Chromatin insulators play a role in gene transcription regulation by defining chromatinboundaries. Genome-wide studies in Drosophila have shown that a large proportion of insulator sites are found in intergenic DNA sequences, supporting a role for these elements as boundaries. However, approximately 40% of insulator sites are also found in intragenic sequences, where they can potentially perform as yet unidentified functions. Here we show that multiple Su(Hw) insulator sites map within the 110 kb sequence of the muscleblind gene (mbl), which also forms a highly condensed chromatin structure in polytene chromosomes. Chromosome Conformation Capture assays indicate that Su(Hw) insulators mediate the organization of higher-order chromatin structures at the mbl locus, resulting in a barrier for the progression of RNA polymeraseII (PolII ), and producing a repressive effect on basal and active transcription. The interference of intragenic insulators in PolII progression suggests a role for insulators in the elongation process. Supporting this interpretation, we found that mutations in su(Hw) and mod(mdg4) also result in changes in the relative abundance of the mblD isoform, by promoting early transcription termination. These results provide experimental evidence for a new role ofintragenic Su(Hw) insulators in higher-order chromatin organization, repression of transcription, and RNA processing.

<p>Borane (BH<sub>3<sub>) chemistry offers unique chemical characteristics that enable boranophosphate (BP) oligonucleotides with potential to enhance RNA therapeutic applications such as RNA interference (RNAi) and RNA aptamers. Further, BP nucleotides are substrates for RNA polymerases which allow the enzymatic synthesis of stereoregular boranophosphate (BP)-RNA molecules of different lengths and properties. We expect that these BP-RNAs will interact in a novel way with the desired target molecules because they can coordinate with a diverse array of ligand sites in proteins or other RNA molecules. This is due to the distinct hydrophobicity, sterospecificity, and polarity properties imparted by the phosphorus-boron (P-B) chemical bond compared to the natural phosphorus-oxygen (P-O) bond. </p><p>The object of this dissertation is to explore the therapeutic applications of the BP-RNA such as siRNA, RNA aptamers, and in addition investigate the immunogenicity of this modification. We used mouse cells to determine if BP-RNA would activate toll-like receptor (TLR 7), which is involved in innate immune response to foreign single stranded RNA (ssRNA). This response is undesired when applied to oligonucleotide therapeutics such as siRNA and RNA aptamers. In terms of RNAi, it would be an advantage to have low immunogenicity and high downregulation activity by the siRNA. To determine the innate immune activation of the BP-RNA through the TLR 7 we used a known activator, the human immunodeficiency virus (HIV) derived single-stranded RNA (ssRNA40) and measured the production of cytokines as a function of the number of modified BP-linkages. The production of cytokines IL-6 and TNF&#945; was quantified after the boranophosphate (BP), phosphorothioate (PS) or natural ssRNA40 were transfected into murine macrophage Raw264.7 cells. Natural and phosphorothioate RNA (PS-RNA) have been shown to be activators of TLR 7 receptors. In contrast, we found that fully modified BP- ssRNA40 did not activate TLR 7. This is relevant in oligonucleotide applications such as siRNA and RNA aptamers where off-target effects such as immune activation after administration are not desired. </p><p>Subsequently, the low immune activation would be an advantage when coupled to RNAi activity of the oligonucleotide. Thus, we explored whether BP modified siRNA molecules would modulate gene expression and if there was an effect on downregulation activity when increasing the number of BH3 modifications on the phosphate backbone. Our therapeutic model was the multi-drug resistance 1 (MDR1) gene that expresses P-glycoprotein (P-gp), which has been notoriously difficult to modulate. The aberrant regulation of genes such as MDR1 in cancer cells are a major cause of chemotherapeutic treatment failure against human cancers. Hence, controlling the expression of cancer genes with antisense technology is a possible cancer therapy. Specifically, correcting the overexpression of p-glycoprotein using modified siRNAs that target and degrade the P-glycoprotein mRNA produced by the MDR1 gene. We found that there is a reduction of siRNA activity with an increasing number of BP-modifications. It appears that there is a fine balance between lack of immune response and gene downregulation when applied to BP-siRNA. </p><p>Finally, we compared the enrichment during the Systematic Evolution of Ligands by EXponential enrichment (SELEX) method of two libraries, one BP-RNA (U&#945;B) compared to a doubly-modified RNA (2'FC & U&#945;B), against a human thrombin. Aptamers modulate protein activity and interfere with protein signaling by binding to the desired protein with high affinity and specificity leading to their use in therapeutic applications where protein activity needs to be controlled or it is anomalous. In the case of blood coagulation, thrombin plays a central role in coagulation signaling cascade and it is a good target to use to control blood coagulation in clinical settings. We attempted to optimize the selection of BP- RNA aptamers through 4-8 rounds of SELEX against the protein thrombin. We found that the selection conditions were not optimal for BP-RNA SELEX possibly due to non-specific binding to a bovine serum albumin (BSA) in the selection buffer.</p> / Dissertation

The SRC gene encodes pp60c-Src, a 60 kDa non-receptor tyrosine kinase that is frequently activated and/or overexpressed in many cancers including colon cancer. In a subset of colon cancer cell lines, it has been shown, that the overexpression of c-Src can be explained, in part, by the transcriptional activation of the SRC gene. As a result, the general goal of this thesis was to further characterize how SRC is transcriptionally regulated in human cancer cell lines. Two highly dissimilar promoters, the housekeeping-like SRC1A promoter, as well as the HIF-1Ñ regulated tissue-specific SRC1Ñ promoter, regulate SRC expression. hnRNP K and the Sp family of factors regulate the SRC1A promoter; however, the true impact of Sp3 on SRC1A activity was not understood. In this thesis, a comprehensive analysis of the effect of Sp3 on SRC1A activity was performed. Physiologically, Sp3 exists as four translational isoforms that, in part, dictate the activation potential of Sp3. In general, the longer forms of Sp3 were modest transcriptional activators of the SRC1A promoter whereas the shorter forms were unable to activate the SRC1A promoter. An analysis of all Sp3 isoforms identified that the shorter Sp3 isoforms could be converted into transcriptional activators of SRC1A if the SUMOylation of a critical lysine residue within the inhibitory domain was prevented. Conversely, SUMOylation of the same isoform had little effect on the activation potential of the longer Sp3 isoforms at the SRC1A promoter. These results suggest that transcriptional activation by Sp3 is promoter context-, isoform- and modification-dependent.<p>SRC is transcriptionally repressed by histone deacetylase inhibitors (HDIs) and despite unsuccessful studies attempting to identify HDI-responsive elements within the SRC promoter regions none could be identified. This finding also suggests that histone deacetylases (HDACs) may be required for SRC expression. Historically, it was believed that HDIs act at the histone level to alter chromatin dynamics through the inactivation of HDACs to result in histone hyperacetylation and increased transcriptional activation. As such, a systematic investigation of the changes in histone H3 and H4 acetylation status at the transcriptionally repressed SRC promoter regions and the transcriptionally activated p21WAF1 promoter region was performed. The p21WAF1 promoter was used as control in this study as p21WAF1 is a classical example of a gene transcriptionally activated by HDIs. Interestingly, similar changes in histone acetylation at the p21WAF1 promoter and both SRC promoter regions were observed. Upon closer examination of acetylation changes at discreet histone residues, it was observed that in the rare case that a particular residue was differentially acetylated upon treatment at the promoter regions analyzed, the SRC1Ñ and p21WAF1 promoter regions demonstrated more similar changes in acetylation as compared to SRC1A. Taken together, these results suggest that histone acetylation status is not an accurate indicator of transcriptional activity following HDI treatment. To further investigate HDI-mediated SRC repression, RNA Pol. II occupancy at the promoter and regions downstream of the promoter were assessed. Despite the continued occupancy of RNA Pol. II at the promoter regions, RNA Pol. II was lost from the 3¡¦ UTR upon treatment with HDIs. These findings suggest that RNA Pol. II . may be sequestered at the promoter regions upon treatment with HDIs possibly as a result of impeded transcription initiation and/or elongation. Further analysis of the phosphorylation status of RNA Pol. II identified that transcriptional initiation was indeed occurring despite HDI treatment; however, productive transcriptional elongation could not be confirmed thus suggesting a role for abrogated elongation in HDI mediated SRC repression. Complimentary analysis of the effects of HDACs on SRC expression suggested that while class I HDACs abrogated SRC expression, class II HDACs were required for the maintenance of SRC transcript levels in a promoter-independent fashion. Together, these results provide the basis for a model whereby HDIs repress SRC transcriptional expression through the inhibition of class II HDAC activity to eventually result in curtailed SRC transcriptional elongation.

The satellite RNA of Lucerne Transient Streak Virus (LTSV) is a 322-nucleotide, single-stranded circular RNA that has a rod-like structure very similar to that of viroids. As it does not encode any translation products and cannot replicate independently of a helper virus, the satellite RNA is proposed to rely on viral-encoded proteins for the replication and/or cell-to-cell movement that facilitate its systemic infection in a host. To investigate the requirements for replication of the LTSV satellite RNA, transgenic plant systems were generated to express the viral RNA-dependent RNA polymerase and predicted viral transport protein independently as well as in combination. Results of infectivity assays of these transgenic lines demonstrated for the first time that the viral-encoded RNA-dependent RNA polymerase is necessary and sufficient for the replication of LTSV satellite RNA, and that no additional viral proteins are required for its cell-to-cell or systemic transport.

The satellite RNA of Lucerne Transient Streak Virus (LTSV) is a 322-nucleotide, single-stranded circular RNA that has a rod-like structure very similar to that of viroids. As it does not encode any translation products and cannot replicate independently of a helper virus, the satellite RNA is proposed to rely on viral-encoded proteins for the replication and/or cell-to-cell movement that facilitate its systemic infection in a host. To investigate the requirements for replication of the LTSV satellite RNA, transgenic plant systems were generated to express the viral RNA-dependent RNA polymerase and predicted viral transport protein independently as well as in combination. Results of infectivity assays of these transgenic lines demonstrated for the first time that the viral-encoded RNA-dependent RNA polymerase is necessary and sufficient for the replication of LTSV satellite RNA, and that no additional viral proteins are required for its cell-to-cell or systemic transport.

Alternative splicing functions to generate proteomic diversity and to regulate gene expression in higher eukaryotes. Genome-wide analyses suggest that alternative splicing and transcription typically regulate different gene sets to achieve cell- and tissue-type specificity. However, within individual cell-types, most alternative splicing events occur co-transcriptionally and are impacted by the transcriptional machinery. Despite many focused studies on co-transcriptional regulation of alternative splicing, its mechanisms and functions in regulation of gene expression are still poorly understood. To investigate relationships between transcription and alternative splicing, I performed microarray profiling of alternative splicing and transcript levels during activation of a T cell line. This experiment revealed that different sets of genes and associated functional categories are regulated by alternative splicing and transcription during T cell activation. I next employed inhibitors of RNA polymerase II (Pol II) elongation and microarray profiling to identify genes with coupled changes in splicing and transcript levels when transcription is impeded in activated T cell. Genes that were affected at both levels were significantly enriched in RNA binding and processing functions, and generally displayed increased alternative exon inclusion and decreased transcript levels when transcription elongation was disrupted. Similar effects were observed when transcription was driven by mutant polymerases with reduced elongation activity, and when cells were subjected to stress treatments. Many of the elongation inhibition-sensitive exons from the affected genes introduce premature termination codons into the mRNA, resulting in spliced mRNAs that are substrates of the nonsense-mediated decay pathway and further reduction in mRNA levels. ChIP-Seq experiment demonstrated that Pol II occupancy specifically increased in introns flanking the affected exons. These results provide evidence that a physiological function of transcription elongation-coupled alternative splicing regulation is to regulate the levels of RNA processing factors under conditions that reduce elongation activity, including cell stress. In summary, my thesis research has provided new insights into the integration of transcription and splicing control. While these two regulatory levels can control different gene sets during the activation of T cells, within a given cell type, they are closely coupled to control specific alternative splicing events that appear to coordinate mRNA and RNA processing factors levels.

Alternative splicing functions to generate proteomic diversity and to regulate gene expression in higher eukaryotes. Genome-wide analyses suggest that alternative splicing and transcription typically regulate different gene sets to achieve cell- and tissue-type specificity. However, within individual cell-types, most alternative splicing events occur co-transcriptionally and are impacted by the transcriptional machinery. Despite many focused studies on co-transcriptional regulation of alternative splicing, its mechanisms and functions in regulation of gene expression are still poorly understood. To investigate relationships between transcription and alternative splicing, I performed microarray profiling of alternative splicing and transcript levels during activation of a T cell line. This experiment revealed that different sets of genes and associated functional categories are regulated by alternative splicing and transcription during T cell activation. I next employed inhibitors of RNA polymerase II (Pol II) elongation and microarray profiling to identify genes with coupled changes in splicing and transcript levels when transcription is impeded in activated T cell. Genes that were affected at both levels were significantly enriched in RNA binding and processing functions, and generally displayed increased alternative exon inclusion and decreased transcript levels when transcription elongation was disrupted. Similar effects were observed when transcription was driven by mutant polymerases with reduced elongation activity, and when cells were subjected to stress treatments. Many of the elongation inhibition-sensitive exons from the affected genes introduce premature termination codons into the mRNA, resulting in spliced mRNAs that are substrates of the nonsense-mediated decay pathway and further reduction in mRNA levels. ChIP-Seq experiment demonstrated that Pol II occupancy specifically increased in introns flanking the affected exons. These results provide evidence that a physiological function of transcription elongation-coupled alternative splicing regulation is to regulate the levels of RNA processing factors under conditions that reduce elongation activity, including cell stress. In summary, my thesis research has provided new insights into the integration of transcription and splicing control. While these two regulatory levels can control different gene sets during the activation of T cells, within a given cell type, they are closely coupled to control specific alternative splicing events that appear to coordinate mRNA and RNA processing factors levels.

The SRC gene encodes pp60c-Src, a 60 kDa non-receptor tyrosine kinase that is frequently activated and/or overexpressed in many cancers including colon cancer. In a subset of colon cancer cell lines, it has been shown, that the overexpression of c-Src can be explained, in part, by the transcriptional activation of the SRC gene. As a result, the general goal of this thesis was to further characterize how SRC is transcriptionally regulated in human cancer cell lines. Two highly dissimilar promoters, the housekeeping-like SRC1A promoter, as well as the HIF-1Ñ regulated tissue-specific SRC1Ñ promoter, regulate SRC expression. hnRNP K and the Sp family of factors regulate the SRC1A promoter; however, the true impact of Sp3 on SRC1A activity was not understood. In this thesis, a comprehensive analysis of the effect of Sp3 on SRC1A activity was performed. Physiologically, Sp3 exists as four translational isoforms that, in part, dictate the activation potential of Sp3. In general, the longer forms of Sp3 were modest transcriptional activators of the SRC1A promoter whereas the shorter forms were unable to activate the SRC1A promoter. An analysis of all Sp3 isoforms identified that the shorter Sp3 isoforms could be converted into transcriptional activators of SRC1A if the SUMOylation of a critical lysine residue within the inhibitory domain was prevented. Conversely, SUMOylation of the same isoform had little effect on the activation potential of the longer Sp3 isoforms at the SRC1A promoter. These results suggest that transcriptional activation by Sp3 is promoter context-, isoform- and modification-dependent.<p>SRC is transcriptionally repressed by histone deacetylase inhibitors (HDIs) and despite unsuccessful studies attempting to identify HDI-responsive elements within the SRC promoter regions none could be identified. This finding also suggests that histone deacetylases (HDACs) may be required for SRC expression. Historically, it was believed that HDIs act at the histone level to alter chromatin dynamics through the inactivation of HDACs to result in histone hyperacetylation and increased transcriptional activation. As such, a systematic investigation of the changes in histone H3 and H4 acetylation status at the transcriptionally repressed SRC promoter regions and the transcriptionally activated p21WAF1 promoter region was performed. The p21WAF1 promoter was used as control in this study as p21WAF1 is a classical example of a gene transcriptionally activated by HDIs. Interestingly, similar changes in histone acetylation at the p21WAF1 promoter and both SRC promoter regions were observed. Upon closer examination of acetylation changes at discreet histone residues, it was observed that in the rare case that a particular residue was differentially acetylated upon treatment at the promoter regions analyzed, the SRC1Ñ and p21WAF1 promoter regions demonstrated more similar changes in acetylation as compared to SRC1A. Taken together, these results suggest that histone acetylation status is not an accurate indicator of transcriptional activity following HDI treatment. To further investigate HDI-mediated SRC repression, RNA Pol. II occupancy at the promoter and regions downstream of the promoter were assessed. Despite the continued occupancy of RNA Pol. II at the promoter regions, RNA Pol. II was lost from the 3¡¦ UTR upon treatment with HDIs. These findings suggest that RNA Pol. II . may be sequestered at the promoter regions upon treatment with HDIs possibly as a result of impeded transcription initiation and/or elongation. Further analysis of the phosphorylation status of RNA Pol. II identified that transcriptional initiation was indeed occurring despite HDI treatment; however, productive transcriptional elongation could not be confirmed thus suggesting a role for abrogated elongation in HDI mediated SRC repression. Complimentary analysis of the effects of HDACs on SRC expression suggested that while class I HDACs abrogated SRC expression, class II HDACs were required for the maintenance of SRC transcript levels in a promoter-independent fashion. Together, these results provide the basis for a model whereby HDIs repress SRC transcriptional expression through the inhibition of class II HDAC activity to eventually result in curtailed SRC transcriptional elongation.

Thesis (Ph. D.)--University of Washington, 2001. / Vita. Includes bibliographical references (leaves 72-93).

Thesis (Ph. D.)--University of Washington, 2003. / Vita. Includes bibliographical references (leaves 112-124).