STAT-1 facilitates the ATM activated checkpoint pathway following DNA damage

DNA damage repair gene mutations and their association with tumor immune regulatory gene expression in muscle invasive bladder cancer subtypes

BACKGROUND

Molecular subtyping of urothelial cancer (UC) has significantly advanced the understanding of bladder tumor heterogeneity and development of prognostic and predictive biomarkers. Evolving evidence across cancers strongly suggests that tumor immunoediting has a profound impact on the behaviour of cancer cells and their adaptation to the co-evolving microenvironment and response to treatment. In alignment with these concepts, recent immune checkpoint blockade (ICB) therapies in UC have demonstrated the predictive potential of mutations in the DNA damage repair (DDR) genes. A comprehensive understanding of DDR gene inactivation associated expression of immune regulatory genes could thus aid in expansion of current immunotherapies and predictive biomarkers for the design of patient-tailored combination treatments.

METHODS

We investigated pre-treatment tumor transcriptomic profiles of the five recently described molecular subtypes of muscle invasive urothelial cancer (MIUC; n = 408) from The Cancer Genome Atlas, to determine subtype specific immune cell abundance, expression of 67 immune regulatory genes, and association with DDR gene inactivation (via mutation, copy number alteration) profiles.

RESULTS

Analysis using CIBERSORT immune cell abundance determination tool showed significant differences in immune cell profiles and abundance between MIUC subtypes. Expression patterns of a selected panel of 67 genes including both immune stimulatory and inhibitory genes, showed significant associations with subtypes, and DDR gene mutation status.

CONCLUSION

Findings from our study provide compelling evidence for co-expression of multiple immune checkpoint genes including, PD-1, PD-L1, IDO1, TIGIT, TIM-3, TGFB1, LAG3, and others, that potentially contribute to compensatory immune evasion in bladder tumors. Our findings also emphasize the urgent need for biomarker discovery approaches that combine molecular subtype, DDR gene mutation status, tumor immune landscape classification, and immune checkpoint gene expression to increase the number of patients responding to immunotherapies.

Mechanism for IL-15-Driven B Cell Chronic Lymphocytic Leukemia Cycling: Roles for AKT and STAT5 in Modulating Cyclin D2 and DNA Damage Response Proteins

Clonal expansion of B cell chronic lymphocytic leukemia (B-CLL) occurs within lymphoid tissue pseudofollicles. IL-15, a stromal cell-associated cytokine found within spleens and lymph nodes of B-CLL patients, significantly boosts in vitro cycling of blood-derived B-CLL cells following CpG DNA priming. Both IL-15 and CpG DNA are elevated in microbe-draining lymphatic tissues, and unraveling the basis for IL-15-driven B-CLL growth could illuminate new therapeutic targets. Using CpG DNA-primed human B-CLL clones and approaches involving both immunofluorescent staining and pharmacologic inhibitors, we show that both PI3K/AKT and JAK/STAT5 pathways are activated and functionally important for IL-15→CD122/ɣc signaling in ODN-primed cells expressing activated pSTAT3. Furthermore, STAT5 activity must be sustained for continued cycling of CFSE-labeled B-CLL cells. Quantitative RT-PCR experiments with inhibitors of PI3K and STAT5 show that both contribute to IL-15-driven upregulation of mRNA for cyclin D2 and suppression of mRNA for DNA damage response mediators ATM, 53BP1, and MDC1. Furthermore, protein levels of these DNA damage response molecules are reduced by IL-15, as indicated by Western blotting and immunofluorescent staining. Bioinformatics analysis of ENCODE chromatin immunoprecipitation sequencing data from cell lines provides insight into possible mechanisms for STAT5-mediated repression. Finally, pharmacologic inhibitors of JAKs and STAT5 significantly curtailed B-CLL cycling when added either early or late in a growth response. We discuss how the IL-15-induced changes in gene expression lead to rapid cycling and possibly enhanced mutagenesis. STAT5 inhibitors might be an effective modality for blocking B-CLL growth in patients.

Progesterone receptors (PR) mediate STAT actions: PR and prolactin receptor signaling crosstalk in breast cancer models

Estrogen is the major mitogenic stimulus of mammary gland development during puberty wherein ER signaling acts to induce abundant PR expression. PR signaling, in contrast, is the primary driver of mammary epithelial cell proliferation in adulthood. The high circulating levels of progesterone during pregnancy signal through PR, inducing expression of the prolactin receptor (PRLR). Cooperation between PR and prolactin (PRL) signaling, via regulation of downstream components in the PRL signaling pathway including JAKs and STATs, facilitates the alveolar morphogenesis observed during pregnancy. Indeed, these pathways are fully integrated via activation of shared signaling pathways (i.e. JAKs, MAPKs) as well as by the convergence of PRs and STATs at target genes relevant to both mammary gland biology and breast cancer progression (i.e. proliferation, stem cell outgrowth, tissue cell type heterogeneity). Thus, rather than a single mediator such as ER, transcription factor cascades (ER>PR>STATs) are responsible for rapid proliferative and developmental programming in the normal mammary gland. It is not surprising that these same mediators typify uncontrolled proliferation in a majority of breast cancers, where ER and PR are most often co-expressed and may cooperate to drive malignant tumor progression. This review will primarily focus on the integration of PR and PRL signaling in breast cancer models and the importance of this cross-talk in cancer progression in the context of mammographic density. Components of these PR/PRL signaling pathways could offer alternative drug targets and logical complements to anti-ER or anti-estrogen-based endocrine therapies.

Biological determinants of radioresistance and their remediation in pancreatic cancer

Despite recent advances in radiotherapy, a majority of patients diagnosed with pancreatic cancer (PC) do not achieve objective responses due to the existence of intrinsic and acquired radioresistance. Identification of molecular mechanisms that compromise the efficacy of radiation therapy and targeting these pathways is paramount for improving radiation response in PC patients. In this review, we have summarized molecular mechanisms associated with the radio-resistant phenotype of PC. Briefly, we discuss the reversible and irreversible biological consequences of radiotherapy, such as DNA damage and DNA repair, mechanisms of cancer cell survival and radiation-induced apoptosis following radiotherapy. We further describe various small molecule inhibitors and molecular targeting agents currently being tested in preclinical and clinical studies as potential radiosensitizers for PC. Notably, we draw attention towards the confounding effects of cancer stem cells, immune system, and the tumor microenvironment in the context of PC radioresistance and radiosensitization. Finally, we discuss the need for examining selective radioprotectors in light of the emerging evidence on radiation toxicity to non-target tissue associated with PC radiotherapy.

Persistent transcriptional responses show the involvement of feed-forward control in a repeated dose toxicity study

Chemical carcinogenesis, albeit complex, often relies on modulation of transcription through activation or repression of key transcription factors. While analyzing extensive networks may hinder the biological interpretation, one may focus on dynamic network motifs, among which persistent feed-forward loops (FFLs) are known to chronically influence transcriptional programming. Here, to investigate the relevance a FFL-oriented approach in depth, we have focused on aflatoxin B1-induced transcriptomic alterations during distinct states of exposure (daily administration during 5days followed by a non-exposed period) of human hepatocytes, by exploring known interactions in human transcription. Several TF-coding genes were persistently deregulated after washout of AFB1. Oncogene MYC was identified as the prominent regulator and driver of many FFLs, among which a FFL comprising MYC/HIF1A was the most recurrent. The MYC/HIF1A FFL was also identified and validated in an independent set as the master regulator of metabolic alterations linked to initiation and progression of carcinogenesis, i.e. the Warburg effect, possibly as result of persistent intracellular alterations arising from AFB1 exposure (nuclear and mitochondrial DNA damage, oxidative stress, transcriptional activation by secondary messengers). In summary, our analysis shows the involvement of FFLs as modulators of gene expression suggestive of a carcinogenic potential even after termination of exposure.

Activation of IFN/STAT1 signalling predicts response to chemotherapy in oestrogen receptor-negative breast cancer

Background:

Oestrogen receptor-negative (ER−) breast cancer is intrinsically sensitive to chemotherapy. However, tumour response is often incomplete, and relapse occurs with high frequency. The aim of this work was to analyse the molecular characteristics of residual tumours and early response to chemotherapy in patient-derived xenografts (PDXs) of breast cancer.

Methods:

Gene and protein expression profiles were analysed in a panel of ER− breast cancer PDXs before and after chemotherapy treatment. Tumour and stromal interferon-gamma expression was measured in xenografts lysates by human and mouse cytokine arrays, respectively.

Results:

The analysis of residual tumour cells in chemo-responder PDX revealed a strong overexpression of IFN-inducible genes, induced early after AC treatment and associated with increased STAT1 phosphorylation, DNA-damage and apoptosis. No increase in IFN-inducible gene expression was observed in chemo-resistant PDXs upon chemotherapy. Overexpression of IFN-related genes was associated with human IFN-γ secretion by tumour cells.

Conclusions:

Treatment-induced activation of the IFN/STAT1 pathway in tumour cells is associated with chemotherapy response in ER− breast cancer. Further validations in prospective clinical trials will aim to evaluate the usefulness of this signature to assist therapeutic strategies in the clinical setting.

Distal regulatory element of the STAT1 gene potentially mediates positive feedback control of STAT1 expression

We previously identified a distal regulatory element located approximately 5.5-kb upstream of the signal transducer and activator of transcription 1 (STAT1) gene, thereafter designating it as 5.5-kb upstream regulatory region (5.5URR). In this study, we investigated the functional roles of 5.5URR in the transcriptional regulation of STAT1 gene. A chromosome conformation capture assay indicated physical interaction of 5.5URR with the STAT1 core promoter. In luciferase reporter assays, 5.5URR-combined STAT1 core promoter exhibited significant increase in reporter activity enhanced by forced STAT1 expression or interferon (IFN) treatment, but STAT1 core promoter alone did not. The 5.5URR contained IFN-stimulated response element and GAS sites, which bound STAT1 complexes in electrophoretic mobility shift assays. Consistently, chromatin immunoprecipitation (ChIP) assays of HEK293 cells with Halo-tagged STAT1 expression indicated the association of Halo-tagged STAT1 with 5.5URR. ChIP assays with IFN treatment demonstrated that IFNs promoted the recruitment of Halo-tagged STAT1 to 5.5URR. Forced STAT1 expression or IFN treatment increased the expression of endogenous STAT1 and other IFN signaling pathway components, such as STAT2, IRF9 and IRF1, besides IFN-responsive genes. Collectively, the results suggest that 5.5URR may provide a regulatory platform for positive feedback control of STAT1 expression possibly to amplify or sustain the intracellular IFN signals.

The DNA damage response and immune signaling alliance: Is it good or bad? Nature decides when and where

The characteristic feature of healthy living organisms is the preservation of homeostasis. Compelling evidence highlight that the DNA damage response and repair (DDR/R) and immune response (ImmR) signaling networks work together favoring the harmonized function of (multi)cellular organisms. DNA and RNA viruses activate the DDR/R machinery in the host cells both directly and indirectly. Activation of DDR/R in turn favors the immunogenicity of the incipient cell. Hence, stimulation of DDR/R by exogenous or endogenous insults triggers innate and adaptive ImmR. The immunogenic properties of ionizing radiation, a prototypic DDR/R inducer, serve as suitable examples of how DDR/R stimulation alerts host immunity. Thus, critical cellular danger signals stimulate defense at the systemic level and vice versa. Disruption of DDR/R-ImmR cross talk compromises (multi)cellular integrity, leading to cell-cycle-related and immune defects. The emerging DDR/R-ImmR concept opens up a new avenue of therapeutic options, recalling the Hippocrates quote "everything in excess is opposed by nature."

Downregulation of MDC1 and 53BP1 by short hairpin RNA enhances radiosensitivity in laryngeal carcinoma cells

DNA double-strand breaks (DSBs) induced by ionizing radiation (IR) are among the most cytotoxic types of DNA damage. The DNA damage response (DDR) may be a reason for the cancer cell resistance to radiotherapy using IR. Identified as critical upstream mediators of the phosphorylation of ataxia telangiectasia-mutated (ATM) pathway, mediator of DNA damage checkpoint 1 (MDC1) and p53-binding proteins 1 (53BP1) may affect the radiosensitivity of tumor cells. In the present study, we generated two HEP-2 cell lines with a stable knockdown of MDC1 or 53BP1 with short hairpin RNA (shRNA), respectively, and investigated the effect of MDC1 and 53BP1 on cell radiosensitivity, cell cycle distribution and the formation of cell foci. Downregulation of the two proteins reduced the number of clonogenic cells that treated with IR. Accumulation of G2/M phase cells was detected after the MDC1 and 53BP1 downregulation. These results indicated that the expression of MDC1 or 53BP1 limited tumor cell sensitivity to radiotherapy and may play an important role in the DNA repair progression. Furthermore, the MDC1 foci was identified and presented in the 53BP1-inhibited cells. By contrast, the 53BP1 foci was absent from the MDC1-inhibited cells. The results confirmed that the recruitment of 53BP1 into the foci occurred in an MDC1-dependent manner.

Stat1 stimulates cap-independent mRNA translation to inhibit cell proliferation and promote survival in response to antitumor drugs

The signal transducer and activator of transcription 1 (Stat1) functions as a tumor suppressor via immune regulatory and cell-autonomous pathways. Herein, we report a previously unidentified cell-autonomous Stat1 function, which is its ability to exhibit both antiproliferative and prosurvival properties by facilitating translation of mRNAs encoding for the cyclin-dependent kinase inhibitor p27(Kip1) and antiapoptotic proteins X-linked inhibitor of apoptosis and B-cell lymphoma xl. Translation of the select mRNAs requires the transcriptional function of Stat1, resulting in the up-regulation of the p110γ subunit of phosphoinositide 3-kinase (PI3K) class IB and increased expression of the translational repressor translation initiation factor 4E (eIF4E)-binding protein 1 (4EBP1). Increased PI3Kγ signaling promotes the degradation of the eIF4A inhibitor programmed cell death protein 4, which favors the cap-independent translation of the select mRNAs under conditions of general inhibition of protein synthesis by up-regulated eIF4E-binding protein 1. As such, Stat1 inhibits cell proliferation but also renders cells increasingly resistant to antiproliferative effects of pharmacological inhibitors of PI3K and/or mammalian target of rapamycin. Stat1 also protects Ras-transformed cells from the genotoxic effects of doxorubicin in culture and immune-deficient mice. Our findings demonstrate an important role of mRNA translation in the cell-autonomous Stat1 functions, with implications in tumor growth and treatment with chemotherapeutic drugs.

Up-regulation of the interferon-related genes in BRCA2 knockout epithelial cells

BRCA2 mutations are significantly associated with early-onset breast cancer, and the tumour-suppressing function of BRCA2 has been attributed to its involvement in homologous recombination (HR)-mediated DNA repair. In order to identify additional functions of BRCA2, we generated BRCA2-knockout HCT116 human colorectal carcinoma cells. Using genome-wide microarray analyses, we have discovered a link between the loss of BRCA2 and the up-regulation of a subset of interferon (IFN)-related genes, including APOBEC3F and APOBEC3G. The over-expression of IFN-related genes was confirmed in different human BRCA2(-/-) and mouse Brca2(-/-) tumour cell lines, and was independent of senescence and apoptosis. In isogenic wild-type BRCA2 cells, we observed over-expression of IFN-related genes after treatment with DNA-damaging agents, and following ionizing radiation. Cells with endogenous DNA damage because of defective BRCA1 or RAD51 also exhibited over-expression of IFN-related genes. Transcriptional activity of the IFN-stimulated response element (ISRE) was increased in BRCA2 knockout cells, and the expression of BRCA2 greatly decreased IFNα-stimulated ISRE reporter activity, suggesting that BRCA2 directly represses the expression of IFN-related genes through the ISRE. Finally, the colony-forming capacity of BRCA2 knockout cells was significantly reduced in the presence of either IFNβ or IFNγ, suggesting that IFNs may have potential as therapeutic agents in cancer cells with BRCA2 mutations. The GEO Accession No. for microarray analysis is GSE54830.

PE‑induced apoptosis in SMMC‑7721 cells: involvement of Erk and Stat signalling pathways

Emerging evidence indicates that the redistribution of phosphatidylethanolamine (PE) across the bilayer of the plasma membrane is an important molecular marker for apoptosis. However, the effect of PE on apoptosis and the underlying mechanism of PE remain unclear. In the current study, MTT and flow cytometric assays were used to examine the effects of PE on apoptosis in SMMC‑7721 cells. The level of mitochondrial membrane potential (ΔΨm) and the expression of Bax, Bcl‑2, caspase‑3, phospho‑Erk and phospho‑Stat1/2 in SMMC‑7721 cells that were exposed to PE were also investigated. The results showed that PE inhibited proliferation, caused G0/G1 phase cell cycle arrest and induced apoptosis in SMMC‑7721 cells in a dose‑dependent manner. Rhodamine 123 staining showed that the treatment of SMMC‑7721 cells with different concentrations of PE for 24 h significantly decreased the level of ΔΨm and exerted dose‑dependent effects. Using immunofluorescence and western blotting, we found that the expression of Bax was upregulated, whereas that of Bcl‑2 was downregulated in PE‑induced apoptotic cells. In addition, these events were accompanied by an increase in caspase‑3 expression in a dose‑dependent manner following PE treatment. PE‑induced apoptosis was accompanied by a decrease in Erk phospho-rylation and by the activation of Stat1/2 phosphorylation in SMMC‑7721 cells. In conclusion, the results suggested that PE‑induced apoptosis is involved in upregulating the Bax/Bcl‑2 protein ratio and decreasing the ΔΨm. Moreover, the results showed that the Erk and Stat1/2 signalling pathways may be involved in the process of PE‑induced apoptosis.

Interferons and their stimulated genes in the tumor microenvironment

Constitutive expression of interferons (IFNs) and activation of their signaling pathways have pivotal roles in host responses to malignant cells in the tumor microenvironment. IFNs are induced by the innate immune system and in tumors through stimulation of Toll-like receptors (TLRs) and through other signaling pathways in response to specific cytokines. Although in the oncologic context IFNs have been thought of more as exogenous pharmaceuticals, the autocrine and paracrine actions of endogenous IFNs probably have even more critical effects on neoplastic disease outcomes. Through high-affinity cell surface receptors, IFNs modulate transcriptional signaling, leading to regulation of more than 2,000 genes with varying patterns of temporal expression. Induction of the gene products by both unphosphorylated and phosphorylated STAT1 after ligand binding results in alterations in tumor cell survival, inhibition of angiogenesis, and augmentation of actions of T, natural killer (NK), and dendritic cells. The interferon-stimulated gene (ISG) signature can be a favorable biomarker of immune response but, in a seemingly paradoxical finding, a specific subset of the full ISG signature indicates an unfavorable response to DNA-damaging interventions such as radiation. IFNs in the tumor microenvironment thus can alter the emergence, progression, and regression of malignancies.

Role of STAT1 in the breast

Signal transducer and activator of transcription-1 (STAT1) plays a role in the transduction of stress and cytokine responses, DNA damage, and activation of B and T cell immune responses. The ability of STAT1 to act as a pro- or anti-apoptotic signaling molecule depends upon the cellular environment and stimulus. Post-translational modifications provide the main method of control over the function of STAT1, however, recent data in the breast has shown that loss of STAT1 from both the tumor and the surrounding mammary epithelium greatly influence the development and response to treatment of breast cancers. Here, we discuss the recent findings of Chan et al. in Breast Cancer Research who described a new role for STAT1 in the development of estrogen receptor (ER)-positive and progesterone receptor (PR)-positive luminal breast cancers.

Phosphorylated signal transducer and activator of transcription-1 immunohistochemical expression is associated with improved survival in patients with oral squamous cell carcinoma

PURPOSE

To estimate whether the immunohistochemical (IHC) expression patterns of the tumor suppressor gene signal transducer and activator of transcription-1 (STAT1) and its active phosphorylated form (PSTAT1) serve as potential prognostic and predictive markers in patients with oral squamous cell carcinoma (OSCC).

MATERIALS AND METHODS

STAT1 and PSTAT1 protein expressions were examined immunohistochemically in OSCC tumor tissues and adjacent normal mucosa from 49 patients who underwent primary surgery. The IHC scores were correlated with all available clinicopathologic parameters that were obtained from a maximum of 7 years of follow-up, including survival and response to adjuvant therapy treatment.

RESULTS

There was a shift toward lower percentages of cells with STAT1 (P < .014) and PSTAT1 (P < .001) detected in OSCC tumors compared with adjacent normal tissue sites. No association with patients' clinicopathologic characteristics was shown. However, for the group of patients who received adjuvant chemotherapy, increased PSTAT1 intensity of staining in OSCC tumors was strongly associated with better overall survival (P = .008).

CONCLUSIONS

This is the first study to concurrently evaluate STAT1 and PSTAT1 IHC expression patterns and their prognostic significance in patients with OSCC, highlighting the potential role of PSTAT1 as a biomarker in therapeutic decision making. Large prospective studies are needed to verify these findings.

STAT3 as a new autophagy regulator

Signal transducers and activators of transcription 3 (STAT3) proteins are cytoplasmic transcription factors that translocate into the nucleus to induce transcription following growth factor or cytokine stimulation. Besides their normal functions, these proteins play an important role in cancer cells through the abnormal activation of cell cycle progression and the deregulation of survival and senescence pathways. New data obtained from the laboratory of Guido Kroemer identifies STAT3 as a new autophagy regulator. In the cytoplasm, in the absence of conventional phosphorylation on the tyrosine 705 residue, STAT3 interacts with the PKR kinase to inhibit eIF2A phosphorylation and so reduce autophagic pathways. This new and nonconventional function of STAT3 has an important role in normal cells but we suggest that it might also affect cancer cells and the response to chemotherapy treatment.

REACTIN: regulatory activity inference of transcription factors underlying human diseases with application to breast cancer

BACKGROUND

Genetic alterations of transcription factors (TFs) have been implicated in the tumorigenesis of cancers. In many cancers, alteration of TFs results in aberrant activity of them without changing their gene expression level. Gene expression data from microarray or RNA-seq experiments can capture the expression change of genes, however, it is still challenge to reveal the activity change of TFs.

RESULTS

Here we propose a method, called REACTIN (REgulatory ACTivity INference), which integrates TF binding data with gene expression data to identify TFs with significantly differential activity between disease and normal samples. REACTIN successfully detect differential activity of estrogen receptor (ER) between ER+ and ER- samples in 10 breast cancer datasets. When applied to compare tumor and normal breast samples, it reveals TFs that are critical for carcinogenesis of breast cancer. Moreover, Reaction can be utilized to identify transcriptional programs that are predictive to patient survival time of breast cancer patients.

CONCLUSIONS

REACTIN provides a useful tool to investigate regulatory programs underlying a biological process providing the related case and control gene expression data. Considering the enormous amount of cancer gene expression data and the increasingly accumulating ChIP-seq data, we expect wide application of REACTIN for revealing the regulatory mechanisms of various diseases.

How should we define STAT3 as an oncogene and as a potential target for therapy?

Aberrant activation of the STAT3 transcription factor has been reported in a large group of tumors and a strong biological basis now defines this protein as an oncogenic driver. Consequently, STAT3 is considered to be a promising target in the field of cancer therapy. For its inhibition to result in a successful therapeutic approach, the definition of a target tumor population identified by specific and detectable alterations is critical. The canonical activation model of STAT3 relies on a constitutive phosphorylation on its 705 tyrosine site, resulting in its dimerization, nuclear translocation, and the consequent activation of cancer genes. Therefore, it is expected that tumors expressing this phosphorylated form are addicted to STAT3 and will be sensitive to existing drugs which are targeting this dimeric form. However, recent results have shown that STAT3 can function as an oncogene in the absence of this tyrosine phosphorylation. This indicates that different forms of the transcription factor also play an important role in tumor growth and chemotherapy resistance. This complicates the definition of STAT3 as an oncogene and as a potential prognosis and predictive biomarker. The obligation to target a defined tumor type implies that future clinical trials should use a precise definition of STAT3 activation. This will allow tumors addicted to this oncogene to be identified correctly, leading to a strong rationale for patient stratification.

Biomarkers of residual disease, disseminated tumor cells, and metastases in the MMTV-PyMT breast cancer model

Cancer metastases arise in part from disseminated tumor cells originating from the primary tumor and from residual disease persisting after therapy. The identification of biomarkers on micro-metastases, disseminated tumors, and residual disease may yield novel tools for early detection and treatment of these disease states prior to their development into metastases and recurrent tumors. Here we describe the molecular profiling of disseminated tumor cells in lungs, lung metastases, and residual tumor cells in the MMTV-PyMT breast cancer model. MMTV-PyMT mice were bred with actin-GFP mice, and focal hyperplastic lesions from pubertal MMTV-PyMT;actin-GFP mice were orthotopically transplanted into FVB/n mice to track single tumor foci. Tumor-bearing mice were treated with TAC chemotherapy (docetaxel, doxorubicin, cyclophosphamide), and residual and relapsed tumor cells were sorted and profiled by mRNA microarray analysis. Data analysis revealed enrichment of the Jak/Stat pathway, Notch pathway, and epigenetic regulators in residual tumors. Stat1 was significantly up-regulated in a DNA-damage-resistant population of residual tumor cells, and a pre-existing Stat1 sub-population was identified in untreated tumors. Tumor cells from adenomas, carcinomas, lung disseminated tumor cells, and lung metastases were also sorted from MMTV-PyMT transplant mice and profiled by mRNA microarray. Whereas disseminated tumors cells appeared similar to carcinoma cells at the mRNA level, lung metastases were genotypically very different from disseminated cells and primary tumors. Lung metastases were enriched for a number of chromatin-modifying genes and stem cell-associated genes. Histone analysis of H3K4 and H3K9 suggested that lung metastases had been reprogrammed during malignant progression. These data identify novel biomarkers of residual tumor cells and disseminated tumor cells and implicate pathways that may mediate metastasis formation and tumor relapse after therapy.

Proteomic profiling of ATM kinase proficient and deficient cell lines upon blockage of proteasome activity

Ataxia Telangiectasia Mutated (ATM) protein kinase is a key effector in the modulation of the functionality of some important stress responses, including DNA damage and oxidative stress response, and its deficiency is the hallmark of Ataxia Telangiectasia (A-T), a rare genetic disorder. ATM modulates the activity of hundreds of target proteins, essential for the correct balance between proliferation and cell death. The aim of this study is to evaluate the phenotypic adaptation at the protein level both in basal condition and in presence of proteasome blockage in order to identify the molecules whose level and stability are modulated through ATM expression. We pursued a comparative analysis of ATM deficient and proficient lymphoblastoid cells by label-free shotgun proteomic experiments comparing the panel of proteins differentially expressed. Through a non-supervised comparative bioinformatic analysis these data provided an insight on the functional role of ATM deficiency in cellular carbohydrate metabolism's regulation. This hypothesis has been demonstrated by targeted metabolic fingerprint analysis SRM (Selected Reaction Monitoring) on specific thermodynamic checkpoints of glycolysis. This article is part of a Special Issue entitled: Translational Proteomics.

STAT1-deficient mice spontaneously develop estrogen receptor α-positive luminal mammary carcinomas

INTRODUCTION

Although breast cancers expressing estrogen receptor-α (ERα) and progesterone receptors (PR) are the most common form of mammary malignancy in humans, it has been difficult to develop a suitable mouse model showing similar steroid hormone responsiveness. STAT transcription factors play critical roles in mammary gland tumorigenesis, but the precise role of STAT1 remains unclear. Herein, we show that a subset of human breast cancers display reduced STAT1 expression and that mice lacking STAT1 surprisingly develop ERα+/PR+ mammary tumors.

METHODS

We used a combination of approaches, including histological examination, gene targeted mice, gene expression analysis, tumor transplantaion, and immunophenotyping, to pursue this study.

RESULTS

Forty-five percent (37/83) of human ERα+ and 22% (17/78) of ERα- breast cancers display undetectable or low levels of STAT1 expression in neoplastic cells. In contrast, STAT1 expression is elevated in epithelial cells of normal breast tissues adjacent to the malignant lesions, suggesting that STAT1 is selectively downregulated in the tumor cells during tumor progression. Interestingly, the expression levels of STAT1 in the tumor-infiltrating stromal cells remain elevated, indicating that single-cell resolution analysis of STAT1 level in primary breast cancer biopsies is necessary for accurate assessment. Female mice lacking functional STAT1 spontaneously develop mammary adenocarcinomas that comprise > 90% ERα+/PR+ tumor cells, and depend on estrogen for tumor engraftment and progression. Phenotypic marker analyses demonstrate that STAT1-/- mammary tumors arise from luminal epithelial cells, but not myoepithelial cells. In addition, the molecular signature of the STAT1-/- mammary tumors overlaps closely to that of human luminal breast cancers. Finally, introduction of wildtype STAT1, but not a STAT1 mutant lacking the critical Tyr701 residue, into STAT1-/- mammary tumor cells results in apoptosis, demonstrating that the tumor suppressor function of STAT1 is cell-autonomous and requires its transcriptional activity.

CONCLUSIONS

Our findings demonstrate that STAT1 suppresses mammary tumor formation and its expression is frequently lost during breast cancer progression. Spontaneous mammary tumors that develop in STAT1-/- mice closely recapitulate the progression, ovarian hormone responsiveness, and molecular characteristics of human luminal breast cancer, the most common subtype of human breast neoplasms, and thus represent a valuable platform for testing novel treatments and detection modalities.

The DNA damage response induces IFN

This study reveals a new complexity in the cellular response to DNA damage: activation of IFN signaling. The DNA damage response involves the rapid recruitment of repair enzymes and the activation of signal transducers that regulate cell-cycle checkpoints and cell survival. To understand the link between DNA damage and the innate cellular defense that occurs in response to many viral infections, we evaluated the effects of agents such as etoposide that promote dsDNA breaks. Treatment of human cells with etoposide led to the induction of IFN-stimulated genes and the IFN-α and IFN-λ genes. NF-κB, known to be activated in response to DNA damage, was shown to be a key regulator of this IFN gene induction. Expression of an NF-κB subunit, p65/RelA, was sufficient for induction of the human IFN-λ1 gene. In addition, NF-κB was required for the induction of IFN regulatory factor-1 and -7 that are able to stimulate expression of the IFN-α and IFN-λ genes. Cells that lack the NF-κB essential modulator lack the ability to induce the IFN genes following DNA damage. Breaks in DNA are generated during normal physiological processes of replication, transcription, and recombination, as well as by external genotoxic agents or infectious agents. The significant finding of IFN production as a stress response to DNA damage provides a new perspective on the role of IFN signaling.

STAT6 expression in glioblastoma promotes invasive growth

BACKGROUND

Glioblastoma (GBM) is a highly aggressive malignant primary brain tumor, characterized by rapid growth, diffuse infiltration of cells into both adjacent and remote brain regions, and a generalized resistance to currently available treatment modalities. Recent reports in the literature suggest that Signal Transducers and Activators of Transcription (STATs) play important roles in the regulation of GBM pathophysiology.

METHODS

STAT6 protein expression was analyzed by Western blotting in GBM cell lines and by immunohistochemistry in a tissue microarray (TMA) of glioma patient tissues. We utilized shRNA against STAT6 to investigate the effects of prolonged STAT6 depletion on the growth and invasion of two STAT6-positive GBM cell lines. Cell proliferation was assessed by measuring (3)H-Thymidine uptake over time. Invasion was measured using an in vitro transwell assay in which cells invade through a type IV collagen matrix toward a chemoattractant (Fetal Bovine Serum). Cells were then stained and counted. Kaplan-Meyer survival curves were generated to show the correlation between STAT6 gene expression and patient survival in 343 glioma patients and in a subset of patients with only GBM. Gene expression microarray and clinical data were acquired from the Rembrandt 1 public data depository (https://caintegrator.nci.nih.gov/rembrandt/). Lastly, a genome-wide expression microarray analysis was performed to compare gene expression in wild-type GBM cells to expression in stable STAT6 knockdown clones.

RESULTS

STAT6 was expressed in 2 GBM cell lines, U-1242MG and U-87MG, and in normal astrocytes (NHA) but not in the U-251MG GBM cell line. In our TMA study, STAT6 immunostaining was visible in the majority of astrocytomas of all grades (I-IV) but not in normal brain tissue. In positive cells, STAT6 was localized exclusively in the nuclei over 95% of the time. STAT6-deficient GBM cells showed a reduction in (3)H-Thymidine uptake compared to the wild-type. There was some variation among the different shRNA- silenced clones, but all had a reduction in (3)H-Thymidine uptake ranging from 35%- 70% in U-1242MG and 40- 50% in U-87MG cells. Additionally, STAT6- depleted cells were less invasive than controls in our in vitro transmembrane invasion assay. Invasiveness was decreased by 25-40% and 30-75% in U-1242MG and U-87MG cells, respectively. The microarray analysis identified matrix metalloproteinase 1 (MMP-1) and urokinase Plasminogen activator (uPA) as potential STA6 target genes involved in the promotion of GBM cell invasion. In a Kaplan-Meier survival curve based on Rembrandt 1 gene expression microarray and clinical data, there was a significant difference in survival (P < 0.05) between glioma patients with up- and down-regulated STAT6. Decreased STAT6 expression correlated with longer survival times. In two subsets of patients with either grade IV tumors (GBM) or Grade II/III astrocytomas, there was a similar trend that however did not reach statistical significance.

CONCLUSIONS

Taken together, these findings suggest a role for STAT6 in enhancing cell proliferation and invasion in GBM, which may explain why up-regulation of STAT6 correlates with shorter survival times in glioma patients. This report thus identifies STAT6 as a new and potentially promising therapeutic target.

Activation of interferon-stimulated genes by gamma-ray irradiation independently of the ataxia telangiectasia mutated-p53 pathway

The ataxia telangiectasia mutated (ATM)-p53 pathway is a well-known main signal transduction pathway for cellular responses, which is activated by γ-ray irradiation. Microarray analysis showed changes in the expressions of IFN-stimulated genes (ISG) in γ-ray-irradiated Balb/cA/Atm-deficient mouse embryonic fibroblasts (MEF) (ATM-KO), indicating that another pathway for cellular responses besides the ATM-p53 pathway was activated by γ-ray irradiation. The basal expression levels of Irf7 and Stat1 in ATM-KO and p53-deficient MEFs (p53-KO) were higher than those in Atm-wild-type MEFs (ATM-WT) and p53-wild-type MEFs (p53-WT), respectively. Irradiation stimulated the expressions of Irf7 and Stat1 in ATM-KO, p53-KO, ATM-WT, and p53-WT, indicating that upregulation of Irf7 and Stat1 expressions by irradiation did not depend on the ATM-p53 pathway. When conditioned medium (CM) obtained from irradiated ATM-WT or ATM-KO was added to nonirradiated MEFs, the expressions of Irf7 and Stat1 increased. We predicted that gene activation in nonirradiated MEFs was caused by IFN-α/β. Unexpectedly, significant amount of IFN-α/β could not be detected in the CM from irradiated ATM-WT or ATM-KO. Meanwhile, increased expression of Ccl5 (RANTES) protein was detected in the CM from irradiated MEFs. These results indicate that ISGs were activated by γ-ray irradiation independently of the ATM-p53 pathway and gene activation was caused by radiation-induced soluble factors.

STAT3 modulates the DNA damage response pathway

The STAT3 transcription factor is well known to function as an anti-apoptotic factor, especially in numerous malignancies. Recently we showed that STAT3 is cytoprotective and that cells lacking STAT3 are more sensitive to oxidative stress. A key feature of oxidative stress involves activation of the DNA damage pathway. However, a role for STAT3 or its contribution in response to DNA damage has not been described. In the present study we show that cells lacking STAT3 are less efficient in repairing damaged DNA. Moreover, STAT3 deficient cells show reduced activity of the ATM-Chk2 and ATR-Chk1 pathways, both important pathways in sensing DNA damage. Finally we show that MDC1, a regulator of the ATM-Chk2 pathway and facilitator of the DNA damage response, is modulated by STAT3 at the transcriptional level. These findings demonstrate that STAT3 is necessary for efficient repair of damaged DNA, partly by modulating the ATM-Chk2 and ATR-Chk1 pathways.

The cdk5 kinase regulates the STAT3 transcription factor to prevent DNA damage upon topoisomerase I inhibition

The STAT3 transcription factors are cytoplasmic proteins that induce gene activation in response to growth factor stimulation. Following tyrosine phosphorylation, STAT3 proteins dimerize, translocate to the nucleus, and activate specific target genes involved in cell-cycle progression. Despite its importance in cancer cells, the molecular mechanisms by which this protein is regulated in response to DNA damage remain to be characterized. In this study, we show that STAT3 is activated in response to topoisomerase I inhibition. Following treatment, STAT3 is phosphorylated on its C-terminal serine 727 residue but not on its tyrosine 705 site. We also show that topoisomerase I inhibition induced the up-regulation of the cdk5 kinase, a protein initially described in neuronal stress responses. In co-immunoprecipitations, cdk5 was found to associate with STAT3, and pulldown experiments indicated that it associates with the C-terminal activation domain of STAT3 upon DNA damage. Importantly, the cdk5-STAT3 pathway reduced DNA damage in response to topoisomerase I inhibition through the up-regulation of Eme1, an endonuclease involved in DNA repair. ChIP experiments indicated that STAT3 can be found associated with the Eme1 promoter when phosphorylated only on its serine 727 residue and not on tyrosine 705. We therefore propose that the cdk5-STAT3 oncogenic pathway plays an important role in the expression of DNA repair genes and that these proteins could be used as predictive markers of tumors that will fail to respond to chemotherapy.

STAT1 and pathogens, not a friendly relationship

STAT1 belongs to the STAT family of transcription factors, which comprises seven factors: STAT1, STAT2, STAT3, STAT4, STAT5A, STAT5B and STAT6. STAT1 is a 91 kDa protein originally identified as the mediator of the cellular response to interferon (IFN) α, and thereafter found to be a major component of the cellular response to IFNγ. STAT1 is, in fact, involved in the response to several cytokines and to growth factors. It is activated by cytokine receptors via kinases of the JAK family. STAT1 becomes phosphorylated and forms a dimer which enters the nucleus and triggers the transcription of its targets. Although not lethal at birth, selective gene deletion of STAT1 in mice leads to rapid death from severe infections, demonstrating its major role in the response to pathogens. Similarly, in humans who do not express STAT1, there is a lack of resistance to pathogens leading to premature death. This indicates a key, non-redundant function of STAT1 in the defence against pathogens. Thus, to successfully infect organisms, bacterial, viral or parasitic pathogens must overcome the activity of STAT1, and almost all the steps of this pathway can be blocked or inhibited by proteins produced in infected cells. Interestingly, some pathogens, like the oncogenic Epstein–Barr virus, have evolved a strategy which uses STAT1 activation.

Candidate protein biodosimeters of human exposure to ionizing radiation

PURPOSE

To conduct a literature review of candidate protein biomarkers for individual radiation biodosimetry of exposure to ionizing radiation.

MATERIALS AND METHODS

Reviewed approximately 300 publications (1973 - April 2006) that reported protein effects in mammalian systems after either in vivo or in vitro radiation exposure.

RESULTS

We found 261 radiation-responsive proteins including 173 human proteins. Most of the studies used high doses of ionizing radiation (>4 Gy) and had no information on dose- or time-responses. The majority of the proteins showed increased amounts or changes in phosphorylation states within 24 h after exposure (range: 1.5- to 10-fold). Of the 47 proteins that are responsive at doses of 1 Gy and below, 6 showed phosphorylation changes at doses below 10 cGy. Proteins were assigned to 9 groups based on consistency of response across species, dose- and time-response information and known role in the radiation damage response.

CONCLUSIONS

ATM (Ataxia telengiectasia mutated), H2AX (histone 2AX), CDKN1A (Cyclin-dependent kinase inhibitor 1A), and TP53 (tumor protein 53) are top candidate radiation protein biomarkers. Furthermore, we recommend a panel of protein biomarkers, each with different dose and time optima, to improve individual radiation biodosimetry for discriminating between low-, moderate-, and high-dose exposures. Our findings have applications for early triage and follow-up medical assessments.

STAT1 pathway mediates amplification of metastatic potential and resistance to therapy

Background

Traditionally IFN/STAT1 signaling is connected with an anti-viral response and pro-apoptotic tumor-suppressor functions. Emerging functions of a constitutively activated IFN/STAT1 pathway suggest an association with an aggressive tumor phenotype. We hypothesized that tumor clones that constitutively overexpress this pathway are preferentially selected by the host microenvironment due to a resistance to STAT1-dependent cytotoxicity and demonstrate increased metastatic ability combined with increased resistance to genotoxic stress.

Methodology/Principal Findings

Here we report that clones of B16F1 tumors grown in the lungs of syngeneic C57BL/6 mice demonstrate variable transcriptional levels of IFN/STAT1 pathway expression. Tumor cells that constitutively overexpress the IFN/STAT1 pathway (STAT1^H genotype) are selected by the lung microenvironment. STAT1^H tumor cells also demonstrate resistance to IFN-gamma (IFNγ), ionizing radiation (IR), and doxorubicin relative to parental B16F1 and low expressors of the IFN/STAT1 pathway (STAT1^L genotype). Stable knockdown of STAT1 reversed the aggressive phenotype and decreased both lung colonization and resistance to genotoxic stress.

Conclusions

Our results identify a pathway activated by tumor-stromal interactions thereby selecting for pro-metastatic and therapy-resistant tumor clones. New therapies targeted against the IFN/STAT1 signaling pathway may provide an effective strategy to treat or sensitize aggressive tumor clones to conventional cancer therapies and potentially prevent distant organ colonization.

STAT3 deletion sensitizes cells to oxidative stress

The transcription factor STAT1 plays a role in promoting apoptotic cell death, whereas the related STAT3 transcription factor protects cardiac myocytes from ischemia/reperfusion (I/R) injury or oxidative stress. Cytokines belonging to the IL-6 family activate the JAK-STAT3 pathway, but also activate other cytoprotective pathways such as the MAPK-ERK or the PI3-AKT pathway. It is therefore unclear whether STAT3 is the only cytoprotective mediator against oxidative stress-induced cell death. Overexpression of STAT3 in primary neonatal rat ventricular myocytes (NRVM) protects against I/R-induced cell death. Moreover, a dominant negative STAT3 adenovirus (Ad ST3-DN) enhanced apoptotic cell death (81.2+/-6.9%) compared to control infected NRVM (46.0+/-3.1%) following I/R. Depletion of STAT3 sensitized cells to apoptotic cell death following oxidative stress. These results provide direct evidence for the role of STAT3 as a cytoprotective transcription factor in cells exposed to oxidative stress.

Stat1 phosphorylation determines Ras oncogenicity by regulating p27 kip1

Inactivation of p27 Kip1 is implicated in tumorigenesis and has both prognostic and treatment-predictive values for many types of human cancer. The transcription factor Stat1 is essential for innate immunity and tumor immunosurveillance through its ability to act downstream of interferons. Herein, we demonstrate that Stat1 functions as a suppressor of Ras transformation independently of an interferon response. Inhibition of Ras transformation and tumorigenesis requires the phosphorylation of Stat1 at tyrosine 701 but is independent of Stat1 phosphorylation at serine 727. Stat1 induces p27 Kip1 expression in Ras transformed cells at the transcriptional level through mechanisms that depend on Stat1 phosphorylation at tyrosine 701 and activation of Stat3. The tumor suppressor properties of Stat1 in Ras transformation are reversed by the inactivation of p27 Kip1. Our work reveals a novel functional link between Stat1 and p27 Kip1, which act in coordination to suppress the oncogenic properties of activated Ras. It also supports the notion that evaluation of Stat1 phosphorylation in human tumors may prove a reliable prognostic factor for patient outcome and a predictor of treatment response to anticancer therapies aimed at activating Stat1 and its downstream effectors.

Sp1-mediated transcriptional regulation of NFBD1/MDC1 plays a critical role in DNA damage response pathway

NFBD1/MDC1 is a large nuclear protein with an anti-apoptotic potential which participates in DNA damage response. Recently, we have demonstrated that NFBD1 has an inhibitory effect on pro-apoptotic p53 and DNA damage-induced transcriptional repression of NFBD1 plays an important role in p53-dependent apoptotic response. In this study, we have found that NFBD1 promoter region contains canonical Sp1-, STAT-1- and NF-Y-binding sites and finally we have identified Sp1 as a transcriptional activator for NFBD1. The 5'-RACE and bioinformatic analyses revealed that NFBD1 encodes at least four transcriptional variants arising from distinct transcriptional start sites. Luciferase reporter assays using a series of NFBD1 promoter deletion mutants demonstrated that the proximal Sp1-binding site is required for the transcriptional activation of NFBD1. Indeed, the endogenous Sp1 was recruited onto the proximal Sp1-binding site as examined by chromatin immunoprecipitation (ChIP) assay and siRNA-mediated knockdown of the endogenous Sp1 in HeLa cells reduced the expression levels of NFBD1, which renders cells sensitive to adriamycin (ADR). In support of this notion, mithramycin A (MA, Sp1 inhibitor) treatment resulted in a significant down-regulation of NFBD1. Taken together, our present findings suggest that Sp1-mediated transcriptional regulation of NFBD1 plays an important role in the regulation of DNA damage response.

Multiple kinases in the interferon-gamma response

Janus kinases (JAKs) and signal transducers and activators of transcription (STATs) are essential for responses to interferons (IFNs), most cytokines, and some growth factors. JAK/STAT signaling is not, however, sufficient for a full IFN-gamma response. Here, a convenient, robust, and quantitative flow cytometry-based kinome-wide siRNA screen has identified nine additional kinases as required for the IFN-gamma class II HLA response, seven for an antiviral response, and two for the cytopathic response to encephalomyocarditis virus (EMCV). As one example, inhibition of the IFN-gamma response by siRNA to ataxia telangiectasia-mutated (ATM) differentially affects a spectrum of IFN-gamma-stimulated mRNAs, with inhibitions being seen as early as 1 h after IFN-gamma stimulation. The implication of ATM, with its previously recognized function in chromatin decondensation, in the control of transcription early in the IFN-gamma response highlights both a role for ATM in cytokine responses and a possible correlation with the chromatin decondensation recently observed in response to IFN-gamma in mammalian cells. This work has, therefore, revealed the simplicity, power, and convenience of quantitative flow cytometry-based siRNA screens, a requirement for ATM and multiple additional kinases in the IFN-gamma response and a possible requirement for two of these kinases in the cytopathic response to EMCV.

ERK and the F-box protein betaTRCP target STAT1 for degradation

The transcription factor STAT1 has roles in development, homeostasis, cellular differentiation, and apoptosis and has been postulated to function as a tumor suppressor. STAT1 is activated by tyrosine or serine phosphorylation in response to specific cytokines or following a variety of stress-induced stimuli. STAT1 activity is carefully regulated to prevent sustained STAT1-mediated transcription, although the molecular mechanisms involved in the modulation of STAT1 stability are poorly understood. Here we show that activated STAT1 is degraded at the proteasome by a mechanism involving the F-box E3 ligase, SCF(betaTRCP). Active p42/p44 MAPK-ERK phosphorylates STAT1 on serine 727 and targets it for proteasomal degradation. SCF(betaTRCP) binds wild-type STAT1 but not the nonphosphorylatable mutant STAT1(S727A). Moreover, silencing betaTRCP expression or pharmacological inhibition of ERK activity stabilized STAT1 expression. These data suggest that constitutively active ERK may inappropriately degrade STAT1, with loss of its pro-apoptotic and tumor suppressor functions.

Gamma-herpesvirus kinase actively initiates a DNA damage response by inducing phosphorylation of H2AX to foster viral replication

DNA virus infection can elicit the DNA damage response in host cells, including ATM kinase activation and H2AX phosphorylation. This is considered to be the host cell response to replicating viral DNA. In contrast, we show that during infection of macrophages murine gamma-herpesvirus 68 (gammaHV68) actively induces H2AX phosphorylation by expressing a viral kinase (orf36). GammaHV68-encoded orf36 kinase and its EBV homolog, BGLF4, induce H2AX phosphorylation independently of other viral genes. The process requires the kinase domain of Orf36 and is enhanced by ATM. Orf36 is important for gammaHV68 replication in infected animals, and orf36, H2AX, and ATM are all critical for efficient gammaHV68 replication in primary macrophages. Thus, activation of proximal components of the DNA damage signaling response is an active viral kinase-driven strategy required for efficient gamma-herpesvirus replication.

NFBD1/MDC1 Associates with p53 and Regulates Its Function at the Crossroad between Cell Survival and Death in Response to DNA Damage

NFBD1/MDC1, which belongs to the BRCT superfamily, has an anti-apoptotic activity and contributes to the early cellular responses to DNA damage. Here we found that NFBD1 protects cells from apoptotic cell death by inhibiting phosphorylation of p53 at Ser-15 under steady state as well as early phase of DNA damage, thereby blocking its transcriptional and pro-apoptotic activities. During late phase of DNA damage, a remarkable reduction of NFBD1 was observed in dying but not in surviving A549 cells bearing wild-type p53. Small interference RNA-mediated knockdown of the endogenous NFBD1 resulted in an increase in sensitivity to adriamycin in A549 cells but not in p53-deficient H1299 cells. Immunoprecipitation and luciferase reporter analyses demonstrated that NFBD1 binds to the NH(2)-terminal region of p53 and strongly inhibits its transcriptional activity. Additionally, BRCT domains, which can interact with p53, reduced the adriamycin-induced phosphorylation levels of p53 at Ser-15 and also suppressed the transcriptional activity of p53. Thus, our present findings strongly suggest that NFBD1 plays an important role in the decision of cell survival and death after DNA damage through the regulation of p53.

Gene Expression Profiling of Breast, Prostate, and Glioma Cells following Single versus Fractionated Doses of Radiation

Studies were conducted to determine whether gene expression profiles following a single dose of radiation would yield equivalent profiles following fractionated radiation in different tumor cell lines. MCF7 (breast), DU145 (prostate), and SF539 (gliosarcoma) cells were exposed to a total radiation dose of 10 Gy administered as a single dose (SD) or by daily multifractions (MF) of 5 x 2 Gy. Following radiation treatment, mRNA was isolated at 1, 4, 10, and 24 h and processed for cDNA microarray analysis. To determine the influence of the tumor microenvironment on gene expression, one cell type (DU145) was evaluated growing as a solid tumor in athymic nude mice for both radiation protocols. Unsupervised hierarchical cluster map analysis showed significant differences in gene expression profiles between SD and MF treatments for cells treated in vitro, with MF yielding a more robust induction compared with SD. Several genes were uniquely up-regulated by MF treatment, including multiple IFN-related genes (STAT1, G1P2, OAS1, OAS3, G1P3, IFITM1) and TGF-beta-associated genes (EGR1, VEGF, THBS1, and TGFB2). DU145 cells grown in vivo exhibited a completely different set of genes induced by both SD and MF compared with the same cells exposed in vitro. The results of the study clearly show distinct differences in the molecular response of cells between SD and MF radiation exposures and show that the tumor microenvironment can significantly influence the pattern of gene expression after radiation exposures.

C-myc activation impairs the NF-kappaB and the interferon response: implications for the pathogenesis of Burkitt's lymphoma

Deregulation of the proto-oncogene c-myc is a key event in the pathogenesis of many tumors. A paradigm is the activation of the c-myc gene by chromosomal translocations in Burkitt lymphoma (BL). Despite expression of a restricted set of Epstein-Barr viral (EBV) antigens, BL cells are not recognized by antigen-specific cytotoxic T cells (CTLs) because of their inability to process and present HLA class I-restricted antigens. In contrast, cells of EBV-driven posttransplant lymphoproliferative disease (PTLD) are recognized and rejected by EBV-specific CTLs. It is not known whether the poor immunogenicity of BL cells is due to nonexpression of viral antigens, overexpression of c-myc, or both. To understand the basis for immune recognition and escape, we have compared the mRNA expression profiles of BL and EBV-immortalized cells (as PTLD model). Among the genes expressed at low level in BL cells, we have identified many genes involved in the NF-kappaB and interferon response that play a pivotal role in antigen presentation and immune recognition. Using a cell line in which EBNA2 and c-myc can be regulated at will, we show that c-MYC negatively regulates STAT1, the central player linking the Type-I and Type-II interferon response. Switching off c-myc expression leads to STAT1 induction through a direct and indirect mechanism involving induction of Type-I interferons. c-MYC thus masks an interferon-inducing activity in these cells. Our findings imply that immune escape of tumor cells is not only a matter of in vivo selection but may be additionally promoted by activation of a cellular oncogene.

STAT1 activation in squamous cell cancer of the oral cavity

BACKGROUND

For patients with squamous cell carcinoma of the oral cavity, both locoregional and distant recurrences are common, and an appropriate adjuvant treatment modality has yet to be defined. Thus, there is an urgent need to identify novel molecular markers with potential prognostic and/or predictive value to improve treatment outcome in these patients. This retrospective study was designed to investigate the predictive and/or prognostic value of STAT1 activation in squamous cell carcinoma of the oral cavity.

METHODS

STAT1 expression and subcellular localization was examined immunohistochemically on a tissue microarray of paraffin-embedded tumor specimens from 89 patients who underwent surgical treatment in the period between 1980 and 1997. A nuclear staining score of greater than 35% was defined as high STAT1 activation.

RESULTS

According to study criteria, 18% of analyzed tumor samples exhibited high STAT1 activation. High STAT1 activation was associated with negative lymph node status. Moreover, in the subgroup of patients who received chemotherapy, high nuclear STAT1 staining in the tumor was associated with good prognosis.

CONCLUSIONS

This is the first report demonstrating the potential predictive value of STAT1 activation status in patients with squamous cell cancer of the oral cavity. If confirmed in large prospective trials, this molecular marker could help in guiding therapeutic decisions in these patients.

Free radical scavenging inhibits STAT phosphorylation following in vivo ischemia/reperfusion injury

The signal transducer and activator of transcription (STAT) family are latent transcription factors involved in a variety of signal transduction pathways, including cell death cascades. STAT1 has been shown to have a crucial role in regulating cardiac cell apoptosis in the myocardium exposed to ischemia/reperfusion (I/R) injury. The free radical scavenger, tempol, is known to have cardioprotective properties, although little is known about the molecular mechanism(s) by which it acts. In the present study, we assessed the levels of phosphorylated STAT1 and STAT3 and examined whether tempol was able to affect STAT activation after in vivo cardiac I/R injury. We observed a reperfusion time-dependent increase in the tyrosine phosphorylation of STAT1 and STAT3 at residues 701 and 705, respectively. Here we show for the first time that tempol dramatically reduced STAT1 and 3 phosphorylation. The reduction in STAT1 and 3 phosphorylation was accompanied by a concomitant decrease in cellular malondialdehyde (MDA) levels. To verify the role of STAT1 in modulating the cardioprotective effect of tempol, rats were injected with the STAT1 activator, IFN-gamma, and tempol during I/R injury. We found that the presence of IFN-gamma abrogated the protective effects of tempol, suggesting that the protective effects of tempol may partly operate by decreasing the phosphorylation of STAT1. This study demonstrates that careful dissection of the molecular mechanisms that underpin I/R injury may reveal cardioprotective targets for future therapy.

Opposing actions of STAT-1 and STAT-3

The signal transducers and activators of transcription (STATs) are a family of transcription factors, which were originally identified on the basis of their ability to transduce a signal from a cellular receptor into the nucleus and modulate the transcription of specific genes. Interestingly, recent studies have demonstrated that STAT-1 plays a key role in promoting apoptosis in a variety of cell types, whereas STAT-3 has an anti-apoptotic effect. Moreover, whilst STAT-3 promotes cellular proliferation and is activated in a variety of tumour cells, STAT-1 appears to have an anti-proliferative effect. Although the initially characterised signal transduction events mediated by STAT-1 and STAT-3 involve the DNA binding and transcriptional activation domains of the factor, some of their other effects appear not to require DNA binding. Therefore, STAT-1 and STAT-3 can mediate the regulation of gene transcription both by direct DNA binding and via a co-activator mechanism and despite their very similar structures, have antagonistic effects on cellular proliferation and apoptosis.