B-catenin is a transcriptional co-activator in the Wnt signaling pathway. Upon Wnt stimulation, cytosolic B-catenin translocates into the nucleus where it forms complexes with members of the TCF /LEF family of transcription factors to activate gene transcription. Translocation into the nucleus is followed by transcriptional activation of B-catenin's target genes, which are involved in proliferation, angiogenesis and oncogenesis, is a crucial step in the progression of a subset of cancers. The cellular expression of B-catenin is known to be regulated by phosphorylation. However, the mechanisms(s) responsible for B-catenin nuclear entry is not well understood. Recently, B-catenin was reported to be post-translationally modified by O-glycosylation in breast cancer cells. We investigated whether O-glycosylation regulates the signal transduction properties of the protein. Our results indicated that while there are higher levels of total B-catenin in the nucleus of two prostate cancer cell lines (DU-145 and LNCaP) compared to that in a normal prostate epithelial cell line (PNT1A), most of it was in the unglycosylated form. Also, the normal prostate cell line exhibited higher levels of O-glycosylated B-catenin in both the nucleus and cytosol than what was seen in the two prostate cancer cell lines. We carried out further experiments using PUGNAc, a non-cytotoxic reversible inhibitor of O-GlcNAcase, which causes a time dependent increase in cellular levels of O-glycosylated B-catenin. Treatment of prostate cancer cells with PUGNAc caused a decrease in the expression of B-catenin in the nucleus with increasing cellular O-glycosylation of the protein suggesting that O-glycosylation was hindering B-catenin nuclear translocation. Additional studies showed that O-glycosylation of B-catenin decreased that transcriptional activity of a TopFlash reporter plasmid and the protein expression of two B-catenin target genes. Our results suggest that O-glycosylation of B-catenin may represent a novel mechanism important in the regulation of the nuclear localization and transcriptional activity of B-catenin. / Thesis / Master of Science (MS)

Thesis (Ph. D.)--University of Washington, 2007. / Vita. Includes bibliographical references (leaves 55-69).

Thesis (Ph. D.)--University of Washington, 2007. / Vita. Includes bibliographical references (leaves 55-62).

The anterior pituitary gland is the major hormonal regulator in the body. The gland contains five secretory cell types whose emergence during development is defined by a tightly regulated array of transcription factors. In adult life, the gland is plastic with the relative proportions of cells varying depending on physiological context. Tumours of the pituitary gland account for 15% of all intracranial tumours in man and are caused by the selective proliferation of one of the secretory cell types. The majority of these (60%) are prolactinomas which consist of very slowly proliferating lactotroph cells, which produce the hormone prolactin. Pituitary tumours are almost never malignant and do not express common genetic markers for cancer, suggesting endogenous proliferative stimuli in the pituitary are the cause of tumour development. Oestrogen causes lactotroph hyperplasia during pregnancy and increases prolactin secretion. Our group previously showed that Wnt-4 mRNA was upregulated during oestrogen-induced lactotroph hyperplasia in Fischer 344 rats. Wnt molecules are key regulatory proteins controlling differentiation, proliferation and migration in development and adult life. Wnt-4 is involved in the emergence of lactotrophs during development, and has been implicated in pituitary tumour formation. Wnt molecules signal through three pathways. The well studied canonical pathway has been implicated in numerous cancers and centres around gene transcription initiated by translocation of β-Catenin into the nucleus. There are two non-canonical pathways: the Wnt-planar cell polarity (PCP) pathway and the Wnt-calcium pathway which are both poorly understood. In this thesis, the expression of Wnt-4 was studied in the pituitary, and effects of downstream signalling pathways in response to oestrogen were assessed. Wnt-4 was expressed in all secretory cell types of the pituitary, as well as the marginal zone (MZ), a region of the pituitary that may harbour stem cells. Oestrogen upregulated Wnt-4 protein in the somatolactotroph GH3 cell line, though this could not be replicated in primary tissue. A number of approaches (western blotting, immunofluorescence, reporter gene assays and mutant β-Catenin overexpression) were utilised to show that the canonical pathway was not activated in the pituitary. Wnt-4 had a clear inhibitory effect on calcium oscillations in GH3 cells, showing for the first time a non-canonical effect in the pituitary, though the downstream effects are currently unknown. Attempts made to study the activation of the PCP pathway were inconclusive. Efforts focused on the distribution of key structural and regulatory proteins in the anterior pituitary and the MZ. The MZ was characterised by a single layer of cells at the border of the anterior and intermediate lobes of the pituitary, with high expression of E-Cadherin and Sox 9, though no change in distribution was observed with oestrogen treatment. In the anterior lobe, oestrogen treatment decreased N and E-Cadherin expression, which could be an indicator of PCP pathway activation during oestrogen induced-lactotroph hyperplasia. Overall, data suggest that Wnt-4 does not directly cause oestrogen-induced lactotroph proliferation, but is likely to play a role in regulating tissue plasticity in the adult gland, as well as in the pathogenesis of pituitary tumours.

PURPOSE: Uveal melanoma (UM) is the most common intraocular malignancy in adults with an incidence of six per one million individuals each year. Globe conserving treatments are currently the standard of care, but unfortunately, despite successful local control, a substantial mortality risk exists due to eventual emergence of distant metastasis, which is invariably lethal. There is therefore an unmet need for novel, effective, targeted therapies for metastatic UM. Somatic mutations in the G-protein α subunits, Gαq and Gα, are present in a mutually exclusive pattern in approximately 80% of UMs, and they abolish the GTPase activity, resulting in a constitutively active protein. We have previously demonstrated that GNAQ-mutant (GNAQ^mt) UMs are addicted to the oncogenic effect of the mutant GNAQ protein and dissected the GNAQ pathway in an attempt to identify druggable targets. Our findings that the mutant GNAQ protein activates the PKC/PKD axis, which activates beta-catenin (β-Catenin), prompted us to investigate the role of PKC and β-Catenin in GNAQ^mt UM. EXPERIMENTAL DESIGN: The GNAQ^mt UM cell lines Mel202 and OMM1.3 were treated with either the PKC inhibitor bisindolylmaleimide I (BIM) alone, the Wnt/β-Catenin inhibitors FH535 or cardamonin alone, the Wnt/β-Catenin activator Wnt-3a alone, or siRNAs for β-Catenin in combination with BIM, and their viability was assessed with the MTT assay. Levels of β-Catenin, phosphorylated AKT, ERK1/2, caspase 3 and LC3BII were assessed with western blotting. β-Catenin mRNA levels were assessed with microarray analysis and RT-PCR. RESULTS: GNAQ^mt UM cells are very sensitive to PKC inhibition and respond with a decrease in cell viability that involves autophagy and cleavage and translocation of LC3BII in autophagosomes, but not caspase activation. PKC inhibition results in the upregulation of β-Catenin protein, but not mRNA levels, through a post-translational mechanism that involved the phosphorylation and activation of AKT, but not ERK1/2. β-Catenin inhibition by either small molecule inhibitors or siRNA resulted in a dose-dependent increase of cell proliferation, whereas β-Catenin activation by Wnt-3a had the opposite effects, resulting in a decrease in cell viability. CONCLUTIONS: Our study demonstrates that PKC is a mediator of the oncogenic effect of mutant Gα protein in UM through the Wnt-3/β-Catenin signaling pathway. These results open exciting opportunities for the development of personalized targeted therapies for UM in a genotype-dependent fashion.

M.Sc. Thesis Dissertation, August 2019, McMaster University / Renal dysplasia, defined as the abnormal development of kidney tissue, is the leading cause of kidney disease in children. While there are numerous causes of renal dysplasia (i.e. genetic, environmental and epigenetic factors), there is no cure to this abnormal defect. Kidney development occurs by two main processes: branching morphogenesis, which forms the collecting duct system, and nephrogenesis, which generates the nephrons, the functional units of the kidney. Our previous studies have demonstrated that β-catenin, a dual-function protein involved in cell adhesion and gene transcription, regulates branching morphogenesis and nephrogenesis. Furthermore, we discovered that nuclear β-catenin levels are increased in kidneys from patients with renal dysplasia, suggesting β-catenin can be a potential therapeutic target to modulate kidney development and renal dysplasia. Quercetin is a flavonoid that reduces β-catenin levels and inhibits its transcriptional activity, leading to improved outcomes in cancer and in kidney fibrosis. The role of quercetin in kidney development and in abnormal defects that arise during kidney development is yet to be examined. Using embryonic mouse kidney organ culture, I found that quercetin treatment resulted in a dose-dependent disruption in branching morphogenesis and nephrogenesis. In addition, quantitative reverse-transcriptase PCR revealed a decreased expression of β-catenin target genes essential for kidney development (i.e. Pax2, Six2 and GDNF). Immunohistochemistry for β-catenin demonstrated that quercetin reduced nuclear β-catenin expression and increased cytoplasmic and membrane-bound expression in a dose-dependent manner. These results were confirmed by Western blot analysis. These novel findings demonstrate that quercetin treatment resulted in decreased levels of nuclear β-catenin, resulting in a decrease in its transcriptional activity which manifested in alterations in kidney developmental processes, suggesting quercetin is effective at reducing nuclear β-catenin in wild-type embryonic kidneys. Next, to determine whether quercetin has any effects on renal dysplasia, I utilized transgenic mice models that overexpress β-catenin in select cells of the embryonic kidney. These models recapitulate the defects observed in human renal dysplasia, including disorganized branching morphogenesis and disrupted nephrogenesis. Quercetin treatment of embryonic dysplastic kidneys resulted in a partial rescue of renal dysplasia which was evident in marked improvements in branching morphogenesis and nephrogenesis, as well as an increase in the number of properly-developing nephrons in the kidney tissue. Analysis of β-catenin expression in quercetin-treated dysplastic kidneys revealed a decrease in nuclear levels and an increase in cytoplasmic and membrane-bound levels, resulting in a reduced expression of target genes (Pax2, Six2, and GDNF). Finally, this partial rescue of renal dysplasia was associated with an improved and organized E-cadherin expression in quercetin-treated dysplastic kidneys, suggesting a possible molecular mechanism of quercetin action in resolving abnormal kidney development. Overall, my findings demonstrate, for the first time, that quercetin reduces β-catenin transcriptional activity in normal and dysplastic kidneys and reduces the severity of defects in renal dysplasia. / Thesis / Master of Science in Medical Sciences (MSMS)

Adenoviruses are non-enveloped, dsDNA tumor viruses responsible for a breadth of pathogenesis including acute respiratory disease and viral myocarditis. Gap junctions, which are formed by connexin proteins, directly couple the cytoplasms of apposed cells enabling immunological, metabolic, and electrical intercellular communication. The gap junction protein connexin43 (Cx43; gene name – GJA1) is the most widely expressed human connexin protein and is the predominant connexin in the working myocardium. Given the immunological role for Cx43 gap junctions, we hypothesized that gap junctions would be targeted during adenoviral infection. We find reduced Cx43 protein due to suppression of GJA1 transcription dependent upon β-catenin during adenoviral infection, with viral protein E4orf1 sufficient to induce β-catenin phosphorylation. Loss of gap junction function occurs prior to reduced Cx43 protein levels with Ad5 infection rapidly inducing Cx43 phosphorylation at residues previously demonstrated to alter gap junction conductance. Direct Cx43 interaction with ZO-1 plays a critical role in gap junction regulation. We find loss of Cx43/ZO-1 complexing during Ad5 infection by co-immunoprecipitation, with complementary studies in human induced pluripotent stem cell derived-cardiomyocytes revealing Cx43 gap junction remodeling concomitant with reduced ZO-1 complexing. These findings demonstrate specific targeting of gap junction function by Ad5 leading to disruptions in intercellular communication which would contribute to dangerous pathological states including arrhythmias in infected hearts. Intercellular junction proteins belonging to classically defined unique junctions exhibit extensive cross-talk and interdependency for expression and localization. We find reduced connexin43 (Cx43) phosphorylation at a known internalization motif, leading us to hypothesize that gap junctions are maintained during adenoviral infection in order to stabilize intercellular junctions and adenoviral receptors therein. Utilizing immunofluorescence confocal microscopy, we demonstrate that Cx43 reductions are primarily cytosolic with Cx43 preservation at the plasma membrane. Click-IT chemistry, a non-radioactive pulse-chase technique, reveals that Cx43 ½ life is extended during adenoviral infection. In order to test if remaining Cx43 exists in de facto gap junctions (i.e. not undocked or cytosolic connexons) we utilized 1 % Triton X-100 solubility fractionation and find Cx43 is indeed primarily junctional during adenoviral infection. Having demonstrated increases in junctional Cx43, we next asked how tightly coupled cells were during adenoviral infection and by ECIS measurements of electrical resistance we demonstrate a transient increase in mechanical coupling during infection. Our future aims are to uncover changes in Coxsackievirus and adenovirus receptor (CAR) protein localization to determine if adenoviral-induced changes to subcellular architecture predisposes neighboring cells to infection and enhances viral spread. These findings will add to the existing model of adenoviral infection and more broadly, contribute to the therapeutic design of adenoviral vectors for cancer and gene therapy. / Doctor of Philosophy / The human heart will beat more than 3 billion times during the average lifetime. This is accomplished by billions of individual heart muscle cells, called cardiomyocytes, contracting in synchrony. Cardiomyocytes require direct cell to cell communication in order to receive the proper cues and work in concert. Outside of the heart, including the lining of the lungs which acts as a first line of defense against invading pathogens, direct cell to cell communication is important for mounting proper immune responses. A primary means by which cells communicate directly with neighboring cells is through gap junctions which are formed of proteins called connexins. Six connexin proteins form a channel in the cell surface that binds to a similar channel on an apposing cell to create a continuous gap junction channel, coupling the cell interiors directly. The most widely expressed human connexin, and the most abundant connexin in the heart, is connexin43 (Cx43; gene name – GJA1). Adenoviruses are pathogens commonly associated with respiratory illnesses in addition to more serious diseases including viral myocarditis, or infection of the heart. Given that Cx43 gap junctions enable direct intercellular communication important in initiating immune responses, we hypothesized that adenovirus would target Cx43 and gap junctions during infection. We find reduced Cx43 protein in cells infected with human adenovirus, and revel that the expression of the GJA1 gene is suppressed. We next focused on potential signaling pathways that are changed during adenoviral infection. β-catenin is a factor with several cellular roles including regulating expression of specific genes including GJA1 (Cx43). We demonstrate β-catenin is activated during adenoviral infection and that this is necessary for reducing Cx43 transcripts. A pathway that activates β-catenin in this manner is the PI3K/Akt signaling axis, which has previously been shown to be turned on during adenovirus infection by a viral protein called E4orf1. We find the adenoviral protein E4orf1 is sufficient to induce β-catenin activation revealing a potential therapeutic target for future studies. We next determined that direct cell to cell communication through gap junctions is reduced before loss of the gap junction protein Cx43 during infection. Gap junctions are modified by the cell to change their ability to couple cells independently of protein levels alone and we find gap junction modifications consistent with altered communication ability. Furthermore, the gap junction protein Cx43 interacts with the cellular skeleton protein Zonula Occludens-1 (ZO-1) during movement into and out of gap junction clusters. We determined alterations in Cx43/ZO-1 interactions consistent with gap junction remodeling. In complimentary studies we find the same gap junction remodeling in cardiomyocytes revealing arrhythmogenic potential during acute adenoviral infection in human heart cells. Localized with gap junctions are several other junction proteins including the Coxsackievirus and adenovirus receptor (CAR) which is critical in cardiac development and also the primary receptor for species C adenoviruses (used in our studies). CAR expression has been demonstrated to alter Cx43 levels and indeed, many junctional proteins influence the expression and/or localization of other junctional proteins. Interestingly, despite reduced Cx43 levels and reduced gap junction function (cell to cell communication), we detected decreases in a gap junction modification that is associated with gap junction degradation, suggesting that new gap junction protein Cx43 is not being made but already synthesized Cx43 is degraded more slowly. We hypothesized Cx43 is maintained during adenoviral infection in order to recruit other junctional components, principally CAR, on uninfected neighbor cells to predispose them to infection. We observed using microscopy that Cx43 reductions are primarily inside the cell but Cx43 is preserved on the cell surface and at junctions between cells. We next asked if the protein is being degraded more slowly and find Cx43 exists for longer in infected cells signifying that it is being degraded more slowly. Utilizing a fractionation technique to separate gap junction connexin from connexon that is non-junctional or inside the cell, we detect an increase in junctional Cx43, revealing maintenance of Cx43 gap junction structures. Having now identified adenoviral-mediated maintenance of Cx43 gap junction structures, we next wanted to test for changing in mechanical coupling (i.e. how tightly are the cells connected to one another) where we demonstrate an increase in mechanical coupling during adenoviral infection. Our future directions are to determine if this increase in Cx43 gap junction maintenance and mechanical coupling is concomitant with changes in CAR expression/localization on uninfected neighboring cells and if altered, does this predispose uninfected neighbors of infected cells to infection.

No description available.

Thesis (Ph. D.)--University of Washington, 2008. / Vita. Includes bibliographical references (leaves 94-105).

Colorectal cancer is estimated to cause approximately 50,000 deaths each year in the United States. Epidemiological studies have demonstrated an inverse association between sunlight exposure, which stimulates the formation of vitamin D in the skin, and colorectal carcinoma. Laboratory studies report that metabolites of vitamin D, acting through the vitamin D receptor (VDR), regulate cellular proliferation, differentiation and apoptosis. In addition, VDR contains a polymorphic variant, FokI, which results in two different isoforms of VDR. We have demonstrated a differential suppression of β-catenin transcriptional activity by these isoforms in the presence of 1,25(OH)₂D₃ (1,25D). Epidemiological evaluation of metachronous colorectal adenoma formation indicates that VDR includes several single nucleotide polymorphisms (SNPs) which influence the odds of developing colorectal adenoma. In addition, we have found full length Adenomatous Polyposis Coli (APC), a frequently mutated tumor suppressor gene in colorectal cancer, augments both the interaction of VDR and β-catenin as well as the suppression of β-catenin transcriptional activity in the presence of 1,25D. We have also demonstrated in epidemiological studies that the presence of a T-A haplotype in APC codons 486 and 1822, respectively, reduces the odds of any metachronous adenoma by 27% [odds ratio (OR), 0.73; 95% confidence interval (95% CI), 0.59 – 0.91]. Taken together, these data support not only a protective role for vitamin D acting through the VDR, but also for an important role of heritable polymorphic variation in VDR and APC in carcinogenesis.