Subsequent and simultaneous electrophysiological investigation of the retina and the visual cortex in neurodegenerative and psychiatric diseases: what are the forecasts for the medicine of tomorrow?

Visual electrophysiological deficits have been reported in neurodegenerative disorders as well as in mental disorders. Such alterations have been mentioned in both the retina and the cortex, notably affecting the photoreceptors, retinal ganglion cells (RGCs) and the primary visual cortex. Interestingly, such impairments emphasize the functional role of the visual system. For this purpose, the present study reviews the existing literature with the aim of identifying key alterations in electroretinograms (ERGs) and visual evoked potentials electroencephalograms (VEP-EEGs) of subjects with neurodegenerative and psychiatric disorders. We focused on psychiatric and neurodegenerative diseases due to similarities in their neuropathophysiological mechanisms. Our research focuses on decoupled and coupled ERG/VEP-EEG results obtained with black-and-white checkerboards or low-level visual stimuli. A decoupled approach means recording first the ERG, then the VEP-EEG in the same subject with the same visual stimuli. The second method means recording both ERG and VEP-EEG simultaneously in the same participant with the same visual stimuli. Both coupled and decoupled results were found, indicating deficits mainly in the N95 ERG wave and the P100 VEP-EEG wave in Parkinson’s, Alzheimer’s, and major depressive disorder. Such results reinforce the link between the retina and the visual cortex for the diagnosis of psychiatric and neurodegenerative diseases. With that in mind, medical devices using coupled ERG/VEP-EEG measurements are being developed in order to further investigate the relationship between the retina and the visual cortex. These new techniques outline future challenges in mental health and the use of machine learning for the diagnosis of mental disorders, which would be a crucial step toward precision psychiatry.

In situ detection of the eIF4F translation initiation complex in mammalian cells and tissues

The eukaryotic translation initiation complex eIF4F plays an important role in gene expression. The methods that are used to monitor the formation of the eIF4F complex are usually indirect and provide no information on its subcellular localization. This protocol describes a proximity ligation assay-based procedure allowing the direct in situ visualization of the eIF4F complex, as well as its absolute quantification per cell using adapted image analysis software.

For complete details on the use and execution of this protocol, please refer to Boussemart et al. (2014).

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In situ detection of the interactions between eIF4E and either eIF4G or 4EBP1

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Co-localization of eIF4F complex and cellular organelles

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Complete 3D quantification of the interactions within the eIF4F complex

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Evaluation of eIF4F complex formation upon clinically relevant treatment perturbation

Abstract IA29: Role of eIF4F in anticancer drug resistance

Recent work, including large-scale genetic and molecular analyses, identified RNA-binding proteins (RBPs) as major players in the hallmarks of cancer. Specific RBPs allow the selective regulation of cancer genes at multiple post-transcriptional levels from pre-mRNA splicing/polyadenylation to mRNA stability/translation. These multiple activities are mediated by RBP binding to mRNAs.

In recent years, we have studied how the eIF4F translation initiation factor bound to the 7-methylguanosine cap structure present at the 5'-end of all cellular mRNAs contributes to tumorigenesis with a focus on its role in chemoresistance as well as the promising use of new small molecule inhibitors of the complex, including flavaglines/rocaglates, hippuristanol and pateamine A. We have specifically shown that, due to its location downstream of the the PI(3)K/AKT/mTOR pathway and the RAS-RAF-MEK-ERK-MNK mitogen-activated protein kinase (MAPK) signal transduction pathways, eIF4F is a nexus of resistance to anti-BRAF and anti-MEK therapies in both BRAF-mutated (melanoma, colon, thyroid) and NRAS-mutated (melanoma) cancer cells. Furthermore, inhibiting the eIF4A component of the eIF4F complex, with a novel flavagline (FL3) that is insensitive to P-glycoprotein-mediated multidrug resistance, synergizes with inhibiting BRAF and MEK to kill BRAF-mutant cancer cells and synergizes with inhibiting MEK to kill NRAS-mutant cancer cells in melanoma.

In parallel, while investigating a set of data based on high-throughput sequencing of polyadenylated transcripts 3'-ends (3'-Seq), we have found that a short eIF4E mRNA isoform is generated through alternative use on an intronic polyadenylation (IPA) site. The global generation of transcripts with shorter 3' untranslated region (3'UTR) is known to occur during enhanced cell proliferation and transformation into cancer cells. However, the involvement of alternative polyadenylation in the response to targeted therapies and in the spreading of cancer cells to metastatic sites is unknown. IPA site usage is known to be widely inhibited by the U1 small ribonucleoprotein particle (U1) bound to an adjacent 5' splice site (5'ss). We have found that targeting U1 with an antisense oligonucleotide (U1-ASO) leads to activation of the use of IPA sites in the eIF4E gene but also in several genes with functions enriched in cell movement and involved in the RAS-RAF-MEK-ERK mitogen-activated protein kinase (MAPK) and PI(3)K-AKT-mTOR signal transduction pathways. We have also demonstrated that the specificity of IPA regulation by U1 during tumor cell spreading is provided by the regulation of its binding to specific 5'ss by the RBP and U1-interacting splicing factor TIA1. The significance of these findings in tumor cell spreading and in the response to targeted therapies will be discussed.

Citation Format: Galina Boldina, Maricarmen Vallejos, Delphine Allard, Isabelle Girault, Hélène Malka-Mahieu, Laurent Désaubry, Martin Dutertre, Caroline Robert, Stéphan Vagner. Role of eIF4F in anticancer drug resistance. [abstract]. In: Proceedings of the AACR Special Conference on Translational Control of Cancer: A New Frontier in Cancer Biology and Therapy; 2016 Oct 27-30; San Francisco, CA. Philadelphia (PA): AACR; Cancer Res 2017;77(6 Suppl):Abstract nr IA29.

Molecular Pathways: The eIF4F Translation Initiation Complex-New Opportunities for Cancer Treatment

The eIF4F complex regulates the cap-dependent mRNA translation process. It is becoming increasingly evident that aberrant activity of this complex is observed in many cancers, leading to the selective synthesis of proteins involved in tumor growth and metastasis. The selective translation of cellular mRNAs controlled by this complex also contributes to resistance to cancer treatments, and downregulation of the eIF4F complex components can restore sensitivity to various cancer therapies. Here, we review the contribution of the eIF4F complex to tumorigenesis, with a focus on its role in chemoresistance as well as the promising use of new small-molecule inhibitors of the complex, including flavaglines/rocaglates, hippuristanol, and pateamine A. Clin Cancer Res; 23(1); 21-25. ©2016 AACR.

Translational regulation of the mRNA encoding the ubiquitin peptidase USP1 involved in the DNA damage response as a determinant of Cisplatin resistance

Cisplatin (cis-diaminedichloroplatin (II), CDDP) is part of the standard therapy for a number of solid tumors including Non-Small-Cell Lung Cancer (NSCLC). The initial response observed is in most cases only transient and tumors quickly become refractory to the drug. Tumor cell resistance to CDDP relies on multiple mechanisms, some of which still remain unknown. In search for such mechanisms, we examined the impact of CDDP on mRNA translation in a sensitive and in a matched resistant NSCLC cell line. We identified a set of genes whose mRNAs are differentially translated in CDDP resistant vs. sensitive cells. The translation of the mRNA encoding the Ubiquitin-Specific Peptidase 1 (USP1), a Ubiquitin peptidase with important function in multiple DNA repair pathways, is inhibited by CDDP exposure in the sensitive cells, but not in the resistant cells. This lack of down-regulation of USP1 expression at the translational level plays a primary role in CDDP resistance since inhibition of USP1 expression or activity by siRNA or the small molecule inhibitor ML323, respectively is sufficient to re-sensitize resistant cells to CDDP. We involved the USP1 mRNA translation as a major mechanism of CDDP resistance in NSCLC cells and suggest that USP1 could be evaluated as a candidate predictive marker and as a therapeutic target to overcome CDDP resistance. More generally, our results indicate that analysis of gene expression at the level of mRNA translation is a useful approach to identify new determinants of CDDP resistance.

Synergistic effects of eIF4A and MEK inhibitors on proliferation of NRAS-mutant melanoma cell lines

Activating mutations of the NRAS (neuroblastoma rat sarcoma viral oncogene) protein kinase, present in many cancers, induce a constitutive activation of both the RAS-RAF-MEK-ERK mitogen-activated protein kinase (MAPK) signal transduction pathway and the PI(3)K-AKT-mTOR, pathway. This in turn regulates the formation of the eIF4F eukaryotic translation initiation complex, comprising the eIF4E cap-binding protein, the eIF4G scaffolding protein and the eIF4A RNA helicase, which binds to the 7-methylguanylate cap (m(7)G) at the 5' end of messenger RNAs. Small molecules targeting MEK (MEKi: MEK inhibitors) have demonstrated activity in NRAS-mutant cell lines and tumors, but resistance sets in most cases within months of treatment. Using proximity ligation assays, that allows visualization of the binding of eIF4E to the scaffold protein eIF4G, generating the active eIF4F complex, we have found that resistance to MEKi is associated with the persistent formation of the eIF4F complex in MEKi-treated NRAS-mutant cell lines. Furthermore, inhibiting the eIF4A component of the eIF4F complex, with a small molecule of the flavagline/rocaglate family, synergizes with inhibiting MEK to kill NRAS-mutant cancer cell lines.