Indiana University-Purdue University Indianapolis (IUPUI) / Gene expression is a highly coordinated process that relies upon appropriate regulation of translation for protein homeostasis. Regulation of protein synthesis largely occurs at the initiation step in which the translational start site is selected by ribosomes and associated initiating factors. In addition to the coding sequences (CDS) for protein products, short upstream open reading frames (uORFs) located in the 5’-leader of mRNAs are selected for translation initiation. While uORFs are largely considered to be inhibitory to translation at the downstream CDS, uORFs can also promote initiation of CDS translation in response to environmental stresses. Multiple transcripts associated with stress adaptation are preferentially translated through uORF-mediated mechanisms during activation of the Integrated Stress Response (ISR). In the ISR, phosphorylation of α subunit of the translation initiation factor eIF2α (eIF2α~P) during environmental stresses results in a global reduction in protein synthesis that functions to conserve energy and nutrient resources and facilitate reprogramming of gene expression. Many key regulators of the ISR network are subject to preferential translation in the response to eIF2α-P. These preferentially translated genes include the pro-apoptotic transcriptional activator Chop that modifies gene expression programs, feedback regulator Gadd34 that targets the catalytic subunit of protein phosphatase 1 to dephosphorylate eIF2α~P, and glutamyl-prolyl tRNA synthetase Eprs that increases the charged tRNA pool and primes the cell for resumption of protein synthesis after stress remediation. Ribosome bypass of at least one inhibitory uORF is a common theme between Chop, Gadd34, and Eprs, which allows for their regulated expression in response to cellular stress. However, different features encoded within the uORFs of the Chop, Gadd34, and Eprs mRNAs provide for regulation of their inhibitory functions, illustrating the complexities of uORF-mediated regulation of gene-specific translation. Importantly, preferentially translated ISR targets can also be transcriptionally regulated in response to cellular stress and misregulation of transcriptional or translational expression of Gadd34 can elicit maladaptive cell responses that contribute to disease. These mechanisms of translation control are conserved throughout species, emphasizing the importance of translation control in appropriate gene expression and the maintenance of protein homeostasis and health in diverse cellular conditions.

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Due to the high energetic expenditure for the cell, the protein biosynthesis in eukaryotes is an extensively controlled process predominantly regulated at the ribosomal biogenesis and translation initiation steps. The ribosomal biogenesis defines the global translational aptitude of the cell. It is a mainly nucleolar process which is regulated at multiple steps (e.g. transcription, rRNA processing and modification, ribosomal protein translation etc). However, the most extensively regulated and the rate limiting step of translation is the initiation. Multiple eukaryotic translation initiation factors (eIFs) function to facilitate this priming step of translation. The initial recognition of the mRNA molecule happens through the 5' cap structure found in all mRNAs of nuclear origin. This event is mediated through the recruitment of heterotrimeric complex eIF4F consisting of cap-binding protein eIF4E, scaffolding protein eIF4G and the RNA helicase eIF4A unwinding secondary structures found in 5'UTR of mRNA and thus thought to facilitate the scanning process. The helicase activity of elF4F complex or of eIF4A alone is further potentiated by eIF4B in vitro. The latter protein is at the focus of present thesis. / Signal transduction regulates multiple cellular processes including mitogenesis, differentiation, apoptosis, chemotaxis etc. Signaling pathways also regulate ribosomal biogenesis to coordinate mitogenic cues, nutrient and energy availability with the translational capacity of the cells. Mounting evidence links PI3K-Akt-mTOR and Ras-MAPK cascades to the translational control. In this thesis, I show that PI3K/mTOR and MAP kinase cascades converge to phosphorylate eIF4B on Ser422. This phosphorylation results in an increased interaction with eIF3, an essential factor bridging between eIF4F and the small ribosomal subunit. Physiological significance of eIF4B phosphorylation on Ser422 has been demonstrated by the stimulatory effect of eIF4B Ser422Asp phosphomimetic mutant on cap-dependent translation. Taken together, this represents a new paradigm of translational control mechanism regulated by signaling crosstalk. The function of eIF4B in vitro is well characterized but its in vivoeffects are disputed in literature. To address this I established HeLa cell line stably expressing shRNA targeting eIF4B. eIF4B silencing inhibits proliferation rates and anchorage-independent growth. Expression of luciferase reporter gene containing 5' terminal oligopyrimidine tract (TOP) is selectively repressed in eIF4B-silenced cells and can be rescued by exogenous eIF4B regardless of Ser422 phosphorylation status. Moreover, the de novo synthesis rates of endogenous ribosomal proteins in serum starved cultures recapitulate the luciferase reporter assay data. Utilizing polysomal analysis, I was able to show more significant inhibition of translation initiation in serum starved eIF4B-silenced cells. Our attempt to discover novel eIF4B-interacting proteins by Mass Spectrometry approach led to the identification of nucleolar RNA helicase DDX21. Confocal microscopy has shown partial co-localization of tagged eIF4B and DDX21 in nucleolar periphery. Pulse chase experiments metabolically labeling rRNA show an attenuated 28S rRNA production and concomitant accumulation of 36S intermediates in eIF4B-silenced cells. Since ribosomal biogenesis is highly coordinated process and requires strict stoichiometry maintenance of ribosomal components the observed inhibition of rRNA processing could be consequential to the decreased ribosomal protein expression. However, given the fact that eIF4B is associated with the nucleolar pre-ribosomal particle complexes its direct effect on rRNA processing cannot be ruled out. Regulation of ribosomal biogenesis by translation initiation factor may represent an important control mechanism allowing cells to co-ordinate these two processes.

Diss. (sammanfattning) Stockholm : Karolinska institutet, 2005. / Härtill 6 uppsatser.

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Le cancer de la prostate (CaP) est devenu un véritable problème de santé publique dans les pays industrialisés. L'hormonothérapie reste le traitement de première ligne le plus efficace dans les cancers avancés mais il n'empêche pas la progression vers un stade androgéno-indépendant (AI), pour lequel la chimiothérapie s'avère peu efficace. Une des stratégies pour améliorer les thérapies actuelles consiste à cibler des gènes de survie surexprimés dans les CaPs AI afin de restaurer la sensibilité aux traitements du CaPs. Hsp27, protéine surexprimée dans ces cancers, à un effet cytoprotecteur qui engendre une résistance aux traitements. Elle est maintenant reconnue comme une cible thérapeutique importante. Rocchi et al. ont développé un oligonucléotide antisense (ASO) de deuxième génération (OGX-427) qui cible l'ARNm d'Hsp27. OGX-427 est actuellement en essai clinique phase II chez des patients atteints de CaPs au Canada et aux Etats-Unis. Mon projet de thèse a porté sur l'étude des mécanismes d'action d'Hsp27 impliqués dans l'évolution AI du CaP. Cette étude a pour but d'améliorer la sureté pharmacologique d'OGX-427, mais aussi d'identifier de nouvelles cibles thérapeutiques visant spécifiquement les cellules tumorales. Mes travaux de thèse ont montré que lors d'un stress cellulaire induit par hormonothérapie et/ou chimiothérapie, Hsp27 interagit avec le facteur eucaryotique d'initiation de la traduction eIF4E et le protège de sa dégradation par la voie ubiquitine/protéasome. Ceci maintient la synthèse protéique et engendre une survie cellulaire impliquée en partie dans l'effet cytoprotecteur médié par Hsp27. / Prostate cancer (PC) has become a real public health issue in industrialized countries, mainly due to patients' relapse by castration-resistant (CR) disease after androgen ablation. One strategy to improve current therapies in advanced PC involves targeting genes that are activated by androgen withdrawal, either to delay or prevent the emergence of the CR phenotype. Hsp27 is over-expressed in this cancer and has been shown to play a cytoprotective role leading to treatments resistance. This protein is now considered as promising therapeutic target. Rocchi, P. et al. developed and patented a second generation antisens oligonucleotides (ASO) targeting Hsp27 that has been licensed (OGX-427) and phase II clinical trials are currently in process in PC in Canada and USA. My PhD project focused on the study of Hsp27 action mechanisms involved in CRPC progression. The present study aims to improve pharmacological safety of OGX-427 and to identify new therapeutic targets specific of CRPC cells. The results of my PhD have shown that during cell stress induced by hormone- and/or chemotherapy, Hsp27 interacts with eukaryotic translation initiation factor eIF4E and protects it from degradation by the ubiquitin/proteasome pathway. This maintains protein synthesis and leads to cell survival, partly involved in the cytoprotection mediated by Hsp27. Our work therefore concerned the characterization of the interaction site between Hsp27 and eIF4E in order to identify potential inhibitors of this interaction that could delay CRPC progression.

Leucoencefalopatia com substância branca evanescente é uma doença geneticamente determinada, causada por mutação no gene do eIF2B. A idade varia do período pré-natal até idade adulta, as manifestações geralmente são desencadeadas por trauma ou infecção. Os sintomas são variáveis, incluem ataxia cerebelar, espasticidade e relativa preservação cognitiva. Os achados de ressonância magnética (RM) são típicos e caracterizam-se por extenso comprometimento da substância branca. Estudamos 10 pacientes, com evolução súbita ou progressiva dos primeiros sintomas, entre 1 a 12 anos de idade. Ataxia e espasticidade estavam presentes em todos os pacientes e funções cognitivas relativamente preservadas. A clínica associada à RM, que demonstrava comprometimento difuso da substância branca, permitiu o diagnóstico / Leukoencephalopathy with vanishing white matter is an inherited disorder caused by mutation in one of five subunits of eIF2B gene. Age of onset varies from prenatal to adulthood and manifestations are commonly triggered by trauma or infection. Symptoms are variable and include cerebellar ataxia and spasticity, with relative sparing of cognitive function. Magnetic resonance imaging (MRI) findings are typically characterized by widespread white matter abnormality. We studied 10 patients, with sudden or slowly progressive symptoms starting between 1-12 years of age. Ataxia and spasticity were present in all patients, and cognitive functions were relatively preserved. MRI studies demonstrated diffuse white matter abnormalities which, combined with clinical findings, allow diagnosis

Nitric oxide (NO) is a neurotransmitter involved in memory processes. Currently, the only recognized physiological signalling pathway controlled by NO is the activation of guanylyl cyclase. In this thesis, we propose an alternative NO-signalling pathway that involves the Heme-regulated eukaryotic initiation factor-2a kinase (HRI) and eIF2a phosphorylation. We have found that the enzyme BACE1, a key protein in Alzheimer’s disease (AD), is controlled by this novel pathway. This pathway would be involved in the physiology of memory formation and learning processes. We have also studied how an external stress factor, the Herpes Simplex Virus 1, can disrupt this cascade leading to a pathological increase in BACE1 and amyloid ß-peptide (Aß) production. Aß aggregates forming fibrils that generate free radicals. These react with NO producing peroxynitrite, which contribute to AD progression. Since NO turns toxic when produced in a pro-oxidant environment we have also studied the effect of peroxynitrite in Stroke. / L’òxid nítric (NO) és un neurotransmissor involucrat en processos de memòria. Actualment, l’única cascada de senyalització fisiològica controlada per NO consisteix en l’activació de la guanilat ciclasa. En aquesta tesi, en proposem una d’alternativa que inclou la fosforilació de eIF2a per la Heme-regulated eukaryotic initiation factor-2a kinase (HRI). Hem mostrat com l’enzim BACE1, una proteïna clau en la malaltia d’Alzheimer (AD), és controlat per aquesta nova cascada de senyalització, que podria estar involucrada en la fisiologia de l’aprenentatge i la memòria. També hem estudiat com un factor d’estrès extern, l’ Herpes Simplex Virus 1, pot pertorbar aquesta cascada donant lloc a increments patològics en BACE1 i pèptid ß-amiloide (Aß). L’Aß agrega formant fibril·les que generen radicals lliures. Aquests reaccionen químicament amb NO produint peroxinitrit, que contribueix a la progressió de l’AD. Pel fet que l’NO esdevé tòxic quan és produït en un entorn pro-oxidant, hem estudiat també l’impacte que el peroxinitrit té en l’ictus.

Leucoencefalopatia com substância branca evanescente é uma doença geneticamente determinada, causada por mutação no gene do eIF2B. A idade varia do período pré-natal até idade adulta, as manifestações geralmente são desencadeadas por trauma ou infecção. Os sintomas são variáveis, incluem ataxia cerebelar, espasticidade e relativa preservação cognitiva. Os achados de ressonância magnética (RM) são típicos e caracterizam-se por extenso comprometimento da substância branca. Estudamos 10 pacientes, com evolução súbita ou progressiva dos primeiros sintomas, entre 1 a 12 anos de idade. Ataxia e espasticidade estavam presentes em todos os pacientes e funções cognitivas relativamente preservadas. A clínica associada à RM, que demonstrava comprometimento difuso da substância branca, permitiu o diagnóstico / Leukoencephalopathy with vanishing white matter is an inherited disorder caused by mutation in one of five subunits of eIF2B gene. Age of onset varies from prenatal to adulthood and manifestations are commonly triggered by trauma or infection. Symptoms are variable and include cerebellar ataxia and spasticity, with relative sparing of cognitive function. Magnetic resonance imaging (MRI) findings are typically characterized by widespread white matter abnormality. We studied 10 patients, with sudden or slowly progressive symptoms starting between 1-12 years of age. Ataxia and spasticity were present in all patients, and cognitive functions were relatively preserved. MRI studies demonstrated diffuse white matter abnormalities which, combined with clinical findings, allow diagnosis

Le récepteur de mort CD95 participe à de nombreuses fonctions physiologiques en transmettant des signaux apoptotiques. Son ligand membranaire, CD95L, est principalement exprimé à la surface des lymphocytes et contrôle ainsi l’homéostasie cellulaire et l’élimination des cellules infectées ou transformées. Certaines situations pathologiques conduisent à une expression ectopique du CD95L par d’autres types cellulaires,associé à son clivage par des métalloprotéases (cl-CD95L). La forme soluble ainsi libérée perd sa capacité à transmettre l’apoptose mais déclenche l’activation de voies non-apoptotiques induisant l’inflammation dans des maladies inflammatoires chroniques comme le lupus érythémateux systémique (LES) ou encore les formes métastatiques du cancer du sein. Dans ces deux pathologies, de fortes quantités de cl-CD95L sont détectées dans le sérum de ces patients et ont été associés à la progression des pathologies. Dans le LES, nous établissons que cl-CD95L contribue au processus inflammatoireen favorisant la transmigration endothéliale des lymphocytes Th17. Cette migration cellulaire dépendante de CD95 nécessitele recrutement de la PLCγ1 sur le domaine juxta-membranaire de CD95 qui induitl’activation du signal calcique. Pour identifier d’autres partenaires moléculaires de CD95, une analyse protéomique a été réalisée et a permis d’identifier une association entre CD95 et la machinerie traductionnelle. Cette interaction nécessite le recrutement d’eIF4A1 au niveau du domaine juxta-membranaire de CD95. Nous avons par ailleurs montré que dans des lignées cancéreuses mammaires, eIF4A1 participe à la traduction de certaines protéines comme la sérine-thréonine kinase Akt pour faciliter l’activation de la voie de signalisation PI3K et la migration cellulaire induite par CD95. Cette étude a donc mis en évidence l’implication d’un nouveau domaine de CD95 dans l’induction des signaux non-apoptotiques. Ce domaine juxta-membranaire a été nommé CID pour « calcium inducing domain ». De plus, ce domaine fusionné à un peptide perméant provenant de la protéine TAT appelé TAT-CIDa montré son efficacité pour inhiber la migration lymphocytaire chez les souris lupiques et offre de nouvelles perspectives pour le développement de traitements améliorants les symptômes inflammatoires du LES. / The death ligand CD95L, mainly expressed by immune cells, contributes to the elimination ofinfected and transformed cells. In pathological contexts, CD95L can be expressed by others cell types such as endothelial cells.CD95L can be cleaved by metalloproteases to generate a soluble CD95L (cl-CD95L) failing to trigger the apoptotic signaling pathwaybutinducing non-pro-apoptotic signaling pathways. cl-CD95L promotes inflammation in chronic inflammatory disorders such as systemic lupus erythematosus (SLE) and increases risks of metastatic dissemination in breast cancer patients. In SLE patients, we established that high amounts of cl-CD95L fuels inflammation by promoting endothelial transmigration of activated Th17 cells. This CD95-drivencell migration requires PLCγ1 recruitment by CD95 and the subsequentimplementation of the calcium signal. To identify in an exhaustive fashion, all molecular partners of CD95, a global proteomic analysis was undertaken. This TAP-Tag approach highlighted a strong association between the translational machinery and CD95. This analysis was confirmed by a two-hybrid approach revealingthat the translation initiation factor eIF4A1 directly interactedwith CD95.In breast cancer cells, we established that eIF4A1 was instrumental in the translation of certain genes such as Akt contributing to the implementation of the CD95-mediated PI3K signaling pathway and cell migration. In this study, we identifiedthe CD95 domaininvolved in the induction of the non-apoptotic signaling pathway. This domain was named CID for “calcium inducing domain”.Moreover, wegenerated a therapeutic molecule consisting of theCID fused to the cationic cell-penetrating HIV TAT domain. TAT-CID prevented the accumulation of Th17 cells in inflamed organs of lupus-prone mice and could turn out to be an original therapeutic molecule to alleviate clinical symptoms in SLE patients.