Retinoblastoma gene product activates expression of the human TGF-beta 2 gene through transcription factor ATF-2

Advances and Challenges in Targeting TGF-β Isoforms for Therapeutic Intervention of Cancer: A Mechanism-Based Perspective

The TGF-β family is a group of 25 kDa secretory cytokines, in mammals consisting of three dimeric isoforms (TGF-βs 1, 2, and 3), each encoded on a separate gene with unique regulatory elements. Each isoform plays unique, diverse, and pivotal roles in cell growth, survival, immune response, and differentiation. However, many researchers in the TGF-β field often mistakenly assume a uniform functionality among all three isoforms. Although TGF-βs are essential for normal development and many cellular and physiological processes, their dysregulated expression contributes significantly to various diseases. Notably, they drive conditions like fibrosis and tumor metastasis/progression. To counter these pathologies, extensive efforts have been directed towards targeting TGF-βs, resulting in the development of a range of TGF-β inhibitors. Despite some clinical success, these agents have yet to reach their full potential in the treatment of cancers. A significant challenge rests in effectively targeting TGF-βs' pathological functions while preserving their physiological roles. Many existing approaches collectively target all three isoforms, failing to target just the specific deregulated ones. Additionally, most strategies tackle the entire TGF-β signaling pathway instead of focusing on disease-specific components or preferentially targeting tumors. This review gives a unique historical overview of the TGF-β field often missed in other reviews and provides a current landscape of TGF-β research, emphasizing isoform-specific functions and disease implications. The review then delves into ongoing therapeutic strategies in cancer, stressing the need for more tools that target specific isoforms and disease-related pathway components, advocating mechanism-based and refined approaches to enhance the effectiveness of TGF-β-targeted cancer therapies.

GLUT3 Promotes Epithelial–Mesenchymal Transition via TGF-β/JNK/ATF2 Signaling Pathway in Colorectal Cancer Cells

Glucose transporter (GLUT) 3, a member of the GLUTs family, is involved in cellular glucose utilization and the first step in glycolysis. GLUT3 is highly expressed in colorectal cancer (CRC) and it leads to poor prognosis to CRC patient outcome. However, the molecular mechanisms of GLUT3 on the epithelial–mesenchymal transition (EMT) process in metastatic CRC is not yet clear. Here, we identified that activation of the c-Jun N-terminal kinase (JNK)/activating transcription factor-2 (ATF2) signaling pathway by transforming growth factor-β (TGF-β) promotes GLUT3-induced EMT in CRC cells. The regulation of GLUT3 expression was significantly associated with EMT-related markers such as E-cadherin, α- smooth muscle actin (α-SMA), plasminogen activator inhibitor-1 (PAI-1), vimentin and zinc finger E-box binding homeobox 1 (ZEB1). We also found that GLUT3 accelerated the invasive ability of CRC cells. Mechanistically, TGF-β induced the expression of GLUT3 through the phosphorylation of JNK/ATF2, one of the SMAD-independent pathways. TGF-β induced the expression of GLUT3 by increasing the phosphorylation of JNK, the nuclear translocation of the ATF2 transcription factor, and the binding of ATF2 to the promoter region of GLUT3, which increased EMT in CRC cells. Collectively, our results provide a new comprehensive mechanism that GLUT3 promotes EMT process through the TGF-β/JNK/ATF2 signaling pathway, which could be a potential target for the treatment of metastatic CRC.

Regulation of senescence traits by MAPKs

A phenotype of indefinite growth arrest acquired in response to sublethal damage, cellular senescence affects normal aging and age-related disease. Mitogen-activated protein kinases (MAPKs) are capable of sensing changes in cellular conditions, and in turn elicit adaptive responses including cell senescence. MAPKs modulate the levels and function of many proteins, including proinflammatory factors and factors in the p21/p53 and p16/RB pathways, the main senescence-regulatory axes. Through these actions, MAPKs implement key traits of senescence-growth arrest, cell survival, and the senescence-associated secretory phenotype (SASP). In this review, we summarize and discuss our current knowledge of the impact of MAPKs in senescence. In addition, given that eliminating or suppressing senescent cells can improve health span, we discuss the function and possible exploitation of MAPKs in the elimination (senolysis) or suppression (senostasis) of senescent cells.

MicroRNA-30b controls endothelial cell capillary morphogenesis through regulation of transforming growth factor beta 2

The importance of microRNA (miRNA) to vascular biology is becoming increasingly evident; however, the function of a significant number of miRNA remains to be determined. In particular, the effect of growth factor regulation of miRNAs on endothelial cell morphogenesis is incomplete. Thus, we aimed to identify miRNAs regulated by pro-angiogenic vascular endothelial growth factor (VEGF) and determine the effects of VEGF-regulated miRNAs and their targets on processes important for angiogenesis. Human umbilical vein endothelial cells (HUVECs) were thus stimulated with VEGF and miRNA levels assessed using microarrays. We found that VEGF altered expression of many miRNA, and for this study focused on one of the most significantly down-regulated miRNA in HUVECs following VEGF treatment, miR-30b. Using specific miRNA mimics, we found that overexpression of miR-30b inhibited capillary morphogenesis in vitro, while depletion of endogenous miR-30b resulted in increased capillary morphogenesis indicating the potential significance of down-regulation of miR-30b as a pro-angiogenic response to VEGF stimulation. MiR-30b overexpression in HUVEC regulated transforming growth factor beta 2 (TGFβ2) production, which led to increased phosphorylation of Smad2, indicating activation of an autocrine TGFβ signaling pathway. Up-regulation of TGFβ2 by miR-30b overexpression was found to be dependent on ATF2 activation, a transcription factor known to regulate TGFβ2 expression, as miR-30b overexpressing cells exhibited increased levels of phosphorylated ATF2 and depletion of ATF2 inhibited miR-30b-induced TGFβ2 expression. However, miR-30b effects on ATF2 were indirect and found to be via targeting of the known ATF2 repressor protein JDP2 whose mRNA levels were indirectly correlated with miR-30b levels. Increased secretion of TGFβ2 from HUVEC was shown to mediate the inhibitory effects of miR-30b on capillary morphogenesis as treatment with a neutralizing antibody to TGFβ2 restored capillary morphogenesis to normal levels in miR-30b overexpressing cells. These results support that the regulation of miR-30b by VEGF in HUVEC is important for capillary morphogenesis, as increased miR-30b expression inhibits capillary morphogenesis through enhanced expression of TGFβ2.

ATF2, a paradigm of the multifaceted regulation of transcription factors in biology and disease

Stringent transcriptional regulation is crucial for normal cellular biology and organismal development. Perturbations in the proper regulation of transcription factors can result in numerous pathologies, including cancer. Thus, understanding how transcription factors are regulated and how they are dysregulated in disease states is key to the therapeutic targeting of these factors and/or the pathways that they regulate. Activating transcription factor 2 (ATF2) has been studied in a number of developmental and pathological conditions. Recent findings have shed light on the transcriptional, post-transcriptional, and post-translational regulatory mechanisms that influence ATF2 function, and thus, the transcriptional programs coordinated by ATF2. Given our current knowledge of its multiple levels of regulation and function, ATF2 represents a paradigm for the mechanistic complexity that can regulate transcription factor function. Thus, increasing our understanding of the regulation and function of ATF2 will provide insights into fundamental regulatory mechanisms that influence how cells integrate extracellular and intracellular signals into a genomic response through transcription factors. Characterization of ATF2 dysfunction in the context of pathological conditions, particularly in cancer biology and response to therapy, will be important in understanding how pathways controlled by ATF2 or other transcription factors might be therapeutically exploited. In this review, we provide an overview of the currently known upstream regulators and downstream targets of ATF2.

Role of areca nut induced JNK/ATF2/Jun axis in the activation of TGF-β pathway in precancerous Oral Submucous Fibrosis

Oral submucous fibrosis (OSF) is potentially premalignant with progressive and irreversible extracellular matrix deposition accompanied by epithelial atrophy and like other fibrotic disorders, is primarily a TGF-β driven disease. OSF is caused by prolonged chewing of areca nut. Our previous studies reported a pivotal role for TGF-β activation and its effects contributing to OSF. However, the mechanism for activation of TGF-β signaling in OSF is still unknown. In this study we demonstrate activation of TGF-β signaling with sub-cytotoxic dose of areca nut in epithelial cells and discovered a key role for pJNK in this process. In good correlation; pJNK was detected in OSF tissues but not in normal tissues. Moreover, activation of JNK was found to be dependent on muscarinic acid receptor induced Ca²⁺/CAMKII as well as ROS. JNK dependent phosphorylation of ATF2/c-Jun transcription factors resulted in TGF-β transcription and its signaling. pATF2/p-c-Jun were enriched on TGF-β promoter and co-localized in nuclei of epithelial cells upon areca nut treatment. In corroboration, OSF tissue sections also had nuclear pATF2 and p-c-Jun. Our results provide comprehensive mechanistic details of TGF-β signaling induced by etiological agent areca nut in the manifestation of fibrosis which can lead to new therapeutic modalities for OSF.

Deoxycholic acid inhibited proliferation and induced apoptosis and necrosis by regulating the activity of transcription factors in rat pancreatic acinar cell line AR42J

The objective of this study is to investigate the effect of deoxycholic acid (DCA) on rat pancreatic acinar cell line AR42J and the functional mechanisms of DCA on AR42J cells. AR42J cells were treated with various concentrations of DCA for 24 h and also treated with 0.4 mmol/L DCA for multiple times, and then, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay was performed to detect the AR42J cell survival rate. Flow cytometric was used to detect the cell apoptosis and necrosis in AR42J cells treated with 0.4 mmol/L and 0.8 mmol/L DCA. The cells treated with phosphate buffer saline (PBS) were served as control. In addition, the DNA-binding activity assays of transcription factors (TFs) in nuclear proteins of cells treated with DCA were determined using Panomics Procarta Transcription Factor Assay Kit. The relative survival rates were markedly decreased (P < 0.05) in a dose- and time-dependent manner. Compared with control group, the cell apoptosis and necrosis ratio were both significantly elevated in 0.4 mmol/L DCA and 0.8 mmol/L DCA groups (P < 0.01). A significant increase (P < 0.05) in the activity of transcription factor 2 (ATF2), interferon-stimulated response element (ISRE), NKX-2.5, androgen receptor (AR), p53, and hypoxia-inducible factor-1 (HIF-1) was observed, and the activity of peroxisome proliferator-activated receptor (PPAR), activator protein 1 (AP1), and E2F1 was reduced (P < 0.05). In conclusion, DCA inhibited proliferation and induced apoptosis and necrosis in AR42J cells. The expression changes of related genes regulated by TFs might be the molecular mechanism of AR42J cell injury.

ATF2 - at the crossroad of nuclear and cytosolic functions

An increasing number of transcription factors have been shown to elicit oncogenic and tumor suppressor activities, depending on the tissue and cell context. Activating transcription factor 2 (ATF2; also known as cAMP-dependent transcription factor ATF-2) has oncogenic activities in melanoma and tumor suppressor activities in non-malignant skin tumors and breast cancer. Recent work has shown that the opposing functions of ATF2 are associated with its subcellular localization. In the nucleus, ATF2 contributes to global transcription and the DNA damage response, in addition to specific transcriptional activities that are related to cell development, proliferation and death. ATF2 can also translocate to the cytosol, primarily following exposure to severe genotoxic stress, where it impairs mitochondrial membrane potential and promotes mitochondrial-based cell death. Notably, phosphorylation of ATF2 by the epsilon isoform of protein kinase C (PKCε) is the master switch that controls its subcellular localization and function. Here, we summarize our current understanding of the regulation and function of ATF2 in both subcellular compartments. This mechanism of control of a non-genetically modified transcription factor represents a novel paradigm for 'oncogene addiction'.

Transcriptional networks in epithelial-mesenchymal transition

Backround

Epithelial-mesenchymal transition (EMT) changes polarized epithelial cells into migratory phenotypes associated with loss of cell-cell adhesion molecules and cytoskeletal rearrangements. This form of plasticity is seen in mesodermal development, fibroblast formation, and cancer metastasis.

Methods and Findings

Here we identify prominent transcriptional networks active during three time points of this transitional process, as epithelial cells become fibroblasts. DNA microarray in cultured epithelia undergoing EMT, validated in vivo, were used to detect various patterns of gene expression. In particular, the promoter sequences of differentially expressed genes and their transcription factors were analyzed to identify potential binding sites and partners. The four most frequent cis-regulatory elements (CREs) in up-regulated genes were SRY, FTS-1, Evi-1, and GC-Box, and RNA inhibition of the four transcription factors, Atf2, Klf10, Sox11, and SP1, most frequently binding these CREs, establish their importance in the initiation and propagation of EMT. Oligonucleotides that block the most frequent CREs restrain EMT at early and intermediate stages through apoptosis of the cells.

Conclusions

Our results identify new transcriptional interactions with high frequency CREs that modulate the stability of cellular plasticity, and may serve as targets for modulating these transitional states in fibroblasts.

A cytoplasmic negative regulator isoform of ATF7 impairs ATF7 and ATF2 phosphorylation and transcriptional activity

Alternative splicing and post-translational modifications are processes that give rise to the complexity of the proteome. The nuclear ATF7 and ATF2 (activating transcription factor) are structurally homologous leucine zipper transcription factors encoded by distinct genes. Stress and growth factors activate ATF2 and ATF7 mainly via sequential phosphorylation of two conserved threonine residues in their activation domain. Distinct protein kinases, among which mitogen-activated protein kinases (MAPK), phosphorylate ATF2 and ATF7 first on Thr71/Thr53 and next on Thr69/Thr51 residues respectively, resulting in transcriptional activation. Here, we identify and characterize a cytoplasmic alternatively spliced isoform of ATF7. This variant, named ATF7-4, inhibits both ATF2 and ATF7 transcriptional activities by impairing the first phosphorylation event on Thr71/Thr53 residues. ATF7-4 indeed sequesters the Thr53-phosphorylating kinase in the cytoplasm. Upon stimulus-induced phosphorylation, ATF7-4 is poly-ubiquitinated and degraded, enabling the release of the kinase and ATF7/ATF2 activation. Our data therefore conclusively establish that ATF7-4 is an important cytoplasmic negative regulator of ATF7 and ATF2 transcription factors.

RB1, development, and cancer

The RB1 gene is the first tumor suppressor gene identified whose mutational inactivation is the cause of a human cancer, the pediatric cancer retinoblastoma. The 25 years of research since its discovery has not only illuminated a general role for RB1 in human cancer, but also its critical importance in normal development. Understanding the molecular function of the RB1 encoded protein, pRb, is a long-standing goal that promises to inform our understanding of cancer, its relationship to normal development, and possible therapeutic strategies to combat this disease. Achieving this goal has been difficult, complicated by the complexity of pRb and related proteins. The goal of this review is to explore the hypothesis that, at its core, the molecular function of pRb is to dynamically regulate the location-specific assembly or disassembly of protein complexes on the DNA in response to the output of various signaling pathways. These protein complexes participate in a variety of molecular processes relevant to DNA including gene transcription, DNA replication, DNA repair, and mitosis. Through regulation of these processes, RB1 plays a uniquely prominent role in normal development and cancer.

Activating transcription factor-2 in survival mechanisms in head and neck carcinoma cells

BACKGROUND

Activating transcription factor-2 (ATF2) is associated with tumor progression but is not well studied in head and neck squamous cell carcinoma (HNSCC). Its effects in stress and its importance in other survival mechanisms were studied.

METHODS

ATF2 expression and nuclear activation were confirmed in HNSCC. After modulation of ATF2, in vitro effects on proliferation and chemosensitivity were studied. Effects on in vivo tumor growth and interleukin 8 (IL-8) expression were determined. Tumor necrosis factor-alpha (TNF-α) treatment was used to further evaluate cytokine production and chemosensitivity.

RESULTS

Reductions of ATF2 resulted in significant nuclear p-ATF2 activation, cisplatin resistance, and augmented IL-8 expression without affecting in vivo tumor growth. In this setting, TNF increases p-p38 phosphorylation and chemosensitivity while further enhancing IL-8 production.

CONCLUSION

Our data suggest regulatory roles for ATF2 in TNF-related mechanisms of HNSCC. Its perturbation and nuclear activation are associated with significant effects on survival and cytokine production.

Tandem E2F binding sites in the promoter of the p107 cell cycle regulator control p107 expression and its cellular functions

The retinoblastoma tumor suppressor (Rb) is a potent and ubiquitously expressed cell cycle regulator, but patients with a germline Rb mutation develop a very specific tumor spectrum. This surprising observation raises the possibility that mechanisms that compensate for loss of Rb function are present or activated in many cell types. In particular, p107, a protein related to Rb, has been shown to functionally overlap for loss of Rb in several cellular contexts. To investigate the mechanisms underlying this functional redundancy between Rb and p107 in vivo, we used gene targeting in embryonic stem cells to engineer point mutations in two consensus E2F binding sites in the endogenous p107 promoter. Analysis of normal and mutant cells by gene expression and chromatin immunoprecipitation assays showed that members of the Rb and E2F families directly bound these two sites. Furthermore, we found that these two E2F sites controlled both the repression of p107 in quiescent cells and also its activation in cycling cells, as well as in Rb mutant cells. Cell cycle assays further indicated that activation of p107 transcription during S phase through the two E2F binding sites was critical for controlled cell cycle progression, uncovering a specific role for p107 to slow proliferation in mammalian cells. Direct transcriptional repression of p107 by Rb and E2F family members provides a molecular mechanism for a critical negative feedback loop during cell cycle progression and tumorigenesis. These experiments also suggest novel therapeutic strategies to increase the p107 levels in tumor cells.

The retinoblastoma tumor suppressor Rb belongs to a family of cell cycle inhibitors along with the related proteins p107 and p130. Strong evidence indicates that the three family members have both specific and overlapping functions and expression patterns in mammalian cells, including in cancer cells. However, the molecular mechanisms underlying the functional differences and similarities among Rb, p107, and p130 are still poorly understood. One proposed mechanism of compensation is a negative feedback loop involving increased p107 transcription in Rb-deficient cells. To dissect the mechanisms controlling p107 expression in both wild-type and Rb-deficient cells, we have engineered inactivating point mutations into the E2F binding sites in the endogenous p107 promoter using gene targeting in mouse embryonic stem cells. Gene expression and DNA binding assays revealed that these two sites are essential for the control of p107 transcription in wild-type and Rb mutant cells, and cell cycle assays showed their importance for normal functions of p107. These experiments identify a key node in cell cycle regulatory networks.

Regulation of RB transcription in vivo by RB family members

In cancer cells, the retinoblastoma tumor suppressor RB is directly inactivated by mutation in the RB gene or functionally inhibited by abnormal activation of cyclin-dependent kinase activity. While variations in RB levels may also provide an important means of controlling RB function in both normal and cancer cells, little is known about the mechanisms regulating RB transcription. Here we show that members of the RB and E2F families bind directly to the RB promoter. To investigate how the RB/E2F pathway may regulate Rb transcription, we generated reporter mice carrying an eGFP transgene inserted into a bacterial artificial chromosome containing most of the Rb gene. Expression of eGFP largely parallels that of Rb in transgenic embryos and adult mice. Using these reporter mice and mutant alleles for Rb, p107, and p130, we found that RB family members modulate Rb transcription in specific cell populations in vivo and in culture. Interestingly, while Rb is a target of the RB/E2F pathway in mouse and human cells, Rb expression does not strictly correlate with the cell cycle status of these cells. These experiments identify novel regulatory feedback mechanisms within the RB pathway in mammalian cells.

Activating transcription factor 2 increases transactivation and protein stability of hypoxia-inducible factor 1alpha in hepatocytes

HIF-1 (hypoxia inducible factor 1) performs a crucial role in mediating the response to hypoxia. However, other transcription factors are also capable of regulating hypoxia-induced target-gene transcription. In a previous report, we demonstrated that the transcription factor ATF-2 (activating transcription factor 2) regulates hypoxia-induced gene transcription, along with HIF-1alpha. In the present study, we show that the protein stability of ATF-2 is induced by hypoxia and the hypoxia-mimic CoCl2 (cobalt chloride), and that ATF-2 induction enhances HIF-1alpha protein stability via direct protein interaction. The knockdown of ATF-2 using small interfering RNA and translation-inhibition experiments demonstrated that ATF-2 plays a key role in the maintenance of the expression level and transcriptional activity of HIF-1alpha. Furthermore, we determined that ATF-2 interacts directly with HIF-1alpha both in vivo and in vitro and competes with the tumour suppressor protein p53 for HIF-1alpha binding. Collectively, these results show that protein stabilization of ATF-2 under hypoxic conditions is required for the induction of the protein stability and transactivation activity of HIF-1alpha for efficient hypoxia-associated gene expression.

Overexpression of phosphorylated-ATF2 and STAT3 in cutaneous angiosarcoma and pyogenic granuloma

BACKGROUND

Activating transcription factor-2/Activator protein-1 (AP-1), Signal transducer and activator of transcription-3 and p53 are important regulators of cellular proliferation, apoptosis, differentiation in the pathogenesis of many human tumors, but the expression of phosphorylated (p)-activating transcription factor-2 (p-ATF2), phosphorylated (p)-signal transducer and activator of transcription-3 (p-STAT3) and p53 family (p63 and p73) has not been investigated in cutaneous angiosarcoma (CAS) and pyogenic granuloma (PG) so far.

OBJECTIVES

To investigate the expression of p-ATF2, p-STAT3 and p53 and its family in cutaneous vascular tumors (CAS and PG).

METHODS

Paraffin-embedded specimens of 14 CAS and 19 PG were subjected to immunohistochemical staining for p-ATF2, p-STAT3, p53, p63 and p73.

RESULTS

P-ATF2 was expressed in 13 out of 14 CAS and in all of 19 PG. P-STAT3 was expressed in all of 14 CAS and 19 PG. P53 was expressed in all of 14 CAS and 19 PG, while both p63 and p73 were negative in CAS and PG. The p-ATF2-, p-STAT3- and p53 expression (% positive cells) in CAS and PG were significantly higher than in normal dermal vessels, but none of these transcription factors distinguished malignant (CAS)- from benign (PG) vascular tumor.

CONCLUSIONS

The present study suggests that overexpression of p-ATF2, p-STAT3 and possibly p53, but not p63 or p73, may contribute to the tumorigenesis of cutaneous vascular tumors.

Conditional deletion of the retinoblastoma (Rb) gene in ovarian granulosa cells leads to premature ovarian failure

The retinoblastoma protein (RB) regulates cell proliferation and survival by binding to the E2F family of transcription factors. Recent studies suggest that RB also regulates differentiation in a variety of cell types, including myocytes, neurons, adipocytes, and chondrocytes. Rb mutations have been found in ovarian cancer; however, the role of RB in normal and abnormal ovarian function remains unclear. To test the hypothesis that loss of Rb induces ovarian tumorigenesis, we generated an ovarian granulosa cell conditional knockout of Rb (Rb cKO) using the Cre/lox recombination system. Rb cKO females showed 100% survival and no ovarian tumor formation through 9 months of age, but they developed progressive infertility. Prepubertal Rb cKO females showed increased ovulation rates compared with controls, correlating with increased follicle recruitment, higher Fshr and Kitl mRNA levels, and lower anti-Müllerian hormone levels. In contrast, the ovulation rate of 6-wk-old females was similar to that of controls. Morphometric analysis of Rb cKO ovaries from 6-wk-old and older females showed increased follicular atresia and apoptosis. Rb cKO ovaries and preantral follicles had abnormal levels of known direct and indirect target genes of RB, including Rbl2/p130, E2f1, Ccne2, Myc, Fos, and Tgfb2. In addition, preantral follicles showed increased expression of the granulosa cell differentiation marker Inha, decreased levels of Foxl2 and Cyp19a1 aromatase, and abnormal expression of the nuclear receptors Nr5a1, Nr5a2, and Nr0b1. Taken together, our results suggest that RB is required for the temporal-specific pattern of expression of key genes involved in follicular development.

ATF2 on the double - activating transcription factor and DNA damage response protein

Signal transduction pathways play a key role in the regulation of key cellular processes, including survival and death. Growing evidence points to changes in signaling pathway that occur during skin tumor development and progression. Such changes impact the activity of downstream substrates, including transcription factors. The activating transcription factor 2 (ATF2) has been implicated in malignant and non-malignant skin tumor developments. ATF2 mediates both transcription and DNA damage control, through its phosphorylation by JNK/p38 or ATM/ATR respectively. Here, we summarize our present understanding of ATF2 regulation, function and contribution to malignant and non-malignant skin tumor development.

Modulation of morphogenesis by noncanonical Wnt signaling requires ATF/CREB family-mediated transcriptional activation of TGFbeta2

Transcriptional readout downstream of canonical Wnt signaling is known to be mediated by beta-catenin activation of well-described targets, but potential transcriptional readout in response to noncanonical Wnt signaling remains poorly understood. Here, we define a transcriptional pathway important in noncanonical Wnt signaling. We have found that Wnt11 is a direct target of a canonical beta-catenin pathway in developing heart and that Wnt11 mutants show cardiac outflow tract defects. We provide genetic and biochemical evidence thatWnt11 signaling affects extracellular matrix composition, cytoskeletal rearrangements and polarized cell movement required for morphogenesis of the cardiac outflow tract. Notably, transforming growth factor beta2 (TGFbeta2), a key effector of organ morphogenesis, is regulated by Wnt11-mediated noncanonical signaling in developing heart and somites via one or more activating transcription factor (ATF)/cyclic AMP response element binding protein (CREB) family members. Thus, we propose that transcriptional readout mediated at least in part by a Wnt11 --> ATF/CREB --> TGFbeta2 pathway is critical in regulating morphogenesis in response to noncanonical Wnt signaling.

Integrative analysis of a cancer somatic mutome

BACKGROUND

The consecutive acquisition of genetic alterations characterizes neoplastic processes. As a consequence of these alterations, molecular interactions are reprogrammed in the context of highly connected and regulated cellular networks. The recent identification of the collection of somatically mutated genes in breast tumors (breast cancer somatic "mutome") allows the comprehensive study of its function and organization in complex networks.

RESULTS

We analyzed functional genomic data (loss of heterozygosity, copy number variation and gene expression in breast tumors) and protein binary interactions from public repositories to identify potential novel components of neoplastic processes, the functional relationships between them, and to examine their coordinated function in breast cancer pathogenesis. This analysis identified candidate tumor suppressors and oncogenes, and new genes whose expression level predicts survival rate in breast cancer patients. Mutome network modeling using different types of pathological and healthy functional relationships unveils functional modules significantly enriched in genes or proteins (genes/proteins) with related biological process Gene Ontology terms and containing known breast cancer-related genes/proteins.

CONCLUSION

This study presents a comprehensive analysis of the breast somatic mutome, highlighting those genes with a higher probability of playing a determinant role in tumorigenesis and better defining molecular interactions related to the neoplastic process.

Competitive Binding of CREB and ATF2 to cAMP/ATF Responsive Element Regulates eNOS Gene Expression in Endothelial Cells

OBJECTIVE

Expression of endothelial nitric oxide synthase (eNOS) is a critical determinant for vascular homeostasis. We examined the effects of Beraprost sodium (BPS), a stable analogue of prostacyclin, on the eNOS gene expression in the presence of inflammatory cytokine interleukin (IL)-1beta in cultured endothelial cells.

METHOD AND RESULTS

Exposure of human and bovine endothelial cells to IL-1beta decreased eNOS expression. Western blot analysis using phospho-specific antibodies showed that IL-1beta stimulated p38 MAP kinase and phosphorylated ATF2. BPS inhibited these effects via protein kinase A (PKA)/cAMP-responsive element binding protein (CREB) activation. Transfection assays using site-specific mutation constructs showed that CRE/ATF elements located at -733 and -603 within the human eNOS promoter are necessary for full IL-1beta responsiveness. BPS attenuated the IL-1beta-mediated decrease in eNOS promoter activity and the expression of eNOS gene through PKA pathway. Electrophoretic gel mobility shift assays showed that IL-1beta increased the binding of phosphorylated ATF2 to CRE/ATF. On treatment with BPS, phosphorylated CREB predominantly bound to CRE/ATF.

CONCLUSIONS

These results indicate that IL-1beta and BPS antagonistically regulates the eNOS expression through the activation of p38 and PKA, respectively. Furthermore, the ability to bind both CREB and ATF2 implicates the CRE/ATF sequence as a potential target for multiple signaling pathways in the regulation of the eNOS gene transcription.

A transcriptional regulatory element screening system reveals a novel E2F1/pRb transcription regulation pathway

We developed a transcriptional regulatory element library which contains 160 independent known transcriptional regulatory elements linked to luciferase reporter vectors. That library proved valuable in the identification of p53 response elements and of E-box sequence preferences of several E-box binding proteins, and we used it to explore E2F1 target regulatory elements. Among those 160 elements, we found 3 E2F1 response elements, an E2F1 consensus sequence, an insulin response element which contained the E2F consensus sequence, and a basal level enhancer (BLE1) which had a nonconsensus E2F binding sequence. BLE1 functioned as multiple copy, with E2F1 in a dose-dependent manner, and had a sequence specificity for E2F1. Electrophoretic mobility shift assay revealed that BLE1 specifically interacts with E2F1 comparable to the E2F element. Interestingly, transactivation via five copies of BLE1 was not repressed but rather was stimulated by E2F1 in combination with the retinoblastoma tumor suppressor protein (pRb). The retinoblastoma control element (RCE) contains a direct repeated BLE1 in the c-fos gene promoter which also functioned like the multiple BLE1. Our data show that E2F1 has potential binding activity to the RCE and a different transcriptional regulation pathway which cooperates with pRb. Our transcriptional regulatory element screening system is useful for identifying novel transcriptional pathways.

Transforming growth factor-beta-1 variants are not associated with chronic nonalcoholic pancreatitis

BACKGROUND

Pancreatic fibrosis is a key pathological feature of chronic pancreatitis. In vivo and in vitro data have demonstrated that pancreatic stellate cells (PSC) play a central role in pancreatic fibrosis. PSC activation and collagen synthesis are highly controlled by transforming growth factor-beta-1 (TGF-beta1). We evaluated whether functionally relevant genetic variants of TGF-beta1 are associated with chronic nonalcoholic pancreatitis.

METHODS

The promotor as well as exon 1 variants of the TGF-beta1 gene (G-800A, Leu10Pro and Arg25Pro) were investigated. Forty-two CP patients with a family history of nonalcoholic chronic pancreatitis (group A) and 88 patients without a family history of nonalcoholic chronic pancreatitis (group B) were studied. One hundred blood donors served as controls (group C).

RESULTS

The allelic frequencies of G-800A, Leu10Pro and Arg25Pro were 12, 38 and 6% in group A; 7, 40 and 6% in group B and 12, 29 and 3% in group C, respectively. The differences were not significant.

CONCLUSION

Functionally relevant genetic variants of the TGF-beta1 gene are not associated with nonalcoholic chronic pancreatitis.

Inhibition of melanoma growth and metastasis by ATF2-derived peptides

The resistance of melanoma to apoptosis, as well as its growth and metastasis capabilities, can be overcome by expression of a peptide derived from amino acid (aa) 51 to 100 of ATF2. Here we show that expression of ATF2((51-100)) in human melanoma cells reduced their growth in nude mice, which was additionally inhibited upon treatment with protein kinase inhibitors UCN-01 or SB203580. Injection of a fusion protein consisting of HIV-TAT and aa 51 to 100 of ATF2 into SW1 melanomas efficiently inhibits their growth and their metastasis up to complete regression. Additionally, expression of a 10aa peptide that corresponds to aa 51 to 60 of ATF2 sensitizes melanoma cells to spontaneous apoptosis, which coincides with activation of caspase 9 and poly(ADP-ribose) polymerase cleavage, and inhibit their growth in vivo. The 10aa peptide increases the association of c-Jun NH(2)-terminal kinase with c-Jun but not with ATF2, resulting in concomitant increase in TRE-mediated transcription. Our study points to mechanisms underlying the activities of the ATF2 peptide while highlighting its possible use in drug design.

Overexpression of activating transcription factor-2 is required for tumor growth and progression in mouse skin tumors

Activating transcription factor (ATF)-2 is a member of the ATF/cyclic AMP-responsive element binding protein family of transcription factors. It has been shown, in vitro, to possess growth factor-independent proliferation and transformation capacity. The information concerning the involvement of ATF-2 in carcinogenesis is rather limited. In a previous report, we showed a progressive increase in the levels of various activator protein (AP)-1 components, including phosphorylated ATF-2, in a series of mouse skin cell lines that represented developmental stages of the mouse skin carcinogenesis system. In the present study, we examined in detail the role of ATF-2 in the development of mouse skin spindle cells A5 and CarB, which correspond to the late and most aggressive stage of the mouse skin carcinogenesis model. To address this issue, we overexpressed a dominant negative form of ATF-2 in the A5 and CarB cell lines and examined their behavior in vitro and in vivo at the molecular and cellular level. The stable transfectants expressed decreased levels of phosphorylated ATF-2 and c-Jun. Subsequently, we observed that dominant negative ATF-2 affected the composition and reduced the activity of AP-1. The above biochemical changes were followed, both in vitro and in vivo in BALB/c severe combined immunodeficient mice, by suppression of the aggressive characteristics of the A5 and CarB mouse skin spindle cells. We attributed this behavior to the significant down-regulation of cyclin D1, cyclin A, and ATF-3, known AP-1 targets implicated in cell cycle control and promotion. In conclusion, our findings underscore a key regulatory role of ATF-2 in tumor growth and progression of mouse skin tumors.

Activating transcription factor 2 expression in the adult human brain: Association with both neurodegeneration and neurogenesis

Activating transcription factor 2 (ATF2) is a member of the activator protein-1 family of transcription factors, which includes c-Jun and c-Fos. ATF2 is highly expressed in the mammalian brain although little is known about its function in nerve cells. Knockout mouse studies show that this transcription factor plays a role in neuronal migration during development but over-expression of ATF2 in neuronal-like cell culture promotes nerve cell death. Using immunohistochemical techniques we demonstrate ATF2 expression in the normal human brain is neuronal, is found throughout the cerebral cortex and is particularly high in the granule cells of the hippocampus, in the brain stem, in the pigmented cells of the substantia nigra and locus coeruleus, and in the granule and molecular cell layers of the cerebellum. In contrast to normal cases, ATF2 expression is down-regulated in the hippocampus, substantia nigra pars compacta and caudate nucleus of the neurological diseases Alzheimer's, Parkinson's and Huntington's, respectively. Paradoxically, an increase in ATF2 expression was found in the subependymal layer of Huntington's disease cases, compared with normal brains; a region reported to contain increased numbers of proliferating progenitor cells in Huntington's disease. We propose ATF2 plays a role in neuronal viability in the normal brain, which is compromised in susceptible regions of neurological diseases leading to its down-regulation. In contrast, the increased expression of ATF2 in the subependymal layer of Huntington's disease suggests a role for ATF2 in some aspect of neurogenesis in the diseased brain.

Transient increase in anti-p-ATF2 immunoreactivity in the late secretion ameloblasts apical to the transition zone of rat incisors

Activating transcription factor 2 (ATF2) was localized in the ameloblasts of rat incisors by immunohistochemistry. A specific antibody against phosphorylated ATF2 (p-ATF2), which is an activated form of ATF2, was detected from the proliferation zone to maturation ameloblasts just after the transition. In the secretion zone, a transient increase in p-ATF2 was observed in the late secretion ameloblast nuclei, where a stronger reactivity of p-ATF2 extended from 1 mm apical to the transition to the transition zone, whereas ameloblast nuclei in most of the maturation zone exhibited either weak or no reactivity. A similar pattern was also observed in the case of c-Jun immunohistochemistry, except for in most of the maturation zone, where strong c-Jun reactivity was detected. Thus, ATF-2 and c-Jun are deeply involved in amelogenesis and, in particular, ATF2 is related to the proliferation, differentiation, secretion and transition zones.

Signalling pathways involved in multisite phosphorylation of the transcription factor ATF-2

The multisite phosphorylation of the transcription factor ATF-2 was investigated using transformed embryonic fibroblasts from wild-type mice and mice deficient in c-Jun N-terminal kinases (JNK)1 and 2, and in the presence and absence of inhibitors of p38 mitogen-activated protein kinase (p38 MAPK) and the classical MAP kinase cascade. In wild-type cells, p38 MAPK and extracellular signal-regulated protein kinase (ERK)1/2 were not rate limiting for the phosphorylation of Thr69, Thr71 or Ser90. In JNK-deficient cells, p38 MAPK substituted for JNK partially in the phosphorylation of Thr69 and p38 MAPK or ERK1/2 in the phosphorylation of Thr71. JNK was the only MAP kinase that phosphorylated Ser90 under the conditions examined.

Prognostic significance of a short sequence insertion in the MCL-1 promoter in chronic lymphocytic leukemia

BACKGROUND

Mcl-1 protein contributes to the longevity of chronic lymphocytic leukemia (CLL) B cells, and its higher expression has been associated with resistance to chemotherapy. We sought structural changes in the MCL-1 gene in CLL patients and associated these with clinical parameters of the disease.

METHODS

The MCL-1 gene from peripheral blood lymphocytes from 58 CLL patients and 18 control subjects and from the RL and BC-3 lymphoma cell lines was sequenced. Mcl-1 mRNA expression (in 20 consecutive patients and four control subjects) was analyzed by RNase protection assay, and Mcl-1 protein expression (in 18 consecutive patients and four controls) was analyzed by western blotting. Genetic changes in MCL-1 were associated with biochemical and clinical characteristics, including expression of CD38, a negative prognostic factor. Cox proportional hazards modeling was used to determine the prognostic importance of changes in the MCL-1 gene, and the Kaplan-Meier method was used to analyze patient survival. All statistical tests were two sided.

RESULTS

A 6- or 18-nucleotide sequence insertion was found in the same site in the MCL-1 promoter in 17 of 58 patients and in BC-3 cells; it was absent in all control subjects and in RL cells. Of 21 CD38-negative patients, 10 had a promoter insertion; of 17 CD38-positive patients, one had a promoter insertion (P =.0099). Patients with a promoter insertion had higher mRNA (median = 26.8 relative units, interquartile range [IQR] = 14.9 to 35.2, versus median = 8.8 relative units, IQR = 3.9 to 15.7, P =.030, U-test) and protein (median = 0.84 relative units, IQR = 0.81 to 1.0 versus median = 0.47, IQR = 0.32 to 0.70, P =.021, U-test) expression, more rapid disease progression (P =.012), poorer response to chemotherapy (P =.001), and shorter overall (P =.0088) and disease-specific (P <.001) survival than patients with a normal promoter. The presence of an MCL-1 promoter insertion had prognostic significance in a Cox model (P =.001).

CONCLUSIONS

The MCL-1 promoter insertion may identify a high-risk group of CD38-negative CLL patients.

Transcriptional switch by activating transcription factor 2-derived peptide sensitizes melanoma cells to apoptosis and inhibits their tumorigenicity

The notorious resistance of melanoma cells to drug treatment can be overcome by expression of a 50-aa peptide derived from activating transcription factor 2 (ATF2(50-100)). Here we demonstrate that ATF2(50-100) induced apoptosis by sequestering ATF2 to the cytoplasm, thereby inhibiting its transcriptional activities. Furthermore, ATF2(50-100) binds to c-Jun N-terminal kinase (JNK) and increases its activity. Mutation within ATF2(50-100) that impairs association with JNK and the inhibition of JNK or c-Jun expression by RNA interference (RNAi) reduces the degree of ATF2(50-100)-induced apoptosis. In contrast, TAM67, a dominant negative of the Jun family of transcription factors, or JunD RNAi attenuates sensitization of melanoma cells expressing ATF2(50-100) to apoptosis after treatment with anisomycin, which is used as a model drug. Mutations within the JNK binding region of ATF2(50-100) or expression of TAM67 or JunD RNAi attenuates inhibition of melanoma's tumorigenicity by ATF2(50-100). We conclude that inhibition of ATF2 in concert with increased JNK/Jun and JunD activities is central for the sensitization of melanoma cells to apoptosis and inhibition of their tumorigenicity.

Transcriptional regulation by the retinoblastoma protein

The retinoblastoma protein (RB) plays a key role in the control of cell proliferation and mediates the terminal differentiation of certain cell types. Increasing evidence suggests that RB functions by contacting and modifying the behaviour of transcription factors. RB can form complexes with E2F and MyoD in vivo, and complexes with a number of other transcription factors have also been demonstrated in vitro. The interaction of regulatory transcription factors with RB may be explained by sequence similarity between RB and two general transcription factors: TBP and TFIIB. Here I review the evidence for a role of RB in the regulation of transcription and highlight some of the likely mechanisms of RB function.

Cell-cycle control and the cartilage growth plate

The longitudinal growth of endochondral bones is governed by proliferation and hypertrophic differentiation of growth plate chondrocytes. Numerous growth factors and hormones have been implicated in the regulation of these processes, but the intracellular mechanisms involved remain much less understood. We had suggested a role of cell-cycle genes in the integration of these diverse extracellular signals and their translation into coordinated proliferation and differentiation of chondrocytes. Numerous recent studies have provided support for such a scenario and provide novel insights into the regulation and function of cell-cycle genes in chondrocytes. This review article summarizes recent progress in the field.

The expression of retinoblastoma and Sp1 is increased by low concentrations of cyclin-dependent kinase inhibitors

We examined the effect of suboptimal concentrations of cyclin-dependent kinase inhibitors, which do not interfere with cell proliferation, on retinoblastoma expression in hamster (Chinese hamster ovary K1) and human (K562 and HeLa) cells. To achieve this, we used the chemical inhibitors roscovitine and olomoucine (which inhibit CDK2 preferentially), UCN-01 (which also inhibits CDK4/6) and p21 (as an intrinsic inhibitor). All chemical inhibitors and overexpression of p21 strongly induced retinoblastoma protein expression. UCN-01-mediated retinoblastoma expression was caused by an increase in both the levels of retinoblastoma mRNA and the stability of the protein. The expression of the transcription factor Sp1, a retinoblastoma-interacting protein, was also enhanced by all the cyclin-dependent kinase inhibitors tested. However, Sp1 expression was caused by an increase in the levels of Sp1 mRNA without modification in the stability of the protein. By using luciferase experiments, the transcriptional activation of both retinoblastoma and Sp1 promoters by UCN-01 was confirmed. Bisindolylmaleimide I, at concentrations causing a similar or higher inhibition of protein kinase C than UCN-01, provoked a lower activation of retinoblastoma and Sp1 expression. Finally, the effects of cyclin-dependent kinase inhibitors on dihydrofolate reductase gene expression were evaluated. Treatment with UCN-01 increased cellular dihydrofolate reductase mRNA levels, and dihydrofolate reductase enzymatic activity was enhanced by UCN-01, roscovitine, olomoucine and p21, in transient transfection experiments. These results support a mechanism for the self-regulation of retinoblastoma expression, and point to the need to establish the appropriate dose of cyclin-dependent kinase inhibitors as antiproliferative agents in anticancer treatments.

Retinoblastoma protein (pRB) was significantly phosphorylated through a Ras-to-MAPK pathway in mutant K-ras stably transfected human adrenocortical cells

Our previous studies have shown that the cell proliferation rate, mRNA levels of p450scc, p450c17, and 3betaHSD, and secretion of cortisol were significantly increased in human adrenocortical cells stably transfected with mutated K-ras expression plasmid "pK568MRSV" after being inducted with IPTG. In addition, the increased level was a time-dependent manner. However, the levels of p450, p450scc, p450c17, 3betaHSD, cortisol, and cell proliferation rate were inhibited by a MEK phospholation inhibitor, PD098059. The above results prove that mutated K-ras oncogene is able to regulate tumorigenesis and steroidogenesis through a Ras-RAF-MEK-MAPK signal transduction pathway. The aim of this study was to investigate regulated factors in this pathway and also examine whether the other signal transduction pathways or other moles involved in tumorigenesis or steroidogenesis. In the first year, we analyzed gene profiles of mutant K-ras-transfected adrenocortical cells by DNA microarray to determine the gene expression related to cell cycle, signal transduction, apoptosis, tumorigenesis, steroidogenesis, and other expressed sequence tag. After being affected by the K-ras mutant, gene expression was significantly increased in some upregulated genes. Human zinc-finger protein 22 increased by 28.5 times, Osteopontin increased by 5.8 times, LIM domain Kinase 2 (LIMK2) increased by 3.3 times, Homo sapiens dual-specificity tyrosine-(Y)-phosphorylation regulated Kinase 2 (DYRK2) increased by 2.2 times, and human syntaxin 3 increased by two times. On the other hand, significant decreases in gene expression were also observed in some downregulated genes. Retinoblastoma binding protein 1 (RBBP1) decreased by four times, Homo sapiens craniofacial development protein 1 (CFDP1) decreased by 2.4 times, DAP Kinase-related apoptosis-inducing protein Kinase 1 (DRAK1) decreased by 2.3 times, SKI-interacting protein (SKIP) decreased by 2.2 times, and human poly(A)-Binding protein (PABP) decreased by 2.1 times. In all significant differentially expressed genes, preliminary analysis by bioinformatics revealed that after induced K-ras mutant expression by isopropyl thiogalctoside (IPTG), the downregulation of RBBP1 gene was most correlated to cell proliferation. RBBP1 can bind with RB/E2F to form a mSIN3-HDAC complex, which induces cell cycle arrest in the G1/G0 stage by repressing transcription of E2F-regulated genes. The result of a Northern blot showed that RBBP1 were inhibited after an induction of IPTG for 36 h. Another Northern blot analysis proved that mRNA levels of cyclin D1 and c-myc increased in proportion to K-ras expression. Finally, Western blot was carried out, and the results showed that phosphorylated pRB also increased. Taken together, we infer that the mutant K-ras oncogene promoted the cells to proceed to the G1/S stage by the inhibiting the formation of RB/RBBP1-dependent repressor complex from binding with the SIN3-HDAC complex, which resulted in the acetylation of histone to active transcription of E2F-regulated genes. However, the roles of the other differentially expressed genes involved in cell proliferation, cell morphologic change, tumorigenesis, or steroidogenesis still need further investigation.

Role for retinoblastoma protein family members in UV-enhanced expression from the human cytomegalovirus immediate early promoters

The expression from a reporter construct driven by a cytomegalovirus (CMV) immediate early (IE) promoter is strongly inducible by UV in human fibroblasts. This response is induced at lower UV fluences in transcription-coupled repair (TCR)-deficient fibroblasts compared with normal fibroblasts and is absent in their simian virus 40-transformed counterparts. In this study we demonstrate that expression of human papilloma virus (HPV) E7 (but not of HPV E6) can attenuate UV-induced expression from the human CMV-IE-driven reporter construct in human fibroblasts. Furthermore, UV-induced expression from the reporter construct appears impaired in murine fibroblasts harboring inactivating mutations in the retinoblastoma (Rb) gene family members p107 and pRb but not in fibroblasts harboring such mutations in the p53 gene. Taken together, these data suggest that one or more members of the pRb family (but not p53) play an essential role in mediating UV-induced expression from the CMV-IE promoter. In this study we report normal UV-upregulation of reporter expression in xeroderma pigmentosum (XP) group E fibroblasts, consistent with normal TCR. Because XP-E cells deficient in the p48 subunit of the damaged DNA-binding protein are impaired in E2F-1-activated transcription, these results also suggest that the (pRb-regulated) transcription factor E2F-1 does not play an essential role in UV-enhanced expression from the CMV-IE promoter.

YY1 is regulated by O-linked N-acetylglucosaminylation (O-glcNAcylation)

YY1 is a zinc finger DNA-binding transcription factor that influences expression of a wide variety of cellular and viral genes. YY1 is essential for the development of mammalian embryos. It regulates the expression of genes with important functions in DNA replication, protein synthesis, and cellular response to external stimuli during cell growth and differentiation. How YY1 accomplishes such a variety of functions is unknown. Here, we show that a subset of the nuclear YY1 appears to be O-GlcNAcylated regardless of the differentiation status of the cells. We found that glucose strongly stimulates O-linked N-acetylglucosaminylation (O-GlcNAcylation) on YY1. Glycosylated YY1 no longer binds the retinoblastoma protein (Rb). Upon dissociation from Rb, the glycosylated YY1 is free to bind DNA. The ability of the O-glycosylation on YY1 to disrupt the complex with Rb leads us to propose that O-glycosylation might have a profound effect on cell cycle transitions that regulate the YY1-Rb heterodimerization and promote the activity of YY1. Our observations provide strong evidence that YY1-regulated transcription is very likely connected to the pathway of glucose metabolism that culminates in the O-GlcNAcylation on YY1, changing its function in transcription.

Regulation of gene transcription by a constitutively active mutant of activating transcription factor 2 (ATF2)

Activating transcription factor 2 (ATF2) belongs to the family of basic region leucine zipper (bZIP) proteins that are characterized by the presence of a basic domain that functions as the DNA-binding domain and a leucine zipper domain that is required for dimerization. Together with bZIP proteins of the Fos and Jun families, ATF2 constitutes the AP-1 transcription factor complex. The biological activity of ATF2 is controlled by phosphorylation of two threonine residues within the N-terminal activation domain. Unphosphorylated ATF2 is trancriptionally silent, excluding simple overexpression studies to identify transcriptional targets of ATF2. We therefore decided to construct a constitutively active ATF2 mutant that would allow us to uncouple the investigation of transcriptional targets and biological functions of ATF2 from the variety of signaling pathways that lead to an activation of ATF2. We exchanged the phosphorylation-dependent activation domain of ATF2 with the constitutively active transcriptional activation domain of the transcription factor CREB2. In transient transfection experiments, this constitutively active ATF2 mutant stimulated c-jun, tumor necrosis factor alpha, and Fas ligand promoter activities. The transcriptional activity of the constitutively active ATF2 mutant could be impaired by dominant-negative forms of ATF2 or c-Jun, indicating that ATF2 and c-Jun utilize a similar dimerization code. In contrast, a dominant-negative CREB2 mutant did not impair ATF2-mediated transcriptional activation, suggesting that CREB2 exhibits a different dimerization specificity than ATF2 or c-Jun.

Polymorphisms in the transforming growth factor beta 1 gene and osteoporosis

Transforming growth factor (TGF)-beta1 is the most abundant growth factor in human bone. It is produced by osteoblasts and inhibits osteoclast proliferation and activity and stimulates proliferation and differentiation of preosteoblasts. Several polymorphisms have been described in the TGF-beta1 gene. Previously, we and others have found associations between some of these polymorphisms and bone mass. We therefore wanted to examine if these polymorphisms are also predictors of osteoporotic fractures. The polymorphisms G(-1639)-A, C(-1348)-T, C(-765)insC, T(29)-C, G(74)-C, 713-8delC, C(788)-T, and T(816-20)-C were examined using RFLP and sequencing in 296 osteoporotic patients with vertebral fractures and 330 normal individuals. Bone mineral density (BMD) was examined at the lumbar spine and at the femoral neck by DXA. Genotype distributions were in H-W equilibrium. Linkage disequilibrium was found between the polymorphisms. The T(816-20)-C genotypes were distributed differently among osteoporotic patients and normal controls. The TT genotype was less common in individuals with osteoporotic fractures (chi(2) = 6.02, P < 0.05). BMD was higher in individuals with the TT-genotype (T(816-20)-C) at the lumbar spine, 0.960 +/- 0.173 g/cm(2) compared with individuals with the TC or CC genotypes: 0.849 +/- 0.181 g/cm(2) and 0.876 +/- 0.179 g/cm(2), respectively (P < 0.001, ANOVA). Similar differences between genotypes were found at the different hip regions as well as at the total hip. Individuals with the TT-genotype (C(-1348)-T) had higher bone mass at the femoral neck: 0.743 +/- 0.134 g/cm(2) compared with 0.703 +/- 0.119 g/cm(2) in individuals with TC or CC genotypes (P < 0.05). Individuals with the CC-genotype (T(29)-C) had higher bone mass at the femoral neck, 0.735 +/- 0.128 g/cm(2) compared with 0.703 +/- 0.120 g/cm(2) in individuals with TC or TT genotypes (P < 0.05) and at the total hip: 0.852 +/- 0.166 g/cm(2) vs. 0.818 +/- 0.149 g/cm(2), respectively (P < 0.05). None of the other polymorphisms were distributed differently in patients and controls and did not affect BMD. In conclusion, The TT genotype of the T(816-20)-C polymorphism is less common in patients with osteoporotic fractures and is associated with higher bone mass both at the lumbar spine and at the hip. The C(-1348)-T and T(29)-C polymorphisms were distributed similarly in osteoporotic patients and normal controls, however, the rare genotypes were associated with higher bone mass at the hip.

Mitogen-activated protein kinase p38 defines the common senescence-signalling pathway

BACKGROUND

Cellular senescence is a state of irreversible growth arrest shown by normal cells, and has been most extensively studied in replicative senescence caused by telomere shortening. Several conditions, including oncogenic Ras over-expression and inappropriate culture conditions, also induce senescence without telomere shortening. However, it remains unclear how a common set of senescence phenotypes is indistinguishably induced in various types of senescence.

RESULTS

We demonstrate that p38 mitogen-activated protein kinase (MAPK) plays important causative roles in senescent cells following telomere shortening, Ras-Raf activation, oxidative stress or inappropriate culture conditions. By monitoring the kinetics of p38 activation, we suggest that p38 is activated not directly by the initial stimuli, but in response to unidentified cellular conditions caused by these stimuli. Importantly, this p38-activating condition appears to be defined quantitatively as a sum of continuous and low-level stresses, and remains even after the initial stimuli are withdrawn, which may explain the well-known irreversible nature of cellular senescence. We also show that papilloma virus E7 abolishes the p38-induced growth arrest but not other senescence-associated phenotypes, indicating the differential role of pRb in the downstream of p38.

CONCLUSION

These results indicate that p38 comprises the senescence-executing pathway in response to diverse stimuli.

Signal transduction in H2O2-induced senescence-like phenotype in human diploid fibroblasts

A stress-induced senescence-like phenotype is induced by exposure of human diploid fibroblasts to subcytotoxic H2O2 stress. Previous studies showed that TGF-beta1 is responsible for the induction of several biomarkers of replicative senescence within 72 h after stress: senescence-like morphology, senescence-associated beta-galactosidase activity, and an increase in the mRNA steady state level of four senescence-associated genes. Other studies showed that the retinoblastoma protein is responsible for the appearance of these biomarkers in the same conditions. Here we show that sustained p38(MAPK) phosphorylation is responsible for both H2O2-induced overexpression of TGF-beta 1 and subsequent TGF-beta 1-induced appearance of these biomarkers. p38(MAPK) phosphorylation is shown to be necessary for a self-sustained TGF-beta 1 overexpression after H2O2 stress through the activation of ATF-2 transcription factor, thereby creating a regulatory loop between sustained p38(MAPK) activation and sustained TGF-beta 1 overexpression after stress. p38(MAPK) activation is also shown to be responsible in part for the growth arrest observed in stress-induced senescence-like phenotype. At 48 h after stress, ATF-2 starts to interact with hypophosphorylated Rb, which allows the biomarkers of stress-induced senescence-like phenotype to appear. This report gives an overall explanation of how a senescence-like phenotype is established after subcytotoxic H2O2 stress.

An ATF2-derived peptide sensitizes melanomas to apoptosis and inhibits their growth and metastasis

Melanomas are among the aggressive tumor types because of their notorious resistance to treatment and their high capacity to metastasize. ATF2 is among transcription factors implicated in the progression of melanoma and its resistance to treatment. Here we demonstrate that the expression of a peptide spanning amino acids 50-100 of ATF2 (ATF2(50-100)) reduces ATF2 transcriptional activities while increasing the expression and activity of c-Jun. Altering the balance of Jun/ATF2 transcriptional activities sensitized melanoma cells to apoptosis, an effect that could be attenuated by inhibiting c-Jun. Inhibition of ATF2 via RNA interference likewise increased c-Jun expression and primed melanoma cells to undergo apoptosis. Growth and metastasis of SW1 and B16F10 mouse melanomas were inhibited by ATF2(50-100) to varying degrees up to a complete regression, depending on the mode (inducible, constitutive, or adenoviral delivery) of its expression.

P38 and activating transcription factor-2 involvement in osteoblast osmotic response to elevated extracellular glucose

Poorly controlled or untreated type I diabetes mellitus is characterized by hyperglycemia and is associated with decreased bone mass and osteoporosis. We have demonstrated that osteoblasts are sensitive to hyperglycemia-associated osmotic stress and respond to elevated extracellular glucose or mannitol by increasing c-jun and collagen I expression. To determine whether MAPKs are involved in this response, MC3T3-E1 osteoblasts were treated with 16.5 mm glucose, mannitol, or contrast dye for 1 h. Immunoblotting of phosphorylated p38 demonstrated activation of p38 MAPK by hyperosmotic stress in vitro and in vivo. Activation peaked at 20 min, remained detectable after 24 h, and was protein kinase C-independent. Activating transcription factor-2 (ATF-2) activation followed the same pattern as phospho-p38. Transactivation of cAMP response element (CRE)- and c-jun promoter (containing a CRE-like element)-reporter constructs increased following hyperosmotic treatment. SB 203580 (a p38 MAPK inhibitor) blocked ATF-2 phosphorylation, CRE transactivation, and c-jun promoter activation. Hyperosmotic activation of collagen I promoter activity was also inhibited by SB 203580, consistent with the involvement of c-jun in collagen I up-regulation. Therefore, we propose that hyperglycemia-induced increases in p38 MAPK activity and ATF-2 phosphorylation contribute to CRE activation and modulation of c-jun and collagen I expression in osteoblasts.

Transcription factor E2F-1 acts as a growth-promoting factor and is associated with adverse prognosis in non-small cell lung carcinomas

Numerous upstream stimulatory and inhibitory signals converge to the pRb/E2F pathway, which governs cell-cycle progression, but the information concerning alterations of E2F-1 in primary malignancies is very limited. Several in vitro studies report that E2F-1 can act either as an oncoprotein or as a tumour suppressor protein. In view of this dichotomy in its functions and its critical role in cell cycle control, this study examined the following four aspects of E2F-1 in a panel of 87 non-small cell lung carcinomas (NSCLCs), previously analysed for defects in the pRb-p53-MDM2 network: firstly, the status of E2F-1 at the protein, mRNA and DNA levels; secondly, its relationship with the kinetic parameters and genomic instability of the tumours; thirdly, its association with the status of its transcriptional co-activator CBP, downstream target PCNA and main cell cycle regulatory and E2F-1-interacting molecules pRb, p53 and MDM2; and fourthly, its impact on clinical outcome. The protein levels of E2F-1 and its co-activator CBP were significantly higher in the tumour area than in the corresponding normal epithelium (p<0.001). E2F-1 overexpression was associated with increased E2F-1 mRNA levels in 82% of the cases examined. The latter finding, along with the low frequency of E2F-1 gene amplification observed (9%), suggests that the main mechanism of E2F-1 protein overexpression in NSCLCs is deregulation at the transcriptional level. Mutational analysis revealed only one sample with asomatic mutation at codon 371 (Glu-->Asp) and one carrying a polymorphism at codon 393 (Gly-->Ser). Carcinomas with increased E2F-1 positivity demonstrated a significant increase in their growth indexes (r=0.402, p=0.001) and were associated with adverse prognosis (p=0.033 by Cox regression analysis). The main determinant of the positive association with growth was the parallel increase between E2F-1 staining and proliferation (r=0.746, p<0.001), whereas apoptosis was not influenced by the status of E2F-1. Moreover, correlation with the status of the pRb-p53-MDM2 network showed that the cases with aberrant pRb expression displayed significantly higher E2F-1 indexes (p=0.033), while a similar association was noticed in the group of carcinomas with deregulation of the p53-MDM2 feedback loop. In conclusion, the results suggest that E2F-1 overexpression may contribute to the development of NSCLCs by promoting proliferation and provide evidence that this role is further enhanced in a genetic background with deregulated pRb-p53-MDM2 circuitry.

An ATF2-derived peptide sensitizes melanomas to apoptosis and inhibits their growth and metastasis

Melanomas are among the aggressive tumor types because of their notorious resistance to treatment and their high capacity to metastasize. ATF2 is among transcription factors implicated in the progression of melanoma and its resistance to treatment. Here we demonstrate that the expression of a peptide spanning amino acids 50-100 of ATF2 (ATF2(50-100)) reduces ATF2 transcriptional activities while increasing the expression and activity of c-Jun. Altering the balance of Jun/ATF2 transcriptional activities sensitized melanoma cells to apoptosis, an effect that could be attenuated by inhibiting c-Jun. Inhibition of ATF2 via RNA interference likewise increased c-Jun expression and primed melanoma cells to undergo apoptosis. Growth and metastasis of SW1 and B16F10 mouse melanomas were inhibited by ATF2(50-100) to varying degrees up to a complete regression, depending on the mode (inducible, constitutive, or adenoviral delivery) of its expression.