists a priori in the daughter cells, ready to engage in gene transcription and thereby contributes to the proliferation and survival of cancer cells. The mechanism by which Sp1 is preserved in cancer cells during mitosis remains unknown. In this study, we observed that Sp1 strongly colocalized with cyclin-dependent kinase 1 (CDK1)/cyclin B1 during mitosis. Moreover, we showed that Sp1 is a novel mitotic substrate of CDK1/cyclin B1 and is phosphorylated by it at Thr 739 before the onset of mitosis. Phospho-Sp1 reduced its DNA-binding ability and facilitated the chromatin condensation process during mitosis. Mutation of Thr739 to alanine resulted in Sp1 remaining in the chromosomes, delayed cell-cycle progression, and eventually led to apoptosis. Screening of Sp1-associated proteins during mitosis by using liquid chromatography/mass spectrometry indicated the tethering of Sp1 to myosin/F-actin. Furthermore, phospho-Sp1 and myosin/F-actin appeared to exist as a congregated ring at the periphery of the chromosome. However, at the end of mitosis and the beginning of interphase, Sp1 was dephosphorylated by PP2A and returned to the chromatin. These results indicate that cancer cells use CDK1 and PP2A to regulate the movement of Sp1 in and out of the chromosomes during cell-cycle progression, which may benefit cancer-cell proliferation.

Reactive oxygen species downregulate catalase expression via methylation of a CpG island in the Oct-1 promoter

Reactive oxygen species (ROS) caused oxidative stress plays a key role in carcinogenesis. The POU domain transcription factor Oct-1 and catalase is closely associated with ROS. However, a correlation between these two key proteins has not been demonstrated before. In this report, we show that Oct-1 acts as an activator of catalase, by binding to the catalase promoter in hepatocellular carcinoma (HCC) cell lines. In addition, we suggest that Oct-1 is downregulated by ROS via CpG island methylation in its promoter. These findings contribute to a better understanding of the epigenetic changes induced by ROS in the process of carcinogenesis.

POU homeodomain protein OCT1 modulates islet 1 expression during cardiac differentiation of P19CL6 cells

Islet 1 (ISL1), a marker of cardiac progenitors, plays a crucial role in cardiogenesis. However, the precise mechanism underlying the activation of its expression is not fully understood. Using the cardiac differentiation model of P19CL6 cells, we show that POU homeodomain protein, OCT1, modulates Isl1 expression in the process of cardiac differentiation. Oct1 knock-down resulted in reduction of Isl1 expression and downregulated mesodermal, cardiac-specific, and signal pathway gene expression. Additionally, the octamer motif located in the proximal region of Isl1 promoter is essential to Isl1 transcriptional activation. Mutation of this motif remarkably decreased Isl1 transcription. Although both OCT1 and OCT4 bound to this motif, it was OCT1 rather than OCT4 that modulated Isl1 expression. Furthermore, the correlation of OCT1 in regulation of Isl1 was revealed by in situ hybridization in early embryos. Collectively, our data highlight a novel role of OCT1 in the regulation of Isl1 expression.

The elements of human cyclin D1 promoter and regulation involved

Cyclin D1 is a cell cycle machine, a sensor of extracellular signals and plays an important role in G1-S phase progression. The human cyclin D1 promoter contains multiple transcription factor binding sites such as AP-1, NF-қB, E2F, Oct-1, and so on. The extracellular signals functions through the signal transduction pathways converging at the binding sites to active or inhibit the promoter activity and regulate the cell cycle progression. Different signal transduction pathways regulate the promoter at different time to get the correct cell cycle switch. Disorder regulation or special extracellular stimuli can result in cell cycle out of control through the promoter activity regulation. Epigenetic modifications such as DNA methylation and histone acetylation may involved in cyclin D1 transcriptional regulation.

A novel mouse c-fos intronic promoter that responds to CREB and AP-1 is developmentally regulated in vivo

Background

The c-fos proto-oncogene is an archetype for rapid and integrative transcriptional activation. Innumerable studies have focused on the canonical promoter, located upstream from the transcriptional start site. However, several regulatory sequences have been found in the first intron.

Methodology/Principal Findings

Here we describe an extremely conserved region in c-fos first intron that contains a putative TATA box, and functional TRE and CRE sites. This fragment drives reporter gene activation in fibroblasts, which is enhanced by increasing intracellular calcium and cAMP and by cotransfection of CREB or c-Fos/c-Jun expression vectors. We produced transgenic mice expressing a lacZ reporter controlled by the intronic promoter. Lac Z expression of this promoter is restricted to the developing central nervous system (CNS) and the mesenchyme of developing mammary buds in embryos 12.5 days post-conception, and to brain tissue in adults. RT-QPCR analysis of tissue mRNA, including the anlage of the mammary gland and the CNS, confirms the existence of a novel, nested mRNA initiated in the first intron.

Conclusions/Significance

Our results provide evidence for a novel, developmentally regulated promoter in the first intron of the c-fos gene.

Insulin stimulates the expression of carbohydrate response element binding protein (ChREBP) by attenuating the repressive effect of Pit-1, Oct-1/Oct-2, and Unc-86 homeodomain protein octamer transcription factor-1

The carbohydrate response element binding protein (ChREBP) has been recognized as a key controller of hepatic lipogenesis. Whereas the function of ChREBP has been extensively investigated, mechanisms underlying its transcription remain largely unknown, although ChREBP production is elevated in a hyperinsulinemic mouse model. We located a conserved Pit-1, Oct-1/Oct-2, and Unc-86 (POU) protein binding site (ATGCTAAT) within the proximal promoter region of human ChREBP. This site interacts with the POU homeodomain protein octamer transcription factor-1 (Oct-1), as detected by gel shift and chromatin immunoprecipitation assays. Oct-1 cotransfection in the human HepG2 cell line repressed ChREBP promoter activity approximately 50-75% (P < 0.01 to P < 0.001), and this repression was dependent on the existence of the POU binding site. Furthermore, overexpression of Oct-1 repressed endogenous ChREBP mRNA and protein expression, whereas knockdown of Oct-1 expression, using a lentivirus-based small hairpin RNA approach, led to increased ChREBP mRNA and protein expression. In contrast, HepG2 cells treated with 10 or 100 nM insulin for 4 or 8 h resulted in an approximately 2-fold increase of ChREBP promoter activity (P < 0.05 to P < 0.01). Insulin (10 nM) also stimulated endogenous ChREBP expression in HepG2 and primary hamster hepatocytes. More importantly, we found that the stimulatory effect of insulin on ChREBP promoter activity was dependent on the presence of the POU binding site, and insulin treatment reduced Oct-1 expression levels. Our observations therefore identify Oct-1 as a transcriptional repressor of ChREBP and suggest that insulin stimulates ChREBP expression via attenuating the repressive effect of Oct-1.

Technological advances in the study of HLA-DRA promoter regulation: extending the functions of CIITA, Oct-1, Rb, and RFX

Several advances were established in examining the interaction of transcriptional factors with the HLA-DRA promoter. First, hydrodynamic injection was used to demonstrate the activation of the promoter by class II transactivator in a live mouse. Second, the Oct-1 DNA-binding site in the HLA-DRA promoter is a negative element in many cells, but here we show that Oct-1 activates the promoter independently of the Oct-1-binding site. Third, the retinoblastoma (Rb) protein is required for the induction of the endogenous HLA-DRA gene, due to a poorly understood, pleiotropic effect on the Oct-1 and YY1 repressive functions at the HLA-DRA promoter. There has never been an indication that direct promoter activation, by Rb, is possible. Here, we report that the first HLA-DRA intron has an Rb-responsive element, as indicated by a transient transfection/promoter reporter assay. Finally, RFX activates a methylated version of an HLA-DRA promoter reporter construct, consistent with the role of RFX in rescuing the expression of the methylated, endogenous HLA-DRA gene. Here, we report that this RFX function is not limited to a specific RFX-binding sequence or to the HLA-DRA promoter. These advances provide bases for novel investigations into the function of the major histocompatibility class II promoter.

NDRG2 suppresses cell proliferation through down-regulation of AP-1 activity in human colon carcinoma cells

Recently, the anti-tumor activity of N-myc downstream-regulated gene 2 (NDRG2) was elucidated, but the molecular mechanism of how NDRG2 works as a tumor suppressor is not well known. To determine the function of NDRG2 as a tumor suppressor, we established stable cell lines expressing NDRG2 protein or its mutant forms, and studied their effects on tumor cell growth. Interestingly, constitutive expression of wild-type NDRG2 induced the growth retardation of SW620 colon carcinoma cells. Introduction of NDRG2 into SW620 cells induced the decrease of c-Jun phosphorylation at Ser63, followed by the attenuation of activator protein-1 (AP-1) function as a transcriptional activator. Subsequently, the down-regulation of cyclin D1, which is known as a major target for AP-1 transcription activator, resulted in cell cycle arrest at G1/S phase. Additionally, treatment of NDRG2-siRNA on NDRG2-expressing cells has induced the recovery of c-Jun phosphorylation and cyclin D1 expression. Cell proliferation of those cells was also increased compared with untreated cells. NDRG2 mutants of which the phosphorylation sites at C-terminal region were removed by deletion or site-directed mutagenesis have shown no effect on cyclin D1 expression and could not induce cell growth retardation. In conclusion, NDRG2 modulates intracellular signals to control cell cycle through the regulation of cyclin D1 expression via phosphorylation pathway.

Oct-1 induces pituitary tumor transforming gene expression in endocrine tumors

As human pituitary tumor transforming gene (hPTTG1) is upregulated in endocrine tumors, we studied regulatory mechanisms for hPTTG1 expression. We identified Oct-1-binding motifs in the hPTTG1 promoter region and show Oct-1-specific binding to the hPTTG1 promoter using chromatin immunoprecipitation. We overexpressed Oct-1 and observed approximately 2.5-fold activation of hPTTG1 promoter luciferase constructs (-2642/-1 and -1717/-1). Transcriptional activation was abrogated by co-transfection of an inactive Oct-1 form lacking the POU domain or by utilizing mutated hPTTG1 promoters or mutants devoid of two Oct-1-binding motifs (-1717/-1mut, -637/-1 or -433/-1). Using biotin-streptavidin pull-down assays, we confirmed Oct-1 binding to the two octamer motifs in the hPTTG1 promoter (-1669/-1631 and -1401/-1361). Endogenous hPTTG1 mRNA and protein increased up to approximately fourfold in Oct-1 transfectants, as measured by real-time PCR and western blot. In contrast, siRNA-mediated suppression of endogenous Oct-1 attenuated both the hPTTG1 mRNA and protein levels. Using confocal immunofluorescence imaging, Oct-1 and hPTTG1 were concordantly upregulated in pituitary (57 and 62%, n=79, P<0.01) and breast tumor specimens (57 and 42%, n=77, P<0.05) respectively. The results show that Oct-1 transactivates hPTTG1, and both proteins are concordantly overexpressed in endocrine tumors, thus offering a mechanism for endocrine tumor hPTTG1 abundance.

Transvection mediated by the translocated cyclin D1 locus in mantle cell lymphoma

In mantle cell lymphoma (MCL) and some cases of multiple myeloma (MM), cyclin D1 expression is deregulated by chromosome translocations involving the immunoglobulin heavy chain (IgH) locus. To evaluate the mechanisms responsible, gene targeting was used to study long-distance gene regulation. Remarkably, these targeted cell lines lost the translocated chromosome (t(11;14)). In these MCL and MM cells, the nonrearranged cyclin D1 (CCND1) locus reverts from CpG hypomethylated to hypermethylated. Reintroduction of the translocated chromosome induced a loss of methylation at the unrearranged CCND1 locus, providing evidence of a transallelic regulatory effect. In these cell lines and primary MCL patient samples, the CCND1 loci are packaged in chromatin-containing CCCTC binding factor (CTCF) and nucleophosmin (NPM) at the nucleolus. We show that CTCF and NPM are bound at the IgH 3′ regulatory elements only in the t(11;14) MCL cell lines. Furthermore, NPM short hairpin RNA produces a specific growth arrest in these cells. Our data demonstrate transvection in human cancer and suggest a functional role for CTCF and NPM.

Inhibitory role of TGIF in the As2O3-regulated p21 WAF1/CIP1 expression

Although arsenic is an infamous carcinogen, it has been effectively used to treat acute promyelocytic leukemia, and can induce cell cycle arrest or apoptosis in human solid tumors. Previously, we had demonstrated that opposing effects of ERK1/2 and JNK on p21 expression in response to arsenic trioxide (As(2)O(3)) are mediated through the Sp1 responsive elements of the p21 promoter in A431 cells. Presently, we demonstrate that Sp1, and c-Jun functionally cooperate to activate p21 promoter expression through Sp1 binding sites (-84/-64) by using DNA affinity binding, chromatin immunoprecipitation, and promoter assays. Surprisingly, As(2)O(3)-induced c-Jun(Ser63/73) phosphorylation can recruit TGIF/HDAC1 to the Sp1 binding sites and then suppress p21 promoter activation. We suggest that, after As(2)O(3 )treatment, the N-terminal domain of c-Jun phosphorylation by JNK recruits TGIF/HDAC1 to the Sp1 sites and then represses p21 expression. That is, TGIF is involved in As(2)O(3)-inhibited p21 expression, and then blocks the cell cycle arrest.

ARA54 is involved in transcriptional regulation of the cyclin D1 gene in human cancer cells

Cyclin D1 is one of the major enhancers of cell cycle progression and its expression is regulated in several growth stimulatory signaling pathways. ARA54 is an androgen receptor (AR) co-activator that enhances AR-dependent transcriptional activation. Although expression of ARA54 mRNA is observed in a variety of human tissues at low levels, the AR- or androgen-independent function of ARA54 in those tissues remains unclear. In this study, we identified a novel role for ARA54 in the regulation of cyclin D1 expression in the absence of AR stimulation in human cancer cells. Depletion of endogenous ARA54 by small interfering RNA decreased both the protein and mRNA levels of cyclin D1. These changes did not result from a reduction in the half-life of either the protein or the mRNA, but from suppression of cyclin D1 gene transcription. In T98G cells, depletion of ARA54 increased the population of cells in G(1) phase, but reduced the population of cells in S phase, leading to a significant increase in the G(1)/S ratio and impaired cell growth. Furthermore, the amount of ARA54 mRNA appeared to positively correlate with cyclin D1 mRNA levels in specimens of clinical colon carcinomas, indicating that ARA54 is not only involved in the regulation of cyclin D1 expression in cultured cell lines but also in clinical cancer specimens. These results suggest that ARA54 might participate in enhancing cell cycle progression and cell proliferation via induction of cyclin D1.

Regulation of the rat CYP4A2 gene promoter by c-Jun and octamer binding protein-1

The physiologically important cytochrome P450 (CYP) 4A2 arachidonic acid omega-hydroxylase gene is widely expressed in rat tissues. Although the induction of CYPs 4A by peroxisome proliferators and dietary lipids is established there is minimal information on the factors that control constitutive expression. To address this issue we cloned 1.4 kb of the CYP4A2 5'-upstream region and identified several DNA elements that resembled the activator protein-1 (AP-1) consensus sequence. Using a series of 5'-truncated reporter constructs a 42 bp region was detected that was responsive to the AP-1 factor c-Jun, which is important in basal gene regulation. The roles of two putative AP-1 elements at -47/-41 and -31/-25 were tested, with the former emerging from studies with mutagenised constructs as the functionally important site. These findings were supported by electromobility shift assay (EMSA) studies that indicated the interaction of the -47/-41 element with c-Jun. The -31/-25 element mediated the suppression of CYP4A2 transactivation by octamer binding protein-1 (oct-1). Thus, mutagenesis of this element relieved the modulatory effect of oct-1 on c-Jun-mediated transactivation. In EMSAs, the binding of nuclear proteins to the -31/-25 element was competed by an oct-1 consensus sequence and supershifted by an anti-oct-1 antibody. Overexpression of c-Jun in rat liver-derived H4IIE cells increased CYP4A2 mRNA to approximately 2-fold of control, but oct-1 overexpression was without significant effect. From chromatin immunoprecipitation assays both c-Jun and oct-1 bound to the CYP4A2 5'-upstream sequence in H4IIE cells. These findings implicate c-Jun and oct-1 as potentially important constitutive factors that modulate the transactivation of the CYP4A2 gene promoter.

Coregulated ataxia telangiectasia-mutated and casein kinase sites modulate cAMP-response element-binding protein-coactivator interactions in response to DNA damage

The cyclic AMP-response element-binding protein (CREB) is a bZIP family transcription factor implicated as an oncoprotein and neuron survival factor. CREB is activated in response to cellular stimuli, including cAMP and Ca(2+), via phosphorylation of Ser-133, which promotes interaction between the kinase-inducible domain (KID) of CREB and the KID-interacting domain of CREB-binding protein (CBP). We previously demonstrated that the interaction between CREB and CBP is inhibited by DNA-damaging stimuli through a mechanism whereby CREB is phosphorylated by the ataxia telangiectasia-mutated (ATM) protein kinase. We now show that the ATM phosphorylation sites in CREB are functionally intertwined with a cluster of coregulated casein kinase (CK) sites. We demonstrate that DNA damage-induced phosphorylation of CREB occurs in three steps. The initial event in the CREB phosphorylation cascade is the phosphorylation of Ser-111, which is carried out by CK1 and CK2 under basal conditions and by ATM in response to ionizing radiation. The phosphorylation of Ser-111 triggers the CK2-dependent phosphorylation of Ser-108 and the CK1-dependent phosphorylation of Ser-114 and Ser-117. The phosphorylation of Ser-114 and Ser-117 by CK1 then renders CREB permissive for ATM-dependent phosphorylation on Ser-121. Mutation of Ser-121 alone abrogates ionizing radiation-dependent repression of CREB-CBP complexes, which can be recapitulated using a CK1 inhibitor. Our findings outline a complex mechanism of CREB phosphorylation in which coregulated ATM and CK sites control CREB transactivation potential by modulating its CBP-binding affinity. The coregulated ATM and CK sites identified in CREB may constitute a signaling motif that is common to other DNA damage-regulated substrates.

Role for Brm in Cell Growth Control

Recently, we have shown implication of Brm, the catalytic subunit of the SWI/SNF chromatin remodeling complex, in repression of cyclin A expression in quiescent cells. Here, we have examined the fate of cells lacking Brm throughout the cycle. We find that despite elevated levels of cyclins A and E, these cells can respond to serum starvation, however, without reaching a canonical G(0) phase as they continue to express high levels of c-Myc and have an abnormally large average size. The response to serum starvation can be correlated with increased levels of Rb proteins p130 and p107 as well as increased association of p27 with the cyclin-dependent kinases, possibly compensating for the higher levels of G(1) cyclins by reducing their associated kinase activity. After serum stimulation, reentry into the cycle occurs normally, but the S phase is delayed and shorter. In addition, the M phase has an increased duration, and we observed frequent faulty chromosome segregation events in anaphase. Altogether, our data suggest that cells can partially overcome the absence of Brm by activating several compensatory mechanisms to control the cell cycle. However, they remain profoundly affected, unable to enter a canonical quiescent state, presenting a shorter S phase, and finally unable to perform correct chromosome segregation.

Sp1 deacetylation induced by phorbol ester recruits p300 to activate 12(S)-lipoxygenase gene transcription

We previous reported that Sp1 recruits c-Jun to the promoter of the 12(S)-lipoxygenase gene in 12-myristate 13-acetate-treated cells. We now show that Sp1 that recruited HDAC1 to the Sp1/cJun complex was constitutively acetylated when cells were exposed to phorbol 12-myristate 13-acetate (PMA) (3 h). Prolonged stimulation of the cells with PMA (9 h), however, caused the dissociation of histone deacetylase 1 (HDAC1) and the deacetylation of Sp1, with the latter being able to recruit p300 that in turn caused the acetylation and dissociation of histone 3, thus enhancing the expression of 12(S)-lipoxygenase. We also overexpressed an Sp1 mutant (K703/A, lacking acetylation sites) in the cell and found that cells recruited more p300 and expressed more 12(S)-lipoxygenase. Taken together, our results indicated that Sp1 recruits HDAC1 together with c-Jun to the gene promoter, followed by deacetylation of Sp1 upon PMA treatment. p300 is then recruited to the gene promoter through the interaction with deacetylated Sp1 to acetylate histone 3, leading to the enhancement of the expression of 12(S)-lipoxygenase.

Role of strain differences on host resistance and the transcriptional response of macrophages to infection withYersinia enterocolitica

The outcome of a host-pathogen encounter is determined by virulence factors of the pathogen and defense factors of the host. We characterized the impact of host factors [resistant (C57BL/6) or susceptible (BALB/c) genetic background and exposure to interferon (IFN)-γ] on transcriptional responses of bone marrow-derived macrophages (BMDM) to infection with Yersinia enterocolitica. IFN-γ treatment more profoundly altered the transcriptome of BMDM than did bacterial infection or genetic background. In BALB/c BMDM, 1,161 genes were differentially expressed in response to Yersinia infection with or without IFN-γ prestimulation. Fourteen genes (1.2%) could only be induced by BALB/c BMDM in response to Yersinia infection after IFN-γ pretreatment. These genes inhibit apoptosis, activate NF-κB and Erk signaling, are chemotactic to neutrophils, and are involved in cytoskeletal reorganization, hence possibly in phagocytosis. Ten of these genes possess a common module of binding sites for Hox, Pou, and Creb transcription factors in 2 kb of upstream genomic sequence, suggesting a possible novel role of these transcription factors in regulation of immune responses. Fifty-two of one thousand fifty differentially expressed genes (4.9%) were induced more strongly by C57BL/6 BMDM in response to Yersinia infection than BALB/c BMDM. These genes activate NK cells, have antibacterial properties, or are involved in sensing chemokines and lipopolysaccharide (LPS). These data show that host resistance factors modulate a surprisingly small, but identifiable and functionally significant, portion of the macrophage transcriptome in response to Yersinia infection.

Cyclin D1 and p21 is elevated in the giant cells of giant cell tumors

Alterations of cell cycle regulatory proteins, especially those that regulate G1 to S transition, have been implicated in the pathogenesis of a wide variety of human tumors. In previous studies we showed that that there is overexpression of cyclin D1 protein predominately in the giant cell component of giant cell tumors of bone. The purpose of this study was to investigate the mechanisms that may be responsible for cyclin D1 accumulation in giant cell tumors. Giant cell tumors have high levels of cyclin D1 mRNA and the giant cell-enriched population of these tumors have significantly more mRNA and protein expression of cyclin D1 than the mononuclear cell population. The giant cells also expressed higher levels of p21 protein and more p21 bound to cyclin D1 than the mononuclear cells. It is possible that p21 may be contributing to the cyclin D1 accumulation that occurs in the giant cells and perhaps even giant cell formation in these tumors. Additional studies are required to confirm the role of p21 in the pathogenesis of these tumors.

The octamer binding transcription factor Oct-1 is a stress sensor

The POU-domain transcription factor Oct-1 is widely expressed in adult tissues and has been proposed to regulate a large group of target genes. Microarray expression profiling was used to evaluate gene expression changes in Oct-1-deficient mouse fibroblasts. A number of genes associated with cellular stress exhibited altered expression. Consistent with this finding, Oct-1-deficient fibroblasts were hypersensitive to gamma radiation, doxorubicin, and hydrogen peroxide and harbored elevated reactive oxygen species. Expression profiling identified a second group of genes dysregulated in Oct-1-deficient fibroblasts following irradiation, including many associated with oxidative and metabolic stress. A number of these genes contain octamer sequences in their immediate 5' regulatory regions, some of which are conserved in human. These results indicate that Oct-1 modulates the activity of genes important for the cellular response to stress.

The proliferative status of thyrotropes is dependent on modulation of specific cell cycle regulators by thyroid hormone

In this report we have examined changes in cell growth parameters, cell cycle effectors, and signaling pathways that accompany thyrotrope growth arrest by thyroid hormone (TH) and growth resumption after its withdrawal. Flow cytometry and immunohistochemistry of proliferation markers demonstrated that TH treatment of thyrotrope tumors resulted in a reduction in the fraction of cells in S-phase that is restored upon TH withdrawal. This is accompanied by dephosphorylation and rephosphorylation of retinoblastoma (Rb) protein. The expression levels of cyclin-dependent kinase 2 and cyclin A, as well as cyclin-dependent kinase 1 and cyclin B, were decreased by TH, and after withdrawal not only did these regulators of Rb phosphorylation and mitosis increase in their expression but so too did the D1 and D3 cyclins. We also noted a rapid induction and subsequent disappearance of the type 5 receptor for the growth inhibitor somatostatin with TH treatment and withdrawal, respectively. Because somatostatin can arrest growth by activating MAPK pathways, we examined these pathways in TtT-97 tumors and found that the ERK pathway and several of its upstream and downstream effectors, including cAMP response element binding protein, were activated with TH treatment and deactivated after its withdrawal. This led to the hypothesis that TH, acting through increased type 5 somatostatin receptor, could activate the ERK pathway leading to cAMP response element binding protein-dependent decreased expression of critical cell cycle proteins, specifically cyclin A, resulting in hypophosphorylation of Rb and its subsequent arrest of S-phase progression. These processes are reversed when TH is withdrawn, resulting in an increase in the fraction of S-phase cells.

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.

Calcium/calmodulin-dependent kinase I and calcium/calmodulin-dependent kinase kinase participate in the control of cell cycle progression in MCF-7 human breast cancer cells

Calcium is universally required for cell growth and proliferation. Calmodulin is the main intracellular receptor for calcium. Although calcium and calmodulin are well known to be required for cell cycle regulation, the target pathways for their action remain poorly defined. Potential targets include the calcium/calmodulin-dependent kinases (CaM-K). The aim of this study was to determine the role of the CaM-Ks on cell proliferation and progress through the cell cycle in breast cancer cells. CaM-KI inhibition with either KN-93 or specific interfering RNA (siRNA) caused an arrest in the cell cycle in the human breast cancer cell line, MCF-7. This arrest occurred in the G(1) phase of the cell cycle. Supporting this finding, CaM-K inhibition using KN-93 also resulted in a reduction of cyclin D1 protein and pRb phosphorylation when cells were compared with control cultures. Furthermore, inhibition of the upstream activator of CaM-KI, CaM-KK, using siRNA also resulted in cell cycle arrest. In summary, CaM-KK and CaM-KI participate in the control of the G(0)-G(1) restriction check point of the cell cycle in human breast cancer cells. This arrest seems due to an inhibition in cyclin D1 synthesis and a reduction in pRb phosphorylation. To the best of our knowledge, this is the first time that CaM-KK has been reported to be involved in mammalian cell cycle regulation and that CaM-Ks are regulating breast cancer cell cycle.

Prolactin signals via Stat5 and Oct-1 to the proximal cyclin D1 promoter

Prolactin (PRL) modulates proliferation in the mammary gland and other tissues, in part through inducing transcription of cyclin D1, a key regulator of G(1) phase cell cycle progression. We showed previously that PRL, via Jak2, induces binding of Stat5 to a distal GAS site (GAS1) in the cyclin D1 promoter. However, full promoter activity requires additional regions, and in this paper we explored PRL-induced activity at sites other than GAS1. We defined a second PRL-responsive region spanning -254 to -180 that contains a second GAS site (GAS2) and an Oct-1 binding site. Although mutational analysis indicated independence from GAS2, proximal promoter activity remained Stat5-dependent, suggesting alternative mechanisms. EMSA showed that Oct-1 binds the -254 to -180 region and that PRL decreased Oct-1 binding, leading to increased PRL-responsiveness of the proximal cyclin D1 promoter in multiple cell lines. This suggests a role for Oct-1 in PRL-dependent control of cyclin D1 transcription.

Activation of CREB/ATF sites by polyomavirus large T antigen

Polyomavirus large T antigen (LT) has a direct role in viral replication and a profound effect on cell phenotype. It promotes cell cycle progression, immortalizes primary cells, blocks differentiation, and causes apoptosis. While much of large T function is related to its effects on tumor suppressors of the retinoblastoma susceptibility (Rb) gene family, we have previously shown that activation of the cyclin A promoter can occur through a non-Rb-dependent mechanism. Here we show that activation occurs via an ATF/CREB site. Investigation of the mechanism indicates that large T can synergize with CREB family members to activate transcription. Experiments with Gal4-CREB constructs show that synergy is independent of CREB phosphorylation by protein kinase A. Examination of synergy with Gal4-CREB deletion constructs indicates that large T acts on the constitutive activation domain of CREB. Large T can bind to CREB in vivo. Genetic analysis shows that the DNA-binding domain (residues 264 to 420) is sufficient to activate transcription when it is localized to the nucleus. Further analysis of the DNA-binding domain shows that while site-specific DNA binding is not required, non-site-specific DNA binding is important for the activation. Thus, CREB binding and DNA binding are both important for large T activation of CREB/ATF sites. In contrast to previous models where large T transactivation occurred indirectly, these results also suggest that large T can act directly at promoters to activate transcription.

Pea3 Transcription Factor Cooperates with USF-1 in Regulation of the Murine bax Transcription without Binding to an Ets-binding Site

The Pea3 transcription factor (which belongs to the PEA3 group) from the Ets family has been shown to be involved in mammary embryogenesis and oncogenesis. However, except for proteinases, only few of its target genes have been reported. In the present report, we identified bax as a Pea3 up-regulated gene. We provide evidence of this regulation by using Pea3 overexpression and Pea3 silencing in a mammary cell line. Both Pea3 and Erm, another member of the PEA3 group, are able to transactivate bax promoter fragments. Although the minimal Pea3-regulated bax promoter does not contain an Ets-binding site, two functional upstream stimulatory factor-regulated E boxes are present. We further demonstrate the ability of Pea3 and USF-1 to cooperate for the transactivation of the bax promoter, mutation of the E boxes dramatically reducing the Pea3 transactivation potential. Although Pea3 did not directly bind to the minimal bax promoter, we provide evidence that USF-1 could form a ternary complex with Pea3 and DNA. Taken together, our results suggest that Pea3 may regulate bax transcription via the interaction with USF-1 but without binding to DNA.

What turns CREB on?

The transactivation domain of the cAMP response element-binding protein (CREB) consists of two major domains. The glutamine-rich Q2 domain, which interacts with the general transcription factor TAFII130/135, is sufficient for the recruitment of a functional RNA polymerase II complex and allows basal transcriptional activity. The kinase-inducible domain, however, mediates signal-induced activation of CREB-mediated transcription. It is generally believed that recruitment of the coactivators CREB-binding protein (CBP) and p300 after signal-induced phosphorylation of this domain at serine-133 strongly enhances CREB-dependent transcription. Transcriptional activity of CREB can also be potentiated by phosphoserine-133-independent mechanisms, and not all stimuli that provoke phosphorylation of serine-133 stimulate CREB-dependent transcription. This review presents an overview of the diversity of stimuli that induce CREB phosphorylation at Ser-133, focuses on phosphoserine-133-dependent and -independent mechanisms that affect CREB-mediated transcription, and discusses different models that may explain the discrepancy between CREB Ser-133 phosphorylation and activation of CREB-mediated transcription.