Phosphorylated 4E-BP1 is associated with poor survival in melanoma

CT-Scan-Assessed Body Composition and Its Association with Tumor Protein Expression in Endometrial Cancer: The Role of Muscle and Adiposity Quantities

Background: Endometrial cancer is strongly associated with obesity, and tumors often harbor mutations in major cancer signaling pathways. To inform the integration of body composition into targeted therapy paradigms, this hypothesis-generating study explores the association between muscle mass, body fat, and tumor proteomics. Methods: We analyzed data from 113 patients in The Cancer Genome Atlas (TCGA) and Cancer Proteomic Tumor Analysis Consortium (CPTAC) cohorts and their corresponding abdominal CT scans. Among these patients, tumor proteomics data were available for 45 patients, and 133 proteins were analyzed. Adiposity and muscle components were assessed at the L3 vertebral level on the CT scans. Patients were stratified into tertiles of muscle and fat mass and categorized into three groups: high muscle/low adiposity, high muscle/high adiposity, and low muscle/all adiposities. Linear and Cox regression models were adjusted for study cohort, stage, histology type, age, race, and ethnicity. Results: Compared with the high-muscle/low-adiposity group, both the high-muscle/high-adiposity (HR = 4.3, 95% CI = 1.0-29.0) and low-muscle (HR = 4.4, 95% CI = 1.3-14.9) groups experienced higher mortality. Low muscle was associated with higher expression of phospho-4EBP1(T37 and S65), phospho-GYS(S641) and phospho-MAPK(T202/Y204) but lower expression of ARID1A, CHK2, SYK, LCK, EEF2, CYCLIN B1, and FOXO3A. High muscle/high adiposity was associated with higher expression of phospho-4EBP1 (T37), phospho-GYS (S641), CHK1, PEA15, SMAD3, BAX, DJ1, GYS, PKM2, COMPLEX II Subunit 30, and phospho-P70S6K (T389) but with lower expression of CHK2, CRAF, MSH6, TUBERIN, PR, ERK2, beta-CATENIN, AKT, and S6. Conclusions: These findings demonstrate an association between body composition and proteins involved in key cancer signaling pathways, notably the PI3K/AKT/MTOR, MAPK/ERK, cell cycle regulation, DNA damage response, and mismatch repair pathways. These findings warrant further validation and assessment in relation to prognosis and outcomes in these patients.

Second-Generation Cap Analogue Prodrugs for Targeting Aberrant Eukaryotic Translation Initiation Factor 4E (eIF4E) Activity in Drug-Resistant Melanoma

Melanoma is the deadliest form of skin cancer with a 5-year survival rate of less than 20%. While significant strides have been made in the field of kinase-targeted and immune-based therapies for melanoma, the development of resistance to these therapeutic agents has hindered the success of treatment. Drug-resistant melanoma is particularly reliant on enhanced cap-dependent translation to drive the production of oncoproteins that promote growth and survival. The m7GpppX cap-binding protein eukaryotic translation initiation factor 4E (eIF4E) is the rate-limiting factor of cap-dependent translation initiation, and its overexpression in melanoma tumors has been shown to drive resistance to BRAFV600E kinase-targeted inhibitors. These findings point to eIF4E-targeted therapies as a promising strategy to overcome drug resistance in melanoma. Herein, we build upon our previous work of developing cell-permeable cap analogue inhibitors to design second-generation cap analogues that inhibit eIF4E-mediated cap-dependent translation in drug-resistant melanoma cells.

A Multi-Omics Pan-Cancer Analysis of 4EBP1 in Cancer Prognosis and Cancer-Associated Fibroblasts Infiltration

Background: Eukaryotic Translation Initiation Factor 4E Binding Protein 1 (4EBP1) involved in inhibition of protein translation and synthesis. However, the phosphoprotein of 4EBP1 (p-4EBP1) promotes the translation and synthesis of several proteins, including multiple classic oncogenic proteins. The prognostic significance of 4EBP1 mRNA, 4EBP1 protein, and p-4EBP1 in Pan-cancer are still unclear.

Methods: In this study, we provided a multi-Omics investigation for the prognostic value of 4EBP1 mRNA, 4EBP1 protein, and different 4EBP1 phosphoproteins in a Pan-cancer manner based on the TCGA projects. We explored the correlation between 4EBP1 expression and the cancer-associated fibroblast (CAFs) infiltration, respectively using the EPIC, MCPCOUNTER, and TIDE algorithms. The functional states of 4EBP1 were explored using single-cell sequencing analysis in Pan-Cancer. Immunohistochemistry staining was used to detect and verify the expression of 4EBP1 in several cancers.

Results: 4EBP1 mRNA was aberrantly overexpressed in most cancers, and was associated with the poor prognosis in ten cancers. Notably, increased 4EBP1 mRNA expression significantly correlated with tumor staging and worse prognosis in BRCA, KIRC, and KIRP, while having the opposite effect in STAD. 4EBP1 expression was associated with the CAFs infiltration level in ten cancer types. Interestingly, the correlation between 4EBP1 and CAFs infiltration had pronounced heterogeneity in digestive system tumors and urinary system tumors. In BLCA, KIRC, and ACC as well as BRCA, 4EBP1 was significantly positively correlated with CAFs infiltration and was associated with a poor prognosis. In STAD and COAD, 4EBP1 is negatively correlated with CAFs infiltration and was associated with a better prognosis. Lastly, the expression and prognostic significance of 4EBP1 protein and different p-4EBP1 varied enormously among cancers.

Conclusion: Our multi-omics study indicates that 4EBP1-driven CAFs infiltration is associated with cancer prognosis and 4EBP1 mRNA, 4EBP1 protein, and p-4EBP1 proteins may serve as potential prognostic biomarkers and therapeutic targets in diverse cancer.

Signal pathways of melanoma and targeted therapy

Melanoma is the most lethal skin cancer that originates from the malignant transformation of melanocytes. Although melanoma has long been regarded as a cancerous malignancy with few therapeutic options, increased biological understanding and unprecedented innovations in therapies targeting mutated driver genes and immune checkpoints have substantially improved the prognosis of patients. However, the low response rate and inevitable occurrence of resistance to currently available targeted therapies have posed the obstacle in the path of melanoma management to obtain further amelioration. Therefore, it is necessary to understand the mechanisms underlying melanoma pathogenesis more comprehensively, which might lead to more substantial progress in therapeutic approaches and expand clinical options for melanoma therapy. In this review, we firstly make a brief introduction to melanoma epidemiology, clinical subtypes, risk factors, and current therapies. Then, the signal pathways orchestrating melanoma pathogenesis, including genetic mutations, key transcriptional regulators, epigenetic dysregulations, metabolic reprogramming, crucial metastasis-related signals, tumor-promoting inflammatory pathways, and pro-angiogenic factors, have been systemically reviewed and discussed. Subsequently, we outline current progresses in therapies targeting mutated driver genes and immune checkpoints, as well as the mechanisms underlying the treatment resistance. Finally, the prospects and challenges in the development of melanoma therapy, especially immunotherapy and related ongoing clinical trials, are summarized and discussed.

Multifaceted control of mRNA translation machinery in cancer

The mRNA translation machinery is tightly regulated through several, at times overlapping, mechanisms that modulate its efficiency and accuracy. Due to their fast rate of growth and metabolism, cancer cells require an excessive amount of mRNA translation and protein synthesis. However, unfavorable conditions, such as hypoxia, amino acid starvation, and oxidative stress, which are abundant in cancer, as well as many anti-cancer treatments inhibit mRNA translation. Cancer cells adapt to the various internal and environmental stresses by employing specialised transcript-specific translation to survive and gain a proliferative advantage. We will highlight the major signaling pathways and mechanisms of translation that regulate the global or mRNA-specific translation in response to the intra- or extra-cellular signals and stresses that are key components in the process of tumourigenesis.

Simultaneous activation of impaired autophagy and the mammalian target of rapamycin pathway in oral squamous cell carcinoma

BACKGROUND

The aim of this study was to conduct a comparative evaluation of the expression levels of autophagy markers and proteins of the mammalian target of rapamycin (mTOR) pathway in normal, margin and tumour tissues of patients with oral squamous cell carcinoma (OSCC).

MATERIALS AND METHODS

Three regional specimens, including normal, margin and tumour tissues, were collected from 26 patients with OSCC. Western blotting, immunohistochemistry and immunofluorescence staining were performed to detect mTOR, eukaryotic translation initiation factor 4E-binding protein 1 (4E-BP1), p70 ribosomal S6 protein kinase (p70S6K) and the corresponding phosphorylated proteins, as well as the light chain 3 (LC3) and sequestosome-1 (SQSTM1, also known as p62) autophagy indicators.

RESULTS

LC3-II, p62, mTOR, phospho-mTOR, 4E-BP1 and phospho-4E-BP1 were highly expressed in the margin and tumour groups. There were positive correlations between mTOR/phospho-mTOR, mTOR/4E-BP1, mTOR/phospho-4E-BP1, mTOR/p70S6K, LC3-II/p62, LC3-II/p70S6K, p62/4E-BP1 and p62/phospho-4E-BP1 in normal group, while LC3-II/p62, LC3-II/mTOR, LC3-II/4E-BP1, LC3-II/phospho-4E-BP1, phospho-4E-BP1/mTOR, phospho-4E-BP1/4E-BP1 and p62/4E-BP1 showed positive relationships in margin group; however, in tumour group, only mTOR/phospho-mTOR, 4E-BP1/phospho-4E-BP1 and phospho-mTOR/p70S6K showed positive correlations.

CONCLUSION

The study suggests that autophagy is impaired in patients with OSCC and impaired autophagy and the mTOR pathway are simultaneously activated in OSCC cells.

Chemoproteomic Profiling Uncovers CDK4-Mediated Phosphorylation of the Translational Suppressor 4E-BP1

Recent estimates of the human proteome suggest there are ∼20,000 protein-coding genes, the protein products of which contain >145,000 phosphosites. Unfortunately, in-depth examination of the human phosphoproteome has outpaced the ability to annotate the kinases that mediate these post-translational modifications. To obtain actionable information about phosphorylation-driven signaling cascades, it is essential to identify the kinases responsible for phosphorylating sites that differ across disease states. To fill in these gaps we have developed an unbiased, chemoproteomic approach for identifying high-confidence kinase-substrate interactions with phosphosite specificity. Using this assay, we uncovered the role of cyclin-dependent kinase 4 (CDK4), a clinically validated kinase important for cell-cycle progression, in regulating cap-dependent translation via phosphorylation of the tumor suppressor 4E-BP1. The discovery of this signaling axis sheds light on the mechanisms by which CDK4/6 inhibitors control cell proliferation and constitutes a successful example of kinase discovery using an activity-based, kinase-directed probe.

Utilization of Proteomic Technologies for Precision Oncology Applications

Genomic analysis of tumor specimens has revealed that cancer is fundamentally a proteomic disease at the functional level: driven by genomically defined derangements, but selected for in the proteins that are encoded and the aberrant activation of signaling and biochemical networks. This activation is measured by posttranslational modifications such as phosphorylation and other modifications that modulate cellular signaling, and these events cannot be effectively measured by genomic analysis alone. Moreover, these signaling networks by and large represent the targets for many FDA-approved and experimental molecularly targeted therapeutics. Consequently, it is important that we consider new classification schemas for oncology based not on tumor site of origin or histology under the microscope but on the functional protein signaling architecture. There are numerous proteomic technologies that could be discussed from a purely technological standpoint, but this chapter will concentrate on an overview of the main proteomic technologies available for conducting protein pathway activation analysis of clinical specimens such as multiplex immunoassays, phospho-specific flow cytometry, reverse phase protein microarrays, quantitative immunohistochemistry, and mass spectrometry. This chapter will focus on the application of these technologies to cancer-based clinical studies evaluating prognostic/predictive markers or for stratifying patients to personalized treatments.

Translation regulation in skin cancer from a tRNA point of view

Protein synthesis is a central and dynamic process, frequently deregulated in cancer through aberrant activation or expression of translation initiation factors and tRNAs. The discovery of tRNA-derived fragments, a new class of abundant and, in some cases stress-induced, small Noncoding RNAs has perplexed the epigenomics landscape and highlights the emerging regulatory role of tRNAs in translation and beyond. Skin is the biggest organ in human body, which maintains homeostasis of its multilayers through regulatory networks that induce translational reprogramming, and modulate tRNA transcription, modification and fragmentation, in response to various stress signals, like UV irradiation. In this review, we summarize recent knowledge on the role of translation regulation and tRNA biology in the alarming prevalence of skin cancer.

Potential role of cyclin F mRNA expression in the survival of skin melanoma patients: Comprehensive analysis of the pathways altered due to cyclin F upregulation

Cyclin F is a part of the Skp, Cullin, F-box containing ligase complex. The activity of cyclin F includes cell cycle control, centrosome duplication and response to DNA damage. The cyclin F expression pattern is very similar to cyclin A, but cyclin F is an orphan cyclin without its cyclin-dependent kinase partner. There is little evidence concerning the role of cyclin F in cancer. In the present study, for the first time, we present analysis from The Cancer Genome Atlas (TCGA) data in the context of expression of cyclin F mRNA in melanoma patients. Our original in silico analysis, not published elsewhere before, revealed that high expression of cyclin F in melanoma patients is associated with worse overall survival. Cyclin F and ribonucleotide reductase family member 2 (RRM2) compose a functional axis responsible for nucleotide metabolism. Impairment in this pathway may contribute to increased DNA damage repair and drug resistance. Additionally, we analyzed the expression of RRM2 mRNA and discovered that high expression of RRM2 is associated with worse overall survival. To shed more light on cyclin F overexpression in melanoma, we analyzed all protein data available in the TCGA melanoma dataset. It was found that in patients with upregulated cyclin F mRNA, we noted increased activity of pathways related to cell cycle and DNA damage repair. These data will support further in vitro and in vivo studies on the involvement of cyclin F in skin cutaneous melanoma.

Recombinant human erythropoietin stimulates melanoma tumor growth through activation of initiation factor eIF4E

Recombinant human erythropoietin (EPO) is standard treatment for anemia in cancer patients. Recent clinical trials suggest that EPO may accelerate tumor progression and increase mortality. However, the evidence supporting a growth-promoting effect of EPO has remained controversial. Employing an in vivo model of B16 murine melanoma, we observed that administration of EPO to tumor bearing C57BL/6 mice resulted in pronounced acceleration of melanoma growth. Our in vitro studies demonstrate that B16 murine melanoma cells express EPOR, both at the protein and mRNA levels. Interestingly, expression of EPOR was retained in the established tumors. EPO stimulation of B16 cells enhanced proliferation and protein synthesis rates, and correlated with activation of the receptor associated Janus kinase 2 (Jak2) as well as phosphorylation of extracellular signal–regulated kinase (Erk) 1/2 and Akt kinases. Treatment with EPO and Jak-2 antagonists significantly inhibited EPO-mediated B16 cell proliferation. Moreover, EPO dose-dependently induced the phosphorylation and activation of the translation initiation factor eIF4E as well as the phosphorylation of its repressor, the eIF4E binding protein 4E-BP1. Finally, using eIF4E small interfering RNA (siRNA), we observed that EPO-mediated stimulation of B16 cell proliferation is eIF4E-dependent. Our results indicate that EPO exerts a powerful stimulatory effect on cell proliferation and de novo protein synthesis in melanoma cells through activation of the initiation factor eIF4E.

Beyond molecular tumor heterogeneity: protein synthesis takes control

One of the daunting challenges facing modern medicine lies in the understanding and treatment of tumor heterogeneity. Most tumors show intra-tumor heterogeneity at both genomic and proteomic levels, with marked impacts on the responses of therapeutic targets. Therapeutic target-related gene expression pathways are affected by hypoxia and cellular stress. However, the finding that targets such as eukaryotic initiation factor (eIF) 4E (and its phosphorylated form, p-eIF4E) are generally homogenously expressed throughout tumors, regardless of the presence of hypoxia or other cellular stress conditions, opens the exciting possibility that malignancies could be treated with therapies that combine targeting of eIF4E phosphorylation with immune checkpoint inhibitors or chemotherapy.

Implication of 4E-BP1 protein dephosphorylation and accumulation in pancreatic cancer cell death induced by combined gemcitabine and TRAIL

Pancreatic cancer cells show varying sensitivity to the anticancer effects of gemcitabine. However, as a chemotherapeutic agent, gemcitabine can cause intolerably high levels of toxicity and patients often develop resistance to the beneficial effects of this drug. Combination studies show that use of gemcitabine with the pro-apoptotic cytokine TRAIL can enhance the inhibition of survival and induction of apoptosis of pancreatic cancer cells. Additionally, following combination treatment there is a dramatic increase in the level of the hypophosphorylated form of the tumour suppressor protein 4E-BP1. This is associated with inhibition of mTOR activity, resulting from caspase-mediated cleavage of the Raptor and Rictor components of mTOR. Use of the pan-caspase inhibitor Z-VAD-FMK indicates that the increase in level of 4E-BP1 is also caspase-mediated. ShRNA-silencing of 4E-BP1 expression renders cells more resistant to cell death induced by the combination treatment. Since the levels of 4E-BP1 are relatively low in untreated pancreatic cancer cells these results suggest that combined therapy with gemcitabine and TRAIL could improve the responsiveness of tumours to treatment by elevating the expression of 4E-BP1.

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.

Phosphorylated 4EBP1 is associated with tumor progression and poor prognosis in Xp11.2 translocation renal cell carcinoma

Two main signaling pathways, PI3K-AKT-mTOR and RAS-MAPK, are involved in transmitting the proliferative signals which play critical roles in human cancers. However, the functions of these pathways in Xp11.2 RCC remain undefined. This study aimed to explore the expression of mTOR and MAPK cascades in Xp11.2 RCC and to assess the prognostic significance of proteins evaluated. Immunohistochemistry was performed to evaluate the expression of 4EBP1, p-4EBP1, p-mTOR, p-S6K and p-MAPK in 36 adult Xp11.2 RCC patients who were confirmed by FISH assay. Cox regression models were used to evaluate the prognostic value of all covariates. Among 36 assessed patients, 14 (38.9%), 26 (72.2%), 16 (44.4%), 19 (52.8%), and 9 (25.0%) patients showed high expression of 4EBP1, p-4EBP1, p-mTOR, p-S6K, and p-MAPK, respectively. We noted that p-4EBP1 expression was significantly correlated with lymph node metastases (P = 0.027). Multivariate analysis showed that high p-4EBP1 expression was an independent adverse prognostic factor for both PFS (HR = 33.750, P = 0.017) and OS (HR = 56.111, P = 0.026). Our findings suggest that p-4EBP1 may serve as a funnel factor that converge the upstream proliferative oncogenic signals. Effective inhibition of the pathways responsible for 4E-BP1 phosphorylation might be a useful strategy to improve the outcome of Xp11.2 RCC patients.

Phosphorylation of eIF4E serine 209 is associated with tumour progression and reduced survival in malignant melanoma

Background:

Melanoma is a disease that primarily arises in the skin but is a derivative of the neural crest. Eukaryotic translation initiation factor 4E (eIF4E) regulates translation of multiple malignancy-associated mRNAs and is overexpressed in many epithelial tumours. However, expression in human tumours derived from the neural crest is unknown. Here, we determined the association of eIF4E and phospho-eIF4E expression in melanocytic lesions with malignant conversion, metastatic potential and patient survival.

Methods:

Archived formalin-fixed, paraffin-embedded surgical specimens from 114 patients with melanocytic lesions were stained immunohistochemically for eIF4E and phospho-eIF4E and evaluated semiquantitatively. The relationship between cytoplasmic and nuclear eIF4E and phospho-eIF4E protein expression, melanocytic lesion subtype and tumour progression was determined. Kaplan–Meier survival analyses and Cox proportional hazard regression were performed.

Results:

Increased eIF4E and phospho-eIF4E expression was highly associated with malignancy (P<0.0001). High nuclear phospho-eIF4E was associated with synchronous or future metastasis (P=0.0059). Kaplan–Meier analyses demonstrated highly significant associations between high histoscores for cytoplasmic and nuclear phospho-eIF4E and reduced survival in all patients (P=0.0003 and 0.0009, respectively).

Conclusions:

Increased melanoma expression of eIF4E and phospho-eIF4E is associated with metastatic potential, reduced survival and increased risk of death.

Integrated Analysis of PTEN and p4EBP1 Protein Expression as Predictors for pCR in HER2-Positive Breast Cancer

BACKGROUND

The PI3K/AKT pathway and phosphatase and tensin homolog (PTEN) aberrations are common in breast cancer. We investigated the correlation between phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit alpha (PIK3CA), PTEN, p4EBP1 (phosphorylated E4 binding protein 1), and pathologic complete response (pCR) in patients receiving neoadjuvant therapy.

EXPERIMENTAL DESIGN

We retrospectively evaluated PIK3CA, PTEN, and p4EBP1 protein expression in centrally HER2-positive patients (n = 181) who received epirubicin cyclophosphamide/trastuzumab followed by docetaxel/trastuzumab alone or concomitant/followed by capecitabine within the GeparQuattro study. PTEN was assessed using the automated quantitative immunofluorescence analysis and was analyzed as a dichotomic variable. p4EBP1 was assessed by immunohistochemistry and used as a continuous and dichotomic variable.

RESULTS

p4EBP1 was available from 137, PTEN from 108, and PIK3CA genotype from 83 patients. Overall, the pCR rate in PTEN-low tumors was 27.6%, and in PTEN-high tumors, it was 57.1% (P = 0.010). pCR rates were not statistically different between PIK3CA wild-type and mutant (35% vs. 22%) or p4EBP1 IRS ≤ 4 and IRS > 4 (39% vs. 33%). pCR rate was 57.1% (8/14) in PTEN-high/PIK3CA wild-type and decreased to 15.4% in PTEN-low/PIK3CA-mutant tumors (P = 0.023). In multivariable analysis adjusted for baseline parameters, PTEN independently predicted pCR in the following cohorts: overall [OR, 7.54; 95% confidence interval (CI), 2.03-28.06; P = 0.003], PIK3CA wild-type (OR, 23.81; 95% CI, 1.75-324.05; P = 0.017), p4EBP1 IRS > 4 (OR, 11.53; 95% CI, 1.84-72.24; P = 0.009), and hormone receptor-positive (OR, 40.91; 95% CI, 2.93-570.44; P = 0.006). p4EBP1 was independently predictive for pCR in PIK3CA wild-type tumors (OR, 0.14; 95% CI, 0.03-0.78; P = 0.025).

CONCLUSIONS

The study showed the potential role of PIK3CA genotype, PTEN, and p4EBP in predicting pCR after anthracycline-taxane-based chemotherapy and anti-HER2 treatment. Clin Cancer Res; 22(11); 2675-83. ©2016 AACR.

Cul1 promotes melanoma cell proliferation by promoting DEPTOR degradation and enhancing cap-dependent translation

Cullin1 (Cul1) serves as a rigid scaffold in the SCF (Skp1/Cullin/Rbx1/F-box protein) E3 ubiquitin ligase complex and has been found to be overexpressed in melanoma and to enhance melanoma cell proliferation by promoting G1-S phase transition. However, the underlying mechanisms involved in the regulation of melanoma cell proliferation by Cul1 remain poorly understood. In the present study, we found that Cul1 promoted mTORC1 activity and cap-dependent translation by enhancing the ubiquitination and degradation of DEPTOR. We further showed that suppression of the eIF4F complex assembly profoundly inhibited the promoting effect of Cul1 on melanoma cell proliferation, while enhancement of the eIF4F complex activity reversed the inhibitory effect of Cul1 depletion on melanoma cell proliferation, indicating that Cul1 contributes to melanoma cell proliferation by activating cap‑dependent translation. These data elucidate the role of Cul1 in cap-dependent translation and improves our understanding of the underlying mechanisms involved in the regulation of melanoma cell proliferation by Cul1.

RAS/MAPK pathway hyperactivation determines poor prognosis in undifferentiated pleomorphic sarcomas

BACKGROUND

Undifferentiated pleomorphic sarcoma (UPS) constitutes the most common subtype of soft tissue sarcoma. However, UPS is clinically and molecularly poorly understood, in great extent due to its intrinsic phenotypic and cytogenetic complexity, which in turn results in the absence of specific prognostic or predictive biomarkers. The RAS/mitogen-activated protein kinases (MAPK) and phosphoinositide 3-kinase inhibitor (PI3K)/mammalian target of rapamycin (mTOR) pathways are considered to be 2 major mechanisms for sarcoma proliferation and survival and to the authors' knowledge their role in UPS remains unclear. The objective of the current study was to investigate whether the RAS/MAPK and PI3K/mTOR pathways are activated in UPS, and whether pathway activation is associated with outcome.

METHODS

Records for patients diagnosed and treated for UPS in the study institution between 2000 and 2009 were reviewed. Phosphorylation status of 4E-binding protein (4E-BP1), eukaryotic translation initiation factor 4E (eIF-4E), S6-RP, and ERK 1/2, together with total forms of 4E-BP1 and eIF-4E, were assessed using immunohistochemistry in paraffin-embedded tumor tissue. Mutational analysis for KRAS; NRAS; BRAF; and phosphatidylinositol-4,5-bisphosphate 3-kinase, catalytic subunit alpha (PIK3CA) oncogenic mutations was performed as well.

RESULTS

Critical lymph nodes within the RAS/MAPK and PI3K/mTOR pathways were found to be activated in >80% of UPS cases. Hyperactivation of the RAS/MAPK pathway, as assessed by expression of phosphorylated ERK 1/2, was found to independently predict a higher risk of disease recurrence and impaired overall survival. Only a KRAS A146V mutation was detected in 1 tumor.

CONCLUSIONS

The RAS/MAPK and PI3K/mTOR pathways are activated in the majority of cases of UPS. The RAS/MAPK pathway distinguishes a subgroup of patients with localized UPS with a worse outcome.

Phosphorylated 4E-binding protein 1 expression is associated with poor prognosis in small-cell lung cancer

Phosphorylation of eukaryotic translation initiation factor 4E (eIF4E) binding protein (4E-BP1) results in release of eIF4E, which sequentially relieves translational repression and enhances oncogenic protein synthesis. We assessed the expression of phosphorylated 4E-BP1 (p-4E-BP1) in small-cell lung cancer (SCLC) and its correlation with clinicopathological factors and patient survival. This study included 117 SCLCs, which comprised 108 primary and 9 metastatic tumor tissues. We performed immunohistochemical staining for p-4E-BP1 in 117 tumors and found that 77 (66 %) were positive for p-4E-BP1 with cytoplasmic and/or nuclear immunostaining. The positive rate of p-4E-BP1 staining was significantly higher in never smokers (p = 0.034) and metastatic tumor tissues (p = 0.027). Patients with p-4E-BP1-positive SCLC tended to have poor performance status, although the difference was not statistically significant (p = 0.087). High p-4E-BP1 expression was significantly correlated with worse overall survival (OS) in all cohorts (p = 0.016). After stratification by clinical stage, p-4E-BP1 expression showed a stronger relationship with OS in patients with limited disease (p = 0.008). In addition, when stratified by treatment status, p-4E-BP1 expression was still significantly associated with worse OS in a subgroup of patients who completed treatment (p = 0.021). Our results indicate that p-4E-BP1 expression could represent oncogenic potential and contribute to the progression and aggressiveness of SCLC, suggesting it could be a candidate prognostic biomarker of SCLC, especially in limited disease.

Prognostic significance of phosphorylated 4E-binding protein 1 in non-small cell lung cancer

Phosphorylation of eukaryotic translation initiation factor 4E (eIF4E) binding protein (4E-BP1) results in release of eIF4E, which sequentially relieves translational repression and enhances oncogenic protein synthesis. We assessed the expression of phosphorylated 4E-BP1 (p-4E-BP1) in non-small cell lung cancer (NSCLC) and its correlation with clinicopathological parameters and patient survival. In addition, we investigated whether phosphorylation site made a difference in outcome. Tissue microarray blocks were generated from 73 NSCLC samples and immunohistochemically stained for p-4E-BP1 Thr37/46 and p-4E-BP1 Thr70. Both p-4E-BP1 Thr37/46 and p-4E-BP1 Thr70 were more highly expressed in squamous cell carcinoma than in adenocarcinoma (P = 0.006 and P = 0.003, respectively). Expression of p-4E-BP1 Thr70 was higher in tumours with a diameter larger than 3 cm (P = 0.024) and nodal metastasis (P = 0.053). High p-4E-BP1 Thr70 expression significantly correlated with worse overall survival (P = 0.001) and was an independent prognostic factor (hazard ratio 2.64, P = 0.004). p-4E-BP1 Thr37/46 had no prognostic significance. Phosphorylation site affected the prognostic significance of p-4E-BP1. p-4E-BP1 Thr70 is a candidate biomarker to predict poor prognosis in patients with NSCLC.

Overexpression of phosphorylated 4E-binding protein 1 and its clinicopathological significances in gastric cancer

Multiple intracellular transforming signals regulate eukaryotic translation initiation factor 4E (eIF4E)-binding protein (4E-BP1). The signals result in hierarchical phosphorylation of 4E-BP1, resulting in release of eIF4E, relieving translational repression and enhancing oncogenic protein synthesis. This study assessed the expression of phosphorylated 4E-BP1 (p-4E-BP1) in gastric cancer and its correlation with clinicopathological parameters and patient survival. Tissue microarray blocks were generated from 179 gastric carcinomas and immunohistochemically stained for p-4E-BP1. The expression of p-4E-BP1 was higher in tumors that were intestinal-type (P=0.028); had a diameter smaller than 5cm (P=0.001); were lower pathological T stage (P<0.001), N stage (P=0.004), or TNM stage (P<0.001); did not have distant metastasis (P=0.027). High p-4E-BP1 expression significantly correlated with prolonged overall survival (P=0.046) and disease-free survival (P=0.035), but was not an independent prognostic factor in multivariate analysis. Our results indicate that p-4E-BP1 is more highly expressed in early gastric cancers than in advanced ones, and has limited potential as an independent prognostic biomarker in patients with gastric cancer. Larger well-controlled studies with molecular validation are warranted to elucidate more exact prognostic significance and working mechanism of p-4E-BP1 in gastric cancer.

Expression of eukaryotic initiation factor 4E and 4E binding protein 1 in colorectal carcinogenesis

Cap dependent translation is mainly regulated at the level of the eukaryotic initiation factor 4E (eIF4E), the activity of which is controlled by phosphorylation and sequestration by its well established regulator, 4E binding protein 1 (4E-BP1). Both eIF4E and 4E-BP1 have been shown to be involved in the malignant progression of multiple human cancers, including colorectal cancer. However, the data on determining the expression of eIF4E, 4E-BP1 and their phosphorylated forms simultaneously in a single patient with colorectal cancer is lacking. Therefore the aim of our study was to explore the roles of these factors in colorectal carcinogenesis by immunohistostaining colorectal tissues (normal, low grade adenoma, high grade adenoma, and adenocarcinoma). Our results showed that the expression levels of eIF4E increased steadily as the cancer progressed from the case of benign dysplasia to an adenocarcinoma; all the while maintaining an unphosphorylated form. On the other hand, total expression levels of 4E-BP1 increased only in the premalignant state of the disease and decreased (but highly phosphorylated or inactivated) or abolished upon malignancy. Taken together, our findings suggest that strong correlations exist between the expression of eIF4E (not p-eIF4E) and tumor grade providing evidence that eIF4E expression plays a pivotal role in the malignant progression of colorectal cancer. Moreover, 4E-BP1 showed a bi-phasic level of expression during carcinogenesis, which is expressed only in hyperplasic or dysplastic tissues as an endogenous tumor suppressor molecule.

The 4E-BP1/eIF4E ratio is a determinant for rapamycin response in esophageal cancer cells

OBJECTIVES

Rapamycin inhibits products of molecular pathways in esophageal squamous cell carcinoma and limits tumor cell growth by targeting 4E-BP1- and eIF4E-dependent gene translation. In this study, we investigate the influence of 4E-BP1-to-eIF4E ratio on rapamycin response in esophageal squamous cell carcinoma cells, and the underlying mechanism is discussed.

METHODS

The response to rapamycin treatment was examined in 6 esophageal cancer cell lines. Adjustment of the 4E-BP1/eIF4E ratio was carried out by knockdown or overexpression of 4E-BP1 and eIF4E. The relationship between Egr-1 and 4E-BP1 expression in esophageal cancer cells was also studied.

RESULTS

The 4E-BP1/eIF4E ratio was adjusted to evaluate the response to rapamycin treatment in TE1 and TE2 esophageal cancer cells. TE2 cells are sensitized to rapamycin treatment after overexpression of 4E-BP1 or knockdown of eIF4E; TE1 cells become resistant to rapamycin after knockdown of 4E-BP1 or overexpression of eIF4E. These data suggest that the 4E-BP1/eIF4E ratio is a determinant for the response of TE1 and TE2 cells to rapamycin treatment. Egr-1 expression was higher in TE2 cells compared with other esophageal cancer cell lines, and its knockdown increased 4E-BP1 expression in TE2 cells, which became sensitive to rapamycin treatment.

CONCLUSIONS

The 4E-BP1/eIF4E ratio is a determinant of the response of rapamycin treatment in esophageal cancer cells. Egr-1 can reduce 4E-BP1 gene expression and render esophageal squamous cell carcinoma cells resistant to rapamycin with a relatively low 4E-BP1/eIF4E ratio. Thus, the 4E-BP1/eIF4E ratio may represent a therapeutic index for the prediction of clinical outcome of rapamycin treatment in patients with esophageal squamous cell carcinoma.

The mTOR effectors 4EBP1 and S6K2 are frequently coexpressed, and associated with a poor prognosis and endocrine resistance in breast cancer: a retrospective study including patients from the randomised Stockholm tamoxifen trials

Introduction

mTOR and its downstream effectors the 4E-binding protein 1 (4EBP1) and the p70 ribosomal S6 kinases (S6K1 and S6K2) are frequently upregulated in breast cancer, and assumed to be driving forces in tumourigenesis, in close connection with oestrogen receptor (ER) networks. Here, we investigated these factors as clinical markers in five different cohorts of breast cancer patients.

Methods

The prognostic significance of 4EBP1, S6K1 and S6K2 mRNA expression was assessed with real-time PCR in 93 tumours from the treatment randomised Stockholm trials, encompassing postmenopausal patients enrolled between 1976 and 1990. Three publicly available breast cancer cohorts were used to confirm the results. Furthermore, the predictive values of 4EBP1 and p4EBP1_S65 protein expression for both prognosis and endocrine treatment benefit were assessed by immunohistochemical analysis of 912 node-negative breast cancers from the Stockholm trials.

Results

S6K2 and 4EBP1 mRNA expression levels showed significant correlation and were associated with a poor outcome in all cohorts investigated. 4EBP1 protein was confirmed as an independent prognostic factor, especially in progesterone receptor (PgR)-expressing cancers. 4EBP1 protein expression was also associated with a poor response to endocrine treatment in the ER/PgR positive group. Cross-talk to genomic as well as non-genomic ER/PgR signalling may be involved and the results further support a combination of ER and mTOR signalling targeted therapies.

Conclusion

This study suggests S6K2 and 4EBP1 as important factors for breast tumourigenesis, interplaying with hormone receptor signalling. We propose S6K2 and 4EBP1 as new potential clinical markers for prognosis and endocrine therapy response in breast cancer.

High prevalence of mTOR complex activity can be targeted using Torin2 in papillary thyroid carcinoma

The mammalian target of rapamycin (mTOR) signaling cascade is a key regulatory pathway controlling initiation of messenger RNA in mammalian cells. Although dysregulation of mTOR signaling has been reported earlier in cancers, there is paucity of data about mTOR expression in papillary thyroid carcinoma (PTC). Therefore, in this study, we investigated the presence of mTORC2 and mTORC1 complexes in a large cohort of >500 PTC samples. Our clinical data showed the presence of active mTORC1 and mTORC2 in 81 and 39% of PTC samples, respectively. Interestingly, coexpression of mTORC1 and mTORC2 activity was seen in a 32.5% (164/504) of the PTC studied and this association was statistically significant (P = 0.0244). mTOR signaling complex was also found to be associated with activated AKT and 4E-BP1. In vitro, using Torin2, a second-generation mTOR inhibitor or gene silencing of mTOR expression prevented mTORC1 and mTORC2 activity leading to inactivation of P70S6, 4E-BP1, AKT and Bad. Inhibition of mTOR activity led to downregulation of cyclin D1, a gene regulated by messenger RNA translation via phosphorylation of 4E-BP1. Torin2 treatment also inhibited cell viability and induced caspase-dependent apoptosis via activation of mitochondrial apoptotic pathway in PTC cells. Finally, Torin2 treatment induces anticancer effect on PTC xenograft tumor growth in nude mice via inhibition of mTORC1 and mTORC2 and its associated pathways. Our results suggest that coexpression of mTORC1 and mTORC2 is seen frequently in the clinical PTC samples and dual targeting of mTORC1 and mTORC2 activity may be an attractive therapeutic target for treatment of PTC.

Uveal melanoma cell growth is inhibited by aminoimidazole carboxamide ribonucleotide (AICAR) partially through activation of AMP-dependent kinase

PURPOSE

To evaluate the effects and mechanism of aminoimidazole carboxamide ribonucleotide (AICAR), an AMP-dependent kinase (AMPK) activator, on the growth of uveal melanoma cell lines.

METHODS

Four different cell lines were treated with AICAR (1-4 mM). Cell growth was assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium (MTT) assay. Cell cycle analysis was conducted by flow cytometry; additionally, expression of cell-cycle control proteins, cell growth transcription factors, and downstream effectors of AMPK were determined by RT-PCR and Western blot.

RESULTS

Aminoimidazole carboxamide ribonucleotide inhibited cell growth, induced S-phase arrest, and led to AMPK activation. Aminoimidazole carboxamide ribonucleotide treatment was associated with inhibition of eukaryotic translation initiation factor 4E-BP1 phosphorylation, a marker of mammalian target of rapamycin (mTOR) pathway activity. Aminoimidazole carboxamide ribonucleotide treatment was also associated with downregulation of cyclins A and D, but had minimal effects on the phosphorylation of ribosomal protein S6 or levels of the macroautophagy marker LC3B. The effects of AICAR were abolished by treatment with dipyridamole, an adenosine transporter inhibitor that blocks the entry of AICAR into cells. Treatment with adenosine kinase inhibitor 5-iodotubericidin, which inhibits the conversion of AICAR to its 5'-phosphorylated ribotide 5-aminoimidazole-4-carboxamide-1-D-ribofuranosyl-5'-monophosphate (ZMP; the direct activator of AMPK), reversed most of the growth-inhibitory effects, indicating that some of AICAR's antiproliferative effects are mediated at least partially through AMPK activation.

CONCLUSIONS

Aminoimidazole carboxamide ribonucleotide inhibited uveal melanoma cell proliferation partially through activation of the AMPK pathway and downregulation of cyclins A1 and D1.

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.

MNK1 pathway activity maintains protein synthesis in rapalog-treated gliomas

High levels of mammalian target of rapamycin complex 1 (mTORC1) activity in malignant gliomas promote tumor progression, suggesting that targeting mTORC1 has potential as a therapeutic strategy. Remarkably, clinical trials in patients with glioma revealed that rapamycin analogs (rapalogs) have limited efficacy, indicating activation of resistance mechanisms. Targeted depletion of MAPK-interacting Ser/Thr kinase 1 (MNK1) sensitizes glioma cells to the mTORC1 inhibitor rapamycin through an indistinct mechanism. Here, we analyzed how MNK1 and mTORC1 signaling pathways regulate the assembly of translation initiation complexes, using the cap analog m7GTP to enrich for initiation complexes in glioma cells followed by mass spectrometry-based quantitative proteomics. Association of eukaryotic translation initiation factor 4E (eIF4E) with eIF4E-binding protein 1 (4EBP1) was regulated by the mTORC1 pathway, whereas pharmacological blocking of MNK activity by CGP57380 or MNK1 knockdown, along with mTORC1 inhibition by RAD001, increased 4EBP1 binding to eIF4E. Furthermore, combined MNK1 and mTORC1 inhibition profoundly inhibited 4EBP1 phosphorylation at Ser65, protein synthesis and proliferation in glioma cells, and reduced tumor growth in an orthotopic glioblastoma (GBM) mouse model. Immunohistochemical analysis of GBM samples revealed increased 4EBP1 phosphorylation. Taken together, our data indicate that rapalog-activated MNK1 signaling promotes glioma growth through regulation of 4EBP1 and indicate a molecular cross-talk between the mTORC1 and MNK1 pathways that has potential to be exploited therapeutically.

4E-BP1 regulates the sensitivity of human glioma cells to chemotherapy through PI3K/Akt/mTOR-independent pathway

Drug resistance is one of the most formidable obstacles for treatment of glioma. Eukaryotic initiation factor 4E-binding protein (4E-BP1), a key component in the rate-limiting step of protein translation initiation, is closely associated with poor prognosis in multiple tumor types. However, it is unclear whether 4E-BP1 is involved in the drug resistance of human glioma. Herein we show that the expression of 4E-BP1 in human SWOZ2-BCNU drug-resistant glioma cells is significantly lower than that of the parent SWOZ2 cell line. Moreover, down-regulation of 4E-BP1 by short interfering RNA significantly impaired the sensitivity of SWOZ2 and U251 cells to carmustine (BCNU). Furthermore, overexpression of 4E-BP1 with plasmid transfection regained this sensitivity. Clinical studies showed that the expression levels of 4E-BP1 in primary glioma tissues were markedly higher than those of recrudescent glioma tissues. Taken together, our results suggest that 4E-BP1 is a novel protein that contributes to acquired drug resistance and it may be a potential target for reversing drug resistance in human glioma.

Pancreatic tumours escape from translational control through 4E-BP1 loss

The mRNA cap-binding protein eIF4E (eukaryotic translation initiation factor 4E) permits ribosome recruitment to capped mRNAs, and its phosphorylated form has an important role in cell transformation. The oncogenic function of eIF4E is, however, antagonised by the hypophosphorylated forms of the inhibitory eIF4E-binding proteins 1 and 2. eIF4E-binding protein 1 and 2 (4E-BP1 and 2) are two major targets of the protein kinase mTOR, and are essential for the antiproliferative effects of mTOR inhibitors. Herein, we report that pancreas expresses specifically and massively 4E-BP1 (4E-BP2 is nearly undetectable). However, 4E-BP1 expression is extinguished in more than half of the human pancreatic ductal adenocarcinomas (PDAC). 4E-BP1 shutoff is recapitulated in a mouse genetic model of PDAC, which is based on a pancreas-specific mutation of Kras, the more frequently mutated oncogene in human pancreatic tumours. 4E-BP1 downregulation enhances eIF4E phosphorylation and facilitates pancreatic cancer cell proliferation in vitro and tumour development in vivo. Furthermore, 4E-BP1 loss combined with the absence of 4E-BP2 renders eIF4E phosphorylation, protein synthesis and cell proliferation resistant to mTOR inhibition. However, proliferation can be better limited by a recently developed compound that mimics the function of 4E-BP1 and 2 independently of mTOR inhibition.

mTOR is frequently active in GH-secreting pituitary adenomas without influencing their morphopathological features

Initiating factors and mechanisms of tumor formation are poorly understood in nonfamilial pituitary adenomas. Alteration of intracellular pathways is an underlying event in numerous neoplasms. Among them, excessive activation of mammalian target of rapamycin (mTOR) pathway and its two main regulators, Akt and Erk, has been detected frequently in solid tumors. This study tests the activation of mTOR pathway in pituitary adenomas and its influence on their morphopathological features. Fifty-three pituitary adenomas were fresh frozen after surgery and analyzed by western blotting using phospho-specific antibodies. The impact of Akt and Erk activation on mTOR pathway was assessed in five primary cultures derived from the excised adenomas using selective kinase inhibitors. Statistical correlations of size, volume, Ki-67 %, Knosp's grading, and somatostatin receptor (SSTR) expression with the activation of mentioned kinases was performed. GHomas showed the highest frequency (71 %) and level of mTOR pathway activity comparing to other adenomas (33 %). No significant correlation was found between mTOR activation and any of the morphopathological features in the studied samples. mTOR kinase phosphorylation was independent of Erk and Akt in primary cultures. Erk activity was significant in all types of adenomas but was the highest in control samples. Its phosphorylation correlated inversely with the Knosp's grading in nonfunctional pituitary adenomas and directly with somatostatin receptor subtype 2 A expression in GHomas. Presented data point to the noteworthy mTOR activity in GHomas. However, the lack of correlation with morphopathological features, its independence of Erk and Akt phosphorylation, and high level of Erk activity in control pituitary necessitate further research for clarifying the role of these pathways in pituitary adenomas.

Putative role of the mTOR/4E-BP1 signaling pathway in the carcinogenesis and progression of gastric cardiac adenocarcinoma

The mammalian target of rapamycin/eukaryotic translation inititiation factor 4E binding protein 1 (mTOR/4E-BP1) transduction pathway is activated in a range of malignant cancers, but its role in human gastric cardiac adenocarcinoma (GCA) has not been well defined. The present study used western blotting and reverse transcription polymerase chain reaction (RT-PCR) to assess the expression of mTOR, 4E-BP1 and eukaryotic translation initiation factor 4E (eIF4E) at the protein and mRNA levels in 33 cases of GCA and paired adjacent normal gastric mucosal tissues. The expression of mTOR at the protein level in GCA was significantly lower than that in the corresponding normal gastric mucosa (0.296 ± 0.27 vs. 1.348 ± 0.80, P<0.05), but the ratio of p-mTOR to mTOR was significantly increased in tumor tissues (1.425 ± 1.07 vs. 0.450 ± 0.24, P<0.05). The expression of 4E-BP1 was significantly decreased in GCA compared with normal tissues (p<0.05), while the levels of phosphorylated 4E-BP1 (p-4E-BP1) were markedly increased in tumor tissues (p<0.05). The levels of phosphorylated eIF4E (p‑eIF4E) were significantly higher in the tumors in comparison to the corresponding normal tissues (1.822 ± 0.63 vs. 0.997 ± 0.38, P<0.05), and the levels of p-eIF4E were closely correlated with lymph node metastasis (p<0.05). The mTOR/4E-BP1 signaling pathway is activated in GCA, with mTOR activated mainly through increased mTOR phosphorylation rather than protein overexpression.

Post-transcriptional regulation in cancer progression : Microenvironmental control of alternative splicing and translation

The microenvironment acts as a conduit for cellular communication, delivering signals that direct development and sustain tissue homeostasis. In pathologies such as cancer, this integral function of the microenvironment is hijacked to support tumor growth and progression. Cells sense the microenvironment via signal transduction pathways culminating in altered gene expression. In addition to induced transcriptional changes, the microenvironment exerts its effect on the cell through regulation of post-transcriptional processes including alternative splicing and translational control. Here we describe how alternative splicing and protein translation are controlled by microenvironmental parameters such as oxygen availability. We also emphasize how these pathways can be utilized to support processes that are hallmarks of cancer such as angiogenesis, proliferation, and cell migration. We stress that cancer cells respond to their microenvironment through an integrated regulation of gene expression at multiple levels that collectively contribute to disease progression.

RSK regulates activated BRAF signalling to mTORC1 and promotes melanoma growth

The Ras/mitogen-activated protein kinase (MAPK) signalling cascade regulates various biological functions, including cell growth, proliferation and survival. As such, this pathway is often deregulated in cancer, including melanomas, which frequently harbour activating mutations in the NRAS and BRAF oncogenes. Hyperactive MAPK signalling is known to promote protein synthesis, but the mechanisms by which this occurs remain poorly understood. Here, we show that expression of oncogenic forms of Ras and Raf promotes the constitutive activation of the mammalian target of rapamycin (mTOR). Using pharmacological inhibitors and RNA interference, we find that the MAPK-activated protein kinase RSK (p90 ribosomal S6 kinase) is partly required for these effects. Using melanoma cell lines carrying activating BRAF mutations, we show that ERK/RSK signalling regulates assembly of the translation initiation complex and polysome formation, as well as the translation of growth-related messenger RNAs containing a 5'-terminal oligopyrimidine (TOP) motif. Accordingly, we find that RSK inhibition abrogates tumour growth in mice. Our findings indicate that RSK may be a valuable therapeutic target for the treatment of tumours characterized by deregulated MAPK signalling, such as melanoma.

Eukaryotic initiation factor 4F: a vulnerability of tumor cells

Protein synthesis is a complex, tightly regulated process in eukaryotic cells and its deregulation is a hallmark of many cancers. Translational control occurs primarily at the rate-limiting initiation step, where ribosomal subunits are recruited to template mRNAs through the concerted action of several eukaryotic initiation factors (eIFs). One factor that interacts with both the mRNA and ribosomes, and appears limiting for translation is eIF4F, a complex composed of the cap-binding protein, eIF4E; the scaffold protein, eIF4G; and the ATP-dependent DEAD-box helicase, eIF4A. eIF4E appears to play an important role in tumor initiation and progression since its overexpression can cooperate with oncogenes to accelerate transformation in cell lines and animal models, and its levels are elevated in many human cancers. This, therefore, represents a vulnerability for transformed cells, and presents an opportunity for therapeutic intervention. In this review, we discuss approaches for targeting eIF4F activity.

Comparison of growth factor signalling pathway utilisation in cultured normal melanocytes and melanoma cell lines

BACKGROUND

The phosphatidylinositol-3-kinase (PI3K-PKB), mitogen activated protein kinase (MEK-ERK) and the mammalian target of rapamycin (mTOR- p70S6K), are thought to regulate many aspects of tumour cell proliferation and survival. We have examined the utilisation of these three signalling pathways in a number of cell lines derived from patients with metastatic malignant melanoma of known PIK3CA, PTEN, NRAS and BRAF mutational status.

METHODS

Western blotting was used to compare the phosphorylation status of components of the PI3K-PKB, MEK-ERK and mTOR-p70S6K signalling pathways, as indices of pathway utilisation.

RESULTS

Normal melanocytes could not be distinguished from melanoma cells on the basis of pathway utilisation when grown in the presence of serum, but could be distinguished upon serum starvation, where signalling protein phosphorylation was generally abrogated. Surprisingly, the differential utilisation of individual pathways was not consistently associated with the presence of an oncogenic or tumour suppressor mutation of genes in these pathways.

CONCLUSION

Utilisation of the PI3K-PKB, MEK-ERK and mTOR-p70S6K signalling pathways in melanoma, as determined by phosphorylation of signalling components, varies widely across a series of cell lines, and does not directly reflect mutation of genes coding these components. The main difference between cultured normal melanocytes and melanoma cells is not the pathway utilisation itself, but rather in the serum dependence of pathway utilisation.

Role and therapeutic potential of PI3K-mTOR signaling in de novo resistance to BRAF inhibition

BRAF inhibition is highly active in BRAF-mutant melanoma, but the degree and duration of responses is quite variable. Improved understanding of the mechanisms of de novo resistance may lead to rational therapeutic strategies with improved efficacy. Proteomic analysis of BRAF-mutant, PTEN-wild-type human melanoma cell lines treated with PLX4720 demonstrated that sensitive and de novo resistant lines exhibit similar RAS-RAF-MEK-ERK pathway inhibition, but the resistant cells exhibited durable activation of S6 and P70S6K. Treatment with the mTOR inhibitor rapamycin blocked activation of P70S6K and S6, but it also increased activation of AKT and failed to induce cell death. Combined treatment with rapamycin and PX-866, a PI3K inhibitor, blocked the activation of S6 and AKT and resulted in marked cell death when combined with PLX4720. The results support the rationale for combined targeting of BRAF and the PI3K-AKT pathways and illustrate how target selection will be critical to such strategies.

High-dose rapamycin induces apoptosis in human cancer cells by dissociating mTOR complex 1 and suppressing phosphorylation of 4E-BP1

mTOR, the mammalian target of rapamycin, has been widely implicated in signals that promote cell cycle progression and survival in cancer cells. Rapamycin, which inhibits mTOR with high specificity, has consequently attracted much attention as an anti-cancer therapeutic. Rapamycin suppresses phosphorylation of S6 kinase at nano-molar concentrations, however at higher micro-molar doses, rapamycin induces apoptosis in several human cancer cell lines. While much is known about the effect of low dose rapamycin treatment, the mechanistic basis for the apoptotic effects of high-dose rapamycin treatment is not understood. We report here that the apoptotic effects of high-dose rapamycin treatment correlate with suppressing phosphorylation of the mTOR complex 1 substrate, eukaryotic initiation factor 4E (eIF4E) binding protein-1 (4E-BP1). Consistent with this observation, ablation of eIF4E also resulted in apoptorsis in MDA-MB 231 breast cancer cells. We also provide evidence that the differential dose effects of rapamycin are correlated with partial and complete dissociation of Raptor from mTORC1 at low and high doses, respectively. In contrast with MDA-MB-231 cells, MCF-7 breast cancer cells survived rapamycin-induced suppression of 4E-BP1 phosphorylation. We show that survival correlated with a hyper-phosphorylation of Akt at S473 at high rapamycin doses, the suppression of which conferred rapamycin sensitivity. This study reveals that the apoptotic effect of rapamycin requires doses that completely dissociate Raptor from mTORC1 and suppress that phosphorylation of 4E-BP1 and inhibit eIF4E.

The CSPG4-specific monoclonal antibody enhances and prolongs the effects of the BRAF inhibitor in melanoma cells

PLX4032 is a BRAF-selective inhibitor shown to be efficacious in the treatment of melanomas presenting with the BRAF(V600E) mutation. However, favorable responses to treatment are short-lived, and complete remission is rarely observed. Therefore, it is important to identify novel therapies designed to enhance treatment responses and to increase the longevity of initial response to BRAF inhibitors. To this end, we characterized the effects of the 225.28 chondroitin sulfate proteoglycan 4 (CSPG4)-specific monoclonal antibody (mAb) capable of blocking multiple signaling pathways important to cell growth, migration, and survival. Addition of 225.28 to the treatment regimen enhanced the in vitro response magnitude and the duration efficacy of PLX4032 in treating CSPG4(+), BRAF(V600E) melanoma cells (melanoma(BRAF(V600E)/CSPG4+) cells). Data presented in this report demonstrated that (1) treatments comprised of PLX4032 and mAb 225.28 were more effective at inhibiting melanoma(BRAF(V600E)/CSPG4+) cell growth than either agent alone, (2) mAb 225.28 prevented/delayed the development of resistance in melanoma(BRAF(V600E)/CSPG4+) cells to PLX4032, and (3) the mechanism of action of the combination therapy caused a down-regulation in multiple signaling pathways. This study provides a foundation for future investigations designed to improve BRAF inhibitor effectiveness in vitro and in vivo for treating melanoma(BRAF(V600E)/CSPG4+) cells in combination with a CSPG4-specific mAb.

High phosphorylated 4E-binding protein 1 expression after chemoradiotherapy is a predictor for locoregional recurrence and worse survival in esophageal squamous cell carcinoma patients

BACKGROUND

As a well-known pivotal factor of 4E-binding protein 1 (4E-BP1) in controlling cancer proliferation, high expression of its phosphorylated form (p-4E-BP1) has been reported to be associated with poor outcome in various human cancers without pretreated with chemoradiotherapy (CRT). However, no data is available regarding the implication of p-4E-BP1 expression after CRT. Therefore, we conducted this study.

METHODS

The expression of p-4E-BP1 was semiquantitatively examined with immunohistochemical staining in 60 ypT1T2 esophageal squamous cell carcinoma (SCC) patients and verified by western blot analysis in representative cases. The impact of p-4E-BP1 expression intensity on cancer recurrence and survival was assessed in combination with clinical and pathological descriptors.

RESULT

The 5-year disease specific survival (DSS) rate of patients with high p-4E-BP1 expression was significantly lower than that of patients with lower p-4E-BP1 expression (5 year DSS: 58% vs. 8.6%, P = 0.00064). Furthermore, in a multivariate analysis by Cox regression model, high p-4E-BP1 expression was confirmed to be an independent prognostic factor (HR: 2.269; unfavorable, P = 0.024) for DSS, while lymph node (HR: 3.016; unfavorable, P = 0.005) was also significant prognostic factor. High p-4E-BP1 expression was specifically associated with locoregional recurrence (LR; P < 0.05). The locoregional control rate reached 97.1% in low p-4E-BP1 tumors.

CONCLUSION

High p-4E-BP1 expression after CRT is a predictor for LR and worse survival in esophageal SCC patients.

Targeting TOR dependence in cancer

A challenge in cancer therapy has been to identify targets whose function is essential for survival of malignant cells but not normal cells. This Perspective discusses recent evidence that novel inhibitors of the kinase TOR can provide an unprecedented balance of anti-cancer efficacy and tolerability.