Effects of 4E-BP1 expression on hypoxic cell cycle inhibition and tumor cell proliferation and survival

Longitudinal dynamics of the tumor hypoxia response: From enzyme activity to biological phenotype

Poor oxygenation (hypoxia) is a common spatially heterogeneous feature of human tumors. Biological responses to tumor hypoxia are orchestrated by the decreased activity of oxygen-dependent enzymes. The affinity of these enzymes for oxygen positions them along a continuum of oxygen sensing that defines their roles in launching reactive and adaptive cellular responses. These responses encompass regulation of all steps in the central dogma, with rapid perturbation of the metabolome and proteome followed by more persistent reprogramming of the transcriptome and epigenome. Core hypoxia response genes and pathways are commonly regulated at multiple inflection points, fine-tuning the dependencies on oxygen concentration and hypoxia duration. Ultimately, shifts in the activity of oxygen-sensing enzymes directly or indirectly endow cells with intrinsic hypoxia tolerance and drive processes that are associated with aggressive phenotypes in cancer including angiogenesis, migration, invasion, immune evasion, epithelial mesenchymal transition, and stemness.

Translational Control by 4E-BP1/2 Suppressor Proteins Regulates Mitochondrial Biosynthesis and Function during CD8+ T Cell Proliferation

CD8⁺ T cell proliferation and differentiation into effector and memory states are high-energy processes associated with changes in cellular metabolism. CD28-mediated costimulation of T cells activates the PI3K/AKT/mammalian target of rapamycin signaling pathway and induces eukaryotic translation initiation factor 4E-dependent translation through the derepression by 4E-BP1 and 4E-BP2. In this study, we demonstrate that 4E-BP1/2 proteins are required for optimum proliferation of mouse CD8⁺ T cells and the development of an antiviral effector function. We show that translation of genes encoding mitochondrial biogenesis is impaired in T cells derived from 4E-BP1/2-deficient mice. Our findings demonstrate an unanticipated role for 4E-BPs in regulating a metabolic program that is required for cell growth and biosynthesis during the early stages of CD8⁺ T cell expansion.

Prothioconazole induces cell cycle arrest by up-regulation of EIF4EBP1 in extravillous trophoblast cells

Prothioconazole (PTC) is a new broad-spectrum triazole antibacterial agent that is being widely used in agriculture. PTC has been linked to a number of reproductive outcomes including embryo implantation disorder; however, the exact mechanism underlying this relationship has yet to be determined. Proper trophoblast proliferation and migration is a prerequisite for successful embryo implantation. To elucidate the underlying molecular perturbations, we detect the effect of PTC on extravillous trophoblast cells proliferation and migration, and investigate its potential mechanisms. Exposure to different concentrations of PTC (0-500 μM) significantly inhibited the cell viability and migration ability (5 μM PTC exposure), and also caused the cell cycle arrest at the lowest dose (1 μM PTC exposure). Transcriptome analysis revealed that PTC exposure disturbed multiple biological processes including cell cycle and apoptosis, consistent with cell phenotype. Specifically, eukaryotic translation initiation factor 4E binding protein 1 (EIF4EBP1, 4E-BP1) was identified as up-regulated in PTC exposure group and knockdown of EIF4EBP1, and attenuated the G1 phase arrest induced by PTC exposure. In summary, our data demonstrated that 4E-BP1 participated in PTC-induced cell cycle arrest in extravillous trophoblast cells by regulating cyclin D1. These findings shed light on the potential adverse effect of PTC exposure on the embryo implantation.

Adaptive immunity at the crossroads of autophagy and metabolism

The function of lymphocytes is dependent on their plasticity, particularly their adaptation to energy availability and environmental stress, and their protein synthesis machinery. Lymphocytes are constantly under metabolic stress, and macroautophagy/autophagy is the primary metabolic pathway that helps cells overcome stressors. The intrinsic role of autophagy in regulating the metabolism of adaptive immune cells has recently gained increasing attention. In this review, we summarize and discuss the versatile roles of autophagy in regulating cellular metabolism and the implications of autophagy for immune cell function and fate, especially for T and B lymphocytes.

Molecular biological investigation of temozolomide and KC7F2 combination in U87MG glioma cell line

Glioblastom Multiforme (GBM) is the most invasive and malignant member of the IV grade of the subclass Astrocytoma according to the last assessment of the 2016 WHO report. Due to the resistance to treatment and weak response, as well as the topographical structure of the blood brain barrier, the treatment is also difficult due to the severe clinical manifestation, and new treatment methods and new therapeutic agents are needed. Temozolomide (TMZ) is widely used in the treatment of glioblastoma and is considered as the primary treatment modality. TMZ, a member of the class of cognitive agents, is currently considered the most effective drug because it can easily pass through the blood brain barrier. Glucose metabolism is a complex energy producing machine that, a glucose molecule produces 38 molecules of ATP after full glycolytic catabolism. According to Otto Warburg's numerous studies cancer cells perform the first glycolytic step without entering the mitochondrial step. These cells produce lactic acid and make the micro-media more acidic even in aerobic conditions. This phenomenon is attributed to the Warburg hypothesis and either as aerobic glycolysis. Although glycolysis enzymes are the primary actors of this phenotypic expression, some genetic and epigenetic factors are no exception. We experimentally used KC7F2 active ingredient to target cancer metabolism. In our study, we evaluated cancer metabolism in combination with the effect of TMZ chemotherapeutic agent, examining the effect of two different agents separately and in combination to observe the effects of cancer cell proliferation, survival, apoptosis and expression of metabolism genes on expression. We observed that the combined effect of reduced the effective dose of the TMZ alkylating agent and that the effect was increased and the effect of the combined teraphy is assessed from a metabolic point of view and that it suppresses aerobic glycolysis.

PI3K-AKT-mTOR and NFκB Pathways in Ovarian Cancer: Implications for Targeted Therapeutics

Ovarian cancer is the most lethal gynecologic malignancy in the United States, with an estimated 22,530 new cases and 13,980 deaths in 2019. Recent studies have indicated that the phosphoinositol 3 kinase (PI3K)/protein kinase B (AKT)/mammalian target of rapamycin (mTOR), as well as the nuclear factor-κ light chain enhancer of activated B cells (NFκB) pathways are highly mutated and/or hyper-activated in a majority of ovarian cancer patients, and are associated with advanced grade and stage disease and poor prognosis. In this review, we will investigate PI3K/AKT/mTOR and their interconnection with NFκB pathway in ovarian cancer cells.

Icariside II, a natural mTOR inhibitor, disrupts aberrant energy homeostasis via suppressing mTORC1-4E-BP1 axis in sarcoma cells

The aberrant energy homeostasis that characterized by high rate of energy production (glycolysis) and energy consumption (mRNA translation) is associated with the development of cancer. As mammalian target of rapamycin (mTOR) is a critical regulator of aberrant energy homeostasis, it is an attractive target for anti-tumor intervention. The flavonoid compound Icariside II (IS) is a natural mTOR inhibitor derived from Epimedium. Koreanum. Herein, we evaluate the effect of IS on aberrant energy homeostasis. The reduction of glycolysis and mRNA translation in U2OS (osteosarcoma), S180 (fibrosarcoma) and SW1535 (chondrosarcoma) cells observed in our study, indicate that, IS inhibits aberrant energy homeostasis. This inhibition is found to be due to suppression of mammalian target of rapamycin complex 1 (mTORC1)-eukaryotic translation initiation factor 4E-binding protein 1 (4E-BP1) axis through blocking the assembly of mTORC1. Furthermore, IS inhibits the cap-dependent translation of c-myc through mTORC1-4E-BP1 axis which links the relationship between mRNA translation and glycolysis. Inhibition of aberrant energy homeostasis by IS, contributes to its in vitro and in vivo anti-proliferation activity. These data indicate that IS disrupts aberrant energy homeostasis of sarcoma cells through suppression of mTORC1-4E-BP1 axis, providing a novel mechanism of IS to inhibit cell proliferation in sarcoma cells.

MenTORing Immunity: mTOR Signaling in the Development and Function of Tissue-Resident Immune Cells

Tissue-resident immune cells must balance survival in peripheral tissues with the capacity to respond rapidly upon infection or tissue damage, and in turn couple these responses with intrinsic metabolic control and conditions in the tissue microenvironment. The serine/threonine kinase mammalian/mechanistic target of rapamycin (mTOR) is a central integrator of extracellular and intracellular growth signals and cellular metabolism and plays important roles in both innate and adaptive immune responses. This review discusses the function of mTOR signaling in the differentiation and function of tissue-resident immune cells, with focus on the role of mTOR as a metabolic sensor and its impact on metabolic regulation in innate and adaptive immune cells. We also discuss the impact of metabolic constraints in tissues on immune homeostasis and disease, and how manipulating mTOR activity with drugs such as rapamycin can modulate immunity in these contexts.

Increased phosphorylation of 4E‑binding protein 1 predicts poor prognosis for patients with colorectal cancer

As demonstrated in previous studies, the phosphorylated form of 4E‑binding protein 1 (p‑4E‑BP1) may be a suitable tumor biomarker. The aim of the current study was to examine the expression status of p‑4E‑BP1 in colorectal cancer (CRC), in order to determine its clinical significance. The present study enrolled 89 patients with CRC that had undergone radical resection. Paired tumor and adjacent normal tissues were evaluated using immunohistochemistry to detect the protein expression of p‑4E‑BP1 and phosphatase and tensin homolog (PTEN). The study identified 53 cases (59.6%) that exhibited moderate or high expression of p‑4E‑BP1 in tumor tissues, compared with little or no expression in the adjacent normal tissues. Conversely, PTEN protein expression was markedly lower in CRC compared with adjacent normal tissues. p‑4E‑BP1 protein upregulation tissues samples was consistent with PTEN downregulation in CRC samples. p‑4E‑BP1 overexpression was predominant in patients with metastasis to the regional lymph nodes. Moderate/high expression of p‑4E‑BP1 protein was significantly associated with adverse overall survival (OS) in patients. Statistical analysis using the Cox proportional hazards model, indicated that p‑4E‑BP1 expression was an independent factor suitable for predicting OS in CRC patients, which was independent of lymph node metastasis. In conclusion, p‑4E‑BP1 protein expression appears to be upregulated in CRC, suggesting that it may be a suitable biomarker for predicting CRC prognosis.

Targeting of PI3K/AKT/mTOR pathway to inhibit T cell activation and prevent graft-versus-host disease development

BACKGROUND

Graft-versus-host disease (GvHD) remains the major obstacle to successful allogeneic hematopoietic stem cell transplantation, despite of the immunosuppressive regimens administered to control T cell alloreactivity. PI3K/AKT/mTOR pathway is crucial in T cell activation and function and, therefore, represents an attractive therapeutic target to prevent GvHD development. Recently, numerous PI3K inhibitors have been developed for cancer therapy. However, few studies have explored their immunosuppressive effect.

METHODS

The effects of a selective PI3K inhibitor (BKM120) and a dual PI3K/mTOR inhibitor (BEZ235) on human T cell proliferation, expression of activation-related molecules, and phosphorylation of PI3K/AKT/mTOR pathway proteins were analyzed. Besides, the ability of BEZ235 to prevent GvHD development in mice was evaluated.

RESULTS

Simultaneous inhibition of PI3K and mTOR was efficient at lower concentrations than PI3K specific targeting. Importantly, BEZ235 prevented naïve T cell activation and induced tolerance of alloreactive T cells, while maintaining an adequate response against cytomegalovirus, more efficiently than BKM120. Finally, BEZ235 treatment significantly improved the survival and decreased the GvHD development in mice.

CONCLUSIONS

These results support the use of PI3K inhibitors to control T cell responses and show the potential utility of the dual PI3K/mTOR inhibitor BEZ235 in GvHD prophylaxis.

Inhibition of mTORC1 signaling sensitizes hepatocellular carcinoma cells to glycolytic stress

Reprogrammed glucose metabolism, especially glycolysis, is profoundly implicated in tumor development or metastasis. As the interconnectedness and flexibility of metabolic signaling, targeting a metabolic signaling molecule may have limited anti-tumor effects. Here, Gene set enrichment analysis (GSEA) was used to explore the accompanied effectors of glycolysis in hepatocellular carcinoma (HCC). Based on the expression of lactate dehydrogenase A (LDHA), a key enzyme in catalyzing pyruvate into lactate, the glycolytic ability of HCC was defined as low group and high group. GSEA of two independent GEO datasets showed that mTORC1 signaling was the most striking metabolic alternations in high group. Pharmacological inhibition of mTORC1 signaling with rapamycin decreased LDHA level and glycolytic capacity of six HCC cell lines. Furthermore, c-Myc was identified as a downstream target of mTORC1 signaling and mediated mTORC1-induced LDHA expression. Importantly, rapamycin sensitized HCC cells to the glycolysis inhibitor 2-deoxyglucose (2-DG) in vitro and in vivo. Meanwhile, genetic silencing several other downstream targets of mTORC1 signaling (TFEB, SREBP-1 and SKAR) failed to enhance or faintly influenced the cytotoxic effects of 2-DG. These results demonstrate that combining rapamycin with 2-DG holds significant promise as prospective clinical treatment in HCC.

PC-1/PrLZ confers resistance to rapamycin in prostate cancer cells through increased 4E-BP1 stability

An important strategy for improving advanced PCa treatment is targeted therapies combined with chemotherapy. PC-1, a prostate Leucine Zipper gene (PrLZ), is specifically expressed in prostate tissue as an androgen-induced gene and is up-regulated in advanced PCa. Recent work confirmed that PC-1 expression promotes PCa growth and androgen-independent progression. However, how this occurs and whether this can be used as a biomarker is uncertain. Here, we report that PC-1 overexpression confers PCa cells resistance to rapamycin treatment by antagonizing rapamycin-induced cytostasis and autophagy (rapamycin-sensitivity was observed in PC-1-deficient (shPC-1) C4-2 cells). Analysis of the mTOR pathway in PCa cells with PC-1 overexpressed and depressed revealed that eukaryotic initiation factor 4E-binding protein 1(4E-BP1) was highly regulated by PC-1. Immunohistochemistry assays indicated that 4E-BP1 up-regulation correlates with increased PC-1 expression in human prostate tumors and in PCa cells. Furthermore, PC-1 interacts directly with 4E-BP1 and stabilizes 4E-BP1 protein via inhibition of its ubiquitination and proteasomal degradation. Thus, PC-1 is a novel regulator of 4E-BP1 and our work suggests a potential mechanism through which PC-1 enhances PCa cell survival and malignant progression and increases chemoresistance. Thus, the PC-1-4E-BP1 interaction may represent a therapeutic target for treating advanced PCa.

Modelling and analysis of an ensemble of eukaryotic translation initiation models

Programmed protein synthesis plays an important role in the cell cycle. Deregulated translation has been observed in several cancers. In this study, the authors constructed an ensemble of mathematical models describing the integration of growth factor signals with translation initiation. Using these models, the authors estimated critical structural features of the translation architecture. Sensitivity and robustness analysis with and without growth factors suggested that a balance between competing regulatory programmes governed translation initiation. Proteins such as Akt and mTor promoted initiation by integrating growth factor signals with the assembly of the 80S initiation complex. However, negative regulators such as PTEN and 4EBP1 restrained initiation in the absence of stimulation. Other proteins such as eIF4E were also found to be structurally critical as deletion of amplification of these components resulted in a network incapable of nominal operation. These findings could help understand the molecular basis of translation deregulation observed in cancer and perhaps lead to new anti-cancer therapeutic strategies. [Includes supplementary material].

Effect of mTORC1/mTORC2 inhibition on T cell function: potential role in graft-versus-host disease control

The mechanistic target of rapamycin (mTOR) pathway is crucial for the activation and function of T cells, which play an essential role in the development of graft-versus-host disease (GvHD). Despite its partial ability to block mTOR pathway, the mTORC1 inhibitor rapamycin has shown encouraging results in the control of GvHD. Therefore, we considered that simultaneous targeting of both mTORC1 and mTORC2 complexes could exert a more potent inhibition of T cell activation and, thus, could have utility in GvHD control. To assess this assumption, we have used the dual mTORC1/mTORC2 inhibitors CC214-1 and CC214-2. In vitro studies confirmed the superior ability of CC214-1 versus rapamycin to block mTORC1 and mTORC2 activity and to reduce T cell proliferation. Both drugs induced a similar decrease in Th1/Th2 cytokine secretion, but CC214-1 was more efficient in inhibiting naïve T cell activation and the expression of T-cell activation markers. In addition, CC214-1 induced specific tolerance against alloantigens, while preserving anti-cytomegalovirus response. Finally, in a mouse model of GvHD, the administration of CC214-2 significantly improved mice survival and decreased GvHD-induced damages. In conclusion, the current study shows, for the first time, the immunosuppressive ability of CC214-1 on T lymphocytes and illustrates the role of CC214-2 in the allogeneic transplantation setting as a possible GvHD prophylaxis agent.

Overexpression of phosphorylated 4E-binding protein 1 predicts lymph node metastasis and poor prognosis of Chinese patients with hilar cholangiocarcinoma

Previous studies have confirmed the role of phosphorylated form of 4E-binding protein 1 (p-4E-BP1) as a good candidate tumor biomarker. The aim of this study was to investigate p-4E-BP1 expression status in hilar cholangiocarcinoma (HCCA) specimens and to clarify its clinical significance. Tissue microarray containing tumor specimens obtained from 61 patients with HCCA were constructed. p-4E-BP1 was investigated by immunohistochemical studies. High/moderate expression p-4E-BP1 was observed in 57.4% (35/61) primary cancer specimens. Overexpression of p-4E-BP1 protein was associated with poor differentiation and regional lymph node metastasis. Survival analysis and Cox proportional hazards model revealed that p-4E-BP1 overexpression was an independent factor in predicting recurrence-free survival and overall survival for HCCA patients, apart from tumor invasion and complete resection. P-4E-BP1 was highly expressed in HCCA. Overexpressed p-4E-BP1 might be a novel biomarker to predict the clinical outcome of patients with resected HCCA.

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.

4-Hydroxytamoxifen induces autophagic death through K-Ras degradation

Tamoxifen is widely used to treat estrogen receptor-positive breast cancer. Recent findings that tamoxifen and its derivative 4-hydroxytamoxifen (OHT) can exert estrogen receptor-independent cytotoxic effects have prompted the initiation of clinical trials to evaluate its use in estrogen receptor-negative malignancies. For example, tamoxifen and OHT exert cytotoxic effects in malignant peripheral nerve sheath tumors (MPNST) where estrogen is not involved. In this study, we gained insights into the estrogen receptor-independent cytotoxic effects of OHT by studying how it kills MPNST cells. Although caspases were activated following OHT treatment, caspase inhibition provided no protection from OHT-induced death. Rather, OHT-induced death in MPNST cells was associated with autophagic induction and attenuated by genetic inhibition of autophagic vacuole formation. Mechanistic investigations revealed that OHT stimulated autophagic degradation of K-Ras, which is critical for survival of MPNST cells. Similarly, we found that OHT induced K-Ras degradation in breast, colon, glioma, and pancreatic cancer cells. Our findings describe a novel mechanism of autophagic death triggered by OHT in tumor cells that may be more broadly useful clinically in cancer treatment.

Gingipain-dependent degradation of mammalian target of rapamycin pathway proteins by the periodontal pathogen Porphyromonas gingivalis during invasion

Porphyromonas gingivalis and Tannerella forsythia are gram-negative pathogens strongly associated with periodontitis. Their abilities to interact, invade and persist within host cells are considered crucial to their pathogenicity, but the mechanisms by which they subvert host defences are not well understood. In this study, we set out to investigate whether P. gingivalis and T. forsythia directly target key signalling molecules that may modulate the host cell phenotype to favour invasion and persistence. Our data identify, for the first time, that P. gingivalis, but not T. forsythia, reduces levels of intracellular mammalian target of rapamycin (mTOR) in oral epithelial cells following invasion over a 4-h time course, via the action of gingipains. The ability of cytochalasin D to abrogate P. gingivalis-mediated mTOR degradation suggests that this effect is dependent upon cellular invasion. We also show that levels of several other proteins in the mTOR signalling pathway are modulated by gingipains, either directly or as a consequence of mTOR degradation including p-4E-BP1. Taken together, our data suggest that P. gingivalis manipulates the mTOR pathway, providing evidence for a potentially novel mechanism by which P. gingivalis mediates its effects on host cell responses to infection.

Genome-wide identification of cancer-related polyadenylated and non-polyadenylated RNAs in human breast and lung cell lines

Eukaryotic mRNAs consist of two forms of transcripts: poly(A)+ and poly(A)-, based on the presence or absence of poly(A) tails at the 3' end. Poly(A)+ mRNAs are mainly protein coding mRNAs, whereas the functions of poly(A)- mRNA are largely unknown. Previous studies have shown that a significant proportion of gene transcripts are poly(A)- or bimorphic (containing both poly(A)+ and poly(A)- transcripts). We compared the expression levels of poly(A)- and poly(A)+ RNA mRNAs in normal and cancer cell lines. We also investigated the potential functions of these RNA transcripts using an integrative workflow to explore poly(A)+ and poly(A)- transcriptome sequences between a normal human mammary gland cell line (HMEC) and a breast cancer cell line (MCF-7), as well as between a normal human lung cell line (NHLF) and a lung cancer cell line (A549). The data showed that normal and cancer cell lines differentially express these two forms of mRNA. Gene ontology (GO) annotation analyses hinted at the functions of these two groups of transcripts and grouped the differentially expressed genes according to the form of their transcript. The data showed that cell cycle-, apoptosis-, and cell death-related functions corresponded to most of the differentially expressed genes in these two forms of transcripts, which were also associated with the cancers. Furthermore, translational elongation and translation functions were also found for the poly(A)- protein-coding genes in cancer cell lines. We demonstrate that poly(A)- transcripts play an important role in cancer development.

4E-BP1 participates in maintaining spindle integrity and genomic stability via interacting with PLK1

The essential function of eIF4E-binding protein 1 (4E-BP1) in translation initiation has been well established; however, the role of 4E-BP1 in normal cell cycle progression is coming to attention. Here, we revealed the role of 4E-BP1 on mitotic regulation and chromosomal DNA dynamics during mitosis. First, we have observed the co-localization of the phosphorylated 4E-BP1 at T37/46 with Polo-like kinase 1 (PLK1) at the centrosomes during. Depression of 4E-BP1 by small interfering RNA in HepG2 or HeLa cells resulted in an increased outcome of polyploidy and aberrant mitosis, including chromosomal DNA misaligned and multi-polar spindles or multiple centrosomes. We observed that 4E-BP1 interacted with PLK1 directly in vitro and in vivo in mitotic cells, and the C-terminal aa 77-118 of 4E-BP1 mediates its interaction with PLK1. PLK1 can phosphorylate 4E-BP1 in vitro. Furthermore, the depletion of 4E-BP1 sensitized HepG2 and HeLa cells to the microtubule disruption agent paclitaxel. These results demonstrate that 4E-BP1, beyond its role in translation regulation, can function as a regulator of mitosis via interacting with PLK1, and possibly plays a role in genomic stability maintaining.

Cap-dependent translation initiation factor eIF4E: an emerging anticancer drug target

Cancer cells tend to be more highly dependent on cap‐dependent translation than normal tissues. Thus, proteins involved in the initiation of cap‐dependent translation have emerged as potential anti‐cancer drug targets. Cap‐dependent translation is initiated by the binding of the factor eIF4E to the cap domain of mRNA. Detailed x‐ray crystal and NMR structures are available for eIF4E in association with cap‐analogs, as well as domains of other initiation factors. This review will summarize efforts to design potential antagonist of eIF4E that could be used as new pharmacological tools and anti‐cancer agents and. Insights drawn from these studies should aid in the design of future inhibitors of eIF4E dependent translation initiation. © 2012 Wiley Periodicals, Inc. Med Res Rev., 32, No. 4, 786‐814, 2012

eIF4F complex disruption causes protein synthesis inhibition during hypoxia in nerve growth factor (NGF)-differentiated PC12 cells

Poor oxygenation (hypoxia) influences important physiological and pathological situations, including development, ischemia, stroke and cancer. Hypoxia induces protein synthesis inhibition that is primarily regulated at the level of initiation step. This regulation generally takes place at two stages, the phosphorylation of the subunit α of the eukaryotic initiation factor (eIF) 2 and the inhibition of the eIF4F complex availability by dephosphorylation of the inhibitory protein 4E-BP1 (eukaryotic initiation factor 4E-binding protein 1). The contribution of each of them is mainly dependent of the extent of the oxygen deprivation. We have evaluated the regulation of hypoxia-induced translation inhibition in nerve growth factor (NGF)-differentiated PC12 cells subjected to a low oxygen concentration (0.1%) at several times. Our findings indicate that protein synthesis inhibition occurs primarily by the disruption of eIF4F complex through 4E-BP1 dephosphorylation, which is produced by the inhibition of the mammalian target of rapamycin (mTOR) activity via the activation of REDD1 (regulated in development and DNA damage 1) protein in a hypoxia-inducible factor 1 (HIF1)-dependent manner, as well as the translocation of eIF4E to the nucleus. In addition, this mechanism is reinforced by the increase in 4E-BP1 levels, mainly at prolonged times of hypoxia.

CA125 (MUC16) gene silencing suppresses growth properties of ovarian and breast cancer cells

The tumour-associated antigen CA125 (mucin 16, MUC16) is commonly expressed in ovarian cancer, and can also be detected in other tumour of epithelial origin, but its physiological role is largely unknown. The aim of the present study was to investigate the impact of MUC16 gene silencing on the growth properties of ovarian and breast cancer cells. We analysed cellular effects linked to oncogenesis, such as proliferation, cell cycle and apoptosis, after transient and stable transfection with MUC16 short hairpin RNA (shRNA) in diverse epithelial cancer cell lines with different MUC16 expression. Furthermore, alterations in cell adhesion, migration and invasion were evaluated in stable MUC16 knockdown clones. The growth of all tested MUC16(+) tumour cells was significantly suppressed by induction of caspase-dependent apoptosis after transient transfection with MUC16 shRNA, irrespective of the initial MUC16 expression level and cancer origin. Growth inhibition could be confirmed in stable MUC16 knockdown clones, albeit caspase-dependent death pathways seemed no longer be activated. In MUC16(low+) ovarian cancer cells, stable MUC16 gene silencing resulted in a substantial blockade of colony formation, cell adhesion, migration and invasiveness associated with reduced activation of metalloproteinases-2 (MMP-2). By contrast, the tested MUC16(high+) cell lines displayed a non-motile and non-invasive phenotype which was not affected by MUC16 knockdown, probably due to the expression of different MUC16 isoforms with divergent functions in individual cell lines. Our results provide evidence for a central role of MUC16 in cancer cell survival pathways. Additionally, MUC16 might also be involved in adhesion, migration and invasion depending on the type of cancer cell.

RNA aptamers to translational components

Potential applications for functional RNAs are rapidly expanding, not only to address functions based on primary nucleotide sequences, but also by RNA aptamers, which can suppress the activity of any target molecule. Aptamers are short DNA or RNA folded molecules that can be selected in vitro on the basis of their high affinity for a target molecule. Here, we summarize RNA aptamers selected against human translation initiation factors, and their superior potentials to recognize and inhibit their target proteins. Importantly, the high affinity of RNA aptamers to proteins without RNA recognition motifs or intrinsic, strong affinity to RNA is achieved through the capture of the protein's global conformation. In other words, RNA has a high potential to form a vast set of tertiary structures, which we would like to refer to as 'RNA plasticity'. This provides us with a solid and promising basis to take steps to create novel RNA molecules of therapeutic potential with distinct structures, which should be equivalent or superior to antibodies.

Inhibiting the hypoxia response for cancer therapy: the new kid on the block

The hypoxia-inducible transcription factor (HIF)-1alpha inhibitor KC7F2 described in this issue of Clinical Cancer Research is the newest addition to an emerging class of antitumor agents targeting the hypoxia response. Here, we discuss the proposed mechanism of action of KC7F2 and its potential strengths and limitations in comparison with other promising HIF-1alpha inhibitors.