Purification and identification of p68 RNA helicase acting as a transcriptional coactivator specific for the activation function 1 of human estrogen receptor alpha

RNA binding protein DDX5 directs tuft cell specification and function to regulate microbial repertoire and disease susceptibility in the intestine

OBJECTIVE

Tuft cells residing in the intestinal epithelium have diverse functions. In the small intestine, they provide protection against inflammation, combat against helminth and protist infections, and serve as entry portals for enteroviruses. In the colon, they had been implicated in tumourigenesis. Commitment of intestinal progenitor cells to the tuft cell lineage requires Rho GTPase Cell Division Cycle 42 (CDC42), a Rho GTPase that acts downstream of the epidermal growth factor receptor and wingless-related integration site signalling cascades, and the master transcription factor POU class 2 homeobox 3 (POU2F3). This study investigates how this pathway is regulated by the DEAD box containing RNA binding protein DDX5 in vivo.

DESIGN

We assessed the role of DDX5 in tuft cell specification and function in control and epithelial cell-specific Ddx5 knockout mice (DDX5ΔIEC) using transcriptomic approaches.

RESULTS

DDX5ΔIEC mice harboured a loss of intestinal tuft cell populations, modified microbial repertoire, and altered susceptibilities to ileal inflammation and colonic tumourigenesis. Mechanistically, DDX5 promotes CDC42 protein synthesis through a post-transcriptional mechanism to license tuft cell specification. Importantly, the DDX5-CDC42 axis is parallel but distinct from the known interleukin-13 circuit implicated in tuft cell hyperplasia, and both pathways augment Pou2f3 expression in secretory lineage progenitors. In mature tuft cells, DDX5 not only promotes integrin signalling and microbial responses, it also represses gene programmes involved in membrane transport and lipid metabolism.

CONCLUSION

RNA binding protein DDX5 directs tuft cell specification and function to regulate microbial repertoire and disease susceptibility in the intestine.

Insights Into the Role of Epigenetic Factors Determining the Estrogen Response in Estrogen-Positive Ovarian Cancer and Prospects of Combining Epi-Drugs With Endocrine Therapy

Ovarian cancer is one of the most lethal malignancies. The population at the risk is continually on the rise due to the acquired drug resistance, high relapse rate, incomplete knowledge of the etiology, cross-talk with other gynecological malignancies, and diagnosis at an advanced stage. Most ovarian tumors are thought to arise in surface epithelium somehow in response to changes in the hormonal environment. Prolonged treatment with hormone replacement therapy (HRT) is also considered a contributing factor. Estrogens influence the etiology and progression of the endocrine/hormone-responsive cancers in a patient-specific manner. The concept of hormonal manipulations got attention during the last half of the 20th century when tamoxifen was approved by the FDA as the first selective estrogen receptor modulator (SERM). Endocrine therapy that has been found to be effective against breast cancer can be an option for ovarian cancer. It is now established that global changes in the epigenetic landscape are not only the hallmark of tumor development but also contribute to the development of resistance to hormone therapy. A set of functionally related genes involved in epigenetic reprogramming are controlled by specific transcription factors (TFs). Thus, the activities of TFs mediate important mechanisms through which epigenetic enzymes and co-factors modify chromatin for the worst outcome in a site-specific manner. Furthermore, the role of epigenetic aberrations involving histone modifications is established in ovarian cancer pathogenesis. This review aims to provide insights on the role of key epigenetic determinants of response as well as resistance to the hormone therapy, the current status of research along with its limitations, and future prospects of epigenetic agents as biomarkers in early diagnosis, prognosis, and personalized treatment strategies. Finally, the possibility of small phytoestrogenic molecules in combination with immunotherapy and epi-drugs targeting ovarian cancer has been discussed.

Molecular Insights into the Recruiting Between UCP2 and DDX5/UBAP2L in the Metabolic Plasticity of Non-Small-Cell Lung Cancer

Mitochondrial uncoupling protein 2 (UCP2) is distributed in tumor cells with a link to the support of systemic metabolic deregulation, and the downregulation of UCP2 has been unveiled as a biomarker of oncogenesis and chemoresistance in non-small-cell lung cancer (NSCLC) cells. However, the underlying mechanism of how UCP2 cooperates with other proteins in this metabolic reprogramming remains largely unsolved. We employed a combined computational and experimental strategy to explore into the recruiting of DDX5 with other proteins, and we unraveled the underlying structural mechanisms. We found that recruiting by ATP-dependent RNA helicase DDX5 (DDX5)/ubiquitin-associated protein 2-like (UBAP2L) might help UCP2 to play the pathological roles in NSCLC cells. According to the view of thermodynamics in physics, UCP2 tends to recruit DDX5 rather than UBAP2L, as shown by the ensemble-based docking, molecular dynamics simulations and molecular mechanics generalized Born surface area (MM/GBSA) approach. Cellular immunofluorescence assays further demonstrated that UCP2 associate with DDX5, and the recruiting of DDX5 with UCP2 at least partially contribute to the metabolic plasticity of NSCLCs via the AKT/mTOR pathway. Our study proposed an efficient way for detecting the protein-protein association via the experimentally validated molecular simulation. Our results shed light on the functional annotation of UCP and DDX family proteins in dysregulated metabolism, and the identification of candidate therapeutic targets for NSCLC.

DDX5 promotes oncogene C3 and FABP1 expressions and drives intestinal inflammation and tumorigenesis

Tumorigenesis in different segments of the intestinal tract involves tissue-specific oncogenic drivers. In the colon, complement component 3 (C3) activation is a major contributor to inflammation and malignancies. By contrast, tumorigenesis in the small intestine involves fatty acid-binding protein 1 (FABP1). However, little is known of the upstream mechanisms driving their expressions in different segments of the intestinal tract. Here, we report that the RNA-binding protein DDX5 binds to the mRNA transcripts of C3 and Fabp1 to augment their expressions posttranscriptionally. Knocking out DDX5 in epithelial cells protected mice from intestinal tumorigenesis and dextran sodium sulfate (DSS)-induced colitis. Identification of DDX5 as a common upstream regulator of tissue-specific oncogenic molecules provides an excellent therapeutic target for intestinal diseases.

Genome-wide R-loop analysis defines unique roles for DDX5, XRN2, and PRMT5 in DNA/RNA hybrid resolution

Genome-wide analysis of R-loop alterations in U2OS cells deficient of DDX5, XRN2, and PRMT5 identify >50,650 DRIP-seq peaks spanning ∼4.5% of the genomic sequence. R-loops near TSS generated intergenic antisense transcription.

DDX5, XRN2, and PRMT5 have been shown to resolve DNA/RNA hybrids (R-loops) at RNA polymerase II transcription termination sites at few genomic loci. Herein, we perform genome-wide R-loop mapping using classical DNA/RNA immunoprecipitation and high-throughput sequencing (DRIP-seq) of loci regulated by DDX5, XRN2, and PRMT5. We observed hundreds to thousands of R-loop gains and losses at transcribed loci in DDX5-, XRN2-, and PRMT5-deficient U2OS cells. R-loop gains were characteristic of highly transcribed genes located at gene-rich regions, whereas R-loop losses were observed in low-density gene areas. DDX5, XRN2, and PRMT5 shared many R-loop gain loci at transcription termination sites, consistent with their coordinated role in RNA polymerase II transcription termination. DDX5-depleted cells had unique R-loop gain peaks near the transcription start site that did not overlap with those of siXRN2 and siPRMT5 cells, suggesting a role for DDX5 in transcription initiation independent of XRN2 and PRMT5. Moreover, we observed that the accumulated R-loops at certain loci in siDDX5, siXRN2, and siPRMT5 cells near the transcription start site of genes led to antisense intergenic transcription. Our findings define unique and shared roles of DDX5, XRN2, and PRMT5 in DNA/RNA hybrid regulation.

DDX5 potentiates HIV-1 transcription as a co-factor of Tat

BACKGROUND

HIV-1 does not encode a helicase and hijacks those of the cell for efficient replication. We and others previously showed that the DEAD box helicase, DDX5, is an essential HIV dependency factor. DDX5 was recently shown to be associated with the 7SK snRNP. Cellular positive transcription elongation factor b (P-TEFb) is bound in an inactive form with HEXIM1/2 on 7SK snRNP. The Tat/P-TEFb complex is essential for efficient processivity of Pol II in HIV-1 transcription elongation and Tat competes with HEXIM1/2 for P-TEFb. We investigated the precise role of DDX5 in HIV replication using siRNA mediated knockdown and rescue with DDX5 mutants which prevent protein-protein interactions and RNA and ATP binding.

RESULTS

We demonstrate a critical role for DDX5 in the Tat/HEXIM1 interaction. DDX5 acts to potentiate Tat activity and can bind both Tat and HEXIM1 suggesting it may facilitate the dissociation of HEXIM1/2 from the 7SK-snRNP complex, enhancing Tat/P-TEFb availability. We show knockdown of DDX5 in a T cell line significantly reduces HIV-1 infectivity and viral protein production. This activity is unique to DDX5 and cannot be substituted by its close paralog DDX17. Overexpression of DDX5 stimulates the Tat/LTR promoter but suppresses other cellular and viral promoters. Individual mutations of conserved ATP binding, RNA binding, helicase related or protein binding motifs within DDX5 show that the N terminal RNA binding motifs, the Walker B and the glycine doublet motifs are essential for this function. The Walker A and RNA binding motifs situated on the transactivation domain are however dispensable.

CONCLUSION

DDX5 is an essential cellular factor for efficient HIV transcription elongation. It interacts with Tat and may potentiate the availability of P-TEFb through sequestering HEXIM1.

Targeting Pin1 by All-Trans Retinoic Acid (ATRA) Overcomes Tamoxifen Resistance in Breast Cancer via Multifactorial Mechanisms

Breast cancer is the most prevalent tumor in women worldwide and about 70% patients are estrogen receptor positive. In these cancer patients, resistance to the anticancer estrogen receptor antagonist tamoxifen emerges to be a major clinical obstacle. Peptidyl-prolyl isomerase Pin1 is prominently overexpressed in breast cancer and involves in tamoxifen-resistance. Here, we explore the mechanism and effect of targeting Pin1 using its chemical inhibitor all-trans retinoic acid (ATRA) in the treatment of tamoxifen-resistant breast cancer. We found that Pin1 was up-regulated in tamoxifen-resistant human breast cancer cell lines and tumor tissues from relapsed patients. Pin1 overexpression increased the phosphorylation of ERα on S118 and stabilized ERα protein. ATRA treatment, resembling the effect of Pin1 knockdown, promoted ERα degradation in tamoxifen-resistant cells. Moreover, ATRA or Pin1 knockdown decreased the activation of ERK1/2 and AKT pathways. ATRA also reduced the nuclear expression and transcriptional activity of ERα. Importantly, ATRA inhibited cell viability and proliferation of tamoxifen-resistant human breast cancer cells in vitro. Slow-releasing ATRA tablets reduced the growth of tamoxifen-resistant human breast cancer xenografts in vivo. In conclusion, ATRA-induced Pin1 ablation inhibits tamoxifen-resistant breast cancer growth by suppressing multifactorial mechanisms of tamoxifen resistance simultaneously, which demonstrates an attractive strategy for treating aggressive and endocrine-resistant tumors.

LncRNA CCAT1 Promotes Prostate Cancer Cell Proliferation by Interacting with DDX5 and MIR-28-5P

Accumulated evidence indicates that CCAT1 functions as an oncogene in the progression of a variety of tumors. However, little is known as to how CCAT1 impacts tumorigenesis in human prostate cancer. In this study, we found from The Cancer Genome Atlas and Memorial Sloan Kettering Cancer Center database that CCAT1 is highly upregulated in castration-resistant prostate cancer (CRPC) compared with androgen-dependent prostate cancer (ADPC). Higher level of CCAT1 leads to increased mortality in patients with CRPC. In vitro and in vivo studies show that CCAT1 promotes prostate cancer cell proliferation as well as the tumor growth of prostate cancer xenografts. Mechanistically, in cytoplasm, CCAT1 sponges MIR-28-5P to prevent the anticancer effect. In nucleus, CCAT1 acts as a scaffold for DDX5 (P68) and AR transcriptional complex to facilitate the expression of AR-regulated genes, thus stimulating CRPC progression. Our findings suggest that CCAT1 is an oncogenic factor in the progression of CRPC with different regulatory mechanisms in the nucleus and cytoplasm of cells.

Estrogen signaling: An emanating therapeutic target for breast cancer treatment

Breast cancer, a most common malignancy in women, was known to be associated with steroid hormone estrogen. The discovery of estrogen receptor (ER) gave us not only a powerful predictive and prognostic marker, but also an efficient target for the treatment of hormone-dependent breast cancer with various estrogen ligands. ER consists of two subtypes i.e. ERα and ERβ, that are mostly G-protein-coupled receptors and activated by estrogen, specially 17β-estradiol. The activation is followed by translocation into the nucleus and binding with DNA to modulate activities of different genes. ERs can manage synthesis of RNA through genomic actions without directly binding to DNA. Receptors are tethered by protein-protein interactions to a transcription factor complex to communicate with DNA. Estrogens also exhibit nongenomic actions, a characteristic feature of steroid hormones, which are so rapid to be considered by the activation of RNA and translation. These are habitually related to stimulation of different protein kinase cascades. Majority of post-menopausal breast cancer is estrogen dependent, mostly potent biological estrogen (E2) for continuous growth and proliferation. Estrogen helps in regulating the differentiation and proliferation of normal breast epithelial cells. In this review we have investigated the important role of ER in development and progression of breast cancer, which is complicated by receptor's interaction with co-regulatory proteins, cross-talk with other signal transduction pathways and development of treatment strategies viz. selective estrogen receptor modulators (SERMs), selective estrogen receptor down regulators (SERDs), aromatase and sulphatase inhibitors.

Mechanistic Investigation of the Androgen Receptor DNA-Binding Domain Inhibitor Pyrvinium

Pyrvinium was identified as the first small molecule inhibitor of the androgen receptor (AR) DNA-binding domain (DBD). It was also among the first small molecules shown to directly inhibit the activity of AR splice variants (ARVs), which has important clinical implications in the treatment of castration-resistant prostate cancer. Important questions about pyrvinium's mechanism of action remain. Here, we demonstrate through mutational analysis that amino acids 609 and 612 are important for pyrvinium action. Nuclear magnetic resonance demonstrates a specific interaction between a soluble pyrvinium derivative and the AR DBD homodimer-DNA complex. Chromatin immunoprecipitation and electrophoretic mobility shift assay experiments demonstrate that, despite an interaction with this complex, pyrvinium does not alter the DNA-binding kinetics in either assay. AR immunoprecipitation followed by mass spectrometry was used to identify proteins whose interaction with AR is altered by pyrvinium. Several splicing factors, including DDX17, had reduced interactions with AR in the presence of pyrvinium. RNA sequencing of prostate cancer cells treated with pyrvinium demonstrated changes in splicing, as well as in several other pathways. However, pyrvinium did not alter the levels of ARVs in several prostate cancer cell lines. Taken together, our new data pinpoint the direct interaction between pyrvinium and AR DBD and shed light on the mechanism by which it inhibits AR transcriptional activity.

Regulatory mechanisms of miR-145 expression and the importance of its function in cancer metastasis

MicroRNAs are post-transcriptional mediators of gene expression and regulation, which play influential roles in tumorigenesis and cancer metastasis. The expression of tumor suppressor miR-145 is reduced in various cancer cell lines, containing both solid tumors and blood malignancies. However, the responsible mechanisms of its down-regulation are a complicated network. miR-145 is potentially able to inhbit tumor cell metastasis by targeting of multiple oncogenes, including MUC1, FSCN1, Vimentin, Cadherin, Fibronectin, Metadherin, GOLM1, ARF6, SMAD3, MMP11, Snail1, ZEB1/2, HIF-1α and Rock-1. This distinctive role of miR-145 in the regulation of metastasis-related gene expression may introduce miR-145 as an ideal candidate for controlling of cancer metastasis by miRNA replacement therapy. The present review aims to discuss the current understanding of the different aspects of molecular mechanisms of miR-145 regulation as well as its role in r metastasis regulation.

Hepatitis B Virus-Associated Hepatocellular Carcinoma and Hepatic Cancer Stem Cells

Chronic Hepatitis B Virus (HBV) infection is linked to hepatocellular carcinoma (HCC) pathogenesis. Despite the availability of a HBV vaccine, current treatments for HCC are inadequate. Globally, 257 million people are chronic HBV carriers, and children born from HBV-infected mothers become chronic carriers, destined to develop liver cancer. Thus, new therapeutic approaches are needed to target essential pathways involved in HCC pathogenesis. Accumulating evidence supports existence of hepatic cancer stem cells (hCSCs), which contribute to chemotherapy resistance and cancer recurrence after treatment or surgery. Understanding how hCSCs form will enable development of therapeutic strategies to prevent their formation. Recent studies have identified an epigenetic mechanism involving the downregulation of the chromatin modifying Polycomb Repressive Complex 2 (PRC2) during HBV infection, which results in re-expression of hCSC marker genes in infected hepatocytes and HBV-associated liver tumors. However, the genesis of hCSCs requires, in addition to the expression of hCSC markers cellular changes, rewiring of metabolism, cell survival, escape from programmed cell death, and immune evasion. How these changes occur in chronically HBV-infected hepatocytes is not yet understood. In this review, we will present the basics about HBV infection and hepatocarcinogenesis. Next, we will discuss studies describing the mutational landscape of liver cancers and how epigenetic mechanisms likely orchestrate cellular reprograming of hepatocytes to enable formation of hCSCs.

DDX59 promotes DNA replication in lung adenocarcinoma

DEAD box proteins are multifunctional proteins involved in every aspect in RNA metabolism and have essential roles in many cellular activities. Despite their importance, many DEAD box proteins remain uncharacterized. In this report, we found DDX59 overexpressed in lung adenocarcinoma. DDX59 knockdown reduced cell proliferation, anchorage-independent cell growth, and caused reduction of tumor formation in immunocompromised mice. In multiple lung cancer cells, we found that DDX59 knockdown inhibits DNA synthesis; wild-type DDX59 but not helicase-defective mutant of DDX59 enhances DNA synthesis. DDX59 knockdown caused reduction of MCM protein levels, decreased the loading of MCM ring protein onto chromatin, and therefore inhibited DNA replication. Our study reveals for the first time that DDX59 has an important role in lung cancer development through promoting DNA replication.

DRH1, a p68-related RNA helicase gene, is required for chromosome breakage in Tetrahymena

The p68 DEAD box helicases comprise a widely conserved protein family involved in a large range of biological processes including transcription, splicing and translation. The genome of the ciliate Tetrahymena thermophile encodes two p68-like helicases, Drh1p and Lia2p. We show that DRH1 is essential for growth and completion of development. In growing cells, Drh1p is excluded from the nucleus and accumulates near cortical basal bodies. In contrast, during sexual reproduction, this protein localizes to meiotic micronuclei, initially in punctate foci in regions where centromeres and telomeres are known to reside and later in post-zygotic differentiating somatic macronuclei. Differentiation of the macronuclear genome involves extensive DNA rearrangements including fragmentation of the five pairs of germline-derived chromosomes into 180 chromosomal sub-fragments that are stabilized by de novo telomere deletion. In addition, thousands of internal eliminated sequences (IESs) are excised from loci dispersed throughout the genome. Strains with DRH1 deleted from the germline nuclei, which do not express the protein during post-zygotic development, fail to fragment the developing macronuclear chromosomes. IES excision still occurs in the absence of DRH1 zygotic expression; thus, Drh1p is the first protein found to be specifically required for chromosome breakage but not DNA elimination.

Summary: The p68-related Drh1protein is essential for both growth and development of the ciliate Tetrahymena thermophila. It localizes to meiotic nuclei and is required for chromosome breakage of developing somatic chromosomes.

Concerted effects of heterogeneous nuclear ribonucleoprotein C1/C2 to control vitamin D-directed gene transcription and RNA splicing in human bone cells

Traditionally recognized as an RNA splicing regulator, heterogeneous nuclear ribonucleoprotein C1/C2 (hnRNPC1/C2) can also bind to double-stranded DNA and function in trans as a vitamin D response element (VDRE)-binding protein. As such, hnRNPC1/C2 may couple transcription induced by the active form of vitamin D, 1,25-dihydroxyvitamin D (1,25(OH)₂D) with subsequent RNA splicing. In MG63 osteoblastic cells, increased expression of the 1,25(OH)₂D target gene CYP24A1 involved immunoprecipitation of hnRNPC1/C2 with CYP24A1 chromatin and RNA. Knockdown of hnRNPC1/C2 suppressed expression of CYP24A1, but also increased expression of an exon 10-skipped CYP24A1 splice variant; in a minigene model the latter was attenuated by a functional VDRE in the CYP24A1 promoter. In genome-wide analyses, knockdown of hnRNPC1/C2 resulted in 3500 differentially expressed genes and 2232 differentially spliced genes, with significant commonality between groups. 1,25(OH)₂D induced 324 differentially expressed genes, with 187 also observed following hnRNPC1/C2 knockdown, and a further 168 unique to hnRNPC1/C2 knockdown. However, 1,25(OH)₂D induced only 10 differentially spliced genes, with no overlap with differentially expressed genes. These data indicate that hnRNPC1/C2 binds to both DNA and RNA and influences both gene expression and RNA splicing, but these actions do not appear to be linked through 1,25(OH)₂D-mediated induction of transcription.

Sodium arsenite inhibited genomic estrogen signaling but induced pERα (Ser118) via MAPK pathway in breast cancer cells

Arsenic (As) is considered a major environmental health threat worldwide due to its widespread contamination in drinking water. Recent studies reported that arsenic is a potential xenoestrogen as it interfered with the action of estrogen (E2) and estrogen receptor (ER) signaling. The present study investigated the effects of sodium arsenite (NaAsO2 ) on estrogen signaling in human breast cancer cells. The results demonstrated that NaAsO2 dose-dependently increased viability of hormone-dependent breast cancer MCF-7 and T47D cells expressing both ERα and ERβ but not hormone-independent MDA-MB-231 cells expressing ERβ. These suggested ERα contribution to NaAsO2 -stimulated breast cancer cells growth. NaAsO2 induced down-regulation of ERα but up-regulation of ERβ protein expressions in T47D cells. Moreover, NaAsO2 dose-dependently inhibited E2-induced ER transcriptional activity as it decreased E2-mediated ERE-luciferase transcription activation and PgR mRNA transcription but increased pS2 mRNA transcription. However, NaAsO2 induced both rapid and sustained activation of ERK1/2 and increased in phosphorylation of ERα at serine 118 residue, c-fos and c-myc protein expressions. These results indicated that NaAsO2 interferes the genomic estrogen-signaling pathway but induces activation of a rapid nongenomic signal transduction through ERK1/2 pathway which may contribute to its proliferative effect on hormone-dependent breast cancer cells. © 2015 Wiley Periodicals, Inc. Environ Toxicol 31: 1133-1146, 2016.

Discovery at the interface: Toward novel anti-proliferative agents targeting human estrogen receptor/S100 interactions

Estrogen Receptor Alpha (ER) is expressed in about 70% of breast cancer and mediates various cellular signaling events including cell cycle. The antiestrogen tamoxifen is currently administered to patients in order to induce regression of the tumor growth of estrogen receptor positive (ER+) breast cancer. However, upon continued administration, patients develop resistance to tamoxifen. In addition, calcium binding proteins (EF-hand proteins) such as, Calmodulin and S100, are significantly overexpressed in breast cancer cells, can activate transcription of target genes by directly binding to ER in lieu of estrogen. Calmodulin antagonists (w7 and melatonin) have been shown to significantly inhibit ER mediated activities including cell proliferation and transcriptional activity. Furthermore, S100P is shown to mediate tamoxifen resistance and cell migration capacity in MCF-7 breast cancer cells. Molecules targeting specific ER-EF hand protein interfaces could potentially provide an alternative therapeutic strategy to combat these scenarios. Using theoretical 3D models of ER-S100 protein we identified ER conformation-sensing regions of the interacting EF hand proteins and evaluated their ability to bind to ER in silico and to inhibit breast cancer cell proliferation and viability in vitro. The recognition motif of the binding interface was sensitive to small changes in partner orientation as evidenced by significant anti cell proliferative activity of the short peptide derived from S100P residues 74-78, when compared with a longer peptide with altered orientation of the recognition motif derived from S100P 74-81. Structural clues and pharmacophores from peptide-ER interactions can be used to design novel anti-cancer agents.

Predictive features of ligand-specific signaling through the estrogen receptor

Some estrogen receptor‐α (ERα)‐targeted breast cancer therapies such as tamoxifen have tissue‐selective or cell‐specific activities, while others have similar activities in different cell types. To identify biophysical determinants of cell‐specific signaling and breast cancer cell proliferation, we synthesized 241 ERα ligands based on 19 chemical scaffolds, and compared ligand response using quantitative bioassays for canonical ERα activities and X‐ray crystallography. Ligands that regulate the dynamics and stability of the coactivator‐binding site in the C‐terminal ligand‐binding domain, called activation function‐2 (AF‐2), showed similar activity profiles in different cell types. Such ligands induced breast cancer cell proliferation in a manner that was predicted by the canonical recruitment of the coactivators NCOA1/2/3 and induction of the GREB1 proliferative gene. For some ligand series, a single inter‐atomic distance in the ligand‐binding domain predicted their proliferative effects. In contrast, the N‐terminal coactivator‐binding site, activation function‐1 (AF‐1), determined cell‐specific signaling induced by ligands that used alternate mechanisms to control cell proliferation. Thus, incorporating systems structural analyses with quantitative chemical biology reveals how ligands can achieve distinct allosteric signaling outcomes through ERα.

Methyltransferase-like 17 physically and functionally interacts with estrogen receptors

Estrogen exerts its physiological and pathological functions through two estrogen receptors (ERs), ERα and ERβ, which act as transcription factors. Coregulators, including coactivators and corepressors, have been shown to be crucial for regulation of ER transcriptional activity. Although many coregulators have been identified to regulate activities of ERs, novel coregulators are still needed to be investigated. Here, we show that human methyltransferase-like 17 (METTL17), whose function is unknown, physically interacts with ERα and ERβ, and functionally acts as a coactivator for ERs. METTL17 interacts with ER in vitro and in yeast and mammalian cells. Activation function-1 (AF1) and AF2 domains of ERs are responsible for the interaction between METTL17 and ERs. Knockdown of METTL17 reduces transcriptional activities of ERα and ERβ in breast cancer cells, whereas METTL17 overexpression increases ERα and ERβ transcriptional activities. Inhibition of METTL17 expression decreases mRNA and protein levels of ER target genes, including PR, cathepsin D, and pS2. Moreover, METTL17 knockdown reduces breast cancer cell growth. These results indicate that METTL17 is a novel coactivator of ERs and may play a role in breast tumorigenesis.

Molecular characterization, origin, and evolution of teleost p68 gene family: Insights from Japanese flounder, Paralichthys olivaceus

Two rounds of whole-genome duplication occurred in the common ancestor of vertebrates. Later, a third round genome duplication occurred in the teleost fishes. As a prototype member of DEAD-box RNA helicases, the function of p68 helicase in development has been well investigated in human, however, limited information is available regarding the regulatory function of this gene in the development of teleosts. In this study, being an important farmed fish in North China, Japanese flounder (Paralichthys olivaceus) was used as model fish to investigate the role of p68 gene in teleost development. Two p68 genes were first identified from Japanese flounder. Molecular characterization of them was performed by analyzing the exon-intron boundaries. Then, we confirmed that such two teleost p68 genes originated from teleost-specific genome duplication through phylogenetic and synteny analyses. Additionally, comparative analyses of amino acid sequences, variation in selective pressure, and expression profiles of p68 genes revealed probable sub-functionalization fate of teleost p68 genes after the duplication. Therefore, this study supplements the evolutionary properties of teleost p68 gene family and provides the groundwork for further studying the regulatory function of p68 genes in the development of teleosts.

Peptidylprolyl Isomerase Pin1 Directly Enhances the DNA Binding Functions of Estrogen Receptor α

The transcriptional activity of estrogen receptor α (ERα), the key driver of breast cancer proliferation, is enhanced by multiple cellular interactions, including phosphorylation-dependent interaction with Pin1, a proline isomerase, which mediates cis-trans isomerization of the N-terminal Ser(P)(118)-Pro(119) in the intrinsically disordered AF1 (activation function 1) domain of ERα. Because both ERα and Pin1 have multiple cellular partners, it is unclear how Pin1 assists in the regulation of ERα transactivation mechanisms and whether the functional effects of Pin1 on ERα signaling are direct or indirect. Here, we tested the specific action of Pin1 on an essential step in ERα transactivation, binding to specific DNA sites. DNA binding analysis demonstrates that stable overexpression of Pin1 increases endogenous ERα DNA binding activity when activated by estrogen but not by tamoxifen or EGF. Increased DNA binding affinity is a direct effect of Pin1 on ERα because it is observed in solution-based assays with purified components. Further, our data indicate that isomerization is required for Pin1-modulation of ERα-DNA interactions. In an unbiased in vitro DNA binding microarray with hundreds of thousands of permutations of ERα-binding elements, Pin1 selectively enhances the binding affinity of ERα to consensus DNA elements. These studies reveal that Pin1 isomerization of phosphorylated ERα can directly regulate the function of the adjacent DNA binding domain, and this interaction is further modulated by ligand binding in the ligand-binding domain, providing evidence for Pin1-dependent allosteric regulation of ERα function.

Overexpression of DHX32 contributes to the growth and metastasis of colorectal cancer

Our previous work demonstrates that DHX32 is upregulated in colorectal cancer (CRC) compared to its adjacent normal tissues. However, how overexpressed DHX32 contributes to CRC remains largely unknown. In this study, we reported that DHX32 was overexpressed in human colon cancer cells. Overexpressed DHX32 promoted SW480 cancer cells proliferation, migration, and invasion, as well as decreased the susceptibility to chemotherapy agent 5-Fluorouracil. Furthermore, PCR array analyses revealed that depleting DHX32 in SW480 colon cancer cells suppressed expression of WISP1, MMP7 and VEGFA in the Wnt pathway, and anti-apoptotic gene BCL2 and CA9, however, elevated expression of pro-apoptotic gene ACSL5. The findings suggested that overexpressed DHX32 played an important role in CRC progression and metastasis and that DHX32 has the potential to serve as a biomarker and a novel therapeutic target for CRC.

Signaling-mediated regulation of MicroRNA processing

miRNAs are important regulatory elements for gene expression that are involved in diverse physiologic and pathologic processes. Canonical miRNA biogenesis consists of a two-step processing, from primary transcripts (pri-miRNA) to precursor miRNAs (pre-miRNA) mediated by Drosha in the nucleus and from pre-miRNAs to mature miRNAs mediated by Dicer in the cytoplasm. Various routes of miRNA maturation that are tightly regulated by signaling cascades and specific to an individual or a subclass of miRNAs have been recently identified. Here, we review the current findings in signaling-mediated miRNA processing as well as their potential clinical relevance in cancer.

P68 RNA helicase as a molecular target for cancer therapy

The DEAD-box family of RNA helicase is known to be required in virtually all cellular processes involving RNA, and p68 is a prototypic one of the family. Reports have indicated that in addition to ATPase and RNA helicase ability, p68 can also function as a co-activator for transcription factors such as estrogen receptor alpha, tumor suppressor p53 and beta-catenin. More than that, post-translational modification of p68 including phosphorylation, acetylation, sumoylation, and ubiquitylation can regulate the coactivation effect. Furthermore, aberrant expression of p68 in cancers highlights that p68 plays an important role for tumorgenesis and development. In this review, we briefly introduce the function and modulation of p68 in cancer cells, and put forward envisagement about future study about p68.

Role of the OB-fold of RNA helicase A in the synthesis of HIV-1 RNA

RNA helicase A (RHA), a DExD/H protein, contains a stretch of repeated arginine and glycine-glycine (RGG) residues and an oligonucleotide/oligosaccharide-binding fold (OB-fold) at the C-terminus. RHA has been reported to function as a transcriptional cofactor. This study shows the role of RGG and OB-fold domains of RHA in the activation of transcription and splicing of HIV-1 RNA. RHA stimulates HIV-1 transcription by enhancing the occupancy of RNA polymerase II on the proviral DNA. Deletion of RGG or both RGG and OB-fold does not change the transcriptional activity of RHA, nor does the stability of viral RNA. However, deletion of both RGG and OB-fold rather than deletion of RGG only results in less production of multiply spliced 6D RNAs. The results suggest that the OB-fold is involved in modulating HIV-1 RNA splicing in the context of some HIV-1 strains while it is dispensable for the activation of HIV-1 transcription.

Pisum sativum p68 DEAD-box protein is ATP-dependent RNA helicase and unique bipolar DNA helicase

DEAD-box helicases play essential role in DNA and RNA metabolism such as replication, repair, recombination, transcription, translation, ribosome biogenesis and splicing which regulate plant growth and development. The presence of helicases in the stress-induced ORFs identified by cDNA microarray indicates that helicases might be playing an important role in stabilizing growth in plants under stress. p68 DEAD-box helicase has been identified and characterized from animal systems but the properties and functions of plant p68 are poorly understood. In this study, the identification, purification and characterization of recombinant p68 from Pisum sativum (Psp68) is presented. Psp68 possesses all the characteristic motifs like DEAD-box ATP-binding and helicase C terminal motifs and is structurally similar to human p68 homologue. Psp68 exhibits ATPase activity in the presence of both DNA and RNA and it binds to DNA as well as RNA. It contains the characteristic RNA helicase activity. Interestingly Psp68 also shows the unique DNA helicase activity, which is bipolar in nature (unwinds DNA in both the 5'-3' and 3'-5' directions). The Km values of Psp68 for ATPase are 0.5126 and 0.9142 mM in the presence of DNA and RNA, respectively. The Km values of Psp68 are 1.6129 and 1.14 nM for DNA helicase and RNA helicase, respectively. The unique properties of Psp68 suggest that it could be a multifunctional protein involved in different aspect of DNA and RNA metabolism. This discovery should make an important contribution to better understanding of nucleic acids metabolism plants.

Low levels of 3,3'-diindolylmethane activate estrogen receptor α and induce proliferation of breast cancer cells in the absence of estradiol

BACKGROUND

3,3'-diindolylmethane (DIM) is an acid-catalyzed dimer of idole-3-carbinol (I3C), a phytochemical found in cruciferous vegetables that include broccoli, Brussels sprouts and cabbage. DIM is an aryl hydrocarbon receptor (AhR) ligand and a potential anticancer agent, namely for the treatment of breast cancer. It is also advertised as a compound that regulates sex hormone homeostasis.

METHODS

Here we make use of RNA expression assays coupled to Chromatin Immunoprecipitation (ChIP) in breast cancer cell lines to study the effect of DIM on estrogen signaling. We further make use of growth assays, as well as fluorescence-activated cell sorting (FACS) assays, to monitor cell growth.

RESULTS

In this study, we report that 'physiologically obtainable' concentrations of DIM (10 μM) activate the estrogen receptor α (ERα) signaling pathway in the human breast cancer cell lines MCF7 and T47D, in a 17β-estradiol (E2)-independent manner. Accordingly, we observe induction of ERα target genes such as GREB1 and TFF1, and an increase in cellular proliferation after treatment with 10 μM DIM in the absence of E2. By using an ERα specific inhibitor (ICI 182 780), we confirm that the transcriptional and proliferative effects of DIM treatment are mediated by ERα. We further show that the protein kinase A signaling pathway participates in DIM-mediated activation of ERα. In contrast, higher concentrations of DIM (e.g. 50 μM) have an opposite and expected effect on cells, which is to inhibit proliferation.

CONCLUSIONS

We document an unexpected effect of DIM on cell proliferation, which is to stimulate growth by inducing the ERα signaling pathway. Importantly, this proliferative effect of DIM happens with potentially physiological concentrations that can be provided by the diet or by taking caplet supplements.

Isolation and functional characterization of the promoter of a DEAD-box helicase Psp68 using Agrobacterium-mediated transient assay

Helicases are molecular motor proteins that perform a variety of cellular functions including transcription, translation, DNA replication and repair, RNA maturation, ribosome synthesis, nuclear export and splicing processes. The p68 is an evolutionarily conserved protein which plays pivotal roles in all aspect RNA metabolism processes. It is well established that helicases provides abiotic stress adaptation in plants but analysis of cis-regulatory elements present in the upstream regions is still infancy. Here we report isolation and functional characterization of the promoter of a DEAD-box helicase Psp68 in response to abiotic stress and hormonal regulation. The promoter of Psp68 was isolated by gene walking PCR from pea genomic DNA library constructed in BD genome walker kit. In silico analysis revealed that promoter of Psp68 contained a TATA, a CAAT motif and also harbors some important stress and hormone associated cis regulatory elements, including E-box, AGAAA, GATA-box, ACGT, GAAAA and GTCTC. Functional analyses were performed by Agrobacterium-mediated transient assay in tobacco leaves. Very high level of GUS activity was observed in agroinfiltrated tobacco leaves by the construct carrying the Psp68 promoter::GUS, subjected to abiotic stress and exogenous hormonal treatments. Stress-inducible nature of Psp68 promoter opens possibility for the study of the gene regulation under stress condition. Therefore, may be useful in the field of agriculture and biotechnology.

Isolation and functional characterization of the promoter of a DEAD-box helicase Psp68 using Agrobacterium-mediated transient assay

Helicases are molecular motor proteins that perform a variety of cellular functions including transcription, translation, DNA replication and repair, RNA maturation, ribosome synthesis, nuclear export and splicing processes. The p68 is an evolutionarily conserved protein which plays pivotal roles in all aspect RNA metabolism processes. It is well established that helicases provides abiotic stress adaptation in plants but analysis of cis-regulatory elements present in the upstream regions is still infancy. Here we report isolation and functional characterization of the promoter of a DEAD-box helicase Psp68 in response to abiotic stress and hormonal regulation. The promoter of Psp68 was isolated by gene walking PCR from pea genomic DNA library constructed in BD genome walker kit. In silico analysis revealed that promoter of Psp68 contained a TATA, a CAAT motif and also harbors some important stress and hormone associated cis regulatory elements, including E-box, AGAAA, GATA-box, ACGT, GAAAA and GTCTC. Functional analyses were performed by Agrobacterium-mediated transient assay in tobacco leaves. Very high level of GUS activity was observed in agroinfiltrated tobacco leaves by the construct carrying the Psp68 promoter::GUS, subjected to abiotic stress and exogenous hormonal treatments. Stress-inducible nature of Psp68 promoter opens possibility for the study of the gene regulation under stress condition. Therefore, may be useful in the field of agriculture and biotechnology.

The Ddx5 and Ddx17 RNA helicases are cornerstones in the complex regulatory array of steroid hormone-signaling pathways

Estrogen and androgen receptors (ER and AR) play key roles in breast and prostate cancers, respectively, where they regulate the transcription of large arrays of genes. The activities of ER and AR are controlled by large networks of protein kinases and transcriptional coregulators, including Ddx5 and its highly related paralog Ddx17. The Ddx5 and Ddx17 RNA helicases are also splicing regulators. Here, we report that Ddx5 and Ddx17 are master regulators of the estrogen- and androgen-signaling pathways by controlling transcription and splicing both upstream and downstream of the receptors. First, Ddx5 and Ddx17 are required downstream of ER and AR for the transcriptional and splicing regulation of a large number of steroid hormone target genes. Second, Ddx5 and Ddx17 act upstream of ER and AR by controlling the expression, at the splicing level, of several key regulators of ER and AR activities. Of particular interest, we demonstrate that Ddx5 and Ddx17 control alternative splicing of the GSK3β kinase, which impacts on both ER and AR protein stability. We also provide a freely available online resource which gives information regarding splicing variants of genes involved in the estrogen- and androgen-signaling pathways.

The DEAD-box RNA helicase DDX5 acts as a positive regulator of Japanese encephalitis virus replication by binding to viral 3' UTR

Japanese encephalitis virus (JEV), one of the causes for epidemic encephalitis, belongs to the family of Flaviviridae. In this study, we demonstrated that cellular DEAD-box RNA helicase DDX5 plays an important role in JEV replication. The knockdown of DDX5 was able to decrease JEV replication, and overexpression of DDX5 mutants lacking the helicase activity also reduced JEV replication, suggesting the helicase activity is essential for JEV replication. DDX5 knockdown did not affect virus assembly and release. GST-pulldown and co-immunoprecipitation experiments demonstrated that DDX5 could interact with JEV core protein, non-structural protein 3 (NS3) and 5 (NS5-MTase and NS5-RdRp domains). Meanwhile, we also confirmed that DDX5 interacts with these viral proteins during JEV infection. Confocal microscopy analysis showed that endogenous DDX5 is recruited to the cytoplasm and colocalizes with these viral proteins and viral RNA. RNA-pulldown experiment showed that DDX5 only binds to the JEV 3' untranslated region (UTR). Finally, we confirmed the role of DDX5 in JEV RNA replication using JEV-replicon system. In conclusion, we identified DDX5 as a positive regulator for JEV replication.

Lessons from the dissection of the activation functions (AF-1 and AF-2) of the estrogen receptor alpha in vivo

Estrogens influence most of the physiological processes in mammals, including but not limited to reproduction, cognition, behavior, vascular system, metabolism and bone integrity. Given this widespread role for estrogen in human physiology, it is not surprising that estrogen influence the pathophysiology of numerous diseases, including cancer (of the reproductive tract as breast, endometrial but also colorectal, prostate,…), as well as neurodegenerative, inflammatory-immune, cardiovascular and metabolic diseases, and osteoporosis. These actions are mediated by the activation of estrogen receptors (ER) alpha (ERα) and beta (ERβ), which regulate target gene transcription (genomic action) through two independent activation functions (AF)-1 and AF-2, but can also elicit rapid membrane initiated steroid signals (MISS). Targeted ER gene inactivation has shown that although ERβ plays an important role in the central nervous system and in the heart, ERα appears to play a prominent role in most of the other tissues. Pharmacological activation or inhibition of ERα and/or ERβ provides already the basis for many therapeutic interventions, from hormone replacement at menopause to prevention of the recurrence of breast cancer. However, the use of these estrogens or selective estrogen receptors modulators (SERMs) have also induced undesired effects. Thus, an important challenge consists now to uncouple the beneficial actions from other deleterious ones. The in vivo molecular "dissection" of ERα represents both a molecular and integrated approach that already allowed to delineate in mouse the role of the main "subfunctions" of the receptor and that could pave the way to an optimization of the ER modulation.

DDX5 facilitates HIV-1 replication as a cellular co-factor of Rev

HIV-1 Rev plays an important role in the late phase of HIV-1 replication, which facilitates export of unspliced viral mRNAs from the nucleus to cytoplasm in infected cells. Recent studies have shown that DDX1 and DDX3 are co-factors of Rev for the export of HIV-1 transcripts. In this report, we have demonstrated that DDX5 (p68), which is a multifunctional DEAD-box RNA helicase, functions as a new cellular co-factor of HIV-1 Rev. We found that DDX5 affects Rev function through the Rev-RRE axis and subsequently enhances HIV-1 replication. Confocal microscopy and co-immunoprecipitation analysis indicated that DDX5 binds to Rev and this interaction is largely dependent on RNA. If the DEAD-box motif of DDX5 is mutated, DDX5 loses almost all of its ability to bind to Rev, indicating that the DEAD-box motif of DDX5 is required for the interaction between DDX5 and Rev. Our data indicate that interference of DDX5-Rev interaction could reduce HIV-1 replication and potentially provide a new molecular target for anti-HIV-1 therapeutics.

Perturbations of RNA helicases in cancer

Helicases are implicated in most stages of the gene expression pathway, ranging from DNA replication, RNA transcription, splicing, RNA transport, ribosome biogenesis, mRNA translation, RNA storage and decay. These enzymes utilize energy derived from nucleotide triphosphate hydrolysis to remodel ribonucleoprotein complexes, RNA, or DNA and in this manner affect the information content or output of RNA. Several RNA helicases have been implicated in the oncogenic process--either through altered expression levels, mutations, or due to their role in pathways required for tumor initiation, progression, maintenance, or chemosensitivity. The purpose of this review is to highlight those RNA helicases for which there is significant evidence implicating them in cancer biology.

Activation of nuclear estrogen receptors induced by low-power laser irradiation via PI3-K/Akt signaling cascade

Low-power laser irradiation (LPLI) has been shown to exert promotive effects on cell survival and proliferation through activation of various signaling pathways. Estrogen receptors (ERs, ERα, and ERβ) are ligand-activated transcription factors, which regulate target gene expression, promote cell proliferation, and resist apoptosis. However, it is unclear whether LPLI could induce ligand-independent activation of ERs. In the present study, we investigated the subcellular pools, nuclear redistribution, and transcriptional activity of ERs under LPLI (1.2 J/cm(2), 633 nm) treatment using single-molecule fluorescence imaging and dual-luciferase reporter assay. We found that ERs were not only localized to nucleus, but also existed in mitochondria. Moreover, we found that LPLI induced nuclear redistribution and transcriptional activity of ERs in a ligand-independent manner. Our further investigation showed that PI3-K/Akt signaling cascade was involved in LPLI-induced activation of ERs. Wortmannin, a PI3-K inhibitor, or triciribine (API-2), a specific Akt inhibitor, potently suppressed the nuclear redistribution and transcriptional activity of ERs induced by LPLI, revealing that PI3-K/Akt signaling cascade was required for the activation of ERs induced by LPLI. Collectively, we demonstrated the first time that LPLI induced the ligand-independent nuclear redistribution and transcriptional activity of ERs, which were dependent on the activity of PI3-K/Akt. Our findings provide direct evidence for the molecular mechanisms of LPLI-induced transcription factor activation.

The DEAD box proteins DDX5 (p68) and DDX17 (p72): multi-tasking transcriptional regulators

Members of the DEAD box family of RNA helicases, which are characterised by the presence of twelve conserved motifs (including the signature D-E-A-D motif) within a structurally conserved 'helicase' core, are involved in all aspects of RNA metabolism. Apart from unwinding RNA duplexes, which established these proteins as RNA helicases, DEAD box proteins have been shown to also catalyse RNA annealing and to displace proteins from RNA. DEAD box proteins generally act as components of large multi-protein complexes and it is thought that interactions, via their divergent N- and C-terminal extensions, with other factors in the complexes may be responsible for the many different functions attributed to these proteins. In addition to their established crucial roles in the manipulation of RNA structure, it is becoming increasingly clear that several members of the DEAD box family act as regulators of transcription. In this review I shall focus on DDX5 (p68) and the highly related DDX17 (p72), two proteins for which there is a large body of evidence demonstrating that they function in transcriptional regulation. This article is part of a Special Issue entitled: The Biology of RNA helicases - Modulation for life.

Estrogen synthesis and signaling pathways during aging: from periphery to brain

Estrogens are the primary female sex hormones and play important roles in both reproductive and non-reproductive systems. Estrogens can be synthesized in non-reproductive tissues such as liver, heart, muscle, bone and brain, and tissue-specific estrogen synthesis is consistent with a diversity of estrogen actions. In this article we review tissue and cell-specific estrogen synthesis and estrogen receptor signaling in three parts: (i) synthesis and metabolism, (ii) the distribution of estrogen receptors and signaling, and (iii) estrogen functions and related disorders, including cardiovascular diseases, osteoporosis, Alzheimer's disease (AD), and Parkinson disease (PD). This comprehensive review provides new insights into estrogens by giving a better understanding of the tissue-specific estrogen effects and their roles in various diseases.

DEAD box RNA helicase functions in cancer

Members of the DEAD box family of RNA helicases are known to be involved in most cellular processes that require manipulation of RNA structure and, in many cases, exhibit other functions in addition to their established ATP-dependent RNA helicase activities. They thus play critical roles in cellular metabolism and in many cases have been implicated in cellular proliferation and/or neoplastic transformation. These proteins generally act as components of multi-protein complexes; therefore their precise role is likely to be influenced by their interacting partners and to be highly context-dependent. This may also provide an explanation for the sometimes conflicting reports suggesting that DEAD box proteins have both pro- and anti-proliferative roles in cancer.

The RNA helicase DDX5/p68 is a key factor promoting c-fos expression at different levels from transcription to mRNA export

It is widely accepted that pre-mRNA maturation, including splicing, is tightly coupled to both transcription and mRNA export, but factors linking the three processes are less understood. By analysing the estrogen-regulated expression of the c-fos mRNA that is processed during transcription, we show that the ddx5 RNA helicase, is required throughout the major nuclear steps of the expression of the c-fos gene, from transcription to mRNA export. Indeed, ddx5, whose recruitment on the c-fos gene was increased upon estrogen treatment, was required for the full transcriptional activation of the c-fos gene. In addition, ddx5 was required for c-fos co-transcriptional RNA splicing. When splicing occurred post-transcriptionally in the absence of ddx5, the c-fos mRNA was poorly exported into the cytosol because of inefficient recruitment of the TAP mRNA export receptor. Finally, ddx5 was present in the c-fos messenger ribonucleoprotein together with mRNA export factors, which further supports that ddx5 is a key operator in the c-fos ‘mRNA factory’.

DDX5 is a positive regulator of oncogenic NOTCH1 signaling in T cell acute lymphoblastic leukemia

Notch signaling is a highly conserved cell-cell communication pathway regulating normal development and tissue homeostasis. Aberrant Notch signaling represents an important oncogenic mechanism for T cell acute lymphoblastic leukemia (T-ALL), an aggressive subset of the most common malignant childhood cancer ALL. Therefore, understanding the molecular regulation of Notch signaling is critical to identify new approaches to block aberrant Notch oncogenic activity. The family of three MAML transcriptional coactivators is crucial for Notch signaling activation. The prototypic member MAML1 is the major coactivator that regulates Notch oncogenic activities in leukemic cells. However, the molecular basis underlying MAML1 coactivator function that contributes to Notch signaling remains unclear. In this study, we performed proteomic studies and identified DDX5, an ATP-dependent DEAD-box RNA helicase, as a component of the MAML1 protein complex. DDX5 interacts with MAML1 in vitro and in vivo, and is associated with the endogenous NOTCH1 transcription activation complex in human T-ALL leukemic cells. Lentivirus-mediated short-hairpin RNA knock-down of DDX5 resulted in decreased expression of Notch target genes, reduced cell proliferation and increased apoptosis in cultured human leukemic cells with constitutive activation of Notch signaling. Also, DDX5 depletion inhibited the growth of human leukemia xenograft in nude mice. Moreover, DDX5 is highly expressed in primary human T-ALL leukemic cells based on the analyses of Oncomine and GEO databases, and Immunohistochemical staining. Our overall findings revealed a critical role of DDX5 in promoting efficient Notch-mediated transcription in leukemic cells, suggesting that DDX5 might be critical for NOTCH1-mediated T-ALL pathogenesis and thus is a potential new target for modulating the Notch signaling in leukemia.

RNA helicases: diverse roles in prokaryotic response to abiotic stress

Similar to proteins, RNA molecules must fold into the correct conformation and associate with protein complexes in order to be functional within a cell. RNA helicases rearrange RNA secondary structure and RNA-protein interactions in an ATP-dependent reaction, performing crucial functions in all aspects of RNA metabolism. In prokaryotes, RNA helicase activity is associated with roles in housekeeping functions including RNA turnover, ribosome biogenesis, translation and small RNA metabolism. In addition, RNA helicase expression and/or activity are frequently altered during cellular response to abiotic stress, implying they perform defined roles during cellular adaptation to changes in the growth environment. Specifically, RNA helicases contribute to the formation of cold-adapted ribosomes and RNA degradosomes, implying a role in alleviation of RNA secondary structure stabilization at low temperature. A common emerging theme involves RNA helicases acting as scaffolds for protein-protein interaction and functioning as molecular clamps, holding RNA-protein complexes in specific conformations. This review highlights recent advances in DEAD-box RNA helicase association with cellular response to abiotic stress in prokaryotes.

Splicing switch of an epigenetic regulator by RNA helicases promotes tumor-cell invasiveness

Both epigenetic and splicing regulation contribute to tumor progression, but the potential links between these two levels of gene-expression regulation in pathogenesis are not well understood. Here, we report that the mouse and human RNA helicases Ddx17 and Ddx5 contribute to tumor-cell invasiveness by regulating alternative splicing of several DNA- and chromatin-binding factors, including the macroH2A1 histone. We show that macroH2A1 splicing isoforms differentially regulate the transcription of a set of genes involved in redox metabolism. In particular, the SOD3 gene that encodes the extracellular superoxide dismutase and plays a part in cell migration is regulated in an opposite manner by macroH2A1 splicing isoforms. These findings reveal a new regulatory pathway in which splicing factors control the expression of histone variant isoforms that in turn drive a transcription program to switch tumor cells to an invasive phenotype.

DDX5 is a multifunctional co-activator of steroid hormone receptors

The vitamin D receptor (VDR), an evolutionarily conserved member of the nuclear receptor superfamily, links the metabolically activated vitamin D ligand, calcitriol, with its vitamin D-responsive target genes that are implicated in diverse physiological processes. By genome-wide protein-protein interaction screening of a keratinocyte cDNA library using VDR as bait, we found that the DEAD box RNA helicase p68, also referred to as DDX5, directly interacts with VDR. Domain analysis reveals that the ligand-binding domain of VDR is responsible for the binding, an interaction typical of NR co-activators. Interestingly, the VDR interacting domain of DDX5 lacks a LXXLL-motif and interaction analysis of helix 12 VDR mutants E420K, E420Q and L417S, known to decrease binding affinity of LxxLL motif-containing co-activators showed no change in their interactions. As further support that this novel interactor might be involved in vitamin D-stimulated transcriptional regulation, we demonstrate that VDR and DDX5 co-localize within the nuclei of HaCaT keratinocytes and sub-cellular protein fractions. In vivo validation studies demonstrate, that overexpression of DDX5 has the capability to enhance both, calcitriol-dependent transcription of known response genes and an extrachromosomal DR3-type reporter response. In agreement with this, shRNA based knock-down of DDX5 in keratinocytes compensates for this particular response. Finally, our findings reveal parallels between the VDR-DDX5 interaction and the well-characterized interaction between DDX5 and human estrogen receptor α and the androgen receptor, thus underscoring the physiological significance of the novel protein-protein interaction.

The RNA helicase p68 (DDX5) is selectively required for the induction of p53-dependent p21 expression and cell-cycle arrest after DNA damage

The RNA helicase p68 (DDX5) is an established co-activator of the p53 tumour suppressor that itself has a pivotal role in orchestrating the cellular response to DNA damage. Although several factors influence the biological outcome of p53 activation, the mechanisms governing the choice between cell-cycle arrest and apoptosis remain to be elucidated. In the present study, we show that, while p68 is critical for p53-mediated transactivation of the cell-cycle arrest gene p21(WAF1/CIP1), it is dispensable for induction of several pro-apoptotic genes in response to DNA damage. Moreover, p68 depletion results in a striking inhibition of recruitment of p53 and RNA Pol II to the p21 promoter but not to the Bax or PUMA promoters, providing an explanation for the selective effect on p21 induction. Importantly, these findings are mirrored in a novel inducible p68 knockout mouse model in which p68 depletion results in a selective inhibition of p21 induction in several tissues. Moreover, in the bone marrow, p68 depletion results in an increased sensitivity to γ-irradiation, consistent with an increased level of apoptosis. These data highlight a novel function of p68 as a modulator of the decision between p53-mediated growth arrest and apoptosis in vitro and in vivo.

MicroRNA in Cancer: The Involvement of Aberrant MicroRNA Biogenesis Regulatory Pathways

MicroRNAs (miRNAs) are small, noncoding RNAs that influence diverse biological outcomes through the repression of target genes during normal development and pathological responses. In particular, the alteration of miRNA expression has dramatic consequences for the progression of tumorigenesis. miRNAs undergo two processing steps that transform a long primary transcript into the mature miRNA. Although the general miRNA biogenesis pathway is well established, it is clear that not all miRNAs are created equally. Recent studies show that miRNA expression is controlled by diverse mechanisms in response to cellular stimuli. In this review, we discuss the mechanisms that govern the regulation of miRNA biogenesis with particular focus on how these mechanisms are perturbed in cancer.

Regulation of the transcriptional activity of nuclear receptors by the MEK/ERK1/2 pathway

Cells undergo continuous and simultaneous external influences regulating their behavior. As an example, during differentiation, they go through different stages of maturation and gene expression is regulated by several simultaneous signaling pathways. We often tend at separating the nuclear pathways from the signaling ones initiated at membrane receptors. However, it is essential to keep in mind that all these pathways are interconnected to achieve a fine regulation of cell functions. The regulation of transcription by nuclear receptors has been thoroughly studied, but it now appears that a critical level of this regulation involves the action of several kinases that target the nuclear receptors themselves as well as their partners. The purpose of this review is to highlight the importance of one family of the mitogen-activated protein kinase (MAPK) superfamily, the MEK/ERK1/2 pathway, in the transcriptional activity of nuclear receptors.

DP97, a DEAD box DNA/RNA helicase, is a target gene-selective co-regulator of the constitutive androstane receptor

The constitutive androstane receptor (CAR) plays a key role in the expression of xenobiotic/steroid and drug metabolizing enzymes and their transporters. In this study, we demonstrated that DP97, a member of the DEAD box DNA/RNA helicase protein family, is a novel CAR-interacting protein. Using HepG2 cells expressing human CAR in the presence of tetracycline, we showed that knockdown of DP97 with small interfering RNAs suppressed tetracycline-inducible mRNA expression of CYP2B6 and UGT1A1 but not CYP3A4. Thus, DP97 was found to be a gene (or promoter)-selective co-activator for hCAR. DP97-mediated CAR transactivation was synergistically enhanced by the co-expression of SRC-1 or PGC1α, therefore it might act as mediator between hCAR and appropriate co-activators.

p68 RNA helicase promotes glioma cell proliferation in vitro and in vivo via direct regulation of NF-κB transcription factor p50

The DEAD-box RNA helicase p68 plays a very important role in early organ development and maturation. However, the role of p68 in glioma is unclear. In this study, we showed that p68 protein levels were significantly elevated in high-grade gliomas compared to low-grade gliomas and normal adjacent brain tissues. Importantly, the expression of p68 was significantly associated with poorer overall survival and enhanced resistance to treatment with radiotherapy plus temozolomide for glioma patients. Ectopic expression of p68 enhanced glioma cell proliferation both in vitro and in vivo. In contrast, knockdown of endogenous p68 prevented glioma cell proliferation. Using a tandem affinity purification assay, we found a new p68-binding protein, nuclear factor (NF)-κB p50. We found that p68 bound with the N-terminal of NF-κB p50, and the mutant of p68 lacking the p50-interaction domain failed to stimulate glioma cell proliferation and tumor growth. Moreover, p68 induced NF-κB p50 accumulation in the nucleus through release of NF-κB p50 from IκBα and increased NF-κB p50 target luciferase transcription activity. Knockdown of NF-κB p50 rescued the phenotypes induced by p68 both in vitro and in vivo. We concluded that p68 induces glioma tumor growth through binding with NF-κB p50, regulating NF-κB p50 nucleus accumulation and transcription activity.