The RET proto-oncogene encodes a receptor tyrosine kinase (RTK) that is widely expressed in neuroendocrine tissues and is essential for embryonic development of the kidney and enteric nervous system. Mutations leading to constitutive activation of the RET protein underlie various tumours of endocrine tissues. Conversely, loss-of-function mutations of RET lead to Hirschsprung disease, a congenital disorder characterized by a loss of enteric neurons throughout the colon and small intestine. Intracellular trafficking of RTKs through multiple cellular compartments has been shown to impact on downstream signalling. To date, the intracellular trafficking of RET has not been investigated. Here, we show that RET is rapidly internalized after activation and that trafficking to cytoplasmic endosomes plays an important role in downstream signalling. RET is alternatively spliced into multiple isoforms that are co-expressed in cells; therefore, we further investigated RET internalization in an isoform-specific context. This study revealed a number of differences between RET isoforms including differences in sub-cellular localization pre-activation, rate of internalization, and ability to recycle to the plasma membrane. Differential trafficking of RET isoforms alter their downstream signalling properties, providing an additional mechanism to explain the distinct contributions of RET isoforms to cellular processes. Finally, we investigated the impact of altered sub-cellular localization in the context of thyroid carcinoma. Activation of RET has been implicated in a number of thyroid tumours that differ in their inherent oncogenicity. We observed that altered subcellular localization of oncogenic forms of RET, RET/PTCs, enhance their oncogenicity. Interestingly, RET/PTC tumours are indolent and rarely metastasize compared to other RET-mediated forms of cancer. Further investigation revealed that RET/PTC oncogenes are expressed off relatively weak promoters, resulting in quantitatively less RET/PTC oncoprotein expression in these tumours compared to mutant RET expression in more aggressive cancers. Together, our results represent the first in-depth study of the trafficking properties of RET and indicate the importance of proper sub-cellular localization and trafficking in the maintenance of normal cell metabolism. / Thesis (Ph.D, Pathology & Molecular Medicine) -- Queen's University, 2009-11-19 22:51:47.38

Cell penetrating peptides (CPPs) have been used in many areas of drug delivery for mediating the delivery of peptides, protein, DNA, siRNA and liposomes. Additionally they have shown an ability to overcome drug resistance in cells enhancing chemotherapeutic activity. Our group has recently designed a promising multifunctional peptide, Tat-LK15, originating from the fusion of Tat peptide (49-57) with the synthetic amphipathic peptide, LK15. TAT-LK15 was found to be efficient at mediating DNA and siRNA delivery to cells especially contributing to the silencing of bcr-abl oncoprotein over a long period of time. To date, Tat-LK15 peptide’s cells uptake mechanism, which is expected to be influenced by the presence of the amphipathic sequence LK15, which is known to be lytic, has not been assessed. The aim of this project is to study the cellular uptake of the Tat-LK15 peptide and any influence it exerts on the uptake of p-glycoproteins substrates. Also we aimed to explore whether the peptide characteristics could be exploited to improve the delivery of the cytotoxic agent, doxorubicin.Flow cytometry and confocal microscopy experiments revealed that Tat-LK15 uptake was dependent on two mechanisms depending on the concentration of peptide used. At low concentrations (2.5µM and below) the uptake of TAMRA-Tat-LK15 peptide appeared to be temperature-dependent and was inhibited by sodium azide suggesting endocytosis as the main route of entry in the studied cell lines. At 5µM and above, the peptide’s uptake was less reliant on temperature and not be inhibited by sodium azide, but relied on membrane potential. Interestingly in K562 cells, the peptide accumulated on the cell membrane.The Tat-LK15 peptide membrane activity was also characterised: Tat-LK15 lytic activity was concentration-dependent. At 5µM the Tat-LK15 peptide led to approximately 60% LDH release in HT29 cells which is likely to be related to the amphipathic sequence, LK15 renowned for its membrane lytic activity. Further to this, the uptake of a membrane impermeant dye (SYTOX® blue) incubated with the peptide was followed as a function of time in K562 cells with a high content screening. The results appeared to substantiate the above findings that Tat-LK15 peptide has a concentration- and time-dependent membrane lytic activity. An MTT assay, after four hours of incubation, indicated very limited variation in cytotoxicity (EC50 ~ 5µM) over six different cell lines. More importantly, an Annexin V assay suggested a possible induction of apoptosis in the MCF-7 cell line, in contrast a Tat-LK15 concentration-dependent necrosis was observed in a K562 cell line. Finally attempts were made to exploit the properties of Tat-LK15 to overcome drug resistance of doxorubicin. Firstly Tat-LK15 peptide co-incubation with a model P-gp substrate (calcein AM) revealed a significant reduction of calcein fluorescence in K562 and HT29 cells and their doxorubicin resistant sublines (p<0.05). Attempts to conjugate doxorubicin to TAT-LK15 proved difficult. Consequently doxorubicin/Tat-LK15 admixtures were used to study whether the P-gp efflux of doxorubicin in doxorubicin resistance sublines could be circumvented. A significant increase of the toxicity relative to doxorubicin alone for long incubation times on several cell lines (p<0.05) indicated that using TAT-LK15 as an additive could potentially be considered as a drug delivery strategy. Thus the concept of conjugating a well known cell penetrating peptide to an amphipathic sequence is worthwhile however the findings in this study are not sufficient to highlight the full potential and major improvements in efficacy needs to be achieved.

Shigella flexneri is a Gram negative facultative anaerobe that infects millions world-wide each year. The route for infection of a host is through the intestinal and rectal epithelium layers, but it also can survive in the environment. Different genes have been found to be up regulated depending upon its presence in the intracellular or extracellular environment, as shown in previous work in the lab. This thesis seeks to examine the role these upregulated genes, bioA and lysA, play in the intracellular activity of S. flexneri. Knock-out mutations in the bioA and lysA genes were created using P1 transduction. To test the effects of these mutations on S. flexneri, plaque, invasion, and attachment assays were performed. It was found that the bioA mutation resulted in fewer plaques being formed, while the lysA mutation resulted in slower forming and incompletely lysed plaques being formed. / text

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The presence of thiols in living systems is critical for the maintenance of cellular redox homeostasis, the maintenance of protein thiol-disulfide ratios and the protection of cells from reactive oxygen species. In addition to the well studied tripeptide glutathione (??-Glu-Cys-Gly), a number of compounds have been identified that contribute to these essential cellular roles. Many of these molecules are of great clinical interest due to their essential role in the biochemistry of a number of deadly pathogens, as well as their possible role as therapeutic agents in the treatment of a number of diseases. A series of studies were undertaken using theoretical, chemical and biochemical approaches on a selection of thiols, ergothioneine, the ovothiols and mycothiol, to further our understanding of these necessary biological components. Ergothioneine is present at significant physiological levels in humans and other mammals; however, a definitive role for this thiol has yet to be determined. It has been implicated in radical scavenging in vivo and shows promise as a therapeutic agent against disease states caused by oxidative damage. Given the clinical importance of this intracellular thiol, further investigation into the behaviour of ergothioneine appeared warranted. A high level theoretical study was performed to determine the thermodynamic driving force behind the instability of the ergothioneine disulfide, as well as the thermodynamics of the reactions of ergothioneine with a selection of biologically relevant reactive oxygen species. These results were compared to those determined for a glutathione model compound, as well as the related ovothiols. The latter are believed to act as hydrogen peroxide scavengers in vivo and are currently under review as possible therapeutics against oxidative damage. The structural differences between the ovothiols and ergothioneine dramatically affect their reactivity and this study investigates the thermodynamic driving forces behind these differences. Mycothiol is the major thiol found in the Actinomycetales bacteria, which include the causative agent of tuberculosis, and the enzymes which use mycothiol have been identified as important targets for the development of novel antimicrobials. To better understand the in vivo behaviour of mycothiol, a thorough conformational search was performed to determine what, if any, trends exist among the low energy conformers expected to be present in solution. Knowledge of the conformations preferred by mycothiol may aid in the design of substrate-based inhibitors targeted at mycothiol-dependent enzymes. In addition, the efforts towards the identification of a mycothiol-dependent glyoxalase system are described. The glyoxalase system is essential for the detoxification of methylglyoxal, a toxic by-product of glycolysis, and this system would serve as a target for the design of new therapeutics against tuberculosis and other pathogenic Actinomycetales bacteria. In addition to the study of intracellular thiols, this work details a preliminary theoretical study of the thermodynamics of the phosphorylation of proteinaceous serine residues by inositol pyrophosphates in eukaryotic cell-free extracts. It has been postulated that this observed activity may represent a novel signalling pathway in eukaryotes. This study focused on the effect of inositol pyrophosphate structure and overall charge on the thermodynamics of these reactions. This information should contribute to our understanding of this novel cellular phosphorylation process.

Breast cancer is the most prevalent form of cancer in women and accounts for 519,000 annual deaths (WHO Statistics). It has long been established that oestrogen (E2) stimulates tumour growth of oestrogen receptor (ER) positive breast cancer and is involved in the pathogenesis of the disease. Consequently, therapeutic approaches targeting the ER were developed. The use of endocrine therapy is an integral component in treating breast cancer however resistance to such drugs is a major limitation. Unfortunately, even initially responding tumours eventually develop resistance - acquired resistance. The aim of this study was to determine which intracellular pathways may be important in conferring acquired endocrine resistance. In order to do so, a three-stage MCF-7 cell model emulating the clinical development of acquired endocrine was used. MCF-7/LCC1 (LCC1) and MCF-7/LCC9 (LCC9) cells lines were derived from the oestrogen dependent and antioestrogen sensitive MCF-7 cell line. LCC1 cells remain responsive to endocrine therapies but their growth is not dependent on oestrogenic stimulus. LCC9 cells, on the other hand are fully resistant to endocrine therapies and completely oestrogen independent. A number of different cell membrane receptors and intracellular pathways have been implicated in endocrine resistance including HER receptor family, PI3K/Akt & MEK/ERK pathways. These pathways are of particular interest since they are able to activate ER in the absence of oestrogenic stimulus. It is likely that several pathways may be important in conferring resistance to endocrine therapies therefore the experiments in this study focussed on the transcriptional regulation of HER receptors, the activation of the Akt pathway and its implication to basic cellular processes. Following E2 treatment (48h), HER2/3/4 mRNA and protein levels were reduced in MCF- 7 and LCC1 but not in the endocrine-resistant LCC9 cell line as measured by QRT-PCR and Western blotting. The anti-estrogen fulvestrant (ICI 182,780) reversed the E2 modulation. A previous study has shown that ER and the HER2 promoter compete for limiting amounts of SRC-1 in oestrogen-responsive ZR-75-1 cells, causing HER2 repression after E2 stimulation (Newman et al.,Oncogene, 19, 490-7, 2000). ER RNAi abolished E2 repression of HER2 in MCF-7 and LCC1 cells. Furthermore, LCC9 cells have reduced SRC-1 recruitment to ER (assessed by ChIP) allowing SRC-1 to bind to the HER2 promoter. SRC-1 RNAi reduced HER2 transcription in MCF7 cells in a manner similar to E2 whilst it did not restore E2 repression in LCC9 suggesting that the latter cells have alternative mechanisms regulating HER2 transcription. RNAis against the other two p160 co-activators TIF2 and AIB1 did not restore E2 mediated HER2 repression in LCC9 cells. The importance of redundancy between p160 co-activators was also determined by performing double knockouts. SRC-1/TIF2 and TIF2/AIB1 double siRNAs had little effect on HER2 mRNA levels however SRC-1/AIB1 siRNA restored oestrogen mediated downregulation of HER2 transcription in LCC9 cells. This data indicates that SRC-1 and AIB1 co-activators play a role in the transcriptional regulation of HER receptor particularly in MCF-7 and LCC1 cells. The regulation of this transcriptional mechanism is altered in resistant LCC9 cells but, as evidenced by the double knockouts, p160 coactivators are still able to affect HER expression in these cells. This mechanism was further studied in primary breast cancer tumour material. The importance of the Akt pathway in this cell line model was also investigated as phospho-Akt levels are elevated in LCC1 and LCC9 cells. This in turn was shown to activate mTOR and ER (Ser167 residue phosphorylation) thereby contributing to increased growth and ligand independent activation of the oestrogen receptor respectively. Activation of PI3K and PTEN is unchanged in LCC1 and LCC9 cells suggesting that these proteins are not responsible for elevated Akt phosphorylation. In contrast, these cells do express higher levels of phospho-IGFR due to the high availability of receptor ligands (IGFI & IGFII). This is likely to be, at least partially, responsible for the elevated Akt activation. Moreover, the role of Akt isoforms was also determined as they are known to have different functions. The levels of Akt 2 phosphorylation are higher in endocrine resistant cell lines in comparison to parental MCF-7 cells. Interestingly, the Akt 3 phosphorylation is present in all cell lines whilst Akt 1 phosphorylation is minimal. Nevertheless, Akt RNAi studies reveal that Akt 1 and 2 siRNA dramatically reduce growth in MCF-7, LCC1 and LCC9 cells. These results suggest that Akt 2 phosphorylation may play a part in conferring endocrine resistance but the other isoforms are also important for normal cellular growth. The cell cycle profiles of LCC1 and LCC9 are very similar to MCF-7. Similarly, migration levels are unchanged in endocrine resistant cell lines. However, in the presence of antioestrogenic drugs, apoptosis in LCC1 and LCC9 cells in reduced in comparison to the parental MCF-7 cell line. Furthermore, LCC1 and LCC9 cells have higher invasion rates. The deregulation of HER receptor expression and elevated Akt activation may together confer survival advantage in LCC1 and LCC9 cells whilst also increasing their invading potential.

F. tularensis is an intracellular pathogen, and is the causative agent of tularemia in humans. The ability of F. tularensis to parasitize host cells is largely dependent upon genes within a pathogenicity island (FPI), including those in the iglABCD operon. Specific mechanisms and gene products involved in regulation of the FPI are not well understood. I initiate the study of this regulatory system by creating an efficient Tn5-based mutagenesis system optimized for use in F. tularensis, and utilize this system to construct a lacZ reporter library. I identify genes differentially regulated in response to growth on two different media, including those in the iglABCD and fslABCD operons, and identify iron availability as a factor contributing to the differential regulation. One of these reporter strains, carrying a chromosomal iglB-lacZ fusion, is used as the basis for a secondary transposon mutagenesis to identify mutations that affect iglABCD expression. One such mutation is in FTL_1542 (migR), a hypothetical protein, and reduces expression of the iglABCD approximately 8-fold. The effect of this mutation on igl expression is likely through its effect on another known virulence regulator, fevR, as demonstrated by data from RT-PCR experiments. I compare the phenotypes of LVS fevR and migR mutant strains in primary macrophage and epithelial cell lines and in neutrophils. The mutation in migR effects growth and intracellular trafficking in macrophages but not epithelial cells, and reverses the ability of wild type F. tularensis to block the respiratory burst in neutrophils. When similar mutations were examined in the human virulent F. tularensis strain Schu S4, migR retained its regulatory role, but did not impair replication in macrophages. The migR mutation in Schu S4 did however have an attenuating effect when administered to mice intranasally. Comparison of LVS and Schu S4 in primary human airway epithelial cell infections revealed an inability of LVS to replicate within these cells, which is in contrast to the robust replication of LVS in cultured epithelial cell lines. Together, this work contributes to the understanding of regulatory mechanisms governing virulence gene expression in F. tularensis and highlights differences between LVS and Schu S4 strains.

<p>The knowledge of the human genome sequence, as revealed in the HUGO project, has created exciting new possibilities for biomedical research. The Swedish Human Proteome Resource (HPR) program aims to make use of this information to gain further insight into the human proteome. Recombinant proteins are generated from coding sequences identified from the human genome sequence and used to produce specific antibodies to target proteins. Antibodies are subsequently utilized for functional analysis of the corresponding proteins using tissue micro arrays. The aim of my project was to investigate the possibility of distinguishing characteristic distribution patterns of intracellular proteins in the resolution capacity offered by light microscopy. A map of representative distribution patterns was created using immunohistological staining with commercially available antibodies toward well-characterised proteins in the cell. Such a map could then aid in interpreting the results of immunohistological staining of intracellular proteins using antibodies produced within the Human Proteome Resource program. Proteins manifested in nucleus, nuclear membrane and plasma membrane were clearly visible at the expected location. Proteins manifested in different organelles in the cytoplasm however, showed all a similar staining pattern, making determination of exact protein location uncertain. A possible explanation is the resolution of the light microscope not being sufficient to visualize certain proteins specific to organelles in the cytoplasm. Results may also have been influenced by the choice of secondary antibody, where the strenghtened signal generated by an enzyme labelled polymer may have a negative effect on depiction of details in the image generated.</p>

The knowledge of the human genome sequence, as revealed in the HUGO project, has created exciting new possibilities for biomedical research. The Swedish Human Proteome Resource (HPR) program aims to make use of this information to gain further insight into the human proteome. Recombinant proteins are generated from coding sequences identified from the human genome sequence and used to produce specific antibodies to target proteins. Antibodies are subsequently utilized for functional analysis of the corresponding proteins using tissue micro arrays. The aim of my project was to investigate the possibility of distinguishing characteristic distribution patterns of intracellular proteins in the resolution capacity offered by light microscopy. A map of representative distribution patterns was created using immunohistological staining with commercially available antibodies toward well-characterised proteins in the cell. Such a map could then aid in interpreting the results of immunohistological staining of intracellular proteins using antibodies produced within the Human Proteome Resource program. Proteins manifested in nucleus, nuclear membrane and plasma membrane were clearly visible at the expected location. Proteins manifested in different organelles in the cytoplasm however, showed all a similar staining pattern, making determination of exact protein location uncertain. A possible explanation is the resolution of the light microscope not being sufficient to visualize certain proteins specific to organelles in the cytoplasm. Results may also have been influenced by the choice of secondary antibody, where the strenghtened signal generated by an enzyme labelled polymer may have a negative effect on depiction of details in the image generated.