Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Neutrophil recruitment to the site of acute inflammation is a multistep process regulated by specific signaling molecules. The signaling mechanisms that regulate neutrophil-endothelial cell interactions remain incompletely understood. p38 mitogen-activated protein kinase (MAPK) signalling was shown to regulate different steps of neutrophil migration in response to inflammatory stimuli. The mitogen- and stress-activated protein kinase-1 (MSK1) can be activated by either extracellular-signal-regulated kinase (ERK) 1/2 or p38 MAPK. The aim of the present study is to investigate the effects of pharmacological suppression of MSK1 by its specific inhibitor, SB747651A, on various steps of neutrophil recruitment. In vivo studies were conducted using real-time and time-lapsed intravital video microscopy of the cremaster microcirculation to determine the dynamic leukocyte-endothelial cell interactions. Intrascrotal injection of macrophage inflammatory protein-2 (MIP-2, 0.2 μg/mouse) decreased leukocyte rolling velocity which was significantly reversed by pre-treatment with SB747651A (intrascrotal injection of 3 mg/kg). SB747651A pre-treatment enhanced MIP-2-induced increase in neutrophil adhesion and emigration. To better understand the effect of SB747651A on different steps of neutrophil recruitment, we placed a small piece of MIP-2-containing agarose gel on the exposed cremaster muscle and studied directed migration of neutrophils in the postcapillary venule and in the tissue. Superfusion of SB747651A (5 μM) on cremaster muscle subjected to MIP-2 gradient significantly increased rolling velocity and adhesion, but decreased emigration of neutrophils in comparison to superfusion of normal saline III without SB747651A. SB747651A treatment significantly affected transmigration time, detachment time, intravascular crawling and the velocity of migration, but not the directionality of migrating neutrophils in tissue. The expression of intercellular adhesion molecule-1 (ICAM-1) in cultured endothelial cells was up-regulated by co-treatment with SB747651A and MIP-2 but not by MIP-2 alone. Flow cytometry analysis showed that co-treatment of bone marrow neutrophils with SB747651A and MIP-2 significantly decreased macrophage antigen-1 (Mac-1) but not lymphocyte function associated antigen-1 (LFA-1) expression as compared with MIP-2 treatment alone. Collectively, our findings demonstrate that pharmacological suppression of MSK1 by SB747651A affects multiple steps of MIP-2-induced neutrophil recruitment in vivo.

The RAS-mitogen-activated protein kinase (MAPK) pathway is an essential signaling mechanism that regulates cellular processes and culminates in the activation of specific gene expression programs. Alterations in the RAS-MAPK signaling cascade can modify epigenetic programs and confer advantages in cell growth and transformation. In fact, deregulation of the cascade is a key event in tumour development with 30% of human cancers harbouring RAS mutations. In breast and pancreatic epithelial cancers, characterization of an aberrant RAS-MAPK pathway has focused on upstream mediators such as receptors and oncogenic RAS molecules but the impact of downstream targets remain poorly defined. Stimulation of the RAS-RAF-MEK-MAPK pathway leads to activation of mitogen- and stress-activated protein kinases 1 and 2 (MSK1/2) which are responsible for the phosphorylation of histone H3 on S10 and S28. We postulate that deregulation of the RAS-MAPK pathway produced by constitutive activation and/ or over-expression of upstream components or mitogen stimulation consequently leads to enhanced MSK1 activity and elevated histone H3 phosphorylation levels. We further hypothesize that MSK1-mediated H3 phosphorylation is critical for immediate early gene (IEG) expression, Ras-driven transformation and is associated with regulatory regions upon gene transcription. In mouse fibroblasts, we present evidence for the critical involvement of MSK1 and H3 phosphorylation as mediators that bridge the aberrant signals driven by the RAS-MAPK pathway with nucleosomal modifications, chromatin remodeling, IEG expression and malignant transformation. We then examined if activation of RAS-MAPK signaling in breast cancer cells elicits similar molecular events. We demonstrate that the RAS-MAPK pathway is induced and enhances the association of MSK1 and H3 phosphorylation on the IEG Trefoil Factor 1 resulting in transcriptional activation. We further observed that mutated K-RAS expression did not correlate with genomic instability or altered signaling in pancreatic cancer cell lines while overexpressed HER2 and EGFR breast cancer cell lines generally exhibit upregulated ERK1/2 and H3 phosphorylation levels. Taken together, our studies contribute to the further understanding of MSK-mediated transcriptional activation in response to RAS-MAPK signaling in oncogene-transformed and cancer cell lines. Inhibition of MSK activity may be an unexplored avenue for combination cancer therapy with abnormal RAS-MAPK signaling pathways.

The RAS-mitogen-activated protein kinase (MAPK) pathway is an essential signaling mechanism that regulates cellular processes and culminates in the activation of specific gene expression programs. Alterations in the RAS-MAPK signaling cascade can modify epigenetic programs and confer advantages in cell growth and transformation. In fact, deregulation of the cascade is a key event in tumour development with 30% of human cancers harbouring RAS mutations. In breast and pancreatic epithelial cancers, characterization of an aberrant RAS-MAPK pathway has focused on upstream mediators such as receptors and oncogenic RAS molecules but the impact of downstream targets remain poorly defined. Stimulation of the RAS-RAF-MEK-MAPK pathway leads to activation of mitogen- and stress-activated protein kinases 1 and 2 (MSK1/2) which are responsible for the phosphorylation of histone H3 on S10 and S28. We postulate that deregulation of the RAS-MAPK pathway produced by constitutive activation and/ or over-expression of upstream components or mitogen stimulation consequently leads to enhanced MSK1 activity and elevated histone H3 phosphorylation levels. We further hypothesize that MSK1-mediated H3 phosphorylation is critical for immediate early gene (IEG) expression, Ras-driven transformation and is associated with regulatory regions upon gene transcription. In mouse fibroblasts, we present evidence for the critical involvement of MSK1 and H3 phosphorylation as mediators that bridge the aberrant signals driven by the RAS-MAPK pathway with nucleosomal modifications, chromatin remodeling, IEG expression and malignant transformation. We then examined if activation of RAS-MAPK signaling in breast cancer cells elicits similar molecular events. We demonstrate that the RAS-MAPK pathway is induced and enhances the association of MSK1 and H3 phosphorylation on the IEG Trefoil Factor 1 resulting in transcriptional activation. We further observed that mutated K-RAS expression did not correlate with genomic instability or altered signaling in pancreatic cancer cell lines while overexpressed HER2 and EGFR breast cancer cell lines generally exhibit upregulated ERK1/2 and H3 phosphorylation levels. Taken together, our studies contribute to the further understanding of MSK-mediated transcriptional activation in response to RAS-MAPK signaling in oncogene-transformed and cancer cell lines. Inhibition of MSK activity may be an unexplored avenue for combination cancer therapy with abnormal RAS-MAPK signaling pathways.

Histone phosphorylation is often a direct outcome of activated intracellular signaling pathways, and functions to translate extracellular signals into appropriate biological outputs such as changes in gene expression. Growth factors and cellular stress trigger rapid and transient expression of immediate-early genes (such as c-fos, c-jun) in mammalian cells, and their induction strongly correlates with a transient phosphorylation of S10 and S28 on histone H3. While many signaling cascades that lead to H3 phosphorylation have been mapped out, mechanistic details of the downstream events and how H3 phosphorylation contributes to transcriptional activation are still poorly defined. To investigate the direct effects of H3 phosphorylation on transcription, we targeted the H3 kinase MSK1 to endogenous c-fos promoter, and found that this is sufficient to activate its expression. Moreover, targeting MSK1 to the tissue-specific -globin gene induces H3S28 phosphorylation and reactivates expression of this polycomb-silenced gene. Mechanistically, H3S28 phosphorylation not only disrupts binding of polycomb repressive complexes, but also induces a methyl-acetylation switch of the adjacent K27 residue. This provides the first indication that H3 phosphorylation is involved in antagonizing polycomb silencing. To further identify post-translational modifications (PTMs) that function together with MSK1-mediated H3 phosphorylation, I developed a novel nucleosome purification approach called Biotinylation-assisted Isolation of CO-modified Nucleosomes (BICON). This technique combines in vivo biotinylation by BirA and H3 phosphorylation by MSK1, allowing enrichment of phosphorylated nucleosomes using streptavidin. I found that MSK1-phosphorylated nucleosomes are hyper-acetylated on H3 and H4, and importantly, I identified a trans-tail crosstalk between H3 phosphorylation and H4 acetylation on K12. This proof-of-principle study demonstrates that BICON can be further adapted to study PTMs and crosstalks associated with other histone-modifying enzymes. Taken together, work described in this thesis shows that histone H3 phosphorylation can initiate additional PTM changes on other residues within the nucleosome, and such crosstalk plays an important role in regulating gene expression.

Histone phosphorylation is often a direct outcome of activated intracellular signaling pathways, and functions to translate extracellular signals into appropriate biological outputs such as changes in gene expression. Growth factors and cellular stress trigger rapid and transient expression of immediate-early genes (such as c-fos, c-jun) in mammalian cells, and their induction strongly correlates with a transient phosphorylation of S10 and S28 on histone H3. While many signaling cascades that lead to H3 phosphorylation have been mapped out, mechanistic details of the downstream events and how H3 phosphorylation contributes to transcriptional activation are still poorly defined. To investigate the direct effects of H3 phosphorylation on transcription, we targeted the H3 kinase MSK1 to endogenous c-fos promoter, and found that this is sufficient to activate its expression. Moreover, targeting MSK1 to the tissue-specific -globin gene induces H3S28 phosphorylation and reactivates expression of this polycomb-silenced gene. Mechanistically, H3S28 phosphorylation not only disrupts binding of polycomb repressive complexes, but also induces a methyl-acetylation switch of the adjacent K27 residue. This provides the first indication that H3 phosphorylation is involved in antagonizing polycomb silencing. To further identify post-translational modifications (PTMs) that function together with MSK1-mediated H3 phosphorylation, I developed a novel nucleosome purification approach called Biotinylation-assisted Isolation of CO-modified Nucleosomes (BICON). This technique combines in vivo biotinylation by BirA and H3 phosphorylation by MSK1, allowing enrichment of phosphorylated nucleosomes using streptavidin. I found that MSK1-phosphorylated nucleosomes are hyper-acetylated on H3 and H4, and importantly, I identified a trans-tail crosstalk between H3 phosphorylation and H4 acetylation on K12. This proof-of-principle study demonstrates that BICON can be further adapted to study PTMs and crosstalks associated with other histone-modifying enzymes. Taken together, work described in this thesis shows that histone H3 phosphorylation can initiate additional PTM changes on other residues within the nucleosome, and such crosstalk plays an important role in regulating gene expression.

La bronchiolite oblitérante (BO) est la principale cause de décès à long terme après transplantation pulmonaire. La BO se manifeste par une diminution des capacités respiratoires liée à l’obstruction des petites voies aériennes par un tissu inflammatoire et fibroprolifératif. Dans cette thèse nous avons étudié l’hypothèse de l’implication de la kinase nucléaire MSK1 dans la BO. Nous avons utilisé la transplantation hétérotopique de trachée comme modèle murin de BO. La pertinence du choix de ce modèle a été confirmée par l’étude de la re-vascularisation fonctionnelle de la greffe après transplantation. Dans ce modèle nous avons montré une augmentation de l’expression et de l’activité de MSK1 pendant le développement de la BO. Le traitement des souris transplantées avec des inhibiteurs pharmacologiques de MSK1 a permis d’inhiber l’inflammation et la fibroprolifération, montrant le rôle de MSK1 dans la BO. Nous avons également mis en place un essai de criblage utilisant la technologie HTRF pour rechercher de nouveaux inhibiteurs de MSK1. Les résultats décrits dans cette thèse, montrent que la kinase MSK1 est une potentielle cible thérapeutique pour combattre la BO. / Obliterative bronchiolitis (OB) is the chronic rejection after lung transplantation and is the main cause for late death post-transplantation. OB is characterized by decrease of the pulmonary function caused by obstruction of the small airways by inflammatory and fibroproliferative tissue. We studied the hypothesis of the implication of the nuclear kinase MSK1 in the OB. The relevance of the model was demonstrated by showing the rapid functional re-vascularization of the graft. In this model the allograft, shows an increased MSK1 expression and activity. We therefore treated mice with pharmacological inhibitors of the MSK1 activity and we demonstrated an inhibition of the inflammation and the fibroproliferation during OB. We next set up an enzymatic assay using the heterogeneous time-resolved fluorescence, to proceed for a screening for new MSK1 inhibitors. In summary, this study proposed MSK1 as potential therapeutic target to combat OB.

No description available.

No description available.

La bronchiolite oblitérante (BO) est la principale cause de décès à long terme après transplantation pulmonaire. La BO se manifeste par une diminution des capacités respiratoires liée à l'obstruction des petites voies aériennes par un tissu inflammatoire et fibroprolifératif. Dans cette thèse nous avons étudié l'hypothèse de l'implication de la kinase nucléaire MSK1 dans la BO. Nous avons utilisé la transplantation hétérotopique de trachée comme modèle murin de BO. La pertinence du choix de ce modèle a été confirmée par l'étude de la re-vascularisation fonctionnelle de la greffe après transplantation. Dans ce modèle nous avons montré une augmentation de l'expression et de l'activité de MSK1 pendant le développement de la BO. Le traitement des souris transplantées avec des inhibiteurs pharmacologiques de MSK1 a permis d'inhiber l'inflammation et la fibroprolifération, montrant le rôle de MSK1 dans la BO. Nous avons également mis en place un essai de criblage utilisant la technologie HTRF pour rechercher de nouveaux inhibiteurs de MSK1. Les résultats décrits dans cette thèse, montrent que la kinase MSK1 est une potentielle cible thérapeutique pour combattre la BO.