The purpose of this study was to determine the endogenous levels of indole-3-acetic acid throughout the life cycle of Chlorella pyrenoidosa, and to show a correlation between onset of cell division and IAA levels.

It was the purpose of this study to investigate the effect of various concentrations of IAA on the nucleic acids of Chlorella pyrenoidosa TX 7-11-05. The time during the life cycle when the greatest effect occurred was investigated by the use of synchronous cultures.

Fungal infections are caused by a variety of fungi, and with a variety of clinical manifestations. Antifungal treatments are limited due to host toxicity and fungi gaining resistance. By utilizing the model organism Saccharomyces cerevisiae, we hope to elucidate the molecular mechanisms of fungal pathogenesis that we can then validate in the human pathogen Candida albicans, as well as explore options for novel therapies. Small molecule signaling is a method by which single-cell organisms can communicate with one another, enabling them to coordinate gene expression. This is a useful tool because it allows microbes to turn on phenotypes that are only valuable when done in large numbers, such as bioluminescence, or virulence traits. We have previously shown that the yeast Saccharomyces cerevisiae synthesizes the secondary metabolite indole-3-acetic acid (IAA) from tryptophan. IAA is secreted into the environment, where it acts as a signal. At low concentrations, the IAA signals yeast to induce virulence traits, while at high concentrations, it is lethal. The purpose of this thesis was to investigate the molecular mechanism of IAA (plant hormone auxin) regulation in fungi, specifically, Saccharomyces cerevisiae and the human pathogen Candida albicans. Towards this end, I first focused my efforts on evaluating the role of S. cerevisiae Grr1, as a putative IAA receptor. By evaluating the IAA response of several Grr1 mutants, I was able to show that the leucine-rich repeat region, while not required for function, likely plays a significant role in maintaining the structural integrity of the protein. Next, I evaluated IAA associated phenotypes, such as filamentation, surface adhesion and IAA uptake of the grr1 null mutant in the human pathogen Candida albicans. Together, these data support the hypothesis that GRR1 regulates IAA response, probably by regulating the IAA uptake carriers.

Natural products are a rich source of lead compounds for treatment of cancer as well as other diseases. Researchers at the National Cancer Institute, as part of their continuing effort to discover anticancer agents from natural sources, created the 60 human tumor cell-line anticancer screen to test natural products for their potential against various types of cancer. Through this screening process a family of natural products called schweinfurthins was discovered to possess potent and differential activity. Of potentially great significance, the pattern of activity that the schweinfurthins displayed in the screen does not correlate with any currently used anticancer drug, indicating that the schweinfurthins likely act via a previously unknown mechanism or on a novel target. Our group has synthesized many of the natural schweinfurthins as well as numerous analogues in an effort to probe the pharmacophore and gain understanding of the key features that are important for potency as well as differential activity. During the course of these studies, it was discovered that the right-half of the molecule is most amenable for modifications. One potential modification to the schweinfurthins is to replace the resorcinol substructure seen in the right-half of the natural product with a heteroaromatic moiety such as a benzofuran or indole system. This change may produce analogues that are potentially more active, that contain motifs that are seen in many therapeutic drugs, and that have improved chemical stability relative to the natural products. With this goal in mind benzofuran and indole containing schweinfurthin analogues were synthesized. Once these compounds were prepared, it was found that such modifications were welltolerated, and in the case of the indole analogues activity in the 60 cell-line screen was equivalent to the corresponding natural product. In an effort to improve that activity, prenyl and geranyl side chains were added to the indole system, at both the C-2 and C-3 positions, to better match the structure of the natural schweinfurthins. In addition, analogues methylated selectively on the indole nitrogen or phenol were synthesized to improve stability. The impact of those modifications on the activity was tested, and potent compounds were found. The left-half of the schweinfurthins is prepared via a Lewis acid mediated cascade of a geranyl epoxide. The protecting group that is typically employed on the terminating phenol, a methoxymethyl ether or MOM group, is cleaved during the reaction. In the past preparation of an analogue that lacked a substituent at the C-5 position, it was found that the MOM cation released during the cyclization would participate in an electrophilic aromatic substitution reaction at the neighbouring position which resulted in the formation of a benzyl methyl ether. In order to probe the scope of this reaction and its potential utility in the synthesis of natural products, several geranyl epoxides with various "protecting groups" on the phenol were prepared and subjected to the cyclization conditions. These investigations have established that stabilization of the liberated cation determines the likelihood and regioselectivity of a tandem electrophilic aromatic substitution reaction.

Indole-3-carbinol (I3C) is a naturally occurring plant alkaloid, found in significant concentrations in cruciferous vegetables such as broccoli and Brussels sprouts. I3C is an unstable compound that undergoes rapid oligomerization in an acidic environment to form higher order condensation products (I3C-ACPs), such as 3-3'-diindolylmethane (DIM). Both I3C and DIM are marketed as dietary supplements and are under investigation as potential chemopreventive agents, despite limited data on the effects of chronic exposure. Previous studies have demonstrated that the chemopreventive potential of I3C and DIM in animal studies is dependent on species, strain, tissue and timing of treatment relative to carcinogen exposure, and long-term post-initiation exposure can even promote tumors. The majority of biological effects from I3C are the result of the abilities DIM and other I3C-ACPs to bind to the aryl hydrocarbon receptor and the subsequent induction of phase I and phase II enzymes. Phase I and phase II enzyme induction in many cases leads to protection from carcinogens by increasing the rate of metabolism and excretion but in some cases enhances carcinogenicity by increasing the rate of bioactivation. It has been demonstrated that modulation of enzyme levels can also result in altered metabolism of compounds that could affect efficacy and toxicity of pharmaceuticals and xenobiotics. The current work utilizes chronic dietary I3C and DIM exposures in rodent models to further elucidate the effect these compounds might have on health, drug metabolism and carcinogenesis. The reduced weight of Fischer 344 rats treated with 2500 ppm I3C for 1 year may be indicative of adverse effects but toxicity was not confirmed by blood chemistry or histopathological examination. Furthermore, no toxicity was observed after a comparable treatment of Sprague-Dawley rats. As observed after acute and sub-chronic exposures to I3C and DIM, we documented significant induction of cytochrome P450 enzymes and a related modification to drug metabolism in liver slice incubations. Evidence is also provided that may suggest that tumor modulation in mice may occur through an estrogenic mechanism. Further studies should be completed to determine the potential for similar responses in humans. / Graduation date: 2004

According to UNAIDS there were 34 million people living with human immunodeficiency virus (HIV) infection at the end of 2010. HIV is the causative agent of acquired immunodeficiency syndrome (AIDS) and the number of people dying of AIDS-related causes at the end of 2010 was 1.8 million. Due to the high mutability of the virus, there is a constant need for new approaches to attack the virus. Splicing of HIV-1 pre-mRNA is a highly regulated process. In order to produce all mRNAs needed to be infectious HIV-1 utilizes alternative splicing ­- from one single transcript more than 35 differently spliced mRNAs can be produced. A new approach to fight HIV-1 could be to interfere with the essential splicing. In this thesis, I describe the regulation of HIV-1 pre-mRNA splicing. SR proteins are involved in the regulation of splicing, both in an early and a late stage. We find that the intracellular concentration of SR proteins is of great importance for HIV-1 to be able to produce the correct amounts of mRNAs. Variations in concentrations of SR proteins lead to big changes in the HIV-1 pre-mRNA splicing pattern. The functions of HIV-1 protein Vpr are diverse and it is essential in vivo. HIV-1 vpr mRNA 13a7 is partially spliced, containing an intron, and the regulation of it is not fully understood. We find that SRp55 and SRp75 induce the production of HIV-1 vpr mRNA 13a7 by inhibiting splice donor 3. We also conclude that this inhibition at least for SRp55 is due to an interaction with the viral RNA element GAR. In the presence of SRp55 we also see an increase in cytoplasmic amounts of intron containing vpr mRNA due to increased nuclear export. Our results show that SRp55 can have several functions in the regulation of HIV-1 splicing: by inhibiting splice donors and by facilitating the export of incompletely spliced mRNAs to the cytoplasm. In conclusion, this thesis describes SRp55 as a regulator of HIV-1 vpr mRNA, both in splicing as well as in nuclear export. These discoveries provide an insight into the regulation of HIV-1 mRNA processing.

The overall goal of this research was to understand the role of inter-kingdom signaling in enterohemorrhagic Escherichia coli (EHEC) infections of the human gastro-intestinal (GI) tract from the perspective of both the invading pathogen and the human intestinal epithelial cells, which they colonize. Differential gene expression of EHEC was studied upon exposure to the human neuroendocrine hormones epinephrine and norepinephrine. We determined that these hormones increase EHEC chemotaxis, motility, biofilm formation, colonization of host cells, and virulence gene expression. We also studied the EHEC response to the GI tract commensal bacterial signaling molecules indole and autoinducer-2 (AI-2). We observed that indole decreases all the EHEC phenotypes that are increased by the human hormones and represses EHEC virulence. However, the effect of AI-2 was similar to that observed with hormones and opposite to that observed with indole, i.e. AI-2 increases EHEC virulence phenotypes. We studied changes in host cell transcriptome in the presence of the commensal bacterial signal indole. Indole increases expression of genes involved in tight junction and gap junction formation, and production of mucins and actin cytoskeleton genes. Indole also down-regulates genes encoding for pro-inflammatory cytokines, chemokines, and Toll-like receptors. The gene expression results were confirmed with phenotypic assays where we observed an increase in trans-epithelial resistance, increase in the anti-inflammatory cytokine IL-10, decrease in the pro-inflammatory cytokine IL-8, decrease in the activity of the pro-inflammatory transcription factor NF-κB, and decrease in colonization by EHEC of the indole-pre-treated HCT-8 cells. We established that factors secreted by epithelial cells are important determinants of EHEC virulence. Gene expression studies showed that 34 out of 41 LEE virulence genes were induced when EHEC was cultured in conditioned medium. In addition, the data showed increased expression of the shiga toxin-2 prophage 933W. These changes in gene expression were corroborated by a 5-fold increase in HCT-8 cell colonization and increased intracellular Stx2 phage titers. We determined that the HCT-8-secreted factor(s) was protein-based and that it was greater than 3 kDa in size. In conclusion, we have characterized the pathogen response to various eukaryotic and prokaryotic GI tract signals. We have established, for the first time, that the commensal bacterial signal indole is an inter-kingdom signal for the host epithelial cells. Overall, our studies provide a greater understanding of host-pathogen interactions.

The effects of polyamines, indole-3-acetic acid ( IAA ) and gibberellic acid ( GA3 ) on root elongation in radish ( Raphanus sativus L. cv. Luh Chin ) were studied. Incubation of radish seedlings in spermine or spermidine at 0.01 mM for 1hour, and then transferred to deionized water for 24 hours at 25¢J in the dark promoted root elongation as compared with concentration at 0.1 or 2 mM. When roots were treated with spermine or spermidine at 1 mM for 5 minutes, and then transferred to deionized water for 24 hours, root length increased significantly compared with controls. However, root length reduced gradually with increasing treatment times. Putrescine did not affect root elongation when treated in the same manner as spermine or spermidine. Exogenous spermidine synthesis inhibitor ( cyclohexylamine ) at 0.01, 0.1, 1 or 2 mM to the roots inhibited root elongation. The inhibition of root elongation was parallel to cyclohexylamine doses. Root length increased when spermine at 1 mM plus IAA at 10¡Â¹ ¡Ñ 6 nM was applied for 1 hour, and then transferred to deionized water for 24 hours compared with spermine at 1 mM plus IAA 10¡Â² or 1¡Ñ 6 nM. Root length was longer when treated with spermidine at 1 mM plus IAA at 10¡Â²¡Ñ 6 nM than at 10¡Â¹ or 1¡Ñ 6 nM. Root treated with spermine at 1 mM plus GA3 at 10¡Â²¡Ñ3 £gM Resulted in a longer root than treated with spermine at 1 mM plus GA3 at 10¡Â¹ or 1¡Ñ 3 £gM. Roots treated with spermidine at 1 mM plus GA3 at 10¡Â²¡Ñ3 £gM promoted root elongation. However, any treatments of spermine or spermidine in combination with IAA or GA3 significantly reduced the root length when compared with controls. Furthermore, either IAA or GA3 could not restore the inhibitory effects of root elongation caused by spermine or spermidine treatment at 1 mM for 1 hour and then transferred to deionized water for 24 hours. Endogenous spermidine and spermine contents after exogenous spermine plus GA3 treatment increased by increasing GA3 concentrations. But endogenous spermidine and spermine contents was the least in spermine 1 mM plus IAA 10¡Â¹ ¡Ñ 6 nM treatment. However, endogenous spermidine contents after exogenous spermidine plus IAA or GA3 application reduced significantly when compared with controls. But there is no significant difference of spermidine content between different exogenous IAA doses. In contrast, spermidine content maintained at a high level in spermidine at 1 mM plus GA3 at 10¡Â²¡Ñ3 £gM as compared with other spermidine plus GA3 combinations. However, endogenous spermine contents were not affected by exogenous spermidine plus IAA or GA3.

Cu-treated peanut seedlings not only showed a significant inhibition in peanut root growth, but also a decrease in endogenous indole-3-acetic acid (IAA) contents . The decline of IAA content in Cu-treated tissues is accompanied by an increase in cationic peroxidase activity. In addition, the increase in cationic peroxidase (pI 8.5) activity is correlated with an increase in cationic peroxidase transcripts. Cu might suppress the growth of peanut roots by inducing the synthesis of the cationic peroxidase isozyme that degrades endogenous IAA, causing the retardation of peanut root growth. The increase in activity of anionic peroxidases (pI 3.5) is also correlated with the rise in lignin content in Cu-treated roots. We suggest that the increase in anionic peroxidases (pI 3.5) induced by Cu might be responsible for lignin synthesis in peanut roots, and remove excess hydrogen peroxide, thus serving a detoxifying role during Cu treatment.

Thesis--Ph. D., University of Hong Kong, 1983.