IkappaB alpha overexpression in human breast carcinoma MCF7 cells inhibits nuclear factor-kappaB activation but not tumor necrosis factor-alpha-induced apoptosis

Inflammation-Driven Regulation of PD-L1 and PD-L2, and Their Cross-Interactions with Protective Soluble TNFα Receptors in Human Triple-Negative Breast Cancer

Pro-inflammatory cytokines play key roles in elevating cancer progression in triple-negative breast cancer (TNBC). We demonstrate that specific combinations between TNFα, IL-1β and IFNγ up-regulated the proportion of human TNBC cells co-expressing the inhibitory immune checkpoints PD-L1 and PD-L2: TNFα + IL-1β in MDA-MB-231 cells and IFNγ + IL-1β in BT-549 cells; in the latter cells, the process depended entirely on STAT1 activation, with no involvement of p65 (CRISPR-Cas9 experiments). Highly significant associations between the pro-inflammatory cytokines and PD-L1/PD-L2 expression were revealed in the TCGA dataset of basal-like breast cancer patients. In parallel, we found that the pro-inflammatory cytokines regulated the expression of the soluble receptors of tumor necrosis factor α (TNFα), namely sTNFR1 and sTNFR2; moreover, we revealed that sTNFR1 and sTNFR2 serve as anti-metastatic and protective factors in TNBC, reducing the TNFα-induced production of inflammatory pro-metastatic chemokines (CXCL8, CXCL1, CCL5) by TNBC cells. Importantly, we found that in the context of inflammatory stimulation and also without exposure to pro-inflammatory cytokines, elevated levels of PD-L1 have down-regulated the production of anti-tumor sTNFR1 and sTNFR2. These findings suggest that in addition to its immune-suppressive activities, PD-L1 may promote disease course in TNBC by inhibiting the protective effects of sTNFR1 and sTNFR2.

Kaempferia parviflora extract inhibits TNF-α-induced release of MCP-1 in ovarian cancer cells through the suppression of NF-κB signaling

Ovarian clear cell carcinoma (OCCC) is an uncommon subtype of epithelial cell ovarian cancers (EOCs) that has poor response to conventional platinum-based therapy. Therefore, finding new potential therapeutic agents is required. Since inflammatory cytokine, tumor necrosis factor alpha (TNF-α), is strongly expressed in EOCs and associated with the level of tumor grade, disruption of this inflammation pathway may provide another potential target for OCCC treatment. We previously reported that Kaempferia parviflora (KP) extract decreased cell proliferation and induced apoptosis. However, the effects of KP on OCCC, especially the aspects related to inflammatory cytokines, have not been elucidated. Our current study demonstrated the effects of KP extract on cytokine production in TNF-α-induced OCCC TOV-21G cell line. This study showed that KP extract inhibited interleukin 6 (IL-6) and monocyte chemoattractant protein-1 (MCP-1) production at both transcription and translation levels via the suppression of nuclear factor-kappa B (NF-κB) signal transduction. In contrast, KP extract increased the expression of inhibitor kappa B (IκB) protein which may delay NF-κB translocation into the nucleus upon TNF-α activation. Moreover, the suppression of cytokines released from KP treated-TOV-21G reduced the migration of monocyte cell (THP-1). KP extract also exhibited the inhibition of IL-6 and MCP-1 production from THP-1 activated by lipopolysaccharides (LPS). Cells treated with KP extract exhibited a decrease in extracellular signal-regulated kinases (ERK1/2) and protein kinase B (AKT) phosphorylation and induced myeloid leukemia cell differentiation protein Mcl-1 (MCL-1) expression. Suppression of inflammatory cytokine and chemokine production and inhibition of tumor-associated macrophage (TAM) migration support the possibility of using KP for OCCC treatment.

A feedback mechanism between PLD and deadenylase PARN for the shortening of eukaryotic poly(A) mRNA tails that is deregulated in cancer cells

The removal of mRNA transcript poly(A) tails by 3′→5′ exonucleases is the rate-limiting step in mRNA decay in eukaryotes. Known cellular deadenylases are the CCR4-NOT and PAN complexes, and poly(A)-specific ribonuclease (PARN). The physiological roles and regulation for PARN is beginning to be elucidated. Since phospholipase D (PLD2 isoform) gene expression is upregulated in breast cancer cells and PARN is downregulated, we examined whether a signaling connection existed between these two enzymes. Silencing PARN with siRNA led to an increase in PLD2 protein, whereas overexpression of PARN had the opposite effect. Overexpression of PLD2, however, led to an increase in PARN expression. Thus, PARN downregulates PLD2 whereas PLD2 upregulates PARN. Co-expression of both PARN and PLD2 mimicked this pattern in non-cancerous cells (COS-7 fibroblasts) but, surprisingly, not in breast cancer MCF-7 cells, where PARN switches from inhibition to activation of PLD2 gene and protein expression. Between 30 and 300 nM phosphatidic acid (PA), the product of PLD enzymatic reaction, added exogenously to culture cells had a stabilizing role of both PARN and PLD2 mRNA decay. Lastly, by immunofluorescence microscopy, we observed an intracellular co-localization of PA-loaded vesicles (0.1-1 nm) and PARN. In summary, we report for the first time the involvement of a phospholipase (PLD2) and PA in mediating PARN-induced eukaryotic mRNA decay and the crosstalk between the two enzymes that is deregulated in breast cancer cells.

Summary: Cell signaling enzyme phospholipase D2 (PLD2) and its reaction product, phospholipid phosphatidic acid (PA), are involved in mediating PARN-induced eukaryotic mRNA decay.

FXR1a-associated microRNP: A driver of specialized non-canonical translation in quiescent conditions

Eukaryotic protein synthesis is a multifaceted process that requires coordination of a set of translation factors in a particular cellular state. During normal growth and proliferation, cells generally make their proteome via conventional translation that utilizes canonical translation factors. When faced with environmental stress such as growth factor deprivation, or in response to biological cues such as developmental signals, cells can reduce canonical translation. In this situation, cells adapt alternative modes of translation to make specific proteins necessary for required biological functions under these distinct conditions. To date, a number of alternative translation mechanisms have been reported, which include non-canonical, cap dependent translation and cap independent translation such as IRES mediated translation. Here, we discuss one of the alternative modes of translation mediated by a specialized microRNA complex, FXR1a-microRNP that promotes non-canonical, cap dependent translation in quiescent conditions, where canonical translation is reduced due to low mTOR activity.

AtHESPERIN: a novel regulator of circadian rhythms with poly(A)-degrading activity in plants

We report the identification and characterization of a novel gene, AtHesperin (AtHESP) that codes for a deadenylase in Arabidopsis thaliana. The gene is under circadian clock-gene regulation and has similarity to the mammalian Nocturnin. AtHESP can efficiently degrade poly(A) substrates exhibiting allosteric kinetics. Size exclusion chromatography and native electrophoresis coupled with kinetic analysis support that the native enzyme is oligomeric with at least 3 binding sites. Knockdown and overexpression of AtHESP in plant lines affects the expression and rhythmicity of the clock core oscillator genes TOC1 and CCA1. This study demonstrates an evolutionary conserved poly(A)-degrading activity in plants and suggests deadenylation as a mechanism involved in the regulation of the circadian clock. A role of AtHESP in stress response in plants is also depicted.

Assaying mRNA deadenylation in vitro

Deadenylation is the removal of poly(A) tails from mRNA. This chapter presents two methods to assay deadenylation in vitro. The first is a quick and quantitative assay for the degradation of radiolabeled poly(A) that can easily be adapted to be used for many different enzymes. The second method uses an extract from Drosophila embryos to catalyze the deadenylation of an RNA dependent on a specific sequence that also directs deadenylation in vivo.

To be or not to be: the regulation of mRNA fate as a survival strategy during mammalian hibernation

Mammalian hibernators undergo profound behavioral, physiological, and biochemical changes in order to cope with hypothermia, ischemia-reperfusion, and finite fuel reserves over days or weeks of continuous torpor. Against a backdrop of global reductions in energy-expensive processes such as transcription and translation, a subset of genes/proteins are strategically upregulated in order to meet challenges associated with hibernation. Consequently, hibernation involves substantial transcriptional and posttranscriptional regulatory mechanisms and provides a phenomenon with which to understand how a set of common genes/proteins can be differentially regulated in order to enhance stress tolerance beyond that which is possible for nonhibernators. The present review focuses on the involvement of messenger RNA (mRNA) interacting factors that play a role in the regulation of gene/protein expression programs that define the hibernating phenotype. These include proteins involved in mRNA processing (i.e., capping, splicing, and polyadenylation) and the possible role of alternative splicing as a means of enhancing protein diversity. Since the total pool of mRNA remains constant throughout torpor, mechanisms which enhance mRNA stability are discussed in the context of RNA binding proteins and mRNA decay pathways. Furthermore, mechanisms which control the global reduction of cap-dependent translation and the involvement of internal ribosome entry sites in mRNAs encoding stress response proteins are also discussed. Finally, the concept of regulating each of these factors in discrete subcellular compartments for enhanced efficiency is addressed. The analysis draws on recent research from several well-studied mammalian hibernators including ground squirrels, bats, and bears.

Paclitaxel in combination with cetuximab exerts antitumor effect by suppressing NF-κB activity in human oral squamous cell carcinoma cell lines

In the present study, we examined the antitumor effect of paclitaxel (PTX) in combination with cetuximab in oral squamous cell carcinoma (OSCC) and the mechanism of its enhanced antitumor activity. Treatment of OSCC (HSC2, HSC3 and HSC4) cells with PTX (0.02 µg/ml) and cetuximab (1 µg/ml) combination resulted in a significant inhibition of cell growth in vitro compared to either agent alone. Moreover, it was found by Hoechst 33258 staining that DNA fragmentation markedly occurred in OSCC cells treated with PTX and cetuximab combination treatment. Furthermore, PTX and cetuximab combination treatment reduced the expression of p65 (NF-κB) protein in OSCC cells. In our in vivo experiment, HSC2 tumor-bearing nude mice were treated with PTX (20 mg/kg/day, twice/week, 3 weeks) and/or cetuximab (20 mg/kg/day, twice/week, 3 weeks). Tumor growth was significantly suppressed by PTX and cetuximab combined treatment when compared to PTX or cetuximab alone, or the untreated control. TUNEL-positive cells were upregulated in HSC2 tumors treated with PTX and cetuximab. In addition, immunohistochemical staining revealed that expression of p65 was downregulated in HSC2 tumors treated with PTX and cetuximab. Our results indicate that cetuximab may enhance the effect of PTX in OSCC through the downregulation of PTX induced p65 expression. Therefore, the combination of PTX and cetuximab might be a promising option for OSCC treatment.

Exonuclease hDIS3L2 specifies an exosome-independent 3'-5' degradation pathway of human cytoplasmic mRNA

Turnover of mRNA in the cytoplasm of human cells is thought to be redundantly conducted by the monomeric 5'-3' exoribonuclease hXRN1 and the 3'-5' exoribonucleolytic RNA exosome complex. However, in addition to the exosome-associated 3'-5' exonucleases hDIS3 and hDIS3L, the human genome encodes another RNase II/R domain protein-hDIS3L2. Here, we show that hDIS3L2 is an exosome-independent cytoplasmic mRNA 3'-5' exonuclease, which exhibits processive activity on structured RNA substrates in vitro. hDIS3L2 associates with hXRN1 in an RNA-dependent manner and can, like hXRN1, be found on polysomes. The impact of hDIS3L2 on cytoplasmic RNA metabolism is revealed by an increase in levels of cytoplasmic RNA processing bodies (P-bodies) upon hDIS3L2 depletion, which also increases half-lives of investigated mRNAs. Consistently, RNA sequencing (RNA-seq) analyses demonstrate that depletion of hDIS3L2, like downregulation of hXRN1 and hDIS3L, causes changed levels of multiple mRNAs. We suggest that hDIS3L2 is a key exosome-independent effector of cytoplasmic mRNA metabolism.

Poly(A)-specific ribonuclease (PARN): an allosterically regulated, processive and mRNA cap-interacting deadenylase

Deadenylation of eukaryotic mRNA is a mechanism critical for mRNA function by influencing mRNA turnover and efficiency of protein synthesis. Here, we review poly(A)-specific ribonuclease (PARN), which is one of the biochemically best characterized deadenylases. PARN is unique among the currently known eukaryotic poly(A) degrading nucleases, being the only deadenylase that has the capacity to directly interact during poly(A) hydrolysis with both the m(7)G-cap structure and the poly(A) tail of the mRNA. In short, PARN is a divalent metal-ion dependent poly(A)-specific, processive and cap-interacting 3'-5' exoribonuclease that efficiently degrades poly(A) tails of eukaryotic mRNAs. We discuss in detail the mechanisms of its substrate recognition, catalysis, allostery and processive mode of action. On the basis of biochemical and structural evidence, we present and discuss a working model for PARN action. Models of regulation of PARN activity by trans-acting factors are discussed as well as the physiological relevance of PARN.

Oct-1 cooperates with the TATA binding initiation complex to control rapid transcription of human iNOS

Expression of the human inducible nitric oxide synthase (hiNOS) is generally undetectable in resting cells, but stimulation by a variety of signals including cytokines induces transcription in most cell types. The tight transcriptional regulation of the enzyme is a complex mechanism many aspects of which remain unknown. Here, we describe an octamer (Oct) element in hiNOS proximal promoter, located close to the TATA box. This site constitutively binds Oct-1 and its deletion abrogates cytokine-induced transcription, showing that it is indispensable though not sufficient for transcription. Increasing the distance between Oct and the TATA box by inserting inert DNA sequence inhibits transcription, and footprinting of this region shows no other protein binding in resting cells, suggesting an interaction between the two complexes. Chromatin immunoprecipitation assays detect the presence of Oct-1, RNA polymerase II and trimethyl K4 histone H3 on the proximal promoter in resting cells, confirming that the gene is primed for transcription before stimulation. RT-PCR of various fragments along the hiNOS gene shows that transcription is initiated in resting cells and this is inhibited by interference with Oct-1 binding to the proximal site of the promoter. We propose that, through interaction with the initiation complex, Oct-1 regulates hiNOS transcription by priming the gene for the rapid response required in an immune response.

Silymarin inhibits cervical cancer cell through an increase of phosphatase and tensin homolog

Silymarin is an active constituent contained in the seeds of the milk thistle plant and is widely used as a hepatic protection agent due to its antioxidant-like activity. In the present study we evaluated the potential action of silymarin against cervical cancer and investigated its mechanism of action. Treatment of cervical cancer cells (C-33A) with silymarin resulted in a significant decrease in cell viability. Silymarin induced apoptosis through the modulation of Bcl-2 family proteins and activation of caspase 3. Silymarin also inhibited the phosphorylation of Akt with an increase in expression of phosphatase and tensin homolog (PTEN). We also observed that silymarin suppressed C-33A cell invasion and wound-healing migration in a concentration-dependent manner. Western-blot analysis showed that silymarin significantly inhibited the expression of matrix metalloproteinase-9 (MMP-9) in C-33A cells. Furthermore, we applied siRNA to lower the PTEN gene, which diminished the anticancer actions of silymarin. Taken together, these results show that silymarin has the potential to suppress the survival, migration and invasion of C-33A cancer cells; thus, it could be developed as a promising agent for the treatment of cervical cancer in the future.

To polyadenylate or to deadenylate: that is the question

mRNA polyadenylation and deadenylation are important processes that allow rapid regulation of gene expression in response to different cellular conditions. Almost all eukaryotic mRNA precursors undergo a co-transcriptional cleavage followed by polyadenylation at the 3' end. After the signals are selected, polyadenylation occurs to full extent, suggesting that this first round of polyadenylation is a default modification for most mRNAs. However, the length of these poly(A) tails changes by the activation of deadenylation, which might regulate gene expression by affecting mRNA stability, mRNA transport, or translation initiation. The mechanisms behind deadenylation activation are highly regulated and associated with cellular conditions such as development, mRNA surveillance, DNA damage response, cell differentiation and cancer. After deadenylation, depending on the cellular response, some mRNAs might undergo an extension of the poly(A) tail or degradation. The polyadenylation/deadenylation machinery itself, miRNAs, or RNA binding factors are involved in the regulation of polyadenylation/deadenylation. Here, we review the mechanistic connections between polyadenylation and deadenylation and how the two processes are regulated in different cellular conditions. It is our conviction that further studies of the interplay between polyadenylation and deadenylation will provide critical information required for a mechanistic understanding of several diseases, including cancer development.

Chemosensitization in non-small cell lung cancer cells by IKK inhibitor occurs via NF-kappaB and mitochondrial cytochrome c cascade

In this study, we demonstrated with mechanistic evidence that parthenolide, a sesquiterpene lactone, could antagonize paclitaxel-mediated NF-κB nuclear translocation and activation by selectively targeting I-κB kinase (IKK) activity. We also found that parthenolide could target IKK activity and then inhibit NF-κB; this promoted cytochrome c release and activation of caspases 3 and 9. Inhibition of caspase activity blocked the activation of caspase cascade, implying that the observed synergy was related to caspases 3 and 9 activation of parthenolide. In contrast, paclitaxel individually induced apoptosis via a pathway independent of the mitochondrial cytochrome c cascade. Finally, exposure to parthenolide resulted in the inhibition of several NF-κB transcript anti-apoptotic proteins such as c-IAP1 and Bcl-xl. These data strengthen the rationale for using parthenolide to decrease the apoptotic threshold via caspase-dependent processes for treatment of non-small cell lung cancer with paclitaxel chemoresistance.

Nuclear deadenylation/polyadenylation factors regulate 3' processing in response to DNA damage

We previously showed that mRNA 3' end cleavage reaction in cell extracts is strongly but transiently inhibited under DNA-damaging conditions. The cleavage stimulation factor-50 (CstF-50) has a role in this response, providing a link between transcription-coupled RNA processing and DNA repair. In this study, we show that CstF-50 interacts with nuclear poly(A)-specific ribonuclease (PARN) using in vitro and in extracts of UV-exposed cells. The CstF-50/PARN complex formation has a role in the inhibition of 3' cleavage and activation of deadenylation upon DNA damage. Extending these results, we found that the tumour suppressor BARD1, which is involved in the UV-induced inhibition of 3' cleavage, strongly activates deadenylation by PARN in the presence of CstF-50, and that CstF-50/BARD1 can revert the cap-binding protein-80 (CBP80)-mediated inhibition of PARN activity. We also provide evidence that PARN along with the CstF/BARD1 complex participates in the regulation of endogenous transcripts under DNA-damaging conditions. We speculate that the interplay between polyadenylation, deadenylation and tumour-suppressor factors might prevent the expression of prematurely terminated messengers, contributing to control of gene expression under different cellular conditions.

The ubiquitin-specific protease USP47 is a novel beta-TRCP interactor regulating cell survival

Ubiquitin-specific proteases (USPs) are a subclass of cysteine proteases that catalyze the removal of ubiquitin (either monomeric or chains) from substrates, thus counteracting the activity of E3 ubiquitin ligases. Although the importance of USPs in a multitude of processes, from hereditary cancer to neurodegeneration, is well established, our knowledge on their mode of regulation, substrate specificity and biological function is quite limited. In this study we identify USP47 as a novel interactor of the E3 ubiquitin ligase, Skp1/Cul1/F-box protein beta-transducin repeat-containing protein (SCF(beta-Trcp)). We found that both beta-Trcp1 and beta-Trcp2 bind specifically to USP47, and point mutations in the beta-Trcp WD-repeat region completely abolished USP47 binding, indicating an E3-substrate-type interaction. However, unlike canonical beta-Trcp substrates, USP47 protein levels were neither affected by silencing of beta-Trcp nor modulated in a variety of processes, such as cell-cycle progression, DNA damage checkpoint responses or tumor necrosis factor (TNF) pathway activation. Notably, genetic or siRNA-mediated depletion of USP47 induced accumulation of Cdc25A, decreased cell survival and augmented the cytotoxic effects of anticancer drugs. In conclusion, we showed that USP47, a novel beta-Trcp interactor, regulates cell growth and survival, potentially providing a novel target for anticancer therapies.

Inhibition of human poly(A)-specific ribonuclease (PARN) by purine nucleotides: kinetic analysis

Poly(A)-specific ribonuclease (PARN) is a cap-interacting and poly(A)-specific 3'-exoribonuclease that efficiently degrades mRNA poly(A) tails. Based on the enzyme's preference for its natural substrates, we examined the role of purine nucleotides as potent effectors of human PARN activity. We found that all purine nucleotides tested can reduce poly(A) degradation by PARN. Detailed kinetic analysis revealed that RTP nucleotides behave as non-competitive inhibitors while RDP and RMP exhibit competitive inhibition. Mg(2 + ) which is a catalytically important mediator of PARN activity can release inhibition of RTP and RDP but not RMP. Although many strategies have been proposed for the regulation of PARN activity, very little is known about the modulation of PARN activity by small molecule effectors, such as nucleotides. Our data imply that PARN activity can be modulated by purine nucleotides in vitro, providing an additional simple regulatory mechanism.

Inhibitory activity of nuclear factor-kappaB potentiates cisplatin-induced apoptosis in A549 cells

Whether inhibiting the activity of nuclear factor (NF)-kappaB potentiates cisplatin-induced apoptosis in non-small cell lung cell line A549 cells was investigated. The recombinant plasmid pcDNA3.1 (+)/IkappaBalpha expressing IkappaBalpha was constructed. The in vitro cultured A549 cells were transfected with pcDNA3.1 (+)/IkappaBalpha alone, or pcDNA3.1 (+)/IkappaBalpha combined with cisplatin. The mitochondrial membrane potential (Deltapsim) was determined by rhodamine 123, the activity of caspase-3 was tested by colorimetric assay, and cell apoptosis was detected by flow cytometry with the annexin V /propidium iodide assay. The results showed that the activity of NF-kappaB in A549 cells was inhibited by transfecting pcDNA3.1(+)/IkappaBalpha. Transfection of pcDNA3.1(+)/IkappaBalpha alone did not promote apoptosis. Treatment of cisplatin alone had a little effect on cell apoptosis. Transfection of pcDNA3.1(+)/IkappaBalpha combined with cisplatin treatment significantly induced apoptosis of A549 cells. It was concluded that inhibiting the activity of NF-B potentiated cisplatin-induced apoptosis of A549 cells.

Independent activation of Akt and NF-kappaB pathways and their role in resistance to TNF-alpha mediated cytotoxicity in gliomas

Tumor associated macrophages (TAMs) constitute a substantial mass in gliomas. The activated macrophages secrete various cytokines that affect diverse functions of tumors. The aim of this study was to elucidate the role of Akt and NF-kappaB pathways in resistance to TNF-alpha mediated cell death in human gliomas using monolayers and multicellular spheroids (MCS) as in vitro models. Akt and NF-kappaB are constitutively expressed and intimately involved in progression of gliomas. The activation of these pathways also renders the tumors resistant to conventional treatments including chemotherapy. While PI3K/Akt is shown to regulate the NF-kappaB activation in diverse systems, other studies place NF-kappaB upstream of Akt activation. Using a stable IkappaBalpha mutant LN-18 cell line and pharmacological inhibitors to PI3K/Akt (LY294002) and Akt (Akt2), we provide evidence that Akt and NF-kappaB are activated independently on stimulation with TNF-alpha and both the pathways contribute towards resistance to TNF-alpha mediated cell death. TNF-alpha-induced NF-kappaB activation independent of PI3K/Akt pathway was also confirmed in human glioma cell lines-LN-229 and U373MG. We also show that NF-kappaB and Akt are activated during spheroidogenesis and their expression is further enhanced on stimulation with TNF-alpha implicating their involvement in resistance to cell death. The findings thus underscore the relevance of spheroids as appropriate in vitro models for studying the signaling pathways in drug induced resistance.

Heregulin β1 promotes breast cancer cell proliferation through Rac/ERK-dependent induction of cyclin D1 and p21Cip1

Accumulating evidence indicates that heregulins, EGF (epidermal growth factor)-like ligands, promote breast cancer cell proliferation and are involved in the progression of breast cancer towards an aggressive and invasive phenotype. However, there is limited information regarding the molecular mechanisms that mediate these effects. We have recently established that HRG (heregulin β1) promotes breast cancer cell proliferation and migration via cross-talk with EGFR (EGF receptor) that involves the activation of the small GTPase Rac1. In the present paper we report that Rac1 is an essential player for mediating the induction of cyclin D1 and p21Cip1 by HRG in breast cancer cells. Inhibition of Rac function by expressing either the Rac-GAP (GTPase-activating protein) β2-chimaerin or the dominant-negative Rac mutant N17Rac1, or Rac1 depletion using RNAi (RNA interference), abolished the cyclin D1 and p21Cip1 induction by HRG. Interestingly, the proliferative effect of HRG was impaired not only when the expression of Rac1 or cyclin D1 was inhibited, but also when cells were depleted of p21Cip1 using RNAi. Inhibition of EGFR, PI3K (phosphoinositide 3-kinase; kinases required for Rac activation by HRG) or MEK [MAPK (mitogen-activated protein kinase)/ERK (extracellular-signal-regulated kinase) kinase] also blocked the up-regulation of cyclin D1 and p21Cip1 by HRG. In addition, we found that HRG activates NF-κB (nuclear factor κB) in a Rac1- and MEK-dependent fashion, and inhibition of NF-κB abrogates cyclin D1/p21Cip1 induction and proliferation by HRG. Taken together, these findings establish a central role for Rac1 in the control of HRG-induced breast cancer cell-cycle progression and proliferation through up-regulating the expression of cyclin D1 and p21Cip1.

Control of mRNA stability by SAPKs

Control of mRNA turnover is an essential step in the regulation of gene expression in eukaryotes. The concerted action of many enzymes regulates the way each mRNA is degraded. Moreover, the degradation of each mRNA is influenced by the environment surrounding the cell. The conection between the environment and changes in the half-lifes of mRNAs is regulated by the activity of stress activated MAP kinases (SAPKs) and their substrates. Here we will describe some of those mechanisms, and how SAPKs regulate mRNA stability in eukaryotic cells.

Apoptosis of dedifferentiated hepatoma cells is independent of NF-kappaB activation in response to LPS

Dedifferentiated hepatoma cells, in contrast to most other cell types including hepatoma cells, undergo apoptosis when treated with lipopolysaccharide (LPS) plus the protein synthesis inhibitor cycloheximide (CHx). We recently reported that the dedifferentiated hepatoma cells also exhibit a strong and prolonged NF-kappaB induction phenotype upon exposure to LPS, suggesting that NF-kappaB signaling may play a pro-survival role, as reported in several other cell systems. To test the role of NF-kappaB in preventing LPS-mediated apoptosis, we examined the dedifferentiated cell line M38. Results show that antioxidants strongly inhibited LPS + CHx-mediated cell death in the M38 cells, yet only modestly inhibited NF-kappaB induction. In addition, inhibition of NF-kappaB translocation by infection of the M38 cells with an adenoviral vector expressing an IkappaBalpha super-repressor did not result in LPS-mediated cell death. These results suggest that unlike TNFalpha induction, the cell survival pathway activated in response to LPS is independent of NF-kappaB translocation in the dedifferentiated cells. Addition of inhibitors of JNK, p38 and ERK pathways also failed to elicit LPS-mediated apoptosis similar to that observed when protein synthesis is prevented. Thus, cell survival pathways other than those involving NF-kappaB inducible gene expression or other well-known pathways appear to be involved in protecting the dedifferentiated hepatoma variant cells from LPS-mediated apoptosis. Importantly, this pro-apoptotic function of LPS appears to be a function of loss of hepatic gene expression, as the parental hepatoma cells resist LPS-mediated apoptosis in the presence of protein synthesis inhibitors.

Differential expression and role of p21cip/waf1 and p27kip1 in TNF-alpha-induced inhibition of proliferation in human glioma cells

Background

The role of TNF-α in affecting the fate of tumors is controversial, while some studies have reported apoptotic or necrotic effects of TNF-α, others provide evidence that endogenous TNF-α promotes growth and development of tumors. Understanding the mechanism(s) of TNF-α mediated growth arrest will be important in unraveling the contribution of tissue associated macrophages in tumor resistance. The aim of this study was to investigate the role of Cyclin Dependent Kinase Inhibitors (CDKI) – p21^cip/waf1 and p27^kip1 in TNF-α mediated responses in context with p53 and activation of NF-κB and Akt pathways. The study was done with human glioma cell lines -LN-18 and LN-229 cells, using monolayer cultures and Multicellular Spheroids (MCS) as in vitro models.

Results

TNF-α induced inhibition of proliferation and enhanced the expression of p21^cip/waf1 and p27^kip1 in LN-18 cells. p21 was induced on exposure to TNF-α, localized exclusively in the nucleus and functioned as an inhibitor of cell cycle but not as an antiapoptotic protein. In contrast, p27 was constitutively expressed, localized predominantly in the cytoplasm and was not involved in arrest of proliferation. Our data using IκBα mutant LN-18 cells and PI3K/Akt inhibitor-LY294002 revealed that the expression of p21 is regulated by NF-κB. Loss of IκBα function in LN-229 cells (p53 positive) did not influence TNF-α induced accumulation of pp53 (Ser-20 p53) suggesting that p53 was not down stream of NF-κB. Spheroidogenesis enhanced p27 expression and p21 induced by TNF-α was significantly increased in the MCS compared to monolayers.

Conclusion

This study demarcates the functional roles for CDKIs-p21^cip/waf1 and p27^kip1 during TNF-α stimulated responses in LN-18 glioma cells. Our findings provide evidence that TNF-α-induced p21 might be regulated by NF-κB or p53 independently. p21 functions as an inhibitor of cell proliferation and does not have a direct role in rendering the cells resistant to TNF-α mediated cytotoxicity.

Rugosin E, an ellagitannin, inhibits MDA-MB-231 human breast cancer cell proliferation and induces apoptosis by inhibiting nuclear factor-κB signaling pathway

In this study, we first report the chemopreventive effect of rugosin E in human breast cancer cell line, MDA-MB-231. Treatment with rugosin E decreased the cell proliferation of MDA-MB-231 cells in a dose-dependent manner. Rugosin E treatment arrested MDA-MB-231 cells at G0/G1 phase. This effect was strongly associated with concomitant decrease in the level of cyclin D1, cyclin D2, cyclin E, cdk2, cdk4, and cdk6, and increase of p21/WAF1. In addition, rugosin E also induced apoptotic cell death. Rugosin E increased in the expression of Bax, Bak, and Bcl-Xs, but decreased the levels of Bcl-2 and Bcl-X(L), and subsequently triggered mitochondria apoptotic pathway (release of cytochrome c, activation of caspase-9, and caspase-3). In addition, pre-treatment of cells with caspase-9 inhibitor blocked rugosin E-induced cell proliferation and apoptosis, indicating caspase-9 activation was involved in rugosin E-mediated MDA-MB-231 cells apoptosis. Rugosin E inhibited the constitutively activated and inducible NF-kappaB in both its DNA-binding activity and transcriptional activity. Furthermore, rugosin E also inhibited the TNF-alpha-activated NF-kappaB-dependent reporter gene expression of cyclin D1, c-Myc, XIAP, Bcl-2, and Bcl-X(L) were all downregulated by rugosin E. Our results indicated that rugosin E inhibits the activation of NF-kappaB, and this may provide a molecular basis for drug development in the prevention and treatment of cancer by rugosin E.

Cell death in response to antimetabolites directed at thymidylate synthase

PURPOSE

Thymidylate synthase (TS) is an indispensable enzyme in the de novo biosynthesis of TMP during DNA replication and cell growth, and has, therefore, been an important target for several classes of antimetabolites used in cancer chemotherapy. While most investigations of the action of TS-directed agents have focused on apoptosis as the primary means of cell death, little is known regarding the role, if any, of non-apoptotic mechanisms. In the present study, we have examined the mode of cell death induced by several TS inhibitors.

METHODS

Apoptosis and necrosis in response to TS inhibitors was assessed. The roles of caspases and the transcriptional regulator nuclear factor kappa B (NFkappaB) in drug-induced cell death were analyzed. Finally, drug-mediated changes in expression of several proteins involved in regulation of apoptosis were analyzed.

RESULTS

Though human colon tumor cells exposed to TS inhibitors undergo classical apoptosis, it is not the predominant mechanism of response; rather, a necrosis-like mechanism prevails. The apoptotic response to TS inhibitors is caspase-dependent, and is promoted by NFkappaB. In contrast, the necrosis-like response is independent of both caspases and NFkappaB. Exposure to TS inhibitors induces PARP cleavage, but does not alter expression of the pro or activated forms of caspases-3 or caspases-8, Fas, or FasL. Treatment with the death-inducing cytokine TNFalpha, like TS inhibitors, results in a limited extent of apoptosis that is both caspase- and NFkappaB-dependent; however, unlike TS inhibitors, the cytokine does not induce necrosis.

CONCLUSION

Classical apoptosis occurs to a limited extent in human colon tumor cells exposed to TS inhibitors, with caspase-independent necrosis being the prinicipal mechanism of cell death. We suggest that the role of necrosis and necrosis-like mechanisms should be considered in future studies of the action of TS-directed antimetabolites, as well as other chemotherapeutic agents.

Distinctive role of integrin-mediated adhesion in TNF-induced PKB/Akt and NF-κB activation and endothelial cell survival

Tumor necrosis factor (TNF) is a pro-inflammatory cytokine exerting pleiotropic effects on endothelial cells. Depending on the vascular context it can induce endothelial cell activation and survival or death. The microenvironmental cues determining whether endothelial cells will survive or die, however, have remained elusive. Here we report that integrin ligation acts permissive for TNF-induced protein kinase B (PKB/Akt) but not nuclear factor (NF)-kappaB activation. Concomitant activation of PKB/Akt and NF-kappaB is essential for the survival of endothelial cells exposed to TNF. Active PKB/Akt strengthens integrin-dependent endothelial cell adhesion, whereas disruption of actin stress fibers abolishes the protective effect of PKB/Akt. Integrin-mediated adhesion also represses TNF-induced JNK activation, but JNK activity is not required for cell death. The alphaVbeta3/alphaVbeta5 integrin inhibitor EMD121974 sensitizes endothelial cells to TNF-dependent cytotoxicity and active PKB/Akt attenuates this effect. Interferon gamma synergistically enhanced TNF-induced endothelial cell death in all conditions tested. Taken together, these observations reveal a novel permissive role for integrins in TNF-induced PKB/Akt activation and prevention of TNF-induced death distinct of NF-kappaB, and implicate the actin cytoskeleton in PKB/Akt-mediated cell survival. The sensitizing effect of EMD121974 on TNF cytotoxicity may open new perspectives to the therapeutic use of TNF as anticancer agent.

Role of the RRM domain in the activity, structure and stability of poly(A)-specific ribonuclease

Poly(A) specific ribonuclease (PARN), which contains a catalytic domain and two RNA-binding domains (R3H and RRM), acts as a key enzyme in eukaryotic organisms to regulate the stability of mRNA by degrading the 3' poly-(A) tail. In this research, the activity, structure and stability were compared between the full-length 74kDa PARN, the proteolytic 54kDa fragment with half of the RRM, and a truncated 46kDa form completely missing the RRM. The results indicated that the 46kDa one had the lowest activity and substrate binding affinity, the most hydrophobic exposure in the native state and the least stability upon denaturation. The dissimilarity in the activity, structure and stability of the three PARNs revealed that the entire RRM domain not only contributed to the substrate binding and efficient catalysis of PARN, but also stabilized the overall structures of the protein. Spectroscopic experiments suggested that the RRM domain might be structurally adjacent to the R3H domain, and thus provide a basis for the cooperative binding of poly(A) by the two RNA-binding domains as well as the catalytic domain.

Expression and purification of recombinant poly(A)-specific ribonuclease (PARN)

PARN is a poly(A)-specific ribonuclease that degrades the poly(A) tail of mRNA. We have established conditions for expressing soluble recombinant human PARN. We investigated different Escherichia coli strains, expression vectors, media and growth conditions. We found that PARN expressed from pET33 in BL21(DE3) grown in TB and induced at OD595 approximately 1 with 1 mM IPTG yielded mg amounts of soluble PARN per litre culture. Further, a purification protocol was established to purify PARN. We use His-tag affinity chromatography, HiTrap Q HP ion exchange chromatography and 7-Me-GTP-Sepharose affinity chromatography. This purification procedure render a 90-95% pure PARN. Purified recombinant PARN has enzymatic activity and will be used for further mechanistic and structural studies.

Naringenin-induced apoptosis via activation of NF-kappaB and necrosis involving the loss of ATP in human promyeloleukemia HL-60 cells

Naringenin (NGEN), a flavonoid, has shown cytotoxicity in various human cancer cell lines and inhibitory effects on tumor growth. In this study, we investigated the apoptosis induced by NGEN via the activation of NF-kappaB and necrosis involving the loss of ATP in human promyeloleukemia HL-60 cells. Exposure to NGEN induced apoptosis dose-dependently up until 0.5mM, but not at 1mM as demonstrated by a quantitative analysis of nuclear morphological change and flow cytometric analysis. An extensive inhibitor for caspases, abolished the NGEN-induced apoptosis. The apoptosis-triggering concentration of NGEN was shown to markedly promote the activation of caspase-3, and slightly promote that of caspase-9, but had no effect on caspase-8. NGEN-induced apoptosis caused by induction of specific NF-kappaB-binding activity and involving the degradation of IkappaBalpha. Incubation with a high concentration of NGEN (1mM) reduced intracellular ATP levels, but no change was observed at lower concentrations. NGEN increased dose-dependently hyperpolarization of mitochondrial membrane potential. This result indicates a common pathway to apoptosis and necrosis by NGEN. One of the mechanisms by NGEN-induced apoptosis may relate to the activation of NF-kappaB that correlates with degradation of IkappaBalpha. Induction of necrosis by NGEN suggests causing by intracellular ATP depletion and mitochondria dysfunctions.

Constitutive activation of NF-kappaB in human hepatocellular carcinoma: evidence of a cytoprotective role

Activation of nuclear factor-kappaB (NF-kappaB) can promote or inhibit apoptosis. Oxidative stress is an important mechanism by which certain anticancer drugs kill cancer cells, and is also one of the mechanisms that activate NF-kappaB. We therefore examined hepatic expression of the NF-kappaB monomer p65 in human hepatocellular carcinoma (HCC) tissue samples from eight patients and compared it with their respective samples of surrounding liver tissues. We also studied the effect of NF-kappaB inhibition in human HCC cells exposed to oxidative stress, by infecting HuH7 cells with a recombinant adenovirus carrying mutant IkappaBalpha (mIkappaBalpha). Cultured HuH7 cells were infected with mIkappaBalpha or beta-galactosidase (beta-Gal) for 24 hr followed by treatment with increasing concentrations of H2O2. Cytotoxicity, NF-kappaB translocation, NF-kappaB DNA binding, cell proliferation, and apoptosis were determined. The monomer p65 was overexpressed in six of eight human HCC tissues. In HuH7 cells, introduction of mIkappaBalpha potently inhibited the translocation, activation, and DNA binding of NF- kappaB. In control (beta-Gal-infected) HuH7 cells, exposure to H2O2 produced a dose-dependent increase in apoptosis, regardless of NF-kappaB status. mIkappaBalpha-mediated inhibition of NF-kappaB activation sensitized HuH7 cells to H2O2-induced inhibition of cell growth, and further promoted cell death. Addition of H2O2 (200-500 microM) to control or mIkappaBalpha-infected HuH7 cells enhanced caspase-3 activity and cleavage. Adenovirus-mediated transfer of mIkappaBalpha potently inhibits NF-kappaB activity in HuH7 cells, and this enhances oxidative stress-induced cell killing.

QN1/KIAA1009: a new essential protein for chromosome segregation and mitotic spindle assembly

We previously reported the involvement of QN1 (quail neuroretina 1) protein in cell cycle control during retinal development. We show here that QN1 is an ATPase conserved through evolution, from fugu to humans. We show that chicken/quail QN1 protein is orthologous to the KIAA1009 protein in humans, the function of which was not known. We demonstrate here for the first time that QN1/KIAA1009 protein is located at the spindle poles of the mitotic apparatus and at centrosomes during mitosis. The siRNA-mediated depletion of KIAA1009 led to abnormal mitosis with chromosome segregation defects and abnormal centrosome separation leading to the death of PC12 and MCF7 cells. Thus, QN1/KIAA1009 is a new microtubule-associated ATPase involved in cell division.

Retinoid-induced activation of NF-κB in APL cells is not essential for granulocytic differentiation, but prolongs the life span of mature cells

All-trans retinoic acid (ATRA) significantly improves the survival of patients with acute promyelocytic leukemia (APL) by inducing granulocytic differentiation of leukemia cells. Since an activation of the transcription factor NF-kappaB occurs during ATRA-induced maturation of APL cells, a mechanistic link between these two processes was investigated. Using an in vitro model for APL, we report that ectopic overexpression of a repressor of NF-kappaB activation did not affect granulocytic differentiation. Importantly, NF-kappaB inhibition markedly resulted in a decreased viability of the differentiated cells, which correlated with increased apoptosis. Apoptosis was accompanied by a sustained activation of the c-Jun N-terminal kinase (JNK). Inhibition of JNK by the specific inhibitor SP600125 or by transfection of a dominant-negative mutant of JNK1 reduced the percentage of apoptotic cells, thus showing that JNK activation constitutes a death signal. Furthermore, impairment of NF-kappaB activation resulted in increased levels of reactive oxygen species (ROS) upon ATRA treatment. ROS accumulation was suppressed by the antioxidant butylated hydroxyanisol, which also abolished ATRA-induced JNK activation and apoptosis. Altogether, our results demonstrate an anti-apoptotic effect of NF-kappaB activation during ATRA-induced differentiation of NB4 cells and identify repression of ROS-mediated JNK activation as a mechanism for this effect. Our observations also suggest that NF-kappaB signalling may contribute to an accumulation of mature APL cells and participate in the development of ATRA syndrome.

Targeting beta-transducin repeat-containing protein E3 ubiquitin ligase augments the effects of antitumor drugs on breast cancer cells

beta-Transducin repeat-containing proteins (beta-TrCP) serve as substrate recognition component of E3 ubiquitin ligases that control stability of important regulators of cell cycle and signal transduction. beta-TrCP function is essential for the induction of nuclear factor kappaB transcriptional activities, which play a key role in proliferation and survival of cancer cells and are often constitutively up-regulated in human breast cancers. Here we show that inhibition of beta-TrCP either by RNAi approach or by forced expression of a dominant-negative beta-TrCP mutant suppresses growth and survival of human breast cancer cells. In addition, inhibition of beta-TrCP augments the antiproliferative effects of anticancer drugs such as doxorubicin, tamoxifen, and paclitaxel on human mammary tumor cells. These data provide the proof of principle that targeting beta-TrCP might be beneficial for anticancer therapies.

Messenger RNA turnover in eukaryotes: pathways and enzymes

The control of mRNA degradation is an important component of the regulation of gene expression since the steady-state concentration of mRNA is determined both by the rates of synthesis and of decay. Two general pathways of mRNA decay have been described in eukaryotes. Both pathways share the exonucleolytic removal of the poly(A) tail (deadenylation) as the first step. In one pathway, deadenylation is followed by the hydrolysis of the cap and processive degradation of the mRNA body by a 5' exonuclease. In the second pathway, the mRNA body is degraded by a complex of 3' exonucleases before the remaining cap structure is hydrolyzed. This review discusses the proteins involved in the catalysis and control of both decay pathways.

Death receptor-induced cell death in prostate cancer

Prostate cancer mortality results from metastasis and is often coupled with progression from androgen-dependent to androgen-independent growth. Unfortunately, no effective treatment for metastatic prostate cancer increasing patient survival is available. The absence of effective therapies reflects in part a lack of knowledge about the molecular mechanisms involved in the development and progression of this disease. Apoptosis, or programmed cell death, is a cell suicide mechanism that enables multicellular organisms to regulate cell number in tissues. Inhibition of apoptosis appears to be a critical pathophysiological factor contributing to the development and progression of prostate cancer. Understanding the mechanism(s) of apoptosis inhibition may be the basis for developing more effective therapeutic approaches. Our understanding of apoptosis in prostate cancer is relatively limited when compared to other malignancies, in particular, hematopoietic tumors. Thus, a clear need for a better understanding of apoptosis in this malignancy remains. In this review we have focused on what is known about apoptosis in prostate cancer and, more specifically, the receptor/ligand-mediated pathways of apoptosis as potential therapeutic targets.

p73alpha expression induces both accumulation and activation of wt-p53 independent of the p73alpha transcriptional activity

The p53 tumor suppressor gene belongs to a multigene family that includes two paralogues, p63 and p73. p73alpha has common activities with p53, such as DNA binding and transactivation, and can thus activate the transcription of p53-responsive genes. Using the adenoviral system, we report that an overexpression of either wt-p73alpha or one of the two transcriptional inactive mutants, deltaNp73alpha or p73alphaR292H, induces an accumulation of the endogenous wt-p53 expressed in the three transformed cell lines, SK-N-SH, MCF-7 and U-2OS, without stimulating the p53 gene transcription. p73-mediated accumulation of p53 protein coincides with an increase of p53-target gene expression in cells expressing either wt-p73alpha or the transcriptional inactive mutant p73alphaR292H, but not deltaNp73alpha that encodes a dominant-negative mutant of both p73 and p53. The fact that an ectopic expression of p73alphaR292H leads to both accumulation of p53 and stimulation of p53 target gene expression strongly suggests that p73alpha is able to induce activation of p53. This was confirmed by showing that p73alphaR292H no longer stimulated Waf1/p21 expression in MCF7/R-A1 cells that expressed a transcriptional inactive mutant of p53. We thus conclude that p73alpha protein was able to both stabilize and activate wt-p53 protein, independent of the p73alpha transcriptional activity.

Chemosensitivity of human pancreatic carcinoma cells is enhanced by IkappaBalpha super-repressor

Pancreatic cancer has an unfavorable prognosis; surgery and chemotherapy at present have only limited value. To improve the prognosis of pancreatic cancer, effective non-surgical therapy is necessary. NF-kappaB is reported to be related to resistance to apoptosis, but its role in chemosensitivity remains controversial. We examined the effects on chemosensitivity of inhibition by induction of the super-repressor IkappaBalpha in pancreatic cancer cell lines, BxPC-3, Capan-1 and Panc-1. IkappaBalpha protein was transduced by infection of adenovirus vector AxCAhIkBDeltaN. Sensitivity to VP-16 and doxorubicin was increased significantly by IkappaBalpha induction in all three pancreatic cell lines. To investigate molecular events during IkappaBalpha induction, we examined the changes in expression of drug-resistance-related genes by real-time RT-PCR and those in apoptosis-related genes by cDNA microarray. There was no common change of gene expression before and after IkappaBalpha induction among the three pancreatic cancer cell lines, except for mdm2. Further examination of other genes is necessary for a better understanding of the molecular mechanisms of enhancement of chemosensitivity through IkappaBalpha induction. However, we have confirmed that IkappaBalpha induction leads to an increase of chemosensitivity of pancreatic cancer. Many problems remain before clinical application of this adenoviral system will be feasible, but our results may ultimately lead to an improved therapy of pancreatic cancer.

A history of poly A sequences: from formation to factors to function

Biological polyadenylation, first recognized as an enzymatic activity, remained an orphan enzyme until poly A sequences were found on the 3' ends of eukarvotic mRNAs. Their presence in bacteria viruses and later in archeae (ref. 338) established their universality. The lack of compelling evidence for a specific function limited attention to their cellular formation. Eventually the newer techniques of molecular biology and development of accurate nuclear processing extracts showed 3' end formation to be a two-step process. Pre-mRNA was first cleaved endonucleolytically at a specific site that was followed by sequential addition of AMPs from ATP to the 3' hydroxyl group at the end of mRNA. The site of cleavage was specified by a conserved hexanucleotide, AAUAAA, from 10 to 30 nt upstream of this 3' end. Extensive purification of these two activities showed that more than 10 polypeptides were needed for mRNA 3' end formation. Most of these were in complexes involved in the cleavage step. Two of the best characterized are CstF and CPSF, while two other remain partially purified but essential. Oddly, the specific proteins involved in phosphodiester bond hydrolysis have yet to be identified. The polyadenylation step occurs within the complex of poly A polymerase and poly A-binding protein, PABII, that controls poly A length. That the cleavage complex, CPSF, is also required for this step attests to a tight coupling of the two steps of 3' and formation. The reaction reconstituted from these RNA-free purified factors correctly processes pre-mRNAs. Meaningful analysis of the role of poly A in mRNA metabolism or function was possible once quantities of these proteins most often over-expressed from cDNA clones became available. The large number needed for two simple reactions of an endonuclease, a polymerase and a sequence recognition factor, pointed to 3' end formation as a regulated process. Polyadenylation itself had appeared to require regulation in cases where two poly A sites were alternatively processed to produce mRNA coding for two different proteins. The 64-KDa subunit of CstF is now known to be a regulator of poly A site choice between two sites in the immunoglobulin heavy chain of B cells. In resting cells the site used favors the mRNA for a membrane-bound protein. Upon differentiation to plasma cells, an upstream site is used the produce a secreted form of the heavy chain. Poly A site choice in the calcitonin pre-mRNA involves splicing factors at a pseudo splice site in an intron downstream of the active poly site that interacts with cleavage factors for most tissues. The molecular basis for choice of the alternate site in neuronal tissue is unknown. Proteins needed for mRNA 3' end formation also participate in other RNA-processing reactions: cleavage factors bind to the C-terminal domain of RNA polymerase during transcription; splicing of 3' terminal exons is stimulated port of by cleavage factors that bind to splicing factors at 3' splice sites. nuclear ex mRNAs is linked to cleavage factors and requires the poly A II-binding protein. Most striking is the long-sought evidence for a role for poly A in translation in yeast where it provides the surface on which the poly A-binding protein assembles the factors needed for the initiation of translation. This adaptability of eukaryotic cells to use a sequence of low information content extends to bacteria where poly A serves as a site for assembly of an mRNA degradation complex in E. coli. Vaccinia virus creates mRNA poly A tails by a streamlined mechanism independent of cleavage that requires only two proteins that recognize unique poly A signals. Thus, in spite of 40 years of study of poly A sequences, this growing multiplicity of uses and even mechanisms of formation seem destined to continue.

Apoptotic effects of selected strains of lactic acid bacteria on a human T leukemia cell line are associated with bacterial arginine deiminase and/or sphingomyelinase activities

The aim of the present work was, first, to analyze the apoptotic effect in vitro of sonicated preparations of selected strains of lactic acid bacteria on normal and tumor human lymphocytes. Incubation with bacterial samples led to a relevant time-dependent apoptotic cell death of Jurkat cells but not normal human peripheral blood lymphocytes. Lactobacillus brevis (CD2) samples were more efficient in inducing apoptosis of Jurkat cells than were samples of Streptococcus thermophilus (S244). In an attempt to characterize the mechanisms underlying these effects, we found that the apoptotic death-inducing ability of S244 preparations could be attributed to the ability of high levels of neutral sphingomyelinase activity to generate relevant amounts of ceramide, a known apoptotic death messenger, in Jurkat cells. On the other hand, our results indicate that apoptosis induced by CD2 samples could also be associated with high levels of arginine deiminase activity, which in turn was able to downregulate polyamine synthesis in Jurkat cells.

Stable inhibition of NF-kappa B in salivary gland cells does not enhance sensitivity to TNF-alpha-induced apoptosis due to upregulation of TRAF-1 expression

The transcription factor NF-kappa B inhibits the apoptotic response induced by TNF-alpha. However, in salivary gland cell clones (ACMT-6 and ACMT-7) in which NF-kappa B activation was suppressed by introduction of a super-repressor form of I kappa B-alpha cDNA, TNF-alpha did not cause apoptosis. Thus, to investigate the molecular mechanism involved in the unresponsiveness of these cell clones to TNF-alpha-induced apoptosis, we examined the effect of TNF-alpha on the expression of antiapoptotic proteins, including TNF receptor-associated factor (TRAF)-1, TRAF-2, cellular inhibitor of apoptosis protein (cIAP)-1, and cIAP-2. Here we show that expression of TRAF-1 was commonly detected by treatment with TNF-alpha in ACMT-6, ACMT-7, and an empty vector-transfected cell clone (ACpRc-1) and that downregulation of TRAF-1 protein by either treatment with an antisense oligonucleotide or introduction of an antisense plasmid resulted in the induction of apoptosis in these cell clones. Our results, therefore, suggest that one of the mechanisms by which cells acquire resistance to TNF-alpha-induced apoptosis is a TNF-alpha induction of TRAF-1.

Accumulation of an inactive form of p53 protein in cells treated with TNF alpha

In MCF-7 cells, TNF alpha induces a G1 arrest with an increased expression of p21/Waf1, an activation of NF-kappa B and an accumulation of p53. NF-kappa B and p53 are two transcriptional factors known to activate p21/Waf1 gene expression. Here we show that p53 inhibition has no effect on p21/Waf1 mRNA accumulation following TNF alpha treatment. In contrast, inactivation of NF-kappa B inhibits p21/Waf1 expression without affecting G1 arrest. The fact that p21/Waf1 gene expression is still stimulated when p53 is inactivated strongly suggests that TNF alpha induces accumulation of an inactive form of p53 protein. This assumption was further supported by the following observations: (i) the p53 DNA-binding activity to its consensus sequence was not stimulated following TNF alpha treatment, (ii) phosphorylation at Ser-15, -20 or -392 was not detected in response to TNF alpha, (iii) the transcription rate of Ddb2, another p53 target gene, was not stimulated by TNF alpha. Finally, the accumulation of p53 in the nuclei of TNF alpha-treated MCF-7 cells was concomitant with an increase in p53 mRNA level, suggesting a regulation at the transcription level.

Phosphoprotein isotope-coded affinity tags: application to the enrichment and identification of low-abundance phosphoproteins

The use of a phosphoprotein isotope-coded affinity tag (PhIAT), which employs differential isotopic labeling and biotinylation, has been shown capable of enriching and identifying mixtures of low-abundance phosphopeptides. A denatured solution of beta-casein was labeled using the PhIAT method, and after proteolytic digestion, the labeled peptides were isolated using immobilized avidin. The recovered peptides were separated by capillary reversed-phase liquid chromatography and identified by tandem mass spectrometry. PhIAT-labeled peptides corresponding to known O-phosphorylated peptides from beta-casein were identified along with the phosphorylated peptides from alphas1-casein and alphas2-casein, known low-level (<5%) contaminants of commercially available beta-casein. All of the casein-phosphorylated residues identified by the present PhIAT approach correspond to previously documented sites of phosphorylation. The results illustrate the efficacy of the PhIAT-labeling strategy to not only enrich mixtures for phosphopeptides but also, more importantly, permit the detection and identification of low-level phosphopeptides. In addition, the differences in the phosphorylation state could be determined between phosphopeptides in comparative samples by stoichiometric conversion using the light and heavy isotopic versions of the PhIAT reagents. Overall, our results exemplify the application of the PhIAT approach and demonstrate its utility for proteome-wide phosphoprotein identification and quantitation.

Nuclear Factor-κB Activation: A Question of Life or Death

Apoptosis is a mode of cell death that plays an important role in both pathological and physiological processes. Research during the last decade has delineated the entire machinery needed for cell death, and its constituents were found to pre-exist in cells. The apoptotic cascade is triggered when cells are exposed to an apoptotic stimulus. It has been known for several years that inhibitors of protein synthesis can potentiate apoptosis that is induced by cytokines and other inducers. Until 1996, it was not understood why protein synthesis inhibitors potentiate apoptosis. Then three reports appeared that suggested the role of the transcription factor NF-kappaB activation in protecting the cells from TNF-induced apoptosis. Since then several proteins have been identified that are regulated by NF-kappaB and are involved in cell survival, proliferation, and protection from apoptosis. It now seems that when a cell is attacked by an apoptotic stimulus, the cell responds first by activating anti-apoptotic mechanisms, which may or may not be followed by apoptosis. Whether or not a cell undergoes proliferation, the survival, or apoptosis, appears to involve a balance between the two mechanisms. Inhibitors of protein synthesis seem to suppress the appearance of protein that are involved in anti-apoptosis. The present review discusses how NF-kappaB controls apoptosis.

Post-transcriptional regulation of gene expression in the plasminogen activation system

The urokinase-mediated plasminogen activation (PA) system has been shown to play a key role in cell migration and tissue invasion by regulating both cell-associated proteolysis and cell-cell and cell-matrix interactions. The expression and activity of the components of this complex system are strictly regulated. The control of the expression occurs both at transcriptional and post-transcriptional levels. This review is focused on the post-transcriptional regulation of gene expression of all components of the PA system.

Identification of four families of yCCR4- and Mg2+-dependent endonuclease-related proteins in higher eukaryotes, and characterization of orthologs of yCCR4 with a conserved leucine-rich repeat essential for hCAF1/hPOP2 binding

BACKGROUND

The yeast yCCR4 factor belongs to the CCR4-NOT transcriptional regulatory complex, in which it interacts, through its leucine-rich repeat (LRR) motif with yPOP2. Recently, yCCR4 was shown to be a component of the major cytoplasmic mRNA deadenylase complex, and to contain a fold related to the Mg2+-dependent endonuclease core.

RESULTS

Here, we report the identification of nineteen yCCR4-related proteins in eukaryotes (including yeast, plants and animals), which all contain the yCCR4 endonuclease-like fold, with highly conserved CCR4-specific residues. Phylogenetic and genomic analyses show that they form four distinct families, one of which contains the yCCR4 orthologs. The orthologs in animals possess a leucine-rich repeat domain. We show, using two-hybrid and far-Western assays, that the human member binds to the human yPOP2 homologs, i.e. hCAF1 and hPOP2, in a LRR-dependent manner.

CONCLUSIONS

We have identified the mammalian orthologs of yCCR4 and have shown that the human member binds to the human yPOP2 homologs, thus strongly suggesting conservation of the CCR4-NOT complex from yeast to human. All members of the four identified yCCR4-related protein families show stricking conservation of the endonuclease-like catalytic motifs of the yCCR4 C-terminal domain and therefore constitute a new family of potential deadenylases in mammals.

Enhanced IkappaB kinase activity is responsible for the augmented activity of NF-kappaB in human head and neck carcinoma cells

The nuclear transcription factor kappaB (NF-kappaB) plays an important role in the development and progression of cancers. However, the mechanism by which cancer cells in the head and neck region acquire high NF-kappaB activity has not yet been clarified. In this study, we examined the NF-kappaB binding activity and the expression of the signal-transduction-related proteins of NF-kappaB in head and neck carcinoma cell lines. These cancer cells showed significantly higher NF-kappaB binding activity than normal oral epithelial and salivary gland cells. We also demonstrated the increased phosphorylation and degradation of IkappaB-alpha protein in cancer cells. Thus, enhanced NF-kappaB activity in cancer cells is attributable to the rapid phosphorylation and degradation of IkappaB-alpha protein. To further elucidate the mechanism involved in this phenomenon, we analyzed both the expression levels of upstream kinases (IkappaB kinase- (IKK-) alpha, IKK-beta, IKK-gamma, and NF-kappaB-inducing kinase (NIK)) and the IKK activity in cells. Although there was no significant difference in the expression levels of NIK, IKK-beta, or IKK-gamma in cancer cell lines compared to those in normal cells, increased expression of IKK-alpha protein was observed in cancer cells. In addition, IKK activity was significantly augmented in cancer cells as compared to normal cells. Thus, our results suggest that enhanced NF-kappaB activity in head and neck cancer cells may be due to the augmentation of IKK activity.