L'obésité est aujourd’hui considérée comme une maladie inflammatoire chronique dite de « bas grade » principalement caractérisée par une augmentation de l’inflammation du tissu adipeux. Les adipocytes et les macrophages sont connus pour jouer un rôle clé dans l’établissement, la progression et le maintien de l'inflammation. Dans mon projet de thèse, nous nous sommes particulièrement intéressés aux mécanismes transcriptionnels impliqués dans l'inflammation chronique en décodant l'action du corégulateur transcriptionnel GPS2 (G protein pathway suppressor 2) dans les adipocytes et les macrophages du tissu adipeux. Dans un premiers temps, nous avons étudié la régulation et les actions de GPS2 (et ses partenaires SMRT et NCOR) dans le tissu adipeux humains de sujets obèses par rapport à des sujets minces. Dans cette première étude, nous avons identifié un mécanisme épigénomique qui participe à la régulation de la transcription des gènes inflammatoires dans les adipocytes lors de l’obésité. Nous avons démontré que la dérégulation de GPS2 contribuait à l'inflammation du tissu adipeux en permettant à la dérépression de certains gènes inflammatoires dont l’interleukine 6. Dans la deuxième étude, nous avons caractérisé les conséquences de l’invalidation de GPS2 dans le phénotype inflammatoire des macrophages ainsi que les conséquences in vivo sur la progression de l’insulino-résistance. Pour ceci, nous avons généré un modèle de souris où GPS2 a été spécifiquement invalidé dans les macrophages (GPS2-MacKO). De manière intéressante, les souris GPS2-MacKO, présentent une expression accrue des gènes impliqués dans la voie de signalisation des TLR et des chimiokines dans les macrophages isolés. Par conséquent, une augmentation significative de l'infiltration des macrophages dans le tissu adipeux est observée dans un contexte d’obésité induisant une altération de l’homéostasie glucidique. Par nos approches génomiques, transcriptomiques et épigénomiques, nous avons pu révéler les voies de signalisations spécifiquement contrôlées par GPS2. Ces travaux démontrent également l’importance des régulations épigénomiques dans l'inflammation métabolique du tissu adipeux durant l'obésité. / Obesity is now considered a chronic low-grade inflammatory disease with increased levels of inflammatory mediators both in circulation and adipose tissue. Among adipose tissue cell types, adipocytes and macrophages are known to play key roles in the progression of inflammation by establishing and maintaining it. In this PhD project, we particularly focus on the transcriptional mechanisms behind the chronic low-grade inflammation by deciphering the action of GPS2 in adipocytes and adipose tissue macrophages. We initially studied the gene regulation and the actions of GPS2 and its partners in adipose tissue and adipocytes of human obese subjects compared to lean subjects. In this first study we identified a novel regulatory pathway that participates in the transcriptional control of inflammation associated with obesity, both in adipose tissue and adipocytes. We have shown that GPS2 and SMRT were differentially expressed and regulated in obese adipocytes. In addition, this dysregulation contributes to inflammation of the adipose tissue by allowing the derepression of specific inflammatory genes. In a second study, in order to go further in the characterisation of the in vivo function of GPS2, we generated a mouse model were GPS2 was specifically invalidated in macrophages. Models of diet-induced obesity were applied in these experiments. Interestingly, GPS2-MacKO mice showed an increased expression of inflammatory genes both in adipose tissue and isolated ATMs (F4/80+ cells) associated with a significant increase of macrophages infiltration in the adipose tissue. Finally, we observed that GPS2-MacKO mice had impaired glucose metabolism as they presented high glucose intolerance as well as an important insulin resistance.

Through endocrine and exocrine functioning, physiological needs are communicated to body systems. Physiological need is met through the actions of intracellular signaling cascades and calibrated through an extensive network of regulatory cross talk within the cells of a given tissue. The insulin receptor belongs to a family of perhaps one of the most well studied family of dual receptor and tyrosine kinases (RTK). The signaling cascade downstream of the insulin RTK can be initiated through Insulin or growth factor ligand binding and bears growing relevance to the projected epidemic of obesity related illness and associated cancers. The primary function of the post-prandial insulin response is to support nutrient uptake and storage. Insulin (IS), Insulin-Like Growth Factor (IGF), and Epidermal Growth Factors (EGF) contribute to glucose metabolism, energetic homeostasis, and anabolic applications through effector kinases downstream of activated (phosphorylated) insulin receptor substrates (IRS). Protein Kinase B (AKT) kinase is one such cytosolic effector known to be of critical importance to anabolic metabolism and general cell survival. Under normal circumstances, AKT activity is dependent upon dual phosphorylation events known to occur at the plasma membrane. In an attempt to better understand the mechanism of AKT recruitment to the plasma membrane, earlier experiments reported that IRS stimulation by Insulin-Like Growth Factors (IGF) and Epidermal Growth Factors (EGF) resulted in downstream poly-ubiquitination and subsequent activation of the AKT kinase. This sequence of post-translational modification events suggested that non-proteolytic AKT ubiquitination, accomplished by the E2 Ubiquitin Conjugating enzyme (UBC13), was an important mediator of AKT activation. Through subsequent experimentation, it was determined that non-proteolytic ubiquitination was a necessary step for AKT activation following IRS activation by Insulin. Furthermore, the same two sites previously described in the context of IGF/EGF signaling were exploited through targeted mutagenesis and shown to synergistically regulate AKT translocation to the plasma membrane. Mutant AKT variants with a single mutation to either ubiquitination site resulted in partial knock down of phosphorylated AKT (pAKT), while variants with double mutations resulted in a complete loss of pAKT detection. Under physiologic conditions UBC13 activity can be antagonized by a small multifunctional protein called G-Protein Pathway Suppressor 2 (GPS2). Bearing the kinetics of an endogenous inhibitor, GPS2-mediated regulation directly inhibits the ubiquitin conjugating activity of the enzyme; thereby restricting AKT non-proteolytic poly-ubiquitination and antagonizing the insulin signaling network through a conserved mechanism. In accordance with this role, we have previously shown that GPS2 presence in adipocytes modulates systemic metabolism by restricting the activation of insulin signaling during the fasted state, whereas in absence of GPS2, the adipose tissue is more efficient at lipid storage, and obesity becomes uncoupled from inflammation and insulin resistance. As we are just beginning to unravel the regulatory network governing the cellular response to nutrient excess and pro-growth signaling, it remains unclear whether UBC13 activity is universally engaged in AKT translocation and activation. Here we have focused on the mitochondrial pool of AKT and investigated its regulation. Our findings add to the growing body of knowledge by demonstrating that in pre-adipocytes mitochondrial AKT is activated, in a UBC13-dependent fashion, following insulin stimulation. We also show that GPS2-mediated inhibition of UBC13 equally antagonizes AKT activation in different subcellular compartments, and that mitochondrial AKT activation is partially Phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K) dependent.

The GPS2 protein (G-protein pathway suppressor 2) is a product of the mammalian gps2 gene. It was originally identified and characterized in the context of G protein mitogen-activated protein kinase (MAPK) signaling pathways. Several studies have linked GPS2 with the inhibition of the ubiquitin conjugating enzyme UBC13. GPS2-mediated inhibition of UBC13 regulates several metabolic and inflammatory pathways. It has been shown that a lack of GPS2 is correlated with an increase in adiposity and inflammation due to the aberrant activity of UBC13 affected pathways. Therefore, understanding the relationship between UBC13 and GPS2 will provide further understanding of the molecular processes involved in adipose tissue levels, inflammation and downstream molecular responses. In this study, we attempt to determine the molecular determinants of GPS2 interaction with UBC13 by optimizing the protein expression protocol required to produce GPS2 protein expression in Escherichia coli in quantities viable for biochemical and structural assays. Our results indicate that optimization of the gps2 sequence is required for efficient GPS2 protein expression in E. coli cells. Thanks to this optimization we have been able to successfully express GPS2 full length and several fragments, however, further optimization will be required for assessing GPS2-UBC13 molecular binding via in vitro binding assays.

OBJECTIVE: Obesity is a chronic disease with high incidence worldwide, which promotes the risk of incidence of type 2 diabetes (T2D). Obesity-induced adipocyte expansion promotes local chronic inflammation in the adipose tissue which is considered a contributing factor to insulin resistance, hyperinsulinemia, and T2D. Many organs, including adipose tissue, involve in the dysregulation of glucose homeostasis in T2D. The crosstalk between adipose tissue/adipocytes and pancreatic ß-cells has provoked scientists' interest for years. Here in this thesis, we focused on the effect carried out by adipocyte-specific GPS2 depletion on insulin secretion from pancreatic ß-cells. METHODS: Conditioned media collected over 24 h from both primary adipocyte and adipose tissue explant cultures from high fat diet (HFD)-fed WT and adipocyte-specific GPS2 knock-out (GPS2-AKO) mice were used to treat INS-1 clonal pancreatic ß-cells or primary islets from chow-diet WT mice. Conditioned media was diluted 1:8 in culture media of clonal INS-1 cells (cultured in media with 4 mM or 11 mM glucose chronically) and primary islets (cultured in media with 11 mM glucose) and incubated for 18 h before measuring insulin secretion. The isolated islets from chow-diet WT mice were also be treated with the primary adipocytes conditioned media from eWAT (epididymal white adipose tissue) of HFD-fed WT and GPS2-AKO mice. In addition, the effect of exosomes extracted from primary adipocyte conditioned media of HFD-fed WT and GPS2-AKO mice on GSIS was investigated in clonal INS-1 cells. Glucose-stimulated insulin secretion (GSIS) was measured to assess differences in insulin secretion by INS-1 cells and islets from mice in response to signaling from WT or GPS2-AKO adipocytes. RESULTS: Adipocyte conditioned media from both WT and GPS2-AKO mice reduced GSIS from INS-1 cells by the same extent compared to a non-treated control. The same result was obtained using media conditioned by adipose tissue explant culture. Exosomes isolated from adipocyte conditioned media from both WT and GPS2-AKO mice also reduced GSIS from INS-1 cells with no significant difference between WT and GPS2-AKO. Islets isolated from chow-diet WT mice treated with adipocyte conditioned media from eWAT of WT and GPS2-AKO mice also showed no significant difference between WT and GPS2-AKO in GSIS compared to our non-treated control. CONCLUSIONS: Both conditioned media and exosomes from primary adipocytes of HFD-fed mice inhibits GSIS from INS-1 cells and isolated islets, but no difference was observed between WT and GPS2-AKO mice. We conclude that the deletion of GPS2 in adipocytes does not influence GSIS from pancreatic ß-cells under our experimental conditions. Conditioned media-induced inhibition of GSIS is mediated by factors that may contribute to adipocyte-ß-cell crosstalk in-vivo. / 2025-11-02T00:00:00Z

Breast cancer is a multifaceted disease that affects 1 in every 8 women. Triple negative breast cancer (TNBC) accounts for ~15-20% of all diagnosed breast cancers and is characterized by the absence of ER, PR, and HER2 on the tumor cell surface. As most cancer therapies to date target these cell surface receptors, TNBC is the only subtype of breast cancer without a targeted therapy and thus prognosis for it remains poor. The heterogeneity of TNBC also makes finding a targeted therapy particularly difficult. This work focuses on different methods of targeting distinct subpopulations of TNBC in order to identify potential novel therapeutic nodes to exploit as targeted therapies. The first chapter describes the use of a directed siRNA synthetic lethality screen to target vulnerabilities associated with basal TNBC, the most common TNBC subtype. The screen identified multiple dependency genes associated with RNA splicing, particularly those in the U4/U6.U5 tri-snRNP complex (PRPF8, PRPF38A). Depletion of these genes or the upstream splicing inhibitor E7107 in basal TNBC cell lines resulted in intronic retention and altered splicing of transcripts in pathways necessary for TNBC survival, including mitosis and apoptosis. In vivo, E7107 hindered the growth of both basal cell line and patient derived xenographs, a phenotype that was enhanced with the addition of the proteasome inhibitor bortezomib. This suggests that splicing and proteasome inhibition could be an effective basal TNBC treatment. The second chapter investigates the role of G-Protein Pathway Suppressor 2 (GPS2) as a tumor suppressor in the PI3K/AKT pathway in TNBC. Previous work has shown that GPS2 acts as a negative regulator of this pathway through inhibition of Ubc13-mediated activation of AKT in the insulin signaling pathway. In this study, MDA-MB231-GPS2KO cells were found to have increased proliferative, migratory, and invasive properties, which were rescued upon treatment with the allosteric AKT inhibitor MK2206. In vivo, GPS2 depleted cells conferred greater tumor burden in an orthotopic mouse model that was also responsive to AKT inhibition. Transcriptomic analysis showed significant overlap between MB231-GPS2KO and MB231 cells modified to have constitutively active AKT, indicating that the phenotypes observed in MB231-GPS2KO were at least in part due to loss of GPS2-mediated regulation of AKT activation. These studies point to GPS2 as a potential biomarker for a subclass of breast cancers that would be responsive to PI3K-class inhibitor drugs. In sum, these studies elucidate interactions and processes that seem to specifically adversely affect TNBC cells, which broaden our knowledge of TNBC biology and its potential weaknesses. / 2022-03-03T00:00:00Z

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