C/EBPbeta regulates metastatic gene expression and confers TNF-alpha resistance to prostate cancer cells

BestCRM: An Exhaustive Search for Optimal Cis-Regulatory Modules in Promoters Accelerated by the Multidimensional Hash Function

The concept of cis-regulatory modules located in gene promoters represents today's vision of the organization of gene transcriptional regulation. Such modules are a combination of two or more single, short DNA motifs. The bioinformatic identification of such modules belongs to so-called NP-hard problems with extreme computational complexity, and therefore, simplifications, assumptions, and heuristics are usually deployed to tackle the problem. In practice, this requires, first, many parameters to be set before the search, and second, it leads to the identification of locally optimal results. Here, a novel method is presented, aimed at identifying the cis-regulatory elements in gene promoters based on an exhaustive search of all the feasible modules' configurations. All required parameters are automatically estimated using positive and negative datasets. To be computationally efficient, the search is accelerated using a multidimensional hash function, allowing the search to complete in a few hours on a regular laptop (for example, a CPU Intel i7, 3.2 GH, 32 Gb RAM). Tests on an established benchmark and real data show better performance of BestCRM compared to the available methods according to several metrics like specificity, sensitivity, AUC, etc. A great practical advantage of the method is its minimum number of input parameters-apart from positive and negative promoters, only a desired level of module presence in promoters is required.

Cancer invasion and metastasis: Insights from murine pubertal mammary gland morphogenesis

Cancer invasion and metastasis accounts for the majority of cancer related mortality. A better understanding of the players that drive the aberrant invasion and migration of tumors cells will provide critical targets to inhibit metastasis. Postnatal pubertal mammary gland morphogenesis is characterized by highly proliferative, invasive, and migratory normal epithelial cells. Identifying the molecular regulators of pubertal gland development is a promising strategy since tumorigenesis and metastasis is postulated to be a consequence of aberrant reactivation of developmental stages. In this review, we summarize the pubertal morphogenesis regulators that are involved in cancer metastasis and revisit pubertal mammary gland transcriptome profiling to uncover both known and unknown metastasis genes. Our updated list of pubertal morphogenesis regulators shows that most are implicated in invasion and metastasis. This review highlights molecular linkages between development and metastasis and provides a guide for exploring novel metastatic drivers.

Targeting Transcription Factors ATF5, CEBPB and CEBPD with Cell-Penetrating Peptides to Treat Brain and Other Cancers

Developing novel therapeutics often follows three steps: target identification, design of strategies to suppress target activity and drug development to implement the strategies. In this review, we recount the evidence identifying the basic leucine zipper transcription factors ATF5, CEBPB, and CEBPD as targets for brain and other malignancies. We describe strategies that exploit the structures of the three factors to create inhibitory dominant-negative (DN) mutant forms that selectively suppress growth and survival of cancer cells. We then discuss and compare four peptides (CP-DN-ATF5, Dpep, Bpep and ST101) in which DN sequences are joined with cell-penetrating domains to create drugs that pass through tissue barriers and into cells. The peptide drugs show both efficacy and safety in suppressing growth and in the survival of brain and other cancers in vivo, and ST101 is currently in clinical trials for solid tumors, including GBM. We further consider known mechanisms by which the peptides act and how these have been exploited in rationally designed combination therapies. We additionally discuss lacunae in our knowledge about the peptides that merit further research. Finally, we suggest both short- and long-term directions for creating new generations of drugs targeting ATF5, CEBPB, CEBPD, and other transcription factors for treating brain and other malignancies.

Natural Products with Antitumor Potential Targeting the MYB-C/EBPβ-p300 Transcription Module

The transcription factor MYB is expressed predominantly in hematopoietic progenitor cells, where it plays an essential role in the development of most lineages of the hematopoietic system. In the myeloid lineage, MYB is known to cooperate with members of the CCAAT box/enhancer binding protein (C/EBP) family of transcription factors. MYB and C/EBPs interact with the co-activator p300 or its paralog CREB-binding protein (CBP), to form a transcriptional module involved in myeloid-specific gene expression. Recent work has demonstrated that MYB is involved in the development of human leukemia, especially in acute T-cell leukemia (T-ALL) and acute myeloid leukemia (AML). Chemical entities that inhibit the transcriptional activity of the MYB-C/EBPβ-p300 transcription module may therefore be of use as potential anti-tumour drugs. In searching for small molecule inhibitors, studies from our group over the last 10 years have identified natural products belonging to different structural classes, including various sesquiterpene lactones, a steroid lactone, quinone methide triterpenes and naphthoquinones that interfere with the activity of this transcriptional module in different ways. This review gives a comprehensive overview on the various classes of inhibitors and the inhibitory mechanisms by which they affect the MYB-C/EBPβ-p300 transcriptional module as a potential anti-tumor target. We also focus on the current knowledge on structure-activity relationships underlying these biological effects and on the potential of these compounds for further development.

C/EBPβ sustains the oncogenic program of AML cells by cooperating with MYB and co-activator p300 in a transcriptional module

Transcription factor MYB is a key regulator of gene expression in hematopoietic cells and has emerged as a novel drug target for acute myeloid leukemia (AML). Studies aiming to identify potential MYB inhibitors have shown that the natural compound helenalin acetate (HA) inhibits viability and induces cell death and differentiation of AML cells by disrupting the MYB-induced gene expression program. Interestingly, CCAAT-box/enhancer binding protein beta (C/EBPβ), a transcription factor known to cooperate with MYB and the co-activator p300 in myeloid cells, rather than MYB itself, was identified as the primary target of HA. This supports a model in which MYB, C/EBPβ and p300 form the core of a transcriptional module that is essential for the maintenance of proliferative potential of AML cells, highlighting a novel role of C/EBPβ as a pro-leukemogenic factor.

C/EBPβ is a MYB- and p300-cooperating pro-leukemogenic factor and promising drug target in acute myeloid leukemia

Transcription factor MYB has recently emerged as a promising drug target for the treatment of acute myeloid leukemia (AML). Here, we have characterized a group of natural sesquiterpene lactones (STLs), previously shown to suppress MYB activity, for their potential to decrease AML cell proliferation. Unlike what was initially thought, these compounds inhibit MYB indirectly via its cooperation partner C/EBPβ. C/EBPβ-inhibitory STLs affect the expression of a large number of MYB-regulated genes, suggesting that the cooperation of MYB and C/EBPβ broadly shapes the transcriptional program of AML cells. We show that expression of GFI1, a direct MYB target gene, is controlled cooperatively by MYB, C/EBPβ, and co-activator p300, and is down-regulated by C/EBPβ-inhibitory STLs, exemplifying that they target the activity of composite MYB-C/EBPβ-p300 transcriptional modules. Ectopic expression of GFI1, a zinc-finger protein that is required for the maintenance of hematopoietic stem and progenitor cells, partially abrogated STL-induced myelomonocytic differentiation, implicating GFI1 as a relevant target of C/EBPβ-inhibitory STLs. Overall, our data identify C/EBPβ as a pro-leukemogenic factor in AML and suggest that targeting of C/EBPβ may have therapeutic potential against AML.

Dominant-Negative ATF5 Compromises Cancer Cell Survival by Targeting CEBPB and CEBPD

The basic leucine zipper transcription factor ATF5 is overexpressed in many tumor types and interference with its expression or function inhibits cancer cell survival. As a potential therapeutic approach to exploit these findings, we created dominant-negative (DN) ATF5 forms lacking DNA-binding ability that retain the ATF5 leucine zipper, and thus associate with and sequester ATF5's requisite leucine zipper-binding partners. Preclinical studies with DN-ATF5, including a cell-penetrating form, show in vitro and in vivo efficacy in compromising cancer cell survival. However, DN-ATF5's targets, and particularly those required for tumor cell survival, have been unknown. We report that cells lacking ATF5 succumb to DN-ATF5, indicating that ATF5 itself is not DN-ATF5's obligate target. Unbiased pull-down assays coupled with mass spectrometry and immunoblotting revealed that DN-ATF5 associates in cells with the basic leucine zipper proteins CEBPB and CEBPD and coiled-coil protein CCDC6. Consistent with DN-ATF5 affecting tumor cell survival by suppressing CEBPB and CEBPD function, DN-ATF5 interferes with CEBPB and CEBPD transcriptional activity, while CEBPB or CEBPD knockdown promotes apoptotic death of multiple cancer cells lines, but not of normal astrocytes. We propose a two-pronged mechanism by which DN-ATF5 kills tumor cells. One is by inhibiting heterodimer formation between ATF5 and CEBPB and CDBPD, thus suppressing ATF5-dependent transcription. The other is by blocking the formation of transcriptionally active CEBPB and CEBPD homodimers as well as heterodimers with partners in addition to ATF5. IMPLICATIONS: This study indicates that the potential cancer therapeutic DN-ATF5 acts by associating with and blocking the transcriptional activities of CEBPB and CEBPD.

AMPK activation inhibits the functions of myeloid-derived suppressor cells (MDSC): impact on cancer and aging

AMP-activated protein kinase (AMPK) has a crucial role not only in the regulation of tissue energy metabolism but it can also control immune responses through its cooperation with immune signaling pathways, thus affecting immunometabolism and the functions of immune cells. It is known that AMPK signaling inhibits the activity of the NF-κB system and thus suppresses pro-inflammatory responses. Interestingly, AMPK activation can inhibit several major immune signaling pathways, e.g., the JAK-STAT, NF-κB, C/EBPβ, CHOP, and HIF-1α pathways, which induce the expansion and activation of myeloid-derived suppressor cells (MDSC). MDSCs induce an immunosuppressive microenvironment in tumors and thus allow the escape of tumor cells from immune surveillance. Chronic inflammation has a key role in the expansion and activation of MDSCs in both tumors and inflammatory disorders. The numbers of MDSCs also significantly increase during the aging process concurrently with the immunosenescence associated with chronic low-grade inflammation. Increased fatty acid oxidation and lactate produced by aerobic glycolysis are important immunometabolic enhancers of MDSC functions. However, it seems that AMPK signaling regulates the functions of MDSCs in a context-dependent manner. Currently, the activators of AMPK signaling are promising drug candidates for cancer therapy and possibly for the extension of healthspan and lifespan. We will describe in detail the AMPK-mediated regulation of the signaling pathways controlling the expansion and activation of immunosuppressive MDSCs. We will propose that the beneficial effects mediated by AMPK activation, e.g., in cancers and the aging process, could be induced by the inhibition of MDSC functions.

Prostate cancer induces C/EBPβ expression in surrounding epithelial cells which relates to tumor aggressiveness and patient outcome

BACKGROUND

Implantation of rat prostate cancer cells into the normal rat prostate results in tumor-stimulating adaptations in the tumor-bearing organ. Similar changes are seen in prostate cancer patients and they are related to outcome. One gene previously found to be upregulated in the non-malignant part of tumor-bearing prostate lobe in rats was the transcription factor CCAAT/enhancer-binding protein-β (C/EBPβ).

METHODS

To explore this further, we examined C/EBPβ expression by quantitative RT-PCR, immunohistochemistry, and Western blot in normal rat prostate tissue surrounding slow-growing non-metastatic Dunning G, rapidly growing poorly metastatic (AT-1), and rapidly growing highly metastatic (MatLyLu) rat prostate tumors-and also by immunohistochemistry in a tissue microarray (TMA) from prostate cancer patients managed by watchful waiting.

RESULTS

In rats, C/EBPβ mRNA expression was upregulated in the surrounding tumor-bearing prostate lobe. In tumors and in the surrounding non-malignant prostate tissue, C/EBPβ was detected by immunohistochemistry in some epithelial cells and in infiltrating macrophages. The magnitude of glandular epithelial C/EBPβ expression in the tumor-bearing prostates was associated with tumor size, distance to the tumor, and metastatic capacity. In prostate cancer patients, high expression of C/EBPβ in glandular epithelial cells in the surrounding tumor-bearing tissue was associated with accumulation of M1 macrophages (iNOS+) and favorable outcome. High expression of C/EBPβ in tumor epithelial cells was associated with high Gleason score, high tumor cell proliferation, metastases, and poor outcome.

CONCLUSIONS

This study suggest that the expression of C/EBP-beta, a transcription factor mediating multiple biological effects, is differentially expressed both in the benign parts of the tumor-bearing prostate and in prostate tumors, and that alterations in this may be related to patient outcome.

C/EBPβ deletion in oncogenic Ras skin tumors is a synthetic lethal event

Therapeutic targeting of specific genetic changes in cancer has proven to be an effective therapy and the concept of synthetic lethality has emerged. CCAAT/enhancer-binding protein-β (C/EBPβ), a basic leucine zipper transcription factor, has important roles in cellular processes including differentiation, inflammation, survival, and energy metabolism. Using a genetically engineered mouse model, we report that the deletion C/EBPβ in pre-existing oncogenic Ha-Ras mouse skin tumors in vivo resulted in rapid tumor regression. Regressing tumors exhibited elevated levels of apoptosis and p53 protein/activity, while adjacent C/EBPβ-deleted skin did not. These results indicate that the deletion of C/EBPβ de-represses p53 in oncogenic Ras tumors but not in normal wild-type Ras keratinocytes, and that C/EBPβ is essential for survival of oncogenic Ras tumors. Co-deletion of C/EBPβ and p53 in oncogenic Ras tumors showed p53 is required for tumor regression and elevated apoptosis. In tumors, loss of a pathway that confers adaptability to a stress phenotype of cancer/tumorigenesis, such as DNA damage, could result in selective tumor cell killing. Our results show that oncogenic Ras tumors display a significant DNA damage/replicative stress phenotype and these tumors have acquired a dependence on C/EBPβ for their survival. RNAseq data analysis of regressing tumors deleted of C/EBPβ indicates a novel interface between p53, type-1 interferon response, and death receptor pathways, which function in concert to produce activation of extrinsic apoptosis pathways. In summary, the deletion of C/EBPβ in oncogenic Ras skin tumors is a synthetic lethal event, making it a promising target for future potential anticancer therapies.

A novel cell-based screening assay for small-molecule MYB inhibitors identifies podophyllotoxins teniposide and etoposide as inhibitors of MYB activity

The transcription factor MYB plays key roles in hematopoietic cells and has been implicated the development of leukemia. MYB has therefore emerged as an attractive target for drug development. Recent work has suggested that targeting MYB by small-molecule inhibitors is feasible and that inhibition of MYB has potential as a therapeutic approach against acute myeloid leukemia. To facilitate the identification of small-molecule MYB inhibitors we have re-designed and improved a previously established cell-based screening assay and have employed it to screen a natural product library for potential inhibitors. Our work shows that teniposide and etoposide, chemotherapeutic agents causing DNA-damage by inhibiting topoisomerase II, potently inhibit MYB activity and induce degradation of MYB in AML cell lines. MYB inhibition is suppressed by caffeine, suggesting that MYB is inhibited indirectly via DNA-damage signalling. Importantly, ectopic expression of an activated version of MYB in pro-myelocytic NB4 cells diminished the anti-proliferative effects of teniposide, suggesting that podophyllotoxins disrupt the proliferation of leukemia cells not simply by inducing general DNA-damage but that their anti-proliferative effects are boosted by inhibition of MYB. Teniposide and etoposide therefore act like double-edged swords that might be particularly effective to inhibit tumor cells with deregulated MYB.

The natural anti-tumor compound Celastrol targets a Myb-C/EBPβ-p300 transcriptional module implicated in myeloid gene expression

Myb is a key regulator of hematopoietic progenitor cell proliferation and differentiation and has emerged as a potential target for the treatment of acute leukemia. Using a myeloid cell line with a stably integrated Myb-inducible reporter gene as a screening tool we have previously identified Celastrol, a natural compound with anti-tumor activity, as a potent Myb inhibitor that disrupts the interaction of Myb with the co-activator p300. We showed that Celastrol inhibits the proliferation of acute myeloid leukemia (AML) cells and prolongs the survival of mice in an in vivo model of AML, demonstrating that targeting Myb with a small-molecule inhibitor is feasible and might have potential as a therapeutic approach against AML. Recently we became aware that the reporter system used for Myb inhibitor screening also responds to inhibition of C/EBPβ, a transcription factor known to cooperate with Myb in myeloid cells. By re-investigating the inhibitory potential of Celastrol we have found that Celastrol also strongly inhibits the activity of C/EBPβ by disrupting its interaction with the Taz2 domain of p300. Together with previous studies our work reveals that Celastrol independently targets Myb and C/EBPβ by disrupting the interaction of both transcription factors with p300. Myb, C/EBPβ and p300 cooperate in myeloid-specific gene expression and, as shown recently, are associated with so-called super-enhancers in AML cells that have been implicated in the maintenance of the leukemia. We hypothesize that the ability of Celastrol to disrupt the activity of a transcriptional Myb-C/EBPβ-p300 module might explain its promising anti-leukemic activity.

IκB-Kinase-epsilon (IKKε) over-expression promotes the growth of prostate cancer through the C/EBP-β dependent activation of IL-6 gene expression

The inflammatory cytokine IL-6 has been shown to induce the nuclear translocation of androgen receptors in prostate cancer cells and to activate the androgen receptors in a ligand-independent manner, suggesting it may contribute to the development of a castrate-resistant phenotype. Elevated IL-6 serum levels have also been associated with metastasis-related morbidity in prostate cancer patients. We have previously established that over-expression of I-kappa-B-kinase-epsilon (IKKε also named IKKi or IκBKε) in hormone-sensitive prostate cancer cell lines induces IL-6 secretion. We have also reported that prostate cancer cell lines lacking androgen receptor expression exhibit high constitutive IKKε expression and IL-6 secretion. In the present study, we validated the impact of IKKε depletion on the in vitro proliferation of castrate-resistant prostate cancer cells, and characterized how IKKε depletion affects tumor growth and IL-6 tumor secretion in vivo through a mouse xenograft-based approach. We observed a significant growth delay in IKKε-silenced PC-3 cells injected in SCID mice fed with a doxycycline-supplemented diet in comparison with mice fed with a normal diet. We also found a decrease in IL-6 secretion levels that strongly correlated with tumor growth inhibition. Finally, using constructs with various IL-6-mutated promoters, we demonstrated that IKKε over-expression induces a NF-κB-independent stimulation of the IL-6 gene promoter through the activation and nuclear accumulation of the transcription factor C/EBP-β. Our study demonstrates the pro-proliferative role of the oncogene IKKε in castrate-resistant prostate cancer cell lines, involving the phosphorylation and nuclear translocation of C/EBP-β that initiates IL-6 gene expression.

Withaferin A, a natural compound with anti-tumor activity, is a potent inhibitor of transcription factor C/EBPβ

Recent work has shown that deregulation of the transcription factor Myb contributes to the development of leukemia and several other human cancers, making Myb and its cooperation partners attractive targets for drug development. By employing a myeloid Myb-reporter cell line we have identified Withaferin A (WFA), a natural compound that exhibits anti-tumor activities, as an inhibitor of Myb-dependent transcription. Analysis of the inhibitory mechanism of WFA showed that WFA is a significantly more potent inhibitor of C/EBPβ, a transcription factor cooperating with Myb in myeloid cells, than of Myb itself. We show that WFA covalently modifies specific cysteine residues of C/EBPβ, resulting in the disruption of the interaction of C/EBPβ with the co-activator p300. Our work identifies C/EBPβ as a novel direct target of WFA and highlights the role of p300 as a crucial co-activator of C/EBPβ. The finding that WFA is a potent inhibitor of C/EBPβ suggests that inhibition of C/EBPβ might contribute to the biological activities of WFA.

Helenalin Acetate, a Natural Sesquiterpene Lactone with Anti-inflammatory and Anti-cancer Activity, Disrupts the Cooperation of CCAAT Box/Enhancer-binding Protein β (C/EBPβ) and Co-activator p300

Recent work has demonstrated pro-oncogenic functions of the transcription factor CCAAT box/enhancer-binding protein β (C/EBPβ) in various tumors, implicating C/EBPβ as an interesting target for the development of small-molecule inhibitors. We have previously discovered that the sesquiterpene lactone helenalin acetate, a natural compound known to inhibit NF-κB, is a potent C/EBPβ inhibitor. We have now examined the inhibitory mechanism of helenalin acetate in more detail. We demonstrate that helenalin acetate is a significantly more potent inhibitor of C/EBPβ than of NF-κB. Our work shows that helenalin acetate inhibits C/EBPβ by binding to the N-terminal part of C/EBPβ, thereby disrupting the cooperation of C/EBPβ with the co-activator p300. C/EBPβ is expressed in several isoforms from alternative translational start codons. We have previously demonstrated that helenalin acetate selectively inhibits only the full-length (liver-enriched activating protein* (LAP*)) isoform but not the slightly shorter (LAP) isoform. Consistent with this, helenalin acetate binds to the LAP* but not to the LAP isoform, explaining why its inhibitory activity is selective for LAP*. Although helenalin acetate contains reactive groups that are able to interact covalently with cysteine residues, as exemplified by its effect on NF-κB, the inhibition of C/EBPβ by helenalin acetate is not due to irreversible reaction with cysteine residues of C/EBPβ. In summary, helenalin acetate is the first highly active small-molecule C/EBPβ inhibitor that inhibits C/EBPβ by a direct binding mechanism. Its selectivity for the LAP* isoform also makes helenalin acetate an interesting tool to dissect the functions of the LAP* and LAP isoforms.

CCAAT/enhancer binding protein β induces motility and invasion of glioblastoma cells through transcriptional regulation of the calcium binding protein S100A4

We have previously shown that decreased expression of CCAAT/enhancer binding protein β (C/EBPβ) inhibits the growth of glioblastoma cells and diminishes their transformation capacity and migration. In agreement with this, we showed that C/EBPβ depletion decreases the mRNA levels of different genes involved in metastasis and invasion. Among these, we found S100 calcium binding protein A4 (S100A4) to be almost undetectable in glioblastoma cells deficient in C/EBPβ. Here, we have evaluated the possible role of S100A4 in the observed effects of C/EBPβ in glioblastoma cells and the mechanism through which S100A4 levels are controlled by C/EBPβ. Our results show that C/EBPβ suppression significantly reduced the levels of S100A4 in murine GL261 and human T98G glioblastoma cells. By employing an S100A4-promoter reporter, we observed a significant induction in the transcriptional activation of the S100A4 gene by C/EBPβ. Furthermore, overexpression of S100A4 in C/EBPβ-depleted glioblastoma cells reverses the enhanced migration and motility induced by this transcription factor. Our data also point to a role of S100A4 in glioblastoma cell invasion and suggest that the C/EBPβ gene controls the invasive potential of GL261 and T98G cells through direct regulation of S100A4. Finally, this study indicates a role of C/EBPβ on the maintenance of the stem cell population present in GL261 glioblastoma cells.

CCAAT/Enhancer binding protein β controls androgen-deprivation-induced senescence in prostate cancer cells

The processes associated with transition to castration independent prostate cancer growth are not well understood. Cellular senescence is a stable cell cycle arrest that occurs in response to sublethal stress. It is often overcome in malignant transformation to confer a survival advantage. CCAAT/Enhancer Binding Protein (C/EBP) β function is frequently deregulated in human malignancies and interestingly, androgen dependent prostate cancer cells express primarily the LIP isoform. We found that C/EBPβ expression is negatively regulated by androgen receptor activity and that treatment of androgen dependent cell lines with anti-androgens increases C/EBPβ mRNA and protein levels. Accordingly, we also find that C/EBPβ levels are significantly elevated in primary prostate cancer samples from castration resistant compared with therapy naive patients. Chromatin immunoprecipitation demonstrated enhanced binding of the androgen receptor to the proximal promoter of the CEBPB gene in the presence of dihydroxytestosterone. Upon androgen deprivation, induction of C/EBPβ is facilitated by active transcription as evident by increased histone 3 acetylation at the C/EBPβ promoter. Also, the androgen agonist R1881 suppresses the activity of a CEBPB promoter reporter. Loss of C/EBPβ expression prevents growth arrest following androgen deprivation or anti-androgen challenge. Accordingly, suppression of C/EBPβ under low androgen conditions results in reduced expression of senescence-associated secretory genes, significantly decreased number of cells displaying heterochromatin foci, and increased numbers of Ki67 positive cells. Ectopic expression of C/EBPβ caused pronounced morphological changes, reduced PC cell growth, and increased the number of senescent LNCaP cells. Lastly, we found that senescence contributes to prostate cancer cell survival under androgen deprivation, and C/EBPβ deficient cells were significantly more susceptible to killing by cytotoxic chemotherapy following androgen deprivation. Our data demonstrate that up-regulation of C/EBPβ is critical for complete maintenance of androgen deprivation induced senescence and that targeting C/EBPβ expression may synergize with anti-androgen or chemotherapy in eradicating prostate cancer.

Medroxyprogesterone acetate differentially regulates interleukin (IL)-12 and IL-10 in a human ectocervical epithelial cell line in a glucocorticoid receptor (GR)-dependent manner

Medroxyprogesterone acetate (MPA), designed to mimic the actions of the endogenous hormone progesterone (P4), is extensively used by women as a contraceptive and in hormone replacement therapy. However, little is known about the steroid receptor-mediated molecular mechanisms of action of MPA in the female genital tract. In this study, we investigated the regulation of the pro-inflammatory cytokine, interleukin (IL)-12, and the anti-inflammatory cytokine IL-10, by MPA versus P4, in an in vitro cell culture model of the female ectocervical environment. This study shows that P4 and MPA significantly increase the expression of the IL-12p40 and IL-12p35 genes, whereas IL-10 gene expression is suppressed in a dose-dependent manner. Moreover, these effects were abrogated when reducing the glucocorticoid receptor (GR) levels with siRNA. Using a combination of chromatin immunoprecipitation (ChIP), siRNA, and re-ChIP assays, we show that recruitment of the P4- and MPA-bound GR to the IL-12p40 promoter requires CCAAT enhancer-binding protein (C/EBP)-β and nuclear factor κB (NFκB), although recruitment to the IL-10 promoter requires signal transducer and activator of transcription (STAT)-3. These results suggest that both P4 and MPA may modulate inflammation in the ectocervix via this genomic mechanism.

Redox-mediated and ionizing-radiation-induced inflammatory mediators in prostate cancer development and treatment

SIGNIFICANCE

Radiation therapy is widely used for treatment of prostate cancer. Radiation can directly damage biologically important molecules; however, most effects of radiation-mediated cell killing are derived from the generated free radicals that alter cellular redox status. Multiple proinflammatory mediators can also influence redox status in irradiated cells and the surrounding microenvironment, thereby affecting prostate cancer progression and radiotherapy efficiency.

RECENT ADVANCES

Ionizing radiation (IR)-generated oxidative stress can regulate and be regulated by the production of proinflammatory mediators. Depending on the type and stage of the prostate cancer cells, these proinflammatory mediators may lead to different biological consequences ranging from cell death to development of radioresistance.

CRITICAL ISSUES

Tumors are heterogeneous and dynamic communication occurs between stromal and prostate cancer cells, and complicated redox-regulated mechanisms exist in the tumor microenvironment. Thus, antioxidant and anti-inflammatory strategies should be carefully evaluated for each patient at different stages of the disease to maximize therapeutic benefits while minimizing unintended side effects.

FUTURE DIRECTIONS

Compared with normal cells, tumor cells are usually under higher oxidative stress and secrete more proinflammatory mediators. Thus, redox status is often less adaptive in tumor cells than in their normal counterparts. This difference can be exploited in a search for new cancer therapeutics and treatment regimes that selectively activate cell death pathways in tumor cells with minimal unintended consequences in terms of chemo- and radio-resistance in tumor cells and toxicity in normal tissues.

BAD dephosphorylation and decreased expression of MCL-1 induce rapid apoptosis in prostate cancer cells

PTEN loss and constitutive activation of the PI3K signaling pathway have been associated with advanced androgen-independent prostate cancer. PTEN-deficient prostate cancer C42Luc cells survive in serum-free media and show relative resistance to apoptosis even in the presence of the PI3K inhibitor ZSTK474. Yet, when ZSTK474 is combined with the translation inhibitor cycloheximide, C42Luc cells undergo apoptosis within 6 hours. We identified dephosphorylation of BAD (Bcl2-associated death promoter) as a main apoptosis-regulatory molecule downstream from PI3K, and loss of MCL-1 (Myeloid cell leukemia -1) as a major target of cycloheximide. The combination of MCL-1 knockdown and expression of phosphorylation-deficient mutant BAD2SA is sufficient to trigger rapid apoptosis in prostate cancer cells. These results establish the mechanism for the synergistic induction of apoptosis by the combination of a PI3K inhibitor and of a protein synthesis inhibitor in PTEN-deficient prostate cancer cells.

MatrixCatch--a novel tool for the recognition of composite regulatory elements in promoters

BACKGROUND

Accurate recognition of regulatory elements in promoters is an essential prerequisite for understanding the mechanisms of gene regulation at the level of transcription. Composite regulatory elements represent a particular type of such transcriptional regulatory elements consisting of pairs of individual DNA motifs. In contrast to the present approach, most available recognition techniques are based purely on statistical evaluation of the occurrence of single motifs. Such methods are limited in application, since the accuracy of recognition is greatly dependent on the size and quality of the sequence dataset. Methods that exploit available knowledge and have broad applicability are evidently needed.

RESULTS

We developed a novel method to identify composite regulatory elements in promoters using a library of known examples. In depth investigation of regularities encoded in known composite elements allowed us to introduce a new characteristic measure and to improve the specificity compared with other methods. Tests on an established benchmark and real genomic data show that our method outperforms other available methods based either on known examples or statistical evaluations. In addition to better recognition, a practical advantage of this method is first the ability to detect a high number of different types of composite elements, and second direct biological interpretation of the identified results. The program is available at http://gnaweb.helmholtz-hzi.de/cgi-bin/MCatch/MatrixCatch.pl and includes an option to extend the provided library by user supplied data.

CONCLUSIONS

The novel algorithm for the identification of composite regulatory elements presented in this paper was proved to be superior to existing methods. Its application to tissue specific promoters identified several highly specific composite elements with relevance to their biological function. This approach together with other methods will further advance the understanding of transcriptional regulation of genes.

C/EBPα, C/EBPα oncoproteins, or C/EBPβ preferentially bind NF-κB p50 compared with p65, focusing therapeutic targeting on the C/EBP:p50 interaction

Canonical nuclear factor kappaB (NF-κB) activation signals stimulate nuclear translocation of p50:p65, replacing inhibitory p50:p50 with activating complexes on chromatin. C/EBP interaction with p50 homodimers provides an alternative pathway for NF-κB target gene activation, and interaction with p50:p65 may enhance gene activation. We previously found that C/EBPα cooperates with p50, but not p65, to induce Bcl-2 transcription and that C/EBPα induces Nfkb1/p50, but not RelA/p65, transcription. Using p50 and p65 variants containing the FLAG epitope at their N- or C-termini, we now show that C/EBPα, C/EBPα myeloid oncoproteins, or the LAP1, LAP2, or LIP isoforms of C/EBPβ have markedly higher affinity for p50 than for p65. Deletion of the p65 transactivation domain did not increase p65 affinity for C/EBPs, suggesting that unique residues in p50 account for specificity, and clustered mutation of HSDL in the "p50 insert" lacking in p65 weakens interaction. Also, in contrast to Nfkb1 gene deletion, absence of the RelA gene does not reduce Bcl-2 or Cebpa RNA in unstimulated cells or prevent interaction of C/EBPα with the Bcl-2 promoter. Saturating mutagenesis of the C/EBPα basic region identifies R300 and nearby residues, identical in C/EBPβ, as critical for interaction with p50. These findings support the conclusion that C/EBPs activate NF-κB target genes via contact with p50 even in the absence of canonical NF-κB activation and indicate that targeting C/EBP:p50 rather than C/EBP:p65 interaction in the nucleus will prove effective for inflammatory or malignant conditions, alone or synergistically with agents acting in the cytoplasm to reduce canonical NF-κB activation.

Cigarette smoke induces C/EBP-β-mediated activation of miR-31 in normal human respiratory epithelia and lung cancer cells

BACKGROUND

Limited information is available regarding mechanisms by which miRNAs contribute to pulmonary carcinogenesis. The present study was undertaken to examine expression and function of miRNAs induced by cigarette smoke condensate (CSC) in normal human respiratory epithelia and lung cancer cells.

METHODOLOGY

Micro-array and quantitative RT-PCR (qRT-PCR) techniques were used to assess miRNA and host gene expression in cultured cells, and surgical specimens. Software-guided analysis, RNA cross-link immunoprecipitation (CLIP), 3' UTR luciferase reporter assays, qRT-PCR, focused super-arrays and western blot techniques were used to identify and confirm targets of miR-31. Chromatin immunoprecipitation (ChIP) techniques were used to evaluate histone marks and transcription factors within the LOC554202 promoter. Cell count and xenograft experiments were used to assess effects of miR-31 on proliferation and tumorigenicity of lung cancer cells.

RESULTS

CSC significantly increased miR-31 expression and activated LOC554202 in normal respiratory epithelia and lung cancer cells; miR-31 and LOC554202 expression persisted following discontinuation of CSC exposure. miR-31 and LOC554202 expression levels were significantly elevated in lung cancer specimens relative to adjacent normal lung tissues. CLIP and reporter assays demonstrated direct interaction of miR-31 with Dickkopf-1 (Dkk-1) and DACT-3. Over-expression of miR-31 markedly diminished Dkk-1 and DACT3 expression levels in normal respiratory epithelia and lung cancer cells. Knock-down of miR-31 increased Dkk-1 and DACT3 levels, and abrogated CSC-mediated decreases in Dkk-1 and DACT-3 expression. Furthermore, over-expression of miR-31 diminished SFRP1, SFRP4, and WIF-1, and increased Wnt-5a expression. CSC increased H3K4Me3, H3K9/14Ac and C/EBP-β levels within the LOC554202 promoter. Knock-down of C/EBP-β abrogated CSC-mediated activation of LOC554202. Over-expression of miR-31 significantly enhanced proliferation and tumorigenicity of lung cancer cells; knock-down of miR-31 inhibited growth of these cells.

CONCLUSIONS

Cigarette smoke induces expression of miR-31 targeting several antagonists of cancer stem cell signaling in normal respiratory epithelia and lung cancer cells. miR-31 functions as an oncomir during human pulmonary carcinogenesis.