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The E2A locus is involved in chromosomal translocations associated with acute lymphoblastic leukemia. The most common of these involves a translocation between chromosomes 1 and 19 (t1;19), resulting in expression of the chimeric oncoprotein E2A-PBX1. A direct interaction between transcriptional activation domain 1 (AD1) of E2A and KIX domain of the histone acetyltransferase (HAT) /co-activator CBP is required for E2A-PBX1-mediated leukemia induction in mice. This thesis examines the functional consequences of the direct, physical interaction between E2A and CBP, for both proteins. We demonstrate that the interaction between E2A and CBP/p300, as well as another HAT/co-activator, p/CAF, results in acetylation of E2A. Mutagenesis-based mapping studies identify several lysine residues as substrates for acetylation. Of particular interest, a conserved lysine (K34) located within AD1 is acetylated in vitro and in vivo. Substitution of this residue to arginine impairs transcriptional activation of a luciferase reporter while substitution to glutamine, mimicking the acetylation, restores E2A-mediated transcriptional activation. Recent studies have shown that several transcription factors can modulate the intrinsic HAT activity of CBP/p300. We were surprised to find that E2A proteins enhance acetylation of histones by CBP, in vitro and in vivo, in a KIX domain-independent manner. Acetylation of E2A is also not required for stimulation of CBP/p300 histone acetylation. It appears that E2A interacts with the other CBP domains to mediate this effect, presumably through allosteric effects. In summary, we demonstrate that acetylation of E2A plays a role in mediating the transcriptional activation activity of E2A. Furthermore, acetylation of E2A enhances its interaction with CBP/p300, at least in the presence of additional nuclear factors. We show evidence that p/CAF may mediate this effect. Enhancement of CBP/p300 HAT activity by oncogenic E2A-PBX1 proteins in vivo, suggests that some of its leukemia-promoting effects may be due to E2A-induced gain of function effects on CBP/p300. The enhanced interaction between acetylated E2A and CBP/p300, as well as the E2A-mediated stimulation of histone acetyltransferase activity might play a role in the DNA-binding-independent induction of proliferation. / Thesis (Ph.D, Pathology & Molecular Medicine) -- Queen's University, 2007-09-26 13:37:21.905

Progress in understanding cancer progression has been hampered over the years by the different types of mutations present and irregular changes of gene regulation associated with any given cancer. In this work, molecular interactions between TALI, LMO1, and decorin were investigated. Numerous studies have shown that ectopic expression of decorin protein induced growth suppression in neoplastic cells of various histogenic origins. Furthermore, ectopic expression of TAL1 and LMOI oncoproteins has been shown to occur in approximately 50% of the cases of T-cell acute lymphoblastic leukemia (T-ALL). It was of interest then to determine the preventive or interactive role decorin played with the oncogenic activity of TAL I and LMO1. In this investigation, decorin was introduced into a murine T-cell line (AKR-DP-603) through the use of the mammalian expression vector pcDNA3.1 (-). This particular cell line was previously engineered to express TALI and LMO1. Protein expression patterns in all cell populations were analyzed using the Western blot technique and a proteoglycan with a molecular weight of 100 kDa before chondroitinase ABC treatment and a core protein of55 kDa after treatment with chondroitinase ABC was seen. This finding is significant since it implies that the pcDNA3. 1(-) vector containing decorin cDNA was present, and the corresponding decorin peptides were expressed in both cytoplasmic and nuclear extracts. Furthermore, Northern blot analysis was performed on total RNA extracts to determine the transcriptional state of endogenous decorin rRNA, as well as exogenously introduced decorin. Northern blot analysis revealed no decorin-specific mRNA transcripts from the various cell populations. This result did not imply a lack of possible regulatory effect on protein and mRNA levels of TALL and LMOI by decorin. Finally, cell growth assays were performed on all cell populations and cell counts were used to assess the growth pattern of each population after serum withdrawal. The results show possible growth suppressive effects of decorin on TAL1 and LMOI expressing cells. Results obtained from this study shed further light on the molecular interactions influencing T-ALL and may also help in the design of potentially beneficial cancer treatments using decorin. / Department of Biology

The non-cluster homeobox gene TLX1 was initially identified at the breakpoint of the t(10;14)(q24;q11) chromosome translocation in the malignant cells. Three independent research groups have generated transgenic mouse models expressing TLX1 in various hemopoietic cells resulting in development of B cell lymphoma and T-ALL. T-ALL tumours were characterized as immature Double Negative or/and Double Positive phenotypes. In addition, all TLX1 transgenic mice showed a long latency for leukemia development suggesting requirement of additional genomic abnormalities for the conversion of premalignant cells to full-blown malignancy. We hypothesized that unresolved double strand DNA breaks might act as additional genetic mutation and contribute to T-ALL progression in TLX1 overexpressed thymocytes. To address this hypothesis, we generated double mutant IgHμ-TLX1TgPrkdcScid/Scid mice, which accelerated the development of leukemia relative to PrkdcScid/Scid littermates. We identified that multiple genes associated with chromosome segregation, apoptosis and cell cycle progression were aberrantly expressed in IgHμ-TLX1TgPrkdcScid/Scid premalignant thymocytes. We found that IgHμ-TLX1TgPrkdcScid/Scid thymocytes were prone to chromosome instability suggesting malfunction of the mitotic spindle assembly checkpoint. In addition to T-ALL, 46% of IgHμ-TLX1TgPrkdcScid/Scid mice developed Acute Myeloid Leukemia, suggesting that the cancer initiating effects of TLX1 are not limited to cells of lymphoid origin. Transplantation experiments revealed that T cell acute lymphoblastic leukemia initiating cells (T-ALL-ICs) reside in the thymus of IgHμ-TLX1TgPrkdcScid/Scid mice and T-ALL-ICs were enriched in the c-kit+CD44+CD25- fraction. We showed that T-ALL tumour cells from IgHμ-TLX1TgPrkdcScid/Scid were transplantable and there was a tendency for the latency period of T-ALL development to be reduced with secondary and tertiary transplantations. We demonstrated that premalignant IgHμ-TLX1TgPrkdcScid/Scid myeloid progenitors exhibited deregulated apoptosis and proliferation. Collectively, our studies demonstrate that TLX1 expression in DNA-PK-deficient cells activats multiple oncogenic pathways leading to apoptosis resistance, accelerated proliferation and deregulation of the spindle assembly checkpoint. We propose that activation of the same pathways supporting survival and proliferation in various cells may be indicative of the universal principles driving TLX1-induced tumourogenesis. Our data provide clinically relevant information of the molecular mechanisms involved in the pathogenesis of leukemia that makes IgHμ-TLX1TgPrkdcScid/Scid mouse model a powerful tool to explore potential treatment options directed to delay disease progression.

Chronic Lymphocytic Leukaemia (CLL) is a disease of B-lymphocytes that account for significant morbidity and mortality in mostly elderly patients (aged ≥ 70 years). The relative survival of patients with CLL has been shown to decrease with patient age, and this age-related reduction in survival was found to correlate with the levels of two inflammatory cytokine levels in the patients’ plasma. The levels of two inflammatory cytokines, interleukin-6 and -8 (IL-6, IL-8) were found to correlate positively with patient age, and increased levels were associated with lower overall survival. Addition of IL-6 or IL-8 to a co-culture system of CLL cells with bone marrow stromal cells increased the CLL-stromal cell adhesion, and co-culturing increased IL-8 secretion. In a search of a treatment regimen that may be effective and readily tolerated by elderly patients, we examined the combination of fludarabine with valproic acid (VPA), an epileptic that was found to inhibit histone deacetylases (HDACs). The combination was synergistic against human leukaemic cells, including primary CLL cells. In a phase II clinical trial where six elderly patients with relapsed, previously treated CLL were enrolled (half of whom were clinically refractory to fludarabine), the VPAfludarabine combination induced reduction in the peripheral and lymph node tumour loads. Mechanistically, the fludarabine treatment induced disruption of the lysosomes, while VPA induced increase in the level and activity of cathepsin B, a lysosomal protease. The VPA-induced increase in cathepsin B levels was observed in in cell lines (in vitro), primary CLL cells (ex vivo) and in patients treated with VPA (in vivo). Chemical inhibition of cathepsin B was sufficient to dampen the VPA-fludarabine cytotoxicity, and the addition activated cathepsin B to leukaemic cell lysates was sufficient to induce caspase cleavage and reduction in anti-apoptotic protein levels. The VPA-fludarabine combination also lowered phospho-Akt levels and ATM activation, which also contributed to the VPA-fludarabine synergy, and VPA treatment lowered ATM levels and phospho-Akt levels in vivo. In summary, there lies a biological explanation for the poor survival observed with elderly patients, and the VPA-fludarabine may be a useful regimen for these patients.

B-cell acute lymphoblastic leukemia (B-ALL) represents a collection of diseases that are categorized into subtypes based on the presence of recurrent cytogenetic abnormalities. These abnormalities often result in the expression of oncogenic drivers that denote a standard- or high-risk for relapse. Currently, survival rates boarder 40% for adult patients and relapses are often observed in patients lacking high-risk markers. Thus, there is an unmet need for biomarkers that can identify all high-risk leukemia, and development of novel therapies based on a better understanding of the molecular drivers of B-ALL. To address this need, I designed a multi-parameter phospho-flow cytometry platform and characterized basal and cytokine-potentiated signaling in adult B-ALL samples. I identified patterns of cytokine-responsiveness across B-ALL patients that correlated with the presence of high-risk oncogenic drivers. Furthermore, I demonstrated that small-molecule inhibitors could abrogate cytokine-induced signaling in high-risk patients suggesting these inhibitors may compliment current chemotherapeutic protocols.

3BP2 was originally identified through its interaction with the ABL kinase. Fusion of ABL with the BCR gene forms the BCR-ABL onco-protein, which is causative in Chronic Myeloid Leukemia (CML) and acute lymphoid leukemia (ALL). Due to the ability of 3BP2 to regulate ABL activity in osteoblasts, we hypothesize that 3BP2 modulates BCR-ABL signalling. Overexpression of 3BP2 in the CML-T1 cell line produced a marked decrease in global tyrosine phosphorylation. 3BP2 overexpression also resulted in a significant increase in CML-T1 cell growth, accompanied by altered ERK1/2, AKT, SYK, LYN, HCK, and CBL phosphorylation and expression. A phospho-SRC family protein and a 116 kDa phospho-protein were identified as 3BP2 interaction partners in response to BCR-ABL activation. BCR-ABL bone marrow transplantation (BMT) models in 3bp2-/- mice exhibit accelerated disease compared to wild-type mice, with altered leukemic phenotype. In conclusion, 3BP2 is able to modulate signalling through BCR-ABL and affect BCR-ABL-induced disease outcome.

B-cell acute lymphoblastic leukemia (B-ALL) represents a collection of diseases that are categorized into subtypes based on the presence of recurrent cytogenetic abnormalities. These abnormalities often result in the expression of oncogenic drivers that denote a standard- or high-risk for relapse. Currently, survival rates boarder 40% for adult patients and relapses are often observed in patients lacking high-risk markers. Thus, there is an unmet need for biomarkers that can identify all high-risk leukemia, and development of novel therapies based on a better understanding of the molecular drivers of B-ALL. To address this need, I designed a multi-parameter phospho-flow cytometry platform and characterized basal and cytokine-potentiated signaling in adult B-ALL samples. I identified patterns of cytokine-responsiveness across B-ALL patients that correlated with the presence of high-risk oncogenic drivers. Furthermore, I demonstrated that small-molecule inhibitors could abrogate cytokine-induced signaling in high-risk patients suggesting these inhibitors may compliment current chemotherapeutic protocols.

Chronic Lymphocytic Leukaemia (CLL) is a disease of B-lymphocytes that account for significant morbidity and mortality in mostly elderly patients (aged ≥ 70 years). The relative survival of patients with CLL has been shown to decrease with patient age, and this age-related reduction in survival was found to correlate with the levels of two inflammatory cytokine levels in the patients’ plasma. The levels of two inflammatory cytokines, interleukin-6 and -8 (IL-6, IL-8) were found to correlate positively with patient age, and increased levels were associated with lower overall survival. Addition of IL-6 or IL-8 to a co-culture system of CLL cells with bone marrow stromal cells increased the CLL-stromal cell adhesion, and co-culturing increased IL-8 secretion. In a search of a treatment regimen that may be effective and readily tolerated by elderly patients, we examined the combination of fludarabine with valproic acid (VPA), an epileptic that was found to inhibit histone deacetylases (HDACs). The combination was synergistic against human leukaemic cells, including primary CLL cells. In a phase II clinical trial where six elderly patients with relapsed, previously treated CLL were enrolled (half of whom were clinically refractory to fludarabine), the VPAfludarabine combination induced reduction in the peripheral and lymph node tumour loads. Mechanistically, the fludarabine treatment induced disruption of the lysosomes, while VPA induced increase in the level and activity of cathepsin B, a lysosomal protease. The VPA-induced increase in cathepsin B levels was observed in in cell lines (in vitro), primary CLL cells (ex vivo) and in patients treated with VPA (in vivo). Chemical inhibition of cathepsin B was sufficient to dampen the VPA-fludarabine cytotoxicity, and the addition activated cathepsin B to leukaemic cell lysates was sufficient to induce caspase cleavage and reduction in anti-apoptotic protein levels. The VPA-fludarabine combination also lowered phospho-Akt levels and ATM activation, which also contributed to the VPA-fludarabine synergy, and VPA treatment lowered ATM levels and phospho-Akt levels in vivo. In summary, there lies a biological explanation for the poor survival observed with elderly patients, and the VPA-fludarabine may be a useful regimen for these patients.

The oncogene Ahi-1 was recently identified through provirus insertional mutagenesis in murine leukemias and lymphomas. Its involvement in human leukemogenesis is demonstrated by gross perturbations in its expression in several leukemic cells lines, particularly in cutaneous T-cell lymphoma (CTCL) cell lines (Hut 78 and Hut 102). Hut 78 is derived from a patient with Sezary syndrome, a common leukemic variant of the human CTCL mycosis fungoides. Aberrant expression of AHI-1 mRNA and protein has been found in CD4⁺CD7⁻ leukemic Sezary cells from patients with Sezary syndrome. Moreover, stable suppression of AHI-1 using retroviral-mediated RNA interference in Hut 78 cells inhibits their transforming activity in vitro and in vivo. In an effort to identify genes involved in AHI-1-mediated leukemic transformation in CTCL, microarray analysis was performed to compare six RNA samples from AHI-1 suppressed Hut 78/sh4 cells to five samples from Hut 78 control cells. Limma and dChip analyses identified 218 and 95 differentially expressed genes, respectively, using a fold change criteria of > or < 2 and a p-value threshold of ≤ 0.01. After evaluation of both analyses, 21 genes were selected based upon interesting structural and functional information, specificity to hematopoietic cells or T-cells, and previous connections to cancer. Expression patterns of these 21 genes were validated by qRT-PCR with p-values < 0.05 ranging from 1.97 x 10⁻¹⁰ to 6.55 x 10⁻³, with the exception of BRDG1 at 5.88 x 10⁻². The observed up-regulation of both BIN1 and HCK in AHI-1 suppressed Hut 78/sh4 cells as compared to control cells further confirmed at the protein level. The tumor suppressor BIN1 is known to physically interact with c-MYC, which also exhibits differential protein expression in these cells. Characterization of BIN1 identified 4 isoforms all of which contain exon 10 and demonstrate alternative splicing of exons 12A and 13. Additionally, qRT-PCR results from primary Sezary samples indicate there is clinical significance in the expression changes detected for BIN1, HCK, REPS2, BRDG1, NKG7 and SPIB. These findings identify several new differentially expressed genes that may play critical roles in AHI-1-mediated leukemic transformation of human CTCL cells.