mTOR downstream effectors, 4EBP1 and eIF4E, are overexpressed and associated with HPV status in precancerous lesions and carcinomas of the uterine cervix

White spot syndrome virus directly activates mTORC1 signaling to facilitate its replication via polymeric immunoglobulin receptor-mediated infection in shrimp

Previous studies have shown that the mechanistic target of rapamycin complex 1 (mTORC1) signaling pathway has antiviral functions or is beneficial for viral replication, however, the detail mechanisms by which mTORC1 enhances viral infection remain unclear. Here, we found that proliferation of white spot syndrome virus (WSSV) was decreased after knockdown of mTor (mechanistic target of rapamycin) or injection inhibitor of mTORC1, rapamycin, in Marsupenaeus japonicus, which suggests that mTORC1 is utilized by WSSV for its replication in shrimp. Mechanistically, WSSV infects shrimp by binding to its receptor, polymeric immunoglobulin receptor (pIgR), and induces the interaction of its intracellular domain with Calmodulin. Calmodulin then promotes the activation of protein kinase B (AKT) by interaction with the pleckstrin homology (PH) domain of AKT. Activated AKT phosphorylates mTOR and results in the activation of the mTORC1 signaling pathway to promote its downstream effectors, ribosomal protein S6 kinase (S6Ks), for viral protein translation. Moreover, mTORC1 also phosphorylates eukaryotic translation initiation factor 4E-binding protein 1 (4EBP1), which will result in the separation of 4EBP1 from eukaryotic translation initiation factor 4E (eIF4E) for the translation of viral proteins in shrimp. Our data revealed a novel pathway for WSSV proliferation in shrimp and indicated that mTORC1 may represent a potential clinical target for WSSV control in shrimp aquaculture.

White spot syndrome virus (WSSV) is the causative pathogen of white spot disease (WSD) and represents the most destructive viral disease of shrimp. The virus has evolved various strategies to escape from host defenses or exploit host biological pathways for its reproduction. Studies on viral immune-escape mechanisms can provide new strategies for disease prevention and control in shrimp aquaculture. Mechanistic target of rapamycin (mTOR) plays a central role in the regulation of cell growth and metabolism, which nucleates two distinct protein complexes, mTOR complex 1 (mTORC1) and mTOR complex 2 (mTORC2) with diverse functions at different levels of the signaling pathway. mTORC1 is reported to be exploited by viruses in their reproduction. However, the detail mechanism remains unclear. In this study, we identified a new mechanism of mTOR being hijacked by WSSV in shrimp (Marsupenaeus japonicus). WSSV infects shrimp by its receptor, pIgR and induces the interaction of the intracellular domain of pIgR with Calmodulin. Calmodulin subsequently promotes the activation of AKT by interaction with the pleckstrin homology domain of the kinase. Activated AKT phosphorylates mTOR and results in the activation of the mTORC1 signaling pathway to promote its downstream effectors, S6Ks, for viral protein synthesis. Moreover, mTORC1 also phosphorylates 4EBP1, which results in the separation of 4EBP1 from eIF4E for the translation of viral proteins in shrimp. Our study reveals a novel strategy for WSSV proliferation in shrimp and indicates that the components of mTORC1 may represent potential clinical targets for WSSV control in shrimp aquaculture.

The expression and significance of p4E-BP1/4E-BP1 in prostate cancer

BACKGROUND

Although the phosphorylation of 4E-BP1 that has been detected in high-grade prostate cancer has been reported in previous studies, overexpression of p4E-BP1 and 4EBP1 and their clinical significance in prostate cancer still remain unknown.

METHODS

One hundred six samples of prostate tissues were collected and analyzed by immunohistochemistry with p4E-BP1 or 4E-BP1 specific antibodies. Everolimus was used to block the phosphorylation of p4E-BP1, and then flow cytometry, clone formation, transwell, and wound healing assays were performed to detect the survival and invasive ability of the prostate cancer cells.

RESULTS

We found that the expression of 4E-BP1 and p4E-BP1 was higher in prostate cancer tissues than in normal tissues. Interestingly, the expression of p4E-BP1 was significantly associated with Gleason score and lymph node metastasis, but had no obvious correlation with PSA and the presence of bone or visceral metastasis. However, no evident correlation was found between the positive expression of 4E-BP1 and these clinical characteristics. In in vitro experiments, we found similar results as the clinical presentation that 4E-BP1 and p4E-BP1 were low expressed in normal prostate epithelial cells, but in prostate cancer cells, as the malignancy increasing, 4E-BP1 and p4E-BP1 expression also gradually increased. Then, we used Everolimus to inhibit the phosphorylation of 4E-BP1 and found that Everolimus effectively reduced cloning formation, inhibited cell migration, and promoted apoptosis in a dose-dependent manner in PC3 cells.

CONCLUSIONS

These findings suggest that p4E-BP1 is a potential biomarker and therapy target for prostate cancer, and patients with high expressions of p4E-BP1 may benefit from Everolimus treatment.

High-risk human papillomavirus-18 uses an mRNA sequence to synthesize oncoprotein E6 in tumors

Cervical cancer is the fourth most common cause of cancer in women worldwide in terms of both incidence and mortality. Persistent infection with high-risk types of human papillomavirus (HPV), namely 16, 18, 31, 33, 35, 39, 45, 51, 52, 56, 58, 59, and 68, constitute a necessary cause for the development of cervical cancer. Viral oncoproteins E6 and E7 play central roles in the carcinogenic process by virtue of their interactions with cell master proteins such as p53, retinoblastoma (Rb), mammalian target of rapamycin (mTOR), and c-MYC. For the synthesis of E6 and E7, HPVs use a bicistronic messenger RNA (mRNA) that has been studied in cultured cells. Here, we report that in cervical tumors, HPV-18, -39, and -45 transcribe E6/E7 mRNAs with extremely short 5' untranslated regions (UTRs) or even lacking a 5' UTR (i.e., zero to three nucleotides long) to express E6. We show that the translation of HPV-18 E6 cistron is regulated by the motif ACCaugGCGCG(C/A)UUU surrounding the AUG start codon, which we term Translation Initiation of Leaderless mRNAs (TILM). This motif is conserved in all HPV types of the phylogenetically coherent group forming genus alpha, species 7, which infect mucosal epithelia. We further show that the translation of HPV-18 E6 largely relies on the cap structure and eIF4E and eIF4AI, two key translation initiation factors linking translation and cancer but does not involve scanning. Our results support the notion that E6 forms the center of the positive oncogenic feedback loop node involving eIF4E, the mTOR cascade, and p53.

Human Positive Coactivator 4 Affects the Progression and Prognosis of Pancreatic Ductal Adenocarcinoma via the mTOR/P70s6k Signaling Pathway

Introduction

Pancreatic cancer is one of the deadliest cancers in the world, and pancreatic ductal adenocarcinoma (PDAC) accounts for 90% of all cases. Human positive coactivator 4 (PC4) is a transcriptional coactivator that has been associated with the development and progression of several tumors. However, no studies investigated the potential role of PC4 in PDAC.

Methods

We investigated PC4 expression in 81 PDAC tissue samples using immunohistochemistry and studied the impact of PC4 expression and the molecular mechanisms of this altered expression on PDAC tumorigenesis and proliferation both in vitro and in vivo.

Results

PC4 overexpression was correlated with a poor outcome in PDAC patients. The RNAi-mediated knockdown of PC4 expression in CFPAC-1 and AsPC-1 cell lines reduced cell proliferation and tumor growth. The loss of PC4 in PDAC inhibits cell growth by inducing cell cycle arrest at the G1/S transition and suppressing the mTOR/p70s6k pathway.

Discussion/Conclusion

Our findings reveal for the first time that PC4 exerts oncogenic functions by activating mTOR/p70s6k signaling pathway-mediated cell proliferation, implying that PC4 is a promising therapeutic target for PDAC.

The high-risk HPV E6 proteins modify the activity of the eIF4E protein via the MEK/ERK and AKT/PKB pathways

Previous studies have proposed that the human papillomavirus (HPV) E6 oncoproteins modify the transcriptional activity of eIF4E through mechanisms dependent on p53 degradation. However, the effect of these oncoproteins on pathways regulating the activity of the eIF4E protein remains poorly understood. Hence, we investigated the mechanisms whereby E6 proteins regulate the activity of the eIF4E protein and its effect on target genes. Overexpression of E6 constructs (HPV-6, HPV-16, HPV-18, and HPV52) showed that E6 oncoproteins increased phosphorylation of the eIF4E protein (Serine-209). This result was mainly mediated by phosphorylation of the 4EBP1 protein via the PI3K/AKT pathway. Additionally, the pharmacological inhibition of eIF4E phosphorylation in cervical cancer cell lines substantially reduced the protein levels of CCND1 and ODC1, indicating that E6 of the high-risk genotypes may modify protein synthesis of the eIF4E target genes by increasing the activity of the AKT and ERK pathways.

Atractylenolide I inhibits colorectal cancer cell proliferation by affecting metabolism and stemness via AKT/mTOR signaling

BACKGROUND

Atractylenolide I (ATL-1) is a natural herbal compound used in traditional Chinese medicine that has exhibited anti-cancer properties. The anti-tumorigenic activity of ATL-1 against colorectal cancer (CRC) and the underlying signaling pathways involved in its mechanisms are examined here.

HYPOTHESIS

ATL-1 exerts therapeutic effect against CRC by disrupting glucose metabolism and cancer stem cell maintenance via AKT/mTOR pathway regulation.

STUDY DESIGN

In vitro studies were performed in COLO205 and HCT116 CRC cell lines and in vivo studies were conducted in a mouse xenograft model of CRC tumor.

METHODS

CRC cells were treated with ATL-1 at various concentrations, with or without inhibitors of AKT or mTOR. Cell proliferation, apoptosis, invasion, stemness maintenance, glucose metabolism, and AKT/mTOR signaling were evaluated. CRC tumor-xenografted mice were treated with an AKT inhibitor and/or ATL-1, and glucose metabolism and stemness maintenance were examined in tumor tissues.

RESULTS

ATL-1 significantly inhibited the invasion of CRC cells by inducing their apoptosis, possibly via the excessive production of reactive oxygen species. Glucose metabolism (Warburg effect) was also altered and stem-like traits were suppressed by ATL-1. In addition, ATL-1 effectively acted as an inhibitor or AKT/mTOR by downregulating the phosphorylation of proteins related to the AKT/mTOR pathway. In vivo studies showed that tumor weight and volume were reduced by ATL-1 and that aerobic glycolysis, stemness maintenance, and AKT/mTOR activation were impaired by ATL-1 in colorectal tumors.

CONCLUSIONS

ATL-1 acts as an effective agent to suppress colorectal tumor progression, mainly by inhibiting CRC cell proliferation through altering apoptosis, glucose metabolism, and stem-like behavior. These processes were mediated by the AKT/mTOR signaling pathway both in vitro and in vivo. ATL-1 may be a potential agent to be used in molecular-targeted strategies for cancer treatment.

Inhibiting MNK Selectively Targets Cervical Cancer via Suppressing eIF4E-Mediated β-Catenin Activation

BACKGROUND

Targeting β-catenin has been shown to have great potential therapeutic value in cervical cancer. Because β-catenin is also essential for normal cells, strategies to specifically target cancer will require identification of druggable factors capable of distinguishing β-catenin signaling pathways between cancer and normal cells.

METHODS

Expression of p-eIF4E and p-β-catenin was analyzed in malignant and normal cervical tissues and cells. The effects and its underlying mechanisms of targeting MNK and eukaryotic translation initiation factor 4E (eIF4E) were determined in cervical cancer and normal cells.

RESULTS

Inhibiting MNK/eIF4E axis selectively targets cervical cancer without affecting normal cervical cells, via suppressing eIF4E-mediated β-catenin activation. We found that eIF4E phosphorylation was upregulated in cervical cancer cells and tissues but not normal cervical counterparts, and its phosphorylation at Ser 209 activates Wnt/β-catenin signaling, promotes growth and migration in cervical cancer, in an MNK-dependent manner. MNK inhibition via genetic small interfering RNA (siRNA) knockdown or pharmacologic inhibitor effectively decreased phosphorylation of eIF4E and β-catenin, leading to reduced β-catenin activity and transcript levels of Wnt target genes in cervical cancer cells. Consistently, we found that MNK kinase inhibitor is effective in inhibiting proliferation and migration, and inducing apoptosis in cervical cancer but not normal cervical cells. The combination of MNK kinase inhibitor with paclitaxel achieved greater efficacy in cervical cancer cells than paclitaxel alone.

CONCLUSIONS

Our work identifies MNK-eIF4E axis as a specific and critical regulator of β-catenin activity in cervical cancer but not normal cervical cells, and suggests that targeting MNK is a useful therapeutic strategy in cervical cancer.

Eukaryotic initiation factor 4E (eIF4E): A recap of the cap-binding protein

Eukaryotic initiation factor 4E (eIF4E), a fundamental effector and rate limiting element of protein synthesis, binds the 7-methylguanosine cap at the 5' end of eukaryotic messenger RNA (mRNA) specifically as a constituent of eIF4F translation initiation complex thus facilitating the recruitment of mRNA to the ribosomes. This review focusses on the engagement of signals contributing to growth factor originated maxim and their role in the activation of eIF4E to achieve a collective influence on cellular growth, with a key focus on conjuring vital processes like protein synthesis. The review invites considerable interest in elevating the appeal of eIF4E beyond its role in regulating translation viz a viz cancer genesis, attributed to its phosphorylation state that improves the prospect for the growth of the cancerous cell. This review highlights the latest studies that have envisioned to target these pathways and ultimately the translational machinery for therapeutic intervention. The review also brings forward the prospect of eIF4E to act as a converging juncture for signaling pathways like mTOR/PI3K and Mnk/MAPK to promote tumorigenesis.

The role of miRNAs in the invasion and metastasis of cervical cancer

Cervical cancer (CC) with early metastasis of the primary tumor results in poor prognosis and poor therapeutic outcomes. MicroRNAs (miRNAs) are small, noncoding RNA molecules that play a substantial role in regulating gene expression post-transcriptionally and influence the development and progression of tumors. Numerous studies have discovered that miRNAs play significant roles in the invasion and metastasis of CC by affecting specific pathways, including Notch, Wnt/β-catenin, and phosphoinositide-3 kinase (PI3K)-Akt pathways. miRNAs also effectively modulate the process of epithelial–mesenchymal transition. Many studies provide new insights into the role of miRNAs and the pathogenesis of metastatic CC. In this review, we will offer an overview and update of our present understanding of the potential roles of miRNAs in metastatic CC.

Dual abrogation of MNK and mTOR: a novel therapeutic approach for the treatment of aggressive cancers

Targeting the translational machinery has emerged as a promising therapeutic option for cancer treatment. Cancer cells require elevated protein synthesis and exhibit augmented activity to meet the increased metabolic demand. Eukaryotic translation initiation factor 4E is necessary for mRNA translation, its availability and phosphorylation are regulated by the PI3K/AKT/mTOR and MNK1/2 pathways. The phosphorylated form of eIF4E drives the expression of oncogenic proteins including those involved in metastasis. In this article, we will review the role of eIF4E in cancer, its regulation and discuss the benefit of dual inhibition of upstream pathways. The discernible interplay between the MNK and mTOR signaling pathways provides a novel therapeutic opportunity to target aggressive migratory cancers through the development of hybrid molecules.

Cervical cancer metastasis to the brain: A case report and review of literature

Background:

Intracranial metastasis from cervical cancer is a rare occurrence.

Methods:

In this study we describe a case of cervical cancer metastasis to the brain and perform an extensive review of literature from 1956 to 2016, to characterize clearly the clinical presentation, treatment options, molecular markers, targeted therapies, and survival of patients with this condition.

Results:

An elderly woman with history of cervical cancer in remission, presented 2 years later with a right temporo-parietal tumor, which was treated with surgery and subsequent stereotactic radiosurgery (SRS) to the resection cavity. She then returned 5 months later with a second solitary right lesion; she again underwent surgery and SRS to the resection cavity with no signs of recurrence 6 months later. According to the reviewed literature, the most common clinical presentation included females with median age of 48 years; presenting symptoms such as headache, weakness/hemiplegia/hemiparesis, seizure, and altered mental status (AMS)/confusion; multiple lesions mostly supratentorially located; poorly differentiated squamous cell carcinoma; and additional recurrences at other sites. The best approach to treatment is a multimodal plan, consisting of SRS or whole brain radiation therapy (WBRT) for solitary brain metastases followed by chemotherapy for systemic disease, surgery and WBRT for solitary brain lesions without systemic disease, and SRS or WBRT followed by chemotherapy for palliative care. The overall prognosis is poor with a mean and median survival time from diagnosis of brain metastasis of 7 and 4.6 months, respectively.

Conclusion:

Future efforts through large prospective randomized trials are warranted to better describe the clinical presentation and identify more effective treatment plans.

Effects of bufalin on the mTOR/p70S6K pathway and apoptosis in esophageal squamous cell carcinoma in nude mice

The aim of this study was to investigate the effects of bufalin on the mammalian target of rapamycin (mTOR/p70S6 kinase (p70S6K) signaling pathway and cell apoptosis in orthotopically transplanted tumors in nude mice. The mice were inoculated with human esophageal squamous cell carcinoma (ESCC) ECA109 cells in order to establish a model of orthotopicall transplanted ESCC tumors. The mice are administered low, medium and high doses of bufalin (0.5, 1.0 and 1.5 mg/kg) or rapamycin, or a combination of both. After the tumors were removed, the mRNA expression levels of mTOR, p70S6K, eukaryotic translation initiation factor 4E-binding protein 1 (4EBP1), cellular inhibitor of apoptosis protein 1 (cIAP1) and caspase-3 were detected by RT-PCR. In addition, we performed western blot analysis and immunohistochemical analysis to determine the protein expression of mTOR, p70S6K, 4EBP1, cIAP1, active caspase-3, Bcl-2 and Bad in the tumor tissue. The results revealed that bufalin exerted a significant anti-tumor effect in the nude mice with ESCC orthotopically transplanted tumors. This was shown by the decrease in the expression of mTOR, p70S6K and 4EBP1, which suggested that bufalin may possibly be used to inhibit tumor growth via the inhibition of the activation of p70S6K and 4EBP1. We also found that bufalin decreased the expression of cIAP1 and Bcl-2, and increased that of active caspase-3 and Bad, thus indicating that bufalin promoted apoptosis. Thus, our findings suggest that bufalin promotes tumor cell apoptosis, and this may be one of the important anti-tumor mechanisms of action of bufalin.