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During carcinogenesis, almost all the biological processes are modified in one way or another. Among these biological processes affected, anomalies in protein synthesis are common in cancers. Indeed, cancer cells are subjected to a wide range of stresses, which include physical injuries, hypoxia, nutrient starvation, as well as mitotic, oxidative or genotoxic stresses. All of these stresses will cause the accumulation of unfolded proteins in the Endoplasmic Reticulum (ER), which is a major organelle that is involved in protein synthesis, preservation of cellular homeostasis, and adaptation to unfavourable environment. The accumulation of unfolded proteins in the endoplasmic reticulum causes stress triggering an unfolded protein response in order to promote cell survival or to induce apoptosis in case of chronic stress. Transcription and also translational reprogramming are tightly controlled during the unfolded protein response to ensure selective gene expression. The majority of stresses, including ER stress, induce firstly a decrease in global protein synthesis accompanied by the induction of alternative mechanisms for initiating the translation of mRNA, later followed by a translational recovery. After a presentation of ER stress and the UPR response, we will briefly present the different modes of translation initiation, then address the specific translational regulatory mechanisms acting during reticulum stress in cancers and highlight the importance of translational control by ER stress in tumours.

Delta-like 4 (DLL4) is a pivotal endothelium specific Notch ligand that has been shown to function as a regulating factor during physiological and pathological angiogenesis. DLL4 functions as a negative regulator of angiogenic branching and sprouting. Interestingly, Dll4 is with Vegf-a one of the few examples of haplo-insufficiency, resulting in obvious vascular abnormalities and in embryonic lethality. These striking phenotypes are a proof of concept of the crucial role played by the bioavailability of VEGF and DLL4 during vessel patterning and that there must be a very fine-tuning of DLL4 expression level. However, to date the expression regulation of this factor was poorly studied. In this study, we showed that the DLL4 5&prime, UTR harbors an Internal Ribosomal Entry Site (IRES) that, in contrast to cap-dependent translation, was efficiently utilized in cells subjected to several stresses including hypoxia and endoplasmic reticulum stress (ER stress). We identified PERK, a kinase activated by ER stress, as the driver of DLL4 IRES-mediated translation, and hnRNP-A1 as an IRES-Trans-Acting Factor (ITAF) participating in the IRES-dependent translation of DLL4 during endoplasmic reticulum stress. The presence of a stress responsive internal ribosome entry site in the DLL4 msRNA suggests that the process of alternative translation initiation, by controlling the expression of this factor, could have a crucial role in the control of endothelial tip cell function.

International audience; Here we report the fabrication of lotus-leaves-like tailored SU8 micropillars and their application in the context of a multi-technique characterization protocol for the investigation of the structural properties of the two estrogen receptors (ERα66/ERα46). ER (α) expression is undoubtedly the most important biomarker in breast cancer, because it provides the index for sensitivity to endocrine treatment. Beside the well-characterized ERα66 isoform, a shorter one (ERα46) was reported to be expressed in breast cancer cell line. The superhydrophobic supports were developed by using a double step approach including an optical lithography process and a plasma reactive ion roughening one. Upon drying on the micropillars, the bio-samples resulted in stretched fibers of different diameters which were then characterized by synchrotron X-ray diffraction (XRD), Raman and FTIR spectroscopy. The evidence of both different spectroscopic vibrational responses and XRD signatures in the two estrogen receptors suggests the presence of conformational changes between the two biomarkers. The SU8 micropillar platform therefore represents a valid tool to enhance the discrimination sensitivity of structural features of this class of biocompunds by exploiting a multi-technique in-situ characterization approach.

Clinical parameters of the breast tumor samples. IDC invasive ductal carcinoma, ILC invasive lobular carcinoma. Figure S2. Expression of Flag-ERα36 in transiently transfected MDA-MB231 as detected by immunocytochemistry using an anti-Flag antibody. Figure S3. Analysis of potential correlation between the clinical parameters of the breast tumor samples and the expression of ERα46 isoform. A significant P value (indicated in red) was only found between ERα46 expression and HER-2 positive breast tumors. IDC invasive ductal carcinoma, ILC invasive Lobular Carcinoma. Figure S4. Results of the proteomic analysis of the ERα46 protein detected in tumor samples. A) Western blot with the SP1 antibody obtained after immunoprecipitation of ERα with HC20 antibody in two human tumors overexpressing the putative ERα46 isoform. B and C) Sequence coverage obtained from the peptides identified by proteomic analysis shown in bold red on ERα66 and on ERα46 isoforms M (methionine): putative translational start sites generating the ERα46 isoform. Figure S5. The stress-induced increase in LucF activity is reproducible in MCF7 cells (A) and is not due to the generation of mono-cistronic LucF transcripts via an internal promoter or cryptic splicing as observed in MDA-Lenti-AB exposed to two siRNAs-lucR (B and C). Figure S6. Modulation profiles of the interaction of ERα46 (red) and ERα66 (blue) with coregulators in A) Apo proteins and B) in response to E2 binding. C) Profile of EC50 values of 4-OH-tamoxifen- (red) and fulvestrant- (blue) induced modulation of ERα46 and ERα66 coregulators interaction when use in antagonists mode with 6.3 nM E2. Figure S7. List of primers used in the expression profiling of target genes. Figure S8. Fold-changes (FC) in gene expression± SEM in MDA-ERα46 and MDA-ERα66 cells in response to 4-h treatment with E2 (10–8 M). P values were determined by Mann-Whitney test. Significant P values are indicated in red. (PPTX 939 kb)

International audience; The ancestral status of estrogen receptor (ER) in the family of the steroid receptors has probably contributed to the pleiotropic actions of estrogens, and in particular of 17β-estradiol (E2). Indeed, in addition to their well described role in sexual development and reproduction, they influence most of the physiological processes. The pathophysiological counterpart of these actions includes prevention of osteoporosis, atheroma and type 2 diabetes,... but also promotion of uterus and breast cancer growth. Thus, the major challenge consists in uncoupling some beneficial actions from other deleterious ones, i.e. selective ER modulation. Tamoxifen and raloxifen are already used as they prevent the recurrence of breast cancer, and mimic estrogen action mainly on bone. Both E2 and tamoxifen exhibit a proliferative and thus protumoral action on the endometrium. Activation of ER alpha (ERα) and beta (ERβ) regulates target gene transcription (genomic action) through two independent activation functions AF-1 and AF-2, but can also elicit rapid membrane initiated steroid signals. In the present review, we attempted to summarize recent advances provided by the in vivo molecular "dissection" of ERα, allowing the uncoupling of some of its actions, and potentially paving the way to optimized selective ER modulators.