Eukaryotic initiation factor 4F: a vulnerability of tumor cells

Solid-type adenoid cystic carcinoma of the breast, a distinct molecular entity enriched in NOTCH and CREBBP mutations

Adenoid cystic carcinoma (ACC) of the breast with a predominant solid pattern is difficult to diagnose with certainty and differentiate from more common triple-negative breast cancers (TNBCs) of basal-phenotype. To better characterize solid ACC, we performed a clinical, morphological, immunohistochemical, and molecular comparative analysis of 33 ACCs of the breast comprising 17 solid variant ACCs and 16 conventional ACCs. Solid ACCs displayed basaloid morphology with an exclusive or predominant epithelial cell population associated with decreased myoepithelial differentiation, while demonstrating MYB protein overexpression similar to the more common type of ACC. Strong and diffuse MYB expression by immunochemistry was observed in 14/17 (82%) of solid ACCs while MYB rearrangements were detected by break apart fluorescence in situ hybridization (FISH) in only 3/16 (19%) of solid ACCs. Conversely, weak MYB immunohistochemical expression was observed in only 7/204 (3%) of TNBC. Solid ACCs displayed a transcriptomic profile distinct from conventional ACCs with 549 genes showing a highly significant differential expression between conventional and solid ACC [false discovery rate (FDR) < 0.01; log2FC > |1|]. EnrichR and Kegg Pathway analyses identified PI3K-Akt and focal adhesion signaling pathways as significantly overexpressed in conventional ACCs compared with solid ACCs which significantly overexpressed the nitrogen metabolism pathway. CREBBP mutations and NOTCH activating gene mutations were only present in solid ACCs, concerning 5/16 (31%) of cases for each gene. Tumors with NOTCH activating mutations displayed a strong diffuse nuclear NICD1 staining, an established marker of Notch pathway activation. Solid ACCs also differed from basal-type TNBC, with fewer TP53 mutations and a more stable genomic profile on array comparative genomic hybridization (CGH). In summary, solid-type ACC of the breast is a distinct molecular entity within the ACC family and is different from common basal-type TNBC. MYB is a diagnostically useful biomarker of solid ACC and NOTCH could be a novel potential therapeutic target in 30% of cases.

The CXCR4-LASP1-eIF4F Axis Promotes Translation of Oncogenic Proteins in Triple-Negative Breast Cancer Cells

Triple-negative breast cancer (TNBC) remains clinically challenging as effective targeted therapies are lacking. In addition, patient mortality mainly results from the metastasized lesions. CXCR4 has been identified to be one of the major chemokine receptors involved in breast cancer metastasis. Previously, our lab had identified LIM and SH3 Protein 1 (LASP1) to be a key mediator in CXCR4-driven invasion. To further investigate the role of LASP1 in this process, a proteomic screen was employed and identified a novel protein-protein interaction between LASP1 and components of eukaryotic initiation 4F complex (eIF4F). We hypothesized that activation of the CXCR4-LASP1-eIF4F axis may contribute to the preferential translation of oncogenic mRNAs leading to breast cancer progression and metastasis. To test this hypothesis, we first confirmed that the gene expression of CXCR4, LASP1, and eIF4A are upregulated in invasive breast cancer. Moreover, we demonstrate that LASP1 associated with eIF4A in a CXCL12-dependent manner via a proximity ligation assay. We then confirmed this finding, and the association of LASP1 with eIF4B via co-immunoprecipitation assays. Furthermore, we show that LASP1 can interact with eIF4A and eIF4B through a GST-pulldown approach. Activation of CXCR4 signaling increased the translation of oncoproteins downstream of eIF4A. Interestingly, genetic silencing of LASP1 interrupted the ability of eIF4A to translate oncogenic mRNAs into oncoproteins. This impaired ability of eIF4A was confirmed by a previously established 5′UTR luciferase reporter assay. Finally, lack of LASP1 sensitizes 231S cells to pharmacological inhibition of eIF4A by Rocaglamide A as evident through BIRC5 expression. Overall, our work identified the CXCR4-LASP1 axis to be a novel mediator in oncogenic protein translation. Thus, our axis of study represents a potential target for future TNBC therapies.

O-GlcNAcylation of core components of the translation initiation machinery regulates protein synthesis

Protein synthesis is essential for cell growth, proliferation, and survival. Protein synthesis is a tightly regulated process that involves multiple mechanisms. Deregulation of protein synthesis is considered as a key factor in the development and progression of a number of diseases, such as cancer. Here we show that the dynamic modification of proteins by O-linked β-N-acetyl-glucosamine (O-GlcNAcylation) regulates translation initiation by modifying core initiation factors eIF4A and eIF4G, respectively. Mechanistically, site-specific O-GlcNAcylation of eIF4A on Ser322/323 disrupts the formation of the translation initiation complex by perturbing its interaction with eIF4G. In addition, O-GlcNAcylation inhibits the duplex unwinding activity of eIF4A, leading to impaired protein synthesis, and decreased cell proliferation. In contrast, site-specific O-GlcNAcylation of eIF4G on Ser61 promotes its interaction with poly(A)-binding protein (PABP) and poly(A) mRNA. Depletion of eIF4G O-GlcNAcylation results in inhibition of protein synthesis, cell proliferation, and soft agar colony formation. The differential glycosylation of eIF4A and eIF4G appears to be regulated in the initiation complex to fine-tune protein synthesis. Our study thus expands the current understanding of protein synthesis, and adds another dimension of complexity to translational control of cellular proteins.

Targeting of the Eukaryotic Translation Initiation Factor 4A Against Breast Cancer Stemness

Breast cancer stem cells (BCSCs) are intrinsically chemoresistant and capable of self-renewal. Following chemotherapy, patients can develop minimal residual disease due to BCSCs which can repopulate into a relapsed tumor. Therefore, it is imperative to co-target BCSCs along with the bulk tumor cells to achieve therapeutic success and prevent recurrence. So, it is vital to identify actionable molecular targets against both BCSCs and bulk tumor cells. Previous findings from our lab and others have demonstrated that inhibition of the emerging drug target eIF4A with Rocaglamide A (RocA) was efficacious against triple-negative breast cancer cells (TNBC). RocA specifically targets the pool of eIF4A bound to the oncogenic mRNAs that requires its helicase activity for their translation. This property enables specific targeting of tumor cells. The efficacy of RocA against BCSCs is unknown. In this study, we postulated that eIF4A could be a vulnerable node in BCSCs. In order to test this, we generated a paclitaxel-resistant TNBC cell line which demonstrated an elevated level of eIF4A along with increased levels of cancer stemness markers (ALDH activity and CD44), pluripotency transcription factors (SOX2, OCT4, and NANOG) and drug transporters (ABCB1, ABCG2, and ABCC1). Furthermore, genetic ablation of eIF4A resulted in reduced expression of ALDH1A1, pluripotency transcription factors and drug transporters. This pointed out that eIF4A is likely associated with selected set of proteins that are critical to BCSCs, and hence targeting eIF4A may eliminate BCSCs. Therefore, we isolated BCSCs from two TNBC cell lines: MDA-Bone-Un and SUM-159PT. Following RocA treatment, the self-renewal ability of the BCSCs was significantly reduced as determined by the efficiency of the formation of primary and secondary mammospheres. This was accompanied by a reduction in the levels of NANOG, OCT4, and drug transporters. Exposure to RocA also induced cell death of the BCSCs as evaluated by DRAQ7 and cell viability assays. RocA treatment induced apoptosis with increased levels of cleaved caspase-3. Overall, we identified that RocA is effective in targeting BCSCs, and eIF4A is an actionable molecular target in both BCSCs and bulk tumor cells. Therefore, anti-eIF4A inhibitors could potentially be combined synergistically with existing chemo-, radio- and/or immunotherapies.

Suppression of EIF4G2 by miR-379 potentiates the cisplatin chemosensitivity in nonsmall cell lung cancer cells

Although microRNAs and EIF4G2 are both known to play pivotal roles in cancer progression, it remains unknown whether these pathways regulate chemosensitivity in a coordinated manner. Here, we show that miR-379 expression is significantly downregulated in chemoresistant nonsmall cell lung cancer (NSCLC) tissues and cells. Manipulation of miR-379 levels could alter the in vitro and in vivo cisplatin (CDDP) resistance in lung cancer (LCa) cells. Mechanistically, miR-379 potentiated LCa chemosensitivity via modulation of CDDP-induced apoptosis by directly targeting the EIF4G2 3'UTR. Additionally, we observed an inverse correlation between miR-379 and EIF4G2 expression in LCa tissues from patients with CDDP-based chemotherapy. Together, our findings shed new light on the potential involvement of miR-379/EIF4G2 cascade in the pathogenesis of CDDP resistance in LCa.

Identification of phenotype-relevant differentially expressed genes in breast cancer demonstrates enhanced quantile discretization protocol's utility in multi-platform microarray data integration

Microarray for transcriptomics experiments often suffer from limited statistical power due to small sample size. Quantile discretization (QD) maps expression values for a sample into a series of equivalently sized 'bins' that represent a discrete numerical range, e.g. [Formula: see text]4 to [Formula: see text]4, which enables normalized data from multiple experiments and/or expression platforms to be combined for re-analysis. We found, however, that informal selection of bin numbers often resulted in loss of the underlying correlation structure in the data through assigning of the same numerical value to genes that are in reality expressed at significantly different levels within a sample. Here we report a procedure for determining an optimal bin number for dataset. Applying this to integrated public breast cancer datasets enabled statistical identification of several differentially expressed tumorigenesis-related genes that were not found when analyzing the individual datasets, and also several cancer biomarkers not previously indicated as having utility in the disease. Notably, differential modulation of translational control and protein synthesis via multiple pathways were found to potentially have central roles in breast cancer development and progression. These findings suggest that our protocol has significant utility in making meaningful novel biomedical discoveries by leveraging the large public expression data repositories.

eIF3 regulates migration, invasion and apoptosis in cadmium transformed 16HBE cells and is a novel biomarker of cadmium exposure in a rat model and in workers

Translation (eukaryotic) initiation factor 3 (eIF3 or TIF3) has been found to be a proto-oncogene in cadmium (Cd) response both in vitro and vivo, but whether eIF3 may serve as a biomarker of Cd exposure is still unclear. This study aimed to investigate whether eIF3 could serve as a novel biomarker of Cd toxicity in cells, animals and workers, and regulate the apoptosis, migration and invasion in human bronchial epithelial cell (16HBE cells) transformation with cadmium chloride (CdCl2). In CdCl2 transformed 16HBE cells, eIF3 expression increased gradually, and sequencing did not identify mutation and methylation of eIF3. In 16HBE cells with eIF3 silencing by siRNA and CdCl2 treated 16HBE cells of the 15th and 35th generations, the apoptosis, migration and invasion were significantly inhibited, and the expressions of relevant genes were also altered (P < 0.05). In CdCl2 treated rats, eIF3 mRNA expression increased to different extents in the blood, liver, kidney, heart and lung, and this increase was dependent on the Cd concentration (P < 0.05). The eIF3 mRNA expression was related to the mRNA expressions of AKT, BAX, BCL-2, E-CADHERIN, CASPASE-3, EGFR, FOXC2, STAT3, TGF-β1 and VIMENTIN (P < 0.05). In 181 workers with Cd exposure, the eIF3 mRNA expression was positively related to the blood Cd, urine Cd and β2-microglobulin content (P < 0.05). This study showed that abnormally expressed eIF3 may regulate the apoptosis, migration and invasion of 16HBE cells with Cd toxicity. This suggests that eIF3 may become a novel and valuable biomarker of Cd toxicity and Cd-induced effects, and may regulate apoptosis, migration and invasion of 16HBE cells. Thus, the detection of eIF3 expression is important for the monitoring of Cd toxicity in humans.

Equol, an isoflavone metabolite, regulates cancer cell viability and protein synthesis initiation via c-Myc and eIF4G

Epidemiological studies implicate dietary soy isoflavones as breast cancer preventives, especially due to their anti-estrogenic properties. However, soy isoflavones may also have a role in promoting breast cancer, which has yet to be clarified. We previously reported that equol, a metabolite of the soy isoflavone daidzein, may advance breast cancer potential via up-regulation of the eukaryotic initiation factor 4GI (eIF4GI). In estrogen receptor negative (ER-) metastatic breast cancer cells, equol induced elevated levels of eIF4G, which were associated with increased cell viability and the selective translation of mRNAs that use non-canonical means of initiation, including internal ribosome entry site (IRES), ribosome shunting, and eIF4G enhancers. These mRNAs typically code for oncogenic, survival, and cell stress molecules. Among those mRNAs translationally increased by equol was the oncogene and eIF4G enhancer, c-Myc. Here we report that siRNA-mediated knockdown of c-Myc abrogates the increase in cancer cell viability and mammosphere formation by equol, and results in a significant down-regulation of eIF4GI (the major eIF4G isoform), as well as reduces levels of some, but not all, proteins encoded by mRNAs that are translationally stimulated by equol treatment. Knockdown of eIF4GI also markedly reduces an equol-mediated increase in IRES-dependent mRNA translation and the expression of specific oncogenic proteins. However, eIF4GI knockdown did not reciprocally affect c-Myc levels or cell viability. This study therefore implicates c-Myc as a potential regulator of the cancer-promoting effects of equol via up-regulation of eIF4GI and selective initiation of translation on mRNAs that utilize non-canonical initiation, including certain oncogenes.

4EBP1/eIF4E and p70S6K/RPS6 axes play critical and distinct roles in hepatocarcinogenesis driven by AKT and N-Ras proto-oncogenes in mice

Concomitant expression of activated forms of v-akt murine thymoma viral oncogene homolog (AKT) and Ras in mouse liver (AKT/Ras) leads to rapid tumor development through strong activation of the mammalian target of rapamycin complex 1 (mTORC1) pathway. mTORC1 functions by regulating p70S6K/ribosomal protein S6 (RPS6) and eukaryotic translation initiation factor 4E-binding protein 1/ eukaryotic translation initiation factor 4E (4EBP1/eIF4E) cascades. How these cascades contribute to hepatocarcinogenesis remains unknown. Here, we show that inhibition of the RPS6 pathway by rapamycin effectively suppressed, whereas blockade of the 4EBP1/eIF4E cascade by 4EBP1A4, an unphosphorylatable form of 4EBP1, significantly delayed, AKT/Ras-induced hepatocarcinogenesis. Combined treatment with rapamycin and 4EBP1A4 completely inhibited AKT/Ras hepatocarcinogenesis. This strong antineoplastic effect was successfully recapitulated by ablating regulatory associated protein of mTORC1, the major subunit of mTORC1, in AKT/Ras-overexpressing livers. Furthermore, we demonstrate that overexpression of eIF4E, the proto-oncogene whose activity is specifically inhibited by 4EBP1, resulted in hepatocellular carcinoma (HCC) development in cooperation with activated Ras. Mechanistically, we identified the ectonucleoside triphosphate diphosphohydrolase 5/ adenylate kinase 1/cytidine monophosphate kinase 1 axis and the mitochondrial biogenesis pathway as targets of the 4EBP1/eIF4E cascade in AKT/Ras and Ras/eIF4E livers as well as in human HCC cell lines and tissues.

CONCLUSIONS

Complete inhibition of mTORC1 is required to suppress liver cancer development induced by AKT and Ras proto-oncogenes in mice. The mTORC1 effectors, RPS6 and eIF4E, play distinct roles and are both necessary for AKT/Ras hepatocarcinogenesis. These new findings might open the way for innovative therapies against human HCC.

Weighing up the possibilities: Controlling translation by ubiquitylation and sumoylation

Regulation of protein synthesis is of fundamental importance to cells. It has a critical role in the control of gene expression, and consequently cell growth and proliferation. The importance of this control is supported by the fact that protein synthesis is frequently upregulated in tumor cells. The major point at which regulation occurs is the initiation stage. Initiation of translation involves the interaction of several proteins to form the eIF4F complex, the recognition of the mRNA by this complex, and the subsequent recruitment of the 40S ribosomal subunit to the mRNA. This results in the formation of the 48S complex that then scans the mRNA for the start codon, engages the methionyl-tRNA and eventually forms the mature 80S ribosome which is elongation-competent. Formation of the 48S complex is regulated by the availability of individual initiation factors and through specific protein-protein interactions. Both of these events can be regulated by post-translational modification by ubiquitin or Ubls (ubiquitin-like modifiers) such as SUMO or ISG15. We provide here a summary of translation initiation factors that are modified by ubiquitin or Ubls and, where they have been studied in detail, describe the role of these modifications and their effects on regulating protein synthesis.

IRE mRNA riboregulators use metabolic iron (Fe(2+)) to control mRNA activity and iron chemistry in animals

A family of noncoding RNAs bind Fe(2+) to increase protein synthesis. The structures occur in messenger RNAs encoding animal proteins for iron metabolism. Each mRNA regulatory sequence, ∼30 ribonucleotides long, is called an IRE (Iron Responsive Element), and folds into a bent, A-RNA helix with a terminal loop. Riboregulatory RNAs, like t-RNAs, r-RNAs micro-RNAs, etc. contrast with DNA, since single-stranded RNA can fold into a variety of complex, three-dimensional structures. IRE-RNAs bind two types of proteins: (1) IRPs which are protein repressors, sequence-related to mitochondrial aconitases. (2) eIF-4F, which bind ribosomes and enhances general protein biosynthesis. The competition between IRP and eIF-4F binding to IRE-RNA is controlled by Fe(2+)-induced changes in the IRE-RNA conformation. Mn(2+), which also binds to IRE-RNA in solution, is a convenient experimental proxy for air-sensitive Fe(2+) studies of in vitro protein biosynthesis and protein binding. However, only Fe(2+) has physiological effects on protein biosynthesis directed by IRE-mRNAs. The structures of the IRE-RNA riboregulators is known indirectly from effects of base substitutions on function, from solution NMR of the free RNA, and of X-ray crystallography of the IRE-RNA-IRP repressor complex. However, the inability to date, to crystallize the free IRE-RNA, and the dissociation of the IRE-RNA-IRP complex when metal binds, have hampered direct identification and characterization of the RNA-metal binding sites. The high conservation of the primary sequence in IRE-mRNA control elements has facilitated their identification and analysis of metal-assisted riboregulator function. Expansion of RNA search analyses beyond primary will likely reveal other, metal-dependent families of mRNA riboregulators.

Phosphorylation of eIF4E promotes EMT and metastasis via translational control of SNAIL and MMP-3

The progression of cancers from primary tumors to invasive and metastatic stages accounts for the overwhelming majority of cancer deaths. Understanding the molecular events which promote metastasis is thus critical in the clinic. Translational control is emerging as an important factor in tumorigenesis. The mRNA cap-binding protein eIF4E is an oncoprotein that plays an important role in cancer initiation and progression. eIF4E must be phosphorylated to promote tumor development. However, the role of eIF4E phosphorylation in metastasis is not known. Here, we show that mice in which eIF4E cannot be phosphorylated are resistant to lung metastases in a mammary tumor model, and that cells isolated from these mice exhibit impaired invasion. We also demonstrate that TGFβ induces eIF4E phosphorylation to promote translation of Snail and Mmp-3 mRNAs, and the induction of epithelial-to-mesenchymal transition (EMT). Furthermore, we describe a new model wherein EMT induced by TGFβ requires translational activation via the non-canonical TGFβ signaling branch acting through eIF4E phosphorylation.

Many roads from mTOR to eIF4F

The process of cell growth depends on a complex co-ordinated programme of macromolecular synthesis that can be tuned to environmental constraints. In eukaryotes, the mTOR [mammalian (or mechanistic) target of rapamycin] signalling pathway is a master regulator of this process, in part by regulating mRNA translation through control of the eIF4F (eukaryotic initiation factor 4F) initiation complex. The present review discusses the role of this relationship in mTOR-regulated gene expression, and its contribution to phenotypes associated with deregulated mTOR signalling, such as cancer.

Second-generation derivatives of the eukaryotic translation initiation inhibitor pateamine A targeting eIF4A as potential anticancer agents

A series of pateamine A (1) derivatives were synthesized for structure/activity relationship (SAR) studies and a selection of previous generation analogs were re-evaluated based on current information regarding the mechanism of action of these translation inhibitors. Structural modifications in the new generation of derivatives focused on alterations to the C19-C22 Z,E-diene and the trienyl side chain of the previously described simplified, des-methyl, des-amino pateamine A (DMDAPatA, 2). Derivatives were tested for anti-proliferative activity in cell culture and for inhibition of mammalian cap-dependent translation in vitro. Activity was highly dependent on the rigidity and conformation of the macrolide and the functionality of the side chain. The only well tolerated substitutions were replacement of the N,N-dimethyl amino group found on the side chain of 2 with other tertiary amine groups. SAR reported here suggests that this site may be modified in future studies to improve serum stability, cell-type specificity, and/or specificity towards rapidly proliferating cells.

Requirement for the eIF4E binding proteins for the synergistic down-regulation of protein synthesis by hypertonic conditions and mTOR inhibition

The protein kinase mammalian target of rapamycin (mTOR) regulates the phosphorylation and activity of several proteins that have the potential to control translation, including p70S6 kinase and the eIF4E binding proteins 4E-BP1 and 4E-BP2. In spite of this, in exponentially growing cells overall protein synthesis is often resistant to mTOR inhibitors. We report here that sensitivity of wild-type mouse embryonic fibroblasts (MEFs) to mTOR inhibitors can be greatly increased when the cells are subjected to the physiological stress imposed by hypertonic conditions. In contrast, protein synthesis in MEFs with a double knockout of 4E-BP1 and 4E-BP2 remains resistant to mTOR inhibitors under these conditions. Phosphorylation of p70S6 kinase and protein kinase B (Akt) is blocked by the mTOR inhibitor Ku0063794 equally well in both wild-type and 4E-BP knockout cells, under both normal and hypertonic conditions. The response of protein synthesis to hypertonic stress itself does not require the 4E-BPs. These data suggest that under certain stress conditions: (i) translation has a greater requirement for mTOR activity and (ii) there is an absolute requirement for the 4E-BPs for regulation by mTOR. Importantly, dephosphorylation of p70S6 kinase and Akt is not sufficient to affect protein synthesis acutely.

Over-expression of human cytomegalovirus miR-US25-2-3p downregulates eIF4A1 and inhibits HCMV replication

It has been reported that human cytomegalovirus (HCMV) miR-US25-2 reduces DNA viral replication including HCMV. However, the mechanism remains unknown. In our study, eukaryotic translation initiation factor 4A1 (eIF4A1) was identified to be a direct target of miR-US25-2-3p. Small interfering RNA (siRNA) and miR-US25-2-3p mediated eIF4A1 knockdown experiments revealed that high level of miR-US25-2-3p in MRC-5 cells decreased HCMV and host genomic DNA synthesis, and inhibited cap-dependent translation and host cell proliferation. However, eIF4A1 up-regulation induced by miR-US25-2-3p inhibitor increased HCMV copy number. Therefore, the over-expression of miR-US25-2-3p and consequent lower expression of eIF4A1 may contribute to the inhibition of HCMV replication.

Magnetic-nanoparticle-decorated polypyrrole microvessels: toward encapsulation of mRNA cap analogues

Many phosphorylated nucleoside derivatives have therapeutic potential, but their application is limited by problems with membrane permeability and with intracellular delivery. Here, we prepared polypyrrole microvessel structures modified with superparamagnetic nanoparticles for use as potential carriers of nucleotides. The microvessels were prepared via the photochemical polymerization of the monomer onto the surface of aqueous ferrofluidic droplets. A complementary physicochemical analysis revealed that a fraction of the nanoparticles was embedded in the microvessel walls, while the other nanoparticles were in the core of the vessel. SQUID (superconducting quantum interference device) measurements indicated that the incorporated nanoparticles retained their superparamagnetic properties; thus, the resulting nanoparticle-modified microvessels can be directed by an external magnetic field. As a result of these features, these microvessels may be useful as drug carriers in biomedical applications. To demonstrate the encapsulation of drug molecules, two labeled mRNA cap analogues, nucleotide-derived potential anticancer agents, were used. It was shown that the cap analogues are located in the aqueous core of the microvessels and can be released to the external solution by spontaneous permeation through the polymer walls. Mass spectrometry analysis confirmed that the cap analogues were preserved during encapsulation, storage, and release. This finding provides a foundation for the future development of anticancer therapies and for the delivery of nucleotide-based therapeutics.

Blood translation elongation factor-1δ is a novel marker for cadmium exposure

Translation elongation factor-1δ (TEF-1δ) has been identified as a novel cadmium-responsive proto-oncogene. However, it is still unclear whether TEF-1δ could be a potential biomarker of cadmium exposure. Rats were treated with CdCl₂ at different concentrations (high dose 1.225, mid-dose 0.612 and low dose 0.306 mg/kg body weight, respectively) for 14 weeks, and the cadmium levels, weight coefficients, serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), blood urea nitrogen (BUN), serum creatinine (SCR), 24-h urine protein (24hPro), urinary creatinine (Cr) and pathological features were determined. The TEF-1δ expression in white blood cells and multiple organs were examined by reverse transcription polymerase chain reaction (PCR) and were also confirmed with fluorescence quantitative PCR. A cadmium dose-dependent increase (p < 0.05) of cadmium levels in blood, urine, liver, kidney, heart and lung, and the weight coefficients was observed. The liver and renal function indictors including AST, ALT, SCR, BUN and 24hPro, were elevated in a cadmium dose-dependent manner (p < 0.05). Significant pathological changes in liver, kidney, heart and lung were indicated. The TEF-1δ expression was up-regulated in both blood and organs (p < 0.05). Moreover, the expression level of blood TEF-1δ was positively correlated to TEF-1δ expression level, cadmium level and toxicity in the organs (p < 0.01). This study indicates that blood TEF-1δ is a novel valuable biomarker for cadmium exposure and its organ toxicity.

Regulation of protein translation initiation in response to ionizing radiation

Background

Proliferating tumor cells require continuous protein synthesis. De novo synthesis of most proteins is regulated through cap-dependent translation. Cellular stress such as ionizing radiation (IR) blocks cap-dependent translation resulting in shut-down of global protein translation which saves resources and energy needed for the stress response. At the same time, levels of proteins required for stress response are maintained or even increased. The study aimed to analyze the regulation of signaling pathways controlling protein translation in response to IR and the impact on Mcl-1, an anti-apoptotic and radioprotective protein, which levels rapidly decline upon IR.

Methods

Protein levels and processing were analyzed by Western blot. The assembly of the translational pre-initiation complex was examined by Immunoprecipitation and pull-down experiments with 7-methyl GTP agarose. To analyze IR-induced cell death, dissipation of the mitochondrial membrane potential and DNA fragmentation were determined by flow cytometry. Protein levels of the different initiation factors were down-regulated using RNA interference approach.

Results

IR induced caspase-dependent cleavage of the translational initiation factors eIF4G1, eIF3A, and eIF4B resulting in disassembly of the cap-dependent initiation complex. In addition, DAP5-dependent initiation complex that regulates IRES-dependent translation was disassembled in response to IR. Moreover, IR resulted in dephosphorylation of 4EBP1, an inhibitor of cap-dependent translation upstream of caspase activation. However, knock-down of eIF4G1, eIF4B, DAP5, or 4EBP1 did not affect IR-induced decline of the anti-apoptotic protein Mcl-1.

Conclusion

Our data shows that cap-dependent translation is regulated at several levels in response to IR. However, the experiments indicate that IR-induced Mcl-1 decline is not a consequence of translational inhibition in Jurkat cells.

Interview: Interview with Future Medicinal Chemistry’s US Senior Editor, Iwao Ojima

Professor Iwao Ojima studied at the University of Tokyo (Japan) before being appointed as a Senior Research Fellow and Group Leader at the Sagami Institute of Chemical Research. He is now Director of the Institute of Chemical Biology and Drug Discovery at State University of New York (USA) and has been a visiting professor in European, North American and Asian academic institutions. Professor Ojima agreed to serve as the US Senior Editor of Future Medicinal Chemistry when it launched in 2009 and continues to provide his expertise to the journal. Professor Ojima spoke to Future Medicinal Chemistry about why medicinal chemistry is such an exciting field to work in, the state of the pharmaceutical industry, and what features and issues make this journal unique.

Interview conducted by Isaac Bruce, Commissioning Editor.

Targeting the liver kinase B1/AMP-activated protein kinase pathway as a therapeutic strategy for hematological malignancies

INTRODUCTION

Despite considerable advances, several hematological malignancies remain incurable with standard treatments. Therefore, there is a need for novel targeted and less toxic therapies, particularly for patients who develop resistance to traditional chemotherapeutic drugs. The liver kinase B1 (LKB1)/AMP-activated protein kinase (AMPK) signaling pathway has recently emerged as a tumor suppressor axis. A critical point is that the LKB1/AMPK network remains functional in a wide range of cancers and could be stimulated by drugs, such as N,N-dimethylimidodicarbonimidic diamide (metformin) or 5-aminoimidazole-4-carboxamide 1-β-D-ribofuranoside (AICAR).

AREAS COVERED

The literature data show that drugs activating LKB1/AMPK signaling induced cell cycle arrest, caspase-dependent apoptosis or autophagy in hematopoietic tumors. Moreover, metformin effectively inhibited mammalian target of rapamycin complex 1 (mTORC1)-controlled oncogenetic protein translation, which does not occur with allosteric mTORC1 inhibitors, such as rapamycin and its derivatives. Metformin was also capable of targeting leukemic stem cells, the most relevant target for leukemia eradication.

EXPERT OPINION

Data emerging from preclinical settings suggest that the LKB1/AMPK pathway is critically involved in regulating proliferation and survival of malignant hematopoietic cells. Thus, it is proposed that drugs activating the LKB1/AMPK axis may offer a novel and less toxic treatment option for some types of hematological malignancies.