DNA-PK phosphorylation sites on Oct-1 promote cell survival following DNA damage

Secrets of DNA-PKcs beyond DNA repair

The canonical role of the DNA-dependent protein kinase catalytic subunit (DNA-PKcs) in repairing DNA double-strand breaks combined with its reported dysregulation in several malignancies has driven the development of DNA-PKcs inhibitors as therapeutics. However, until recently the relationship between DNA-PKcs and tumorigenesis has been primarily investigated with regard to its role in non-homologous end joining (NHEJ) repair. Emerging research has uncovered non-canonical DNA-PKcs functions involved with transcriptional regulation, telomere maintenance, metabolic regulation, and immune signaling all of which may also impinge on tumorigenesis. This review mainly discusses these non-canonical roles of DNA-PKcs in cellular biology and their potential contribution to tumorigenesis, as well as evaluating the implications of targeting DNA-PKcs for cancer therapy.

Antitumor effects of pyrrole-imidazole polyamide modified with alkylating agent on prostate cancer cells

Androgens and androgen receptor (AR) have a central role in prostate cancer progression by regulating its downstream signaling. Although androgen depletion therapy (ADT) is the primary treatment for most prostate cancers, they acquires resistance to ADT and become castration resistant prostate cancers (CRPC). AR complex formation with multiple transcription factors is important for enhancer activity and transcriptional regulation, which can contribute to cancer progression and resistance to ADT. We previously demonstrated that OCT1 collaborates with AR in prostate cancer, and that a pyrrole-imidazole (PI) polyamide (PIP) targeting OCT1 inhibits cell and castration-resistant tumor growth (Obinata D et al. Oncogene 2016). PIP can bind to DNA non-covalently without a drug delivery system unlike most DNA targeted therapeutics. In the present study, we developed a PIP modified with a DNA alkylating agent, chlorambucil (ChB) (OCT1-PIP-ChB). Then its effect on the growth of prostate cancer LNCaP, 22Rv1, and PC3 cells, pancreatic cancer BxPC3 cells, and colon cancer HCT116 cells, as well as non-cancerous MCF-10A epithelial cells, were analyzed. It was shown that the IC50s of OCT1-PIP-ChB for 22Rv1 and LNCaP were markedly lower compared to other cells, including non-cancerous MCF-10A cells. Comprehensive gene expression analysis of CRPC model 22Rv1 cells treated with IC50 concentrations of OCT1-PIP-ChB revealed that the gene group involved in DNA double-strand break repair was the most enriched among gene sets repressed by OCT1-PIP-ChB treatment. Importantly, in vivo study using 22Rv1 xenografts, we showed that OCT1-PIP-ChB significantly reduced tumor growth compared to the control group without showing obvious adverse effects. Thus, the PIP combined with ChB can exert a significant inhibitory effect on prostate cancer cell proliferation and castration-resistant tumor growth, suggesting a potential role as a therapeutic agent.

Overexpression of OCT-1 gene is a biomarker of adverse prognosis for diffuse large B-cell lymphoma (DLBCL): data from a retrospective cohort of 77 Brazilian patients

BACKGROUND

OCT-1 gene is a member of the POU-homeodomain family of transcriptional regulators of B-lymphocyte differentiation by controlling expression of B-cell specific genes. BCL-2 gene is a potent inhibitor of apoptosis and it is essential during B-cell differentiation into germinal center. These genes may be expressed in diffuse large B-cell lymphoma (DLBCL), but the role of BCL-2 in its prognosis has been contradictory, and OCT-1 has yet to be tested.

METHODS

In this study, we aimed to investigate the prognostic impact of OCT-1 and BCL-2 expression in DLBCL treated in the real world with immunochemotherapy in a single center. BCL-2 and OCT-1 genes were available in 78.5% (77/98) DLBCL patients, and the RNA for quantitative real-time PCR was isolated from formalin-fixed paraffin-embedded samples. The values obtained for gene expression were transformed in categorical variable according to their median.

RESULTS

Cohort median age was 54.5 years (15-84), 49 (50%) were male, 38/77 (49.4%) and 40/77 (51.9%) presented OCT-1 and BCL-2 expression ≥ median, respectively. The overall response rate (ORR) in all patients was 68.4% (67/98), 65,3% (64/98) of patients acquired complete response, and 3.1% (3/98) partial response, while 6.1% (6/98) were primary refractory. The median follow-up was 3.77 years (95% CI: 3.2-4.1), with 5.43 (95% CI: 2.2-NR) of overall survival (OS) and 5.15 years (95% CI: 2.9-NA) of progression free survival (PFS). OCT-1 ≥ median was associated with shorter OS at univariate analysis (p = 0.013; [HR] 2.450, 95% CI: 1.21-4.96) and PFS (p = 0.019; [HR] 2.270, 95%CI: 1.14-4.51) and BCL-2 gene overexpression presented worse PFS (p = 0.043, [HR] 2.008, 95% CI: 1.02-3.95). At multivariate analysis, OCT-1 overexpression was associated with poor PFS (p = 0.035, [HR] 2.22, 95% CI: 1.06-4.67).

CONCLUSION

In this study, we showed that overexpression of OCT1 gene was an independent prognostic factor of adverse outcomes in DLBCL.

The POU-Domain Transcription Factor Oct-6/POU3F1 as a Regulator of Cellular Response to Genotoxic Stress

DNA damage and the generation of reactive oxygen species (ROS) are key mechanisms of apoptotic cell death by commonly used genotoxic drugs. However, the complex cellular response to these pharmacologic agents remains yet to be fully characterized. Several studies have described the role of transcription factor octamer-1 (Oct-1)/Pit-1, Oct-1/2, and Unc-86 shared domain class 2 homeobox 1 (POU2F1) in the regulation of the genes important for cellular response to genotoxic stress. Evaluating the possible involvement of other POU family transcription factors in these pathways, we revealed the inducible expression of Oct-6/POU3F1, a regulator of neural morphogenesis and epidermal differentiation, in cancer cells by genotoxic drugs. The induction of Oct-6 occurs at the transcriptional level via reactive oxygen species (ROS) and ataxia telangiectasia mutated- and Rad3-related (ATR)-dependent mechanisms, but in a p53 independent manner. Moreover, we provide evidence that Oct-6 may play a role in the regulation of cellular response to DNA damaging agents. Indeed, by using the shRNA approach, we demonstrate that in doxorubicin-treated H460 non-small-cell lung carcinoma (NSCLC) cells, Oct-6 depletion leads to a reduced G2-cell cycle arrest and senescence, but also to increased levels of intracellular ROS and DNA damage. In addition, we could identify p21 and catalase as Oct-6 target genes possibly mediating these effects. These results demonstrate that Oct-6 is expressed in cancer cells after genotoxic stress, and suggests its possible role in the control of ROS, DNA damage response (DDR), and senescence.

Diversity among POU transcription factors in chromatin recognition and cell fate reprogramming

The POU (Pit-Oct-Unc) protein family is an evolutionary ancient group of transcription factors (TFs) that bind specific DNA sequences to direct gene expression programs. The fundamental importance of POU TFs to orchestrate embryonic development and to direct cellular fate decisions is well established, but the molecular basis for this activity is insufficiently understood. POU TFs possess a bipartite 'two-in-one' DNA binding domain consisting of two independently folding structural units connected by a poorly conserved and flexible linker. Therefore, they represent a paradigmatic example to study the molecular basis for the functional versatility of TFs. Their modular architecture endows POU TFs with the capacity to accommodate alternative composite DNA sequences by adopting different quaternary structures. Moreover, associations with partner proteins crucially influence the selection of their DNA binding sites. The plentitude of DNA binding modes confers the ability to POU TFs to regulate distinct genes in the context of different cellular environments. Likewise, different binding modes of POU proteins to DNA could trigger alternative regulatory responses in the context of different genomic locations of the same cell. Prominent POU TFs such as Oct4, Brn2, Oct6 and Brn4 are not only essential regulators of development but have also been successfully employed to reprogram somatic cells to pluripotency and neural lineages. Here we review biochemical, structural, genomic and cellular reprogramming studies to examine how the ability of POU TFs to select regulatory DNA, alone or with partner factors, is tied to their capacity to epigenetically remodel chromatin and drive specific regulatory programs that give cells their identities.

Reprint of: Importins in the maintenance and lineage commitment of ES cells

The nucleus of a eukaryotic cell is separated from the cytoplasm by a nuclear envelope, and nuclear pores within the envelope facilitate nucleocytoplasmic transport and the exchange of information. Gene regulation is a key component of biological activity regulation in the cell. Transcription factors control the expression levels of various genes that are necessary for the maintenance or conversion of cellular states during animal development. Because transcription factor activities determine the extent of transcription of target genes, the number of active transcription factors must be tightly regulated. In this regard, the nuclear translocation of a transcription factor is an important determinant of its activity. Therefore, it is becoming clear that the nucleocytoplasmic transport machinery is involved in cell differentiation and organism development. This review examines the regulation of transcription factors by the nucleocytoplasmic transport machinery in ES cells.

Importins in the maintenance and lineage commitment of ES cells

The nucleus of a eukaryotic cell is separated from the cytoplasm by a nuclear envelope, and nuclear pores within the envelope facilitate nucleocytoplasmic transport and the exchange of information. Gene regulation is a key component of biological activity regulation in the cell. Transcription factors control the expression levels of various genes that are necessary for the maintenance or conversion of cellular states during animal development. Because transcription factor activities determine the extent of transcription of target genes, the number of active transcription factors must be tightly regulated. In this regard, the nuclear translocation of a transcription factor is an important determinant of its activity. Therefore, it is becoming clear that the nucleocytoplasmic transport machinery is involved in cell differentiation and organism development. This review examines the regulation of transcription factors by the nucleocytoplasmic transport machinery in ES cells.

Different N-terminal isoforms of Oct-1 control expression of distinct sets of genes and their high levels in Namalwa Burkitt's lymphoma cells affect a wide range of cellular processes

Oct-1 transcription factor has various functions in gene regulation. Its expression level is increased in several types of cancer and is associated with poor survival prognosis. Here we identified distinct Oct-1 protein isoforms in human cells and compared gene expression patterns and functions for Oct-1A, Oct-1L, and Oct-1X isoforms that differ by their N-terminal sequences. The longest isoform, Oct-1A, is abundantly expressed and is the main Oct-1 isoform in most of human tissues. The Oct-1L and the weakly expressed Oct-1X regulate the majority of Oct-1A targets as well as additional sets of genes. Oct-1X controls genes involved in DNA replication, DNA repair, RNA processing, and cellular response to stress. The high level of Oct-1 isoforms upregulates genes related to cell cycle progression and activates proliferation both in Namalwa Burkitt's lymphoma cells and primary human fibroblasts. It downregulates expression of genes related to antigen processing and presentation, cytokine-cytokine receptor interaction, oxidative metabolism, and cell adhesion, thus facilitating pro-oncogenic processes.

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

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

Oct-1, to go or not to go? That is the PolII question

The Oct transcription factors recognise an octamer DNA element from which they regulate transcription of specific target genes. Oct-1 is the only member of the subfamily that is ubiquitously expressed and has a wide role in transcriptional control. Through interaction with various partner proteins, Oct-1 can modulate accessibility to the chromatin to recruit the transcription machinery and form the pre-initiation complex. The recruited PolII is induced to initiate transcription and stalled until elongation is triggered on interaction with signalling transcription factors. In this way, Oct-1 can fulfil general roles in transcription by opening the chromatin as well as transduce extracellular signals by relaying activation through various interacting partners. The emerging picture of Oct-1 is that of a complex and versatile transcription factor with fundamental functions in cell homeostasis and signal response in general as well as cell specific contexts. This article is part of a Special Issue entitled: The Oct Transcription Factor Family, edited by Dr. Dean Tantin.

Oct-2 forms a complex with Oct-1 on the iNOS promoter and represses transcription by interfering with recruitment of RNA PolII by Oct-1

Oct-1 (POU2f1) and Oct-2 (POU2f2) are members of the POU family of transcription factors. They recognize the same DNA sequence but fulfil distinct functions: Oct-1 is ubiquitous and regulates a variety of genes while Oct-2 is restricted to B-cells and neurones. Here we examine the interplay and regulatory mechanisms of these factors to control the inducible nitric oxide synthase (iNOS, NOS2). Using two breast cancer cell lines as a comparative model, we found that MCF-7 express iNOS upon cytokine stimulation while MDA-MB-231 do not. Oct-1 is present in both cell lines but MDA-MB-231also express high levels of Oct-2. Manipulation of Oct-2 expression in these cell lines demonstrates that it is directly responsible for the repression of iNOS in MDA-MB-231. In MCF-7 cells Oct-1 binds the iNOS promoter, recruits RNA PolII and triggers initiation of transcription. In MDA-MB-231 cells, both Oct-1 and Oct-2 bind the iNOS promoter, forming a higher-order complex which fails to recruit RNA PolII, and as a consequence iNOS transcription does not proceed. Unravelling the mechanisms of transcription factor activity is paramount to the understanding of gene expression patterns that determine cell behaviour.

Oct transcription factors in development and stem cells: insights and mechanisms

The POU domain family of transcription factors regulates developmental processes ranging from specification of the early embryo to terminal differentiation. About half of these factors display substantial affinity for an 8 bp DNA site termed the octamer motif, and are hence known as Oct proteins. Oct4 (Pou5f1) is a well-known Oct factor, but there are other Oct proteins with varied and essential roles in development. This Primer outlines our current understanding of Oct proteins and the regulatory mechanisms that govern their role in developmental processes and concludes with the assertion that more investigation into their developmental functions is needed.

Regulation of Oct1/Pou2f1 transcription activity by O-GlcNAcylation

The Oct1 transcription factor is a potent regulator of stress responses, metabolism, and tumorigenicity. Although Oct1 is regulated by phosphorylation and ubiquitination, the presence and importance of other modifications is unknown. Here we show that Oct1 is modified by O-linked β-N-acetylglucosamine (O-GlcNAc) moieties. We map two sites of O-GlcNAcylation at positions T255 and S728 within human Oct1. Under anchorage-independent overgrowth conditions, Oct1 associates 3-fold more strongly with the Gadd45a promoter and mediates transcriptional repression. Increased binding correlates with quantitative reductions in Oct1 nuclear periphery-associated puncta, and a reduced association with lamin B1. The O-GlcNAc modification sites are important for both Gadd45a repression and anchorage-independent survival. In contrast to chronic overgrowth conditions, following acute nutrient starvation Oct1 mediates Gadd45a activation. The O-GlcNAc sites are also important for Gadd45a activation under these conditions. We also, for the first time, identify specific Oct1 ubiquitination sites. The findings suggest that Oct1 integrates metabolic and stress signals via O-GlcNAc modification to regulate target gene activity.

Interactions of the ubiquitous octamer-binding transcription factor-1 with both the signal transducer and activator of transcription 5 and the glucocorticoid receptor mediate prolactin and glucocorticoid-induced β-casein gene expression in mammary epithelial cells

Regulation of milk protein gene expression by lactogenic hormones (prolactin and glucocorticoids) provides an attractive model for studying the mechanisms by which protein and steroid hormones synergistically regulate gene expression. β-Casein is one of the major milk proteins and its expression in mammary epithelial cells is stimulated by lactogenic hormones. The signal transducer and activator of transcription 5 and glucocorticoid receptor are essential downstream mediators of prolactin and glucocorticoid signaling, respectively. Previous studies have shown that mutating the octamer-binding site of the β-casein gene proximal promoter dramatically reduces the hormonal induction of the promoter activity. However, little is known about the underlying molecular mechanisms. In this report, we show that lactogenic hormones rapidly induce the binding of octamer-binding transcription factor-1 to the β-casein promoter and this induction is not mediated by either increasing the expression of octamer-binding transcription factor-1 or inducing its translocation to the nucleus. Rather, lactogenic hormones induce physical interactions between the octamer-binding transcription factor-1, signal transducer and activator of transcription 5, and glucocorticoid receptor to form a ternary complex, and these interactions enhance or stabilize the binding of these transcription factors to the promoter. Abolishing these interactions significantly reduces the hormonal induction of β-casein gene transcription. Thus, our study indicates that octamer-binding transcription factor-1 may serve as a master regulator that facilitates the DNA binding of both signal transducer and activator of transcription 5 and glucocorticoid receptor in hormone-induced β-casein expression, and defines a novel mechanism of regulation of tissue-specific gene expression by the ubiquitous octamer-binding transcription factor-1.

Systematic analysis of somatic mutations in phosphorylation signaling predicts novel cancer drivers

Large-scale cancer genome sequencing has uncovered thousands of gene mutations, but distinguishing tumor driver genes from functionally neutral passenger mutations is a major challenge. We analyzed 800 cancer genomes of eight types to find single-nucleotide variants (SNVs) that precisely target phosphorylation machinery, important in cancer development and drug targeting. Assuming that cancer-related biological systems involve unexpectedly frequent mutations, we used novel algorithms to identify genes with significant phosphorylation-associated SNVs (pSNVs), phospho-mutated pathways, kinase networks, drug targets, and clinically correlated signaling modules. We highlight increased survival of patients with TP53 pSNVs, hierarchically organized cancer kinase modules, a novel pSNV in EGFR, and an immune-related network of pSNVs that correlates with prolonged survival in ovarian cancer. Our findings include multiple actionable cancer gene candidates (FLNB, GRM1, POU2F1), protein complexes (HCF1, ASF1), and kinases (PRKCZ). This study demonstrates new ways of interpreting cancer genomes and presents new leads for cancer research.

RanBPM is an inhibitor of ERK signaling

Ran-binding protein M (RanBPM) is a nucleocytoplasmic protein of yet unknown function. We have previously shown that RanBPM inhibits expression of the anti-apoptotic factor Bcl-2 and promotes apoptosis induced by DNA damage. Here we show that the effects of RanBPM on Bcl-2 expression occur through a regulation of the ERK signaling pathway. Transient and stable down-regulation of RanBPM stimulated ERK phosphorylation, leading to Bcl-2 up-regulation, while re-expression of RanBPM reversed these effects. RanBPM was found to inhibit MEK and ERK activation induced by ectopic expression of active RasV12. Activation of ERK by active c-Raf was also prevented by RanBPM. Expression of RanBPM correlated with a marked decrease in the protein levels of ectopically expressed active c-Raf and also affected the expression of endogenous c-Raf. RanBPM formed a complex with both active c-Raf, consisting of the C-terminal kinase domain, and endogenous c-Raf in mammalian cells. In addition, RanBPM was found to decrease the binding of Hsp90 to c-Raf. Finally, we show that loss of RanBPM expression confers increased cell proliferation and cell migration properties to HEK293 cells. Altogether, these findings establish RanBPM as a novel inhibitor of the ERK pathway through an interaction with the c-Raf complex and a regulation of c-Raf stability, and provide evidence that RanBPM loss of expression results in constitutive activation of the ERK pathway and promotes cellular events leading to cellular transformation and tumorigenesis.

Gadd45a transcriptional induction elicited by the Aurora kinase inhibitor MK-0457 in Bcr-Abl-expressing cells is driven by Oct-1 transcription factor

The advantage of Aurora kinase (AK) inhibitors in chronic myeloid leukemia (CML) therapy mostly arises from "off-target" effects on tyrosine kinase (TK) activity of wild type (wt) or mutated Bcr-Abl proteins which drive the disease resistance to imatinib (IM). We proved that the AK inhibitor MK-0457 induces the growth arrest DNA damage-inducible (Gadd) 45a through recruitment of octamer-binding (Oct)-1 transcription factor at a critical promoter region for gene transcription and covalent modifications of histone H3 (lysine 14 acetylation, lysine 9 de-methylation). Such epigenetic chromatin modifications may depict a general mechanism promoting the re-activation of tumor suppressor genes silenced by Bcr-Abl.

Negative regulation of human U6 snRNA promoter by p38 kinase through Oct-1

Recruitment of Oct-1 protein to the octamer sequence of U6 promoter is critical for optimal transcription by RNA polymerase III. Here we report that p38 kinase inhibitors, SB202190 and SB203580, stimulated U6 promoter activity and this stimulation can be observed only in the presence of octamer sequence. SB202190-treated cell nuclear extract had about 50% increase in Oct-1 binding activity suggesting that the increased U6 promoter activity by p38 kinase inhibitor is mediated through Oct-1. Mutation in octamer sequence significantly reduced the SB202190-stimulated U6 promoter transcription and the distance between octamer and proximal sequence element of U6 promoter is also critical for the p38 kinase inhibitor-stimulated activity. Exogenous Oct-1 expression showed a concentration-dependent activation of U6 promoter that was further stimulated by the p38 kinase inhibitors. When cells were treated with p38 kinase inducer, hydrogen peroxide or phorbol 12-myristate 13-acetate (PMA), U6 promoter activity was down regulated and this inhibition was reversed by p38 kinase inhibitors. Over-expression of p38α kinase down-regulated U6 promoter activity and this inhibition was further enhanced by PMA and p38 kinase inhibitors reversed this inhibition. p38 kinase inhibitor-treated cells had 50% more U6 RNA than the control cells. Taken together, our results show a negative correlation between the p38 kinase levels and Oct-1 binding on U6 promoter, suggesting that U6 promoter is negatively regulated by p38 kinase.

Lymphocyte development: integration of DNA damage response signaling

Lymphocytes traverse functionally discrete stages as they develop into mature B and T cells. This development is directed by cues from a variety of different cell surface receptors. To complete development, all lymphocytes must express a functional nonautoreactive heterodimeric antigen receptor. The genes that encode antigen receptor chains are assembled through the process of V(D)J recombination, a reaction that proceeds through DNA double-stranded break (DSB) intermediates. These DSBs are generated by the RAG endonuclease in G1-phase developing lymphocytes and activate ataxia-telangiectasia mutated (ATM), the kinase that orchestrates cellular DSB responses. The canonical DNA damage response includes cell cycle arrest, DNA break repair, and apoptosis of cells when DSBs are not repaired. However, recent studies have demonstrated that ATM activation in response to RAG DSBs also regulates a transcriptional program including many genes with no known function in canonical DNA damage responses. Rather, these genes have activities that would be important for lymphocyte development. Here, these findings and the broader concept that signals initiated by physiologic DNA DSBs provide cues that regulate cell type-specific processes and functions are discussed.

Cdx2 homeoprotein inhibits non-homologous end joining in colon cancer but not in leukemia cells

Cdx2, a gene of the paraHox cluster, encodes a homeodomain transcription factor that plays numerous roles in embryonic development and in homeostasis of the adult intestine. Whereas Cdx2 exerts a tumor suppressor function in the gut, its abnormal ectopic expression in acute leukemia is associated to a pro-oncogenic function. To try to understand this duality, we have hypothesized that Cdx2 may interact with different protein partners in the two tissues and set up experiments to identify them by tandem affinity purification. We show here that Cdx2 interacts with the Ku heterodimer specifically in intestinal cells, but not in leukemia cells, via its homeodomain. Ku proteins do not affect Cdx2 transcriptional activity. However, Cdx2 inhibits in vivo and in vitro the DNA repair activity mediated by Ku proteins in intestinal cells. Whereas Cdx2 does not affect the recruitment of Ku proteins and DNA-PKcs into the DNA repair complex, it inhibits DNA-PKcs activity. Thus, we report here a new function of Cdx2, acting as an inhibitor of the DNA repair machinery, that may contribute to its tumor suppressor function specifically in the gut.

Ku regulates signaling to DNA damage response pathways through the Ku70 von Willebrand A domain

The Ku heterodimer (Ku70/Ku80) is a main component of the nonhomologous end-joining (NHEJ) pathway that repairs DNA double-strand breaks (DSBs). Ku binds the broken DNA end and recruits other proteins to facilitate the processing and ligation of the broken end. While Ku interacts with many proteins involved in DNA damage/repair-related functions, few interactions have been mapped to the N-terminal von Willebrand A (vWA) domain, a predicted protein interaction domain. The mutagenesis of Ku70 vWA domain S155/D156 unexpectedly increased cell survival following ionizing radiation (IR) treatment. DNA repair appeared unaffected, but defects in the activation of apoptosis and alterations in the DNA damage signaling response were identified. In particular, Ku70 S155A/D156A affected the IR-induced transcriptional response of several activating transcription factor 2 (ATF2)-regulated genes involved in apoptosis regulation. ATF2 phosphorylation and recruitment to DNA damage-induced foci was increased in Ku70-deficient cells, suggesting that Ku represses ATF2 activation. Ku70 S155A/D156A substitutions further enhanced this repression. S155A substitution alone was sufficient to confer enhanced survival, whereas alteration to a phosphomimetic residue (S155D) reversed this effect, suggesting that S155 is a phosphorylation site. Thus, these findings infer that Ku links signals from the DNA repair machinery to DNA damage signaling regulators that control apoptotic pathways.

Cellular transcription factor Oct-1 interacts with the Epstein-Barr virus BRLF1 protein to promote disruption of viral latency

The Epstein-Barr virus (EBV) latent-to-lytic switch is an essential part of the viral life cycle, but the cellular factors that promote viral reactivation are not well defined. In this report, we demonstrate that the cellular transcription factor Oct-1 cooperates with the EBV immediate-early protein BRLF1 (R, Rta) to induce lytic viral reactivation. We show that cotransfected Oct-1 enhances the ability of BRLF1 to activate lytic gene expression in 293 cells stably infected with a BRLF1-defective EBV mutant (BRLF1-stop) and that Oct-1 increases BRLF1-mediated activation of lytic EBV promoters in reporter gene assays. We find that Oct-1 interacts directly with BRLF1 in vitro and that a mutant BRLF1 protein (the M140A mutant) attenuated for the ability to interact with Oct-1 in vitro is also resistant to Oct-1-mediated transcriptional enhancement in 293 BRLF1-stop cells. Furthermore, we show that cotransfected Oct-1 augments BRLF1 binding to a variety of lytic EBV promoters in chromatin immunoprecipitation (ChIP) assays (including the BZLF1, BMRF1, and SM promoters) and that BRLF1 tethers Oct-1 to lytic EBV promoters. In addition, we demonstrate that an Oct-1 mutant defective in DNA binding (the S335D mutant) still retains the ability to enhance BRLF1 transcriptional effects. Finally, we show that knockdown of endogenous Oct-1 expression reduces the level of constitutive lytic EBV gene expression in both EBV-positive B-cell and EBV-positive epithelial cell lines. These results suggest that Oct-1 acts as a positive regulator of EBV lytic gene expression and that this effect is at least partially mediated through its interaction with the viral protein BRLF1.

Computational identification of transcriptional regulators in human endotoxemia

One of the great challenges in the post-genomic era is to decipher the underlying principles governing the dynamics of biological responses. As modulating gene expression levels is among the key regulatory responses of an organism to changes in its environment, identifying biologically relevant transcriptional regulators and their putative regulatory interactions with target genes is an essential step towards studying the complex dynamics of transcriptional regulation. We present an analysis that integrates various computational and biological aspects to explore the transcriptional regulation of systemic inflammatory responses through a human endotoxemia model. Given a high-dimensional transcriptional profiling dataset from human blood leukocytes, an elementary set of temporal dynamic responses which capture the essence of a pro-inflammatory phase, a counter-regulatory response and a dysregulation in leukocyte bioenergetics has been extracted. Upon identification of these expression patterns, fourteen inflammation-specific gene batteries that represent groups of hypothetically ‘coregulated’ genes are proposed. Subsequently, statistically significant cis-regulatory modules (CRMs) are identified and decomposed into a list of critical transcription factors (34) that are validated largely on primary literature. Finally, our analysis further allows for the construction of a dynamic representation of the temporal transcriptional regulatory program across the host, deciphering possible combinatorial interactions among factors under which they might be active. Although much remains to be explored, this study has computationally identified key transcription factors and proposed a putative time-dependent transcriptional regulatory program associated with critical transcriptional inflammatory responses. These results provide a solid foundation for future investigations to elucidate the underlying transcriptional regulatory mechanisms under the host inflammatory response. Also, the assumption that coexpressed genes that are functionally relevant are more likely to share some common transcriptional regulatory mechanism seems to be promising, making the proposed framework become essential in unravelling context-specific transcriptional regulatory interactions underlying diverse mammalian biological processes.

Hydrogen peroxide stimulates nuclear import of the POU homeodomain protein Oct-1 and its repressive effect on the expression of Cdx-2

Background

The ubiquitously expressed POU homeodomain protein Oct-1 serves as a sensor for stress induced by irradiation. We found recently that in pancreatic and intestinal endocrine cells, Oct-1 also functions as a sensor for cyclic AMP (cAMP). The caudal homeobox gene Cdx-2 is a transactivator of proglucagon (gcg) and pro-insulin genes. Oct-1 binds to Cdx-2 promoter and represses its expression. cAMP elevation leads to increased nuclear exclusion of Oct-1, associated with reduced recruitment of nuclear co-repressors to the Cdx-2 promoter and increased Cdx-2 expression.

Results

We show in this study that inducing oxidative stress by hydrogen peroxide (H₂O₂) increased nuclear Oct-1 content in both pancreatic α and β cell lines, as well as in a battery of other cells. This increase was then attributed to accelerated nuclear import of Oct-1, assessed by Fluorescence Recovery After Photobleaching (FRAP) using green fluorescence protein (EGFP) tagged Oct-1 molecule. H₂O₂ treatment was then shown to stimulate the activities of DNA-dependent protein kinase (DNA-PK) and c-jun N-terminal kinase (JNK). Finally, increased Oct-1 nuclear content upon H₂O₂ treatment in a pancreatic α cell line was associated with reduced Cdx-2 and gcg mRNA expression.

Conclusion

These observations suggest that Oct-1 functions as a sensor for both metabolic and stress/survival signaling pathways via altering its nuclear-cytoplasmic shuttling.

POU homeodomain protein Oct-1 functions as a sensor for cyclic AMP

Cyclic AMP is a fundamentally important second messenger for numerous peptide hormones and neurotransmitters that control gene expression, cell proliferation, and metabolic homeostasis. Here we show that cAMP works with the POU homeodomain protein Oct-1 to regulate gene expression in pancreatic and intestinal endocrine cells. This ubiquitously expressed transcription factor is known as a stress sensor. We found that it also functions as a repressor of Cdx-2, a proglucagon gene activator. Through a mechanism that involves the activation of exchange protein activated by cyclic AMP, elevation of cAMP leads to enhanced phosphorylation and nuclear exclusion of Oct-1 and reduced interactions between Oct-1 or nuclear co-repressors and the Cdx-2 gene promoter, detected by chromatin immunoprecipitation. In rat primary pancreatic islet cells, cAMP elevation also reduces nuclear Oct-1 content, which causes increased proglucagon and proinsulin mRNA expression. Our study therefore identifies a novel mechanism by which cAMP regulates hormone-gene expression and suggests that ubiquitously expressed Oct-1 may play a role in metabolic homeostasis by functioning as a sensor for cAMP.

Stem cells, stress, metabolism and cancer: a drama in two Octs

It is a classic story of two related transcription factors. Oct4 is a potent regulator of pluripotency during early mammalian embryonic development, and is notable for its ability to convert adult somatic cells to pluripotency. The widely expressed Oct1 protein shares significant homology with Oct4, binds to the same sequences, regulates common target genes, and shares common modes of upstream regulation, including the ability to respond to cellular stress. Both proteins are also associated with malignancy, yet Oct1 cannot substitute for Oct4 in the generation of pluripotency. The molecular underpinnings of these phenomena are emerging, as are the consequences for adult stem cells and cancer, and thereby hangs a tale.

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

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

Oct-1 functions as a transactivator in the hormonal induction of beta-casein gene expression

The ubiquitous transcription factor Oct-1 is involved in the hormonal regulation of the transcription of the major milk protein beta-casein through an interaction with the prolactin receptor, the STAT-5, and the glucocorticoid receptor (GR). In this study, this interaction was further demonstrated using Oct-1-deficient cells. In addition, Oct-1 mRNA expression is shown to increase during pregnancy and reach the highest levels during early lactation in mouse mammary gland. In reconstituted COS-7 cells, the endogenous Oct-1 binding activity rapidly increased within 5 min upon the lactogenic hormone treatment, indicating potential post-transcriptional/translational modification of Oct-1 by prolactin and glucocorticoids. Furthermore, STAT-5B was as effective as STAT-5A in the interaction with Oct-1 during hormonal induction, and a GR mutant, which carries mutations at multiple potential phosphorylation sites, functioned similarly to the wild-type GR, indicating that these phosphorylation sites may not be involved in the interaction of GR with Oct-1 on the beta-casein gene promoter.

A general mechanism for transcription regulation by Oct1 and Oct4 in response to genotoxic and oxidative stress

Oct1 and Oct4 are homologous transcription factors with similar DNA-binding specificities. Here we show that Oct1 is dynamically phosphorylated in vivo following exposure of cells to oxidative and genotoxic stress. We further show that stress regulates the selectivity of both proteins for specific DNA sequences. Mutation of conserved phosphorylation target DNA-binding domain residues in Oct1, and Oct4 confirms their role in regulating binding selectivity. Using chromatin immunoprecipitation, we show that association of Oct4 and Oct1 with a distinct group of in vivo targets is inducible by stress, and that Oct1 is essential for a normal post-stress transcriptional response. Finally, using an unbiased Oct1 target screen we identify a large number of genes targeted by Oct1 specifically under conditions of stress, and show that several of these inducible Oct1 targets are also inducibly bound by Oct4 in embryonic stem cells following stress exposure.

Involvement of Oct-1 in the regulation of CDKN1A in response to clinically relevant doses of ionizing radiation

CDKN1A is a cyclin-dependent kinase inhibitor that plays a critical role in cell cycle checkpoint regulation. It is transcriptionally induced by TP53 (p53) following exposure to ionizing radiation (IR). Induction of CDKN1A after irradiation is closely related to IR-sensitivity of tumor cells, but the underlying mechanisms remain obscure because conventional reporter gene systems respond poorly to IR unless hyperlethal doses are used. Here, we performed a promoter analysis of the CDKN1A gene following irradiation with clinically relevant doses of IR using the adeno-associated virus-mediated reporter system which we have recently shown to be highly responsive to IR. We demonstrate that there are regulatory elements at -1.1 kb, -1.4 kb, and -1.8 kb, and deletion of these elements attenuate induction of the CDKN1A gene promoter in response to 0.2-2.0 Gy of IR. EMSA and ChIP assays showed that Oct-1 binds constitutively to the elements at -1.1 kb and -1.8 kb. Functional involvement of Oct-1 was confirmed by RNA interference targeting the Oct-1 gene, which suppressed both the basal and IR-inducible components of the CDKN1A expression. Thus, our results reveal that Oct-1 is crucial to the TP53-mediated regulation of the CDKN1A gene promoter following exposure to clinically relevant doses of IR.

Death in the AIRE

When thymic epithelia begin to synthesize peripheral tissue antigens such as insulin, we are seeing the result of autoimmune regulator (AIRE) activity and the workings of central tolerance. AIRE is an extraordinary protein that repatterns the transcriptome of medullary thymic epithelia (mTECs) to produce a stroma decorated with peripheral self-peptides. These peptidic arrays are used to purge self-reactive T cells, thereby averting autoimmunity. We now propose that an inherently cytotoxic event such as global chromatin modification paves the way for AIRE action. This injury stimulus might impose temporal restrictions for the T-cell education process and is endured, at least transiently, by the unique cellular environment provided by the medullary thymic epithelia.