Biology

BCR-ABL1 results from t(9;22)(q34;q11) reciprocal translocation resulting in BCR-ABL1 kinase expression, initiating chronic myeloid leukemia in chronic phase (CML-CP). At the initial stages of CML-CP both oncogenic BCR-ABL1 kinase and normal ABL1 kinase are expressed, however, loss of ABL1 kinase expression in CML-CP can result from an interstitial deletion in the normal chromosome 9 [del(9q34)] which may be combined with the transcriptional silencing of the alternative ABL1 promoter within the translocation eventually leading to disease progression and drug resistance. We found that BCR-ABL1 Abl1-/- cells generated a CML-blast phase (BP)-like disease phenotype in NOD-SCID mice compared to the BCR-ABL1 Abl1+/+ cells. To determine the mechanisms responsible for blastic transformation of BCR-ABL1 Abl1-/- cells, we examined the role of ABL1 in proliferation, differentiation, apoptosis, genomic instability, and stemness. The presence of ABL1 inhibited proliferation in BCR-ABL1 cells as BCR-ABL1 Abl1-/- cells had higher clonogenic activity and proliferative rate compared to their wild-type counterparts. ABL1 is essential for myeloid differentiation since BCR-ABL1 Abl1-/- cells showed an immature blast phenotype when stained with Wright-Giemsa and myeloid differentiation markers Gr-1 and CD11b. ABL1 promoted apoptosis in response to genotoxic stress as revealed by reduced clonogenicity and expression of p53, phosphoserine-15 p53 and activated caspase 3 in BCR-ABL1 Abl1+/+ compared to knock-out cells. Although the absence of ABL1 did not enhance ROS and oxidative DNA damage, it appears that an impaired DNA damage response may be responsible for higher chromosome numbers and an accumulation of high numbers of chromosomal aberrations in BCR-ABL1 Abl1-/- cells. We detected an expansion of Lin-c-Kit+Sca-1+ leukemia stem cells (LSCs) in BCR-ABL1 Abl1-/- cells compared to BCR-ABL1 Abl1+/+ or non-transformed counterparts; among the LSCs, there was a higher percentage of CD34-Flt3- long-term and CD34+Flt3- short-term stem cells. These results showed that ABL1 is involved in regulating the LSC compartment in BCR-ABL1 cells. DNA microarray analysis revealed changes in mRNA levels of several genes involved in proliferation, myeloid differentiation, apoptosis, DNA damage response and `stemness' in BCR-ABL1 Abl1-/- cells in comparison to BCR-ABL1 Abl1+/+ cells. Together, these results demonstrate a critical role of ABL1 as a tumor suppressor in BCR-ABL1-induced leukemia, prolonging survival in mice by suppressing proliferation and expansion of LSC, inducing myeloid differentiation, apoptosis and DNA damage response in BCR-ABL1 cells. Loss of ABL1 was also found to contribute to Imatinib resistance in BCR-ABL1 cells. Moreover, we hypothesized that enhancement of the tumor-suppressor function of ABL1 may have a significant impact on CML treatment. A small molecule activator of ABL1 kinase, 5-(1,3-diaryl-1H-pyrazol-4-yl)hydantoin (DPH), have been reported to interact with the myristoyl-binding site of ABL1 and destabilize the…

Biochemistry

BCR-ABL is known as the most common translocation in the myeloproliferative (MPD) disorder chronic myelogenous leukemia (CML); it is the first leukemia to be described and associated with a consistent cytogenetic abnormality, termed the Philadelphia chromosome (Ph1). Ph1 is a shortened chromosome 22 that is the consequence of a reciprocal translocation between chromosomes 9 and 22, t(9;22)(q34;q11). BCR-ABL is known to display constitutively active tyrosine kinase activity that leads to the recruitment of downstream effectors of cell proliferation and survival, via several adapter proteins (e.g., GRB2, GAB2, CRKL.) and signaling pathways (e.g., RAS, PI3K, JAK STAT, PDk2-NFkB), all thought to contribute to the pathogenesis of CML. CML, essentially consists of 3 different phases based on disease severity; namely Chronic Phase (CP-AML), Accelerated Phase (AP-CML) and blast crisis (BC-CML). Imatinib, a small molecule ABL kinase inhibitor has been highly effective in treating chronic phase (CP) CML patients. However, a substantial number of patients undergo relapse due to development of resistance to imatinib therapy that leads to BC-CML, which is invariably fatal within weeks to months. Additional genetic aberrations assist in progression and identification of key players that are responsible for transformation is of utmost importance from a therapeutic point of view. Growth arrest DNA damage 45a (Gadd45a) gene, a member in the gadd45 family of genes including Gadd45b & Gadd45g, was identified as a myeloid differentiation primary response gene. There is evidence consistent with it's involvement in G2/M cell cycle arrest and apoptosis in response to multiple stressors, including genotoxic and oncogenic stress. Gadd45a has been shown to participate in cell cycle arrest, DNA repair, cell survival and apoptosis in response to environmental and physiological stress, via protein-protein interactions with key regulators such as PCNA, histones, cdk1, p21, MEKK4, MKK7 and p38. To investigate the effect of Gadd45a in the development of CML, we performed adaptive bone marrow transplantation experiments with either wild type or Gadd45a null myeloid progenitors expressing 210-kD BCR-ABL fusion oncoprotein. We showed that that loss of Gadd45a accelerated BCR-ABL driven CML and correlated with enlarged liver and spleen pointing to more aggressive leukemia. Additionally, we demonstrated that Gadd45a expression in presence of BCR-ABL was independent/distinct from well-known tumor suppressor p53, which suggests that Gadd45a could be considered as a prime and novel candidate for intervention in CML therapy. We also showed that transformed Gadd45a deficient progenitors in the presence of BCR-ABL, exhibited increased proliferation, increased survival and decreased apoptosis when compared to WT/BCR-ABL counterparts. Additionally, we demonstrate that recipients transplanted with Gadd45ako/BCR-ABL bone marrow exhibit increased number of Leukemic stem cells (LSC) harboring BCR-ABL which correlated with accelerated disease…

Molecular Biology and Genetics

JLP (JNK associated Leucine zipper protein) is a scaffolding protein that has been shown to interact with and activate the JNK/p38MAPK pathway. Its interaction with various signaling proteins is associated with coordinated regulation of cellular processes such as endocytosis, motility, neurite outgrowth, cell proliferation and apoptosis. Here, we undertook a mass spectrometric approach to identify novel interaction partners of JLP and identified the mitotic Ser/Thr kinase, Polo like Kinase 1 (PLK1) and the Fox transcription factor, Forkhead box protein K1 (FoxK1), as proteins that interact with and form a ternary complex with JLP during mitosis. Domain mapping studies showed that the N-terminal domain of JLP interacts with the polo-box domain (PBD) of PLK1 in a phosphorylation-dependent manner. Our results indicate that, JLP is phospho-primed on Thr351, which is recognized by the PBD of PLK1 and leads to phosphorylation of JLP at additional sites. Moreover, treatment of cells with the PLK1 inhibitor BI2536 affects this interaction, demonstrating the importance of PLK1 kinase activity in this process. Because JLP is a scaffolding protein that recruits proteins to mediate specific cell signaling events, the interaction of JLP with PLK1 likely results in the recruitment of other proteins to this complex. To test this hypothesis, we carried out SILAC labeling of proteins in mitotic cells in the presence or absence of BI2536. Through mass-spectrometry, we identified the FoxK1 transcription factor as a PLK1-dependent JLP-interacting protein. Furthermore, we show that JLP, PLK1 and FoxK1 form a ternary complex that is present only during mitosis. Knockdown of PLK1 and not JLP affected the interaction between JLP and FoxK1, indicating that the formation of the ternary complex is PLK1-dependent. FoxK1 is a known transcriptional repressor of the cyclin dependent kinase inhibitor, p21/WAF1. Knockdown of JLP in U2OS cells resulted in increased FoxK1 protein levels and a reduction of p21 expression. Moreover, immunofluorescence studies in asynchronous cells showed that FoxK1 is excluded from the nucleus during mitosis and that a fraction of FoxK1 localizes to the midbody region during cytokinesis. Analysis of FoxK1 protein in cells exiting S-phase suggests that FoxK1 is post-translationally modified during mitosis. In this study we characterized the ternary complex formed between JLP, PLK1 and FoxK1 during mitosis. Based on our observations, we propose that formation of the JLP/PLK1/FoxK1 ternary complex regulates the stability and/or transcriptional activity of FoxK1.

Temple University – Theses

Molecular Biology and Genetics

Ovarian cancer is currently the most fatal gynecologic cancer and the fifth leading cause of fatal cancer in women overall. As compared to the better-characterized malignancies, such as such as prostate, breast and colorectal cancers, there have been no major changes in methods of detection or treatment of ovarian cancers since the 1970's. As a result, the incidence and age-adjusted death rates for this disease have improved only marginally since that time. The molecular changes required for ovarian cancer pathogenesis remain poorly defined. Lysophosphatidic acid (LPA) has emerged as a biomarker present in the ascitic fluid and serum of ovarian cancer patients. Subsequent studies have identified LPA as an agonist for G protein coupled receptors (GPCRs). LPA has been well characterized as a pro-migratory factor in ovarian cancer and other cell systems. However, the role of LPA in mediating a proliferative response in ovarian cancer cells has yet to be fully characterized. In addition, the identity of the G protein pathways involved in this proliferative response remains a major unresolved question in the field. To investigate the mitogenic role of LPA in ovarian cancers, a panel of representative human ovarian cancer cells was assembled. A series of immunoblot and RT-PCR analyses was used to profile the LPA receptors and Gα-subunits expressed in these cells. In addition to verifying the migratory effect of LPA in these cells, a series of proliferation assays were used to investigate the potential role for LPA as a mitogen. The results indicate that stimulation with LPA results in a robust and statistically significant proliferative response. This response was quantified using multiple approaches. In addition, the proliferative response was observed in three independent ovarian cancer cell lines using concentrations of LPA within the range found in vivo in the ascitic fluid of ovarian cancer patients. Taken together, these data for the first time validate the role of LPA as a mitogen in ovarian cancer cells. To gain further insight into the oncogenic signaling response stimulated by LPA, activation of the mitogen activated protein kinase (MAPK) modules was determined. Using a series of immunoblot analyses and kinase assays, LPA was found to stimulate ERK as well as JNK modules. To investigate the functional roles of these pathways, a series of proliferation assays were carried out using inhibitors of ERK and JNK signaling. Consistent with the role of ERK as a crucial regulator of growth-factor induced proliferation in other cell systems, the results demonstrated a significantly attenuated growth response to LPA with ERK inhibition. Moreover, additional studies demonstrated for the first time that inhibition of JNK signaling significantly attenuates the proliferative response to LPA. In order to investigate the potential role of Gα12 in mediating the oncogenic response to LPA, the activation status of Gα12 was monitored in ovarian cancer cells stimulated with LPA. These studies…

Molecular Biology and Genetics

The Gadd45 family of proteins (Gadd45a, Gadd45b, and Gadd45g) has been shown to act as stress sensors in response to various physiological and environmental stressors, including oncogenic stress. However, the role of Gadd45b in senescence remained unclear. Here, we show for the first time that primary mouse embryo fibroblasts (MEFs) from Gadd45b null mice proliferate slowly; accumulate increased levels of DNA damage, and senesce prematurely. Notably, this is in contrast with Gadd45a null MEFs that show enhanced growth rate and escape senescence. This difference in growth rate increases with increasing passage number, suggesting that senescence results from exposure to environmental stressors. The impaired proliferation and increased senescence in Gadd45b null MEFs can be partially reversed by culturing cells at physiological oxygen levels, indicating that in the absence of Gadd45b, primary MEFs are less able to cope with elevated levels of oxidative stress. Interestingly, in contrast to other senescent MEFs, which arrest at G1 phase of cell cycle, Gadd45b null MEFs arrest at the G2/M phase of cell cycle. Furthermore, FACS analysis of Gadd45b null MEFs showed less phospho-histone H3-positive cells compared to wild type MEFs indicating that Gadd45b null MEFs are arrested in G2 phase rather than M phase. Interestingly, other stressors such as sub-lethal H2O2 and UV irradiation, that are known to increase oxidative stress, triggered increased premature senescence in Gadd45b null MEFs compared to wild type MEFs. By staining embryos for SA-β-gal gal, we also show that embryos from Gadd45b null mice exhibit increased SA-β-gal gal staining compared to wild type embryos, thus providing in vivo evidence for increased senescence in Gadd45b null mice. Finally, investigating the effect of loss of Gadd45b on senescence related diseases, we show that loss of Gadd45b promotes senescence and aging phenotypes in the skin as well as increased senescence and attenuated fibrotic response to CCl4 induced liver fibrosis. Together, these results highlight a novel and significant role for Gadd45b in the senescence response of cells to stress.

Temple University – Theses

Molecular Biology and Genetics

The Gadd45 family of proteins is known to play a central role as cellular stress sensors that modulate the response of mammalian cells to different stressors, including oncogenic stress. Gadd45a expression is regulated during myeloid cell differentiation, and is also induced in response to acute stimulation with cytokines, myeloablation and inflammation. The proto-oncogene C-myc plays a pivotal role in growth control, differentiation and apoptosis in hematopoietic cells. Deregulated Myc in hematopoietic cells blocks the differentiation program and prevents normal homeostatic cellular apoptosis, which alters the balance of cell populations, often participating in leukemogenesis. The status of Gadd45a expression has been shown to impact on different cancers, including breast cancer and leukemia. How the stress response gene Gadd45a modulates oncogenic stress imparted by deregulated c-Myc in myeloid cells has not been investigated. We hypothesized that Gadd45a and its interacting partner proteins can modulate specific pro-survival or pro-apoptotic signaling pathways, altering the cellular response to oncogenic myc in myeloid cells. Gadd45a may play different roles in proliferating and differentiating cells, and myeloid cells in vivo are at all stages of myeloid development. Therefore, to understand how Gadd45a status impacts on proliferating and differentiating myeloid cells, we decided to study the effect of loss of Gadd45a in myc-expressing cells that are either proliferating or stimulated to undergo differentiation. Therefore, to address this issue we utilized bone marrow from wild-type (wt) and Gadd45a null mice, and retrovirally infected these cells to express constitutive Myc or empty vector control. Using these cells we have shown that bone marrow deficient in Gadd45a and expressing constitutive Myc, display decreased apoptosis under proliferating conditions, yet increased apoptosis in media containing the differentiation inducing cytokine GM-CSF. We show that in expansion media loss of Gadd45a in the presence of Myc elicits its function through the activation of p38, with evidence supporting a role for PU.1 and Mcl-1 expression, which are downstream of p-p38. In contrast, deregulated C-Myc and loss of Gadd45a does not signal through p-38 in GM-CSF, but surprisingly there is a decrease in cytokine receptor expression. This data demonstrates that Gadd45a may be required for optimal cytokine receptor expression in myeloid cells, which can impact on survival of the cells. Although in primary bone marrow Gadd45a status had no effect on differentiation of Myc expressing cells, the loss of Gadd45a in Hoxb8 generated cell lines shifted differentiation towards increased neutrophils. Determining the role of Gadd45a on the biological outcome of myeloid cells in response to deregulated c-Myc will provide vital information in understanding the function of Gadd45a in the development and progression of Myc expressing myeloid leukemia.

Temple University – Theses

Microbiology and Immunology

In chronic myelogenous leukemia (CML), activation of BCR-ABL, the product of the bcr-abl chimeric gene, leads to constitutive activation of pathways that increase genomic instability through endogenous production of reactive oxygen species (ROS) that cause oxidative DNA damage and inactivate the function of repair proteins leading to unfaithful DNA repair. If misrepaired, oxidative DNA damage, such as 8-oxoguanine (8-oxoG), may result in point mutations and/or DNA double-strand breaks (DSBs) leading to drug resistance to the BCR-ABL kinase inhibitor imatinib mesylate (IM) and accumulation of chromosomal aberrations associated with malignant CML progression from a benign chronic phase (CP) to a fatal blast phase (BP). To determine which population of CML-CP cells, leukemia stem cells (LSCs) and/or leukemia progenitor cells (LPCs), displays elevated levels of ROS and oxidative DNA damage, and whether these elevated levels of ROS and oxidative DNA damage in CML-CP subpopulations result in the accumulation of genomic instability, we employed the tetracycline-inducible SCLtTA/BCR-ABL transgenic mouse model. We showed that LSCs, including the quiescent subpopulation, but not LPCs, displayed elevated levels of ROS and oxidative DNA damage, perhaps due to deregulated expression of genes involved in ROS metabolism, resulting in genomic instability manifested by both point mutations and genetic alterations. We also examined the effect of IM on ROS, oxidative DNA damage and genomic instability displayed by CML-CP subpopulations, and determined that elevated ROS and oxidative DNA damage were not inhibited by IM in quiescent LSCs, nor was genomic instability and deregulated gene expression prevented. To explore underlying mechanisms, i.e. BCR-ABL expression levels, by which CML-CP cells accumulate genomic instability, we examined the effect of low and high BCR-ABL expression on ROS and oxidative DNA damage in BCR-ABL-transduced human CD34+ cells. We detected elevated ROS and oxidative DNA damage in high BCR-ABL-expressing CD34+ cells compared to low BCR-ABL-expressing cells. Furthermore, BCR-ABL exerted a kinase-dependent effect on ROS-dependent DNA damage. These data support the hypothesis that genomic instability may originate from LSCs, but do not exclude the potential role of LPCs, and may have important clinical implications for CML treatment since additional genetic aberrations that encode primary resistance may protect LSCs, including the quiescent subpopulation, from eradication by tyrosine kinase inhibitors (TKIs), and the continuous accumulation of genetic errors may trigger disease relapse and progression.

Temple University – Theses

Molecular Biology and Genetics

Selective killing of tumor cells requires the identification of drug targets critical to pathways that drive or support cancer progression. Protein kinases are an important class of intracellular enzymes involved in the regulation of biochemical pathways, deregulation of these kinases has been strongly implicated in cancer progression. To identify possible oncogenic kinases to which tumor cells might be selectively addicted, we screened the ON108 series of ATP-mimetic small molecule inhibitors in various triple negative breast cancer (TNBC) and normal cell lines. This approach led us to the identification of a novel kinase inhibitor, ON108600. We first examined the in vitro and in vivo effects of ON108600. ON108600 was found to be a potent inhibitor of Casein Kinase 2 (CK2) and the Dual-Specificity-Tyrosine (Y)-Phosphorylation-Regulated-Kinase (DYRK) family of serine-threonine kinases, both of which have been implicated in cancer progression. ON108600 showed broad-spectrum anti-proliferative and cytotoxic activity in multiple TNBC cell lines whilst having little or no effect on normal cells. Treatment of cancer cells with ON108600 resulted in inhibition of downstream signaling mediated by substrates of CK2. Further, ON108600 selectively arrested cancer cells in the mitotic phase of the cell cycle and activated the caspase-signaling cascade. We next performed x-ray crystallographic studies of ON108600-CK2 to determine the structural basis of ON108600-CK2 interaction. The co-crystal structure of ON108600-CK2 revealed that ON108600 binds in the active site pocket of CK2α wherein it mimics the binding of ATP and GTP in the CK2 active site. Notably, ON108600 mimics not only the shape and electrostatics of ATP/GTP, but also their hydration patterns in the CK2 active site pocket. Structural studies further revealed that ON108600 induces a conformational change in the β4-β5 loop of the catalytic subunit, which is known to interact with the β-regulatory subunit of CK2 and is critical for substrate recognition and activation. Lastly, we examined the efficacy of ON108600 in Triple Negative Breast Cancer (TNBC) and its ability to target and eliminate chemo-resistant Tumor-Initiating Stem Cells (TI-SCs) in TNBC. Clonogenic survival and sphere forming ability of purified CD44high CD24-/low TI-SCs from MDAMB-231 and Hs578t cells was potently inhibited by ON108600 treatment. We also observed that paclitaxel-resistant MDAMB-231 cells had increased levels of the CD44high CD24-/low stem cell- like population that correlated with increased expression of kinases CK2α2, DYRK1A and DYRK1B and these cells were sensitive to ON108600 treatment. Significantly, ON108600 showed robust antitumor efficacy as a single agent in a highly aggressive orthotopic TNBC xenograft model showing ~60% tumor growth inhibition. Immunohistochemical analysis of ON108600 treated tumors showed that a significant percentage of cells were apoptotic, indicating that activation of caspase mediated apoptosis…

Molecular Biology and Genetics

Chronic Myelogenous Leukemia (CML) is a hematological disease originated with a chromosomal translocation t(9;22)(q34;q11) in a pluripotent hematopoietic stem cell. CML typically evolves in 3 different clinical phases: chronic and accelerated phases, and blast crisis. Disease progression is associated with the acquisition of secondary mutations that can be of very diverse origins, including inactivation of tumor suppressor genes, as well as inhibition of differentiation, DNA repair and telomere maintenance. While current therapies are very often successful, the remaining issues of resistance and the fact that therapy will not cure CML make it important that new therapy capable of effectively curing it be developed. The early growth response-1 (Egr-1) gene is a zinc-finger transcription factor localized to the human chromosome 5. Egr-1 belongs to a family of early response genes whose expression is rapidly stimulated by growth factors, hormones and neurotransmitters. In addition, Egr-1 is a myeloid differentiation primary response (MYD) gene, and is a positive regulator of terminal myeloid differentiation that potentiates macrophage differentiation. It also has been shown that Egr-1 plays a role in the development, growth control and survival of several cell types, such as T cells, B cells, and neuronal cells in addition to myeloid cells. There is a large amount of evidence consistent with Egr-1 behaving as a tumor suppressor in hematopoietic cells, both in vivo & in vitro, in both humans & mice, making it a prime candidate for a role in CML. In this study we asked if Egr-1 would behave as a tumor suppressor in CML. To answer that we investigated the function of Egr-1 in BCR-ABL driven leukemia using a mouse m bone marrow transplantation (BMT) model. We observe that loss of Egr-1 accelerates the onset of BCR-ABL driven CML. Furthermore, through Facs analysis we showed that most animals developed myeloid leukemia, determined by the observation that the majority of GFP+ cells in the BM were positive for Gr-1 and negative for B220. Interestingly a small cohort of mice developed B-cell acute lymphoid leukemia (B-ALL); this included both WT BCR-ABL and Egr-1 KO BCR-ABL BM-transplanted groups. In addition, we demonstrated that the loss of Egr-1 caused a more aggressive leukemia, which resulted not only in more rapid onset of disease but also greater enlargement of spleen and liver, as well as a tendency to more aggressive lung infiltration of leukemic cells. We also showed that decreased apoptosis, increased proliferation rates and resulting increased viability are consistent with, and probably contribute to, the increased leukemic potential of Egr-1 KO BCR-ABL BM. In addition, we demonstrated that Egr-1 expression was downregulated in BCR-ABL expressing BM cells in vitro, and in spleens of transplanted leukemic mice. Moreover, a very interesting observation, consistent with the rapid onset and aggression of disease, was that the bone marrow of leukemic mice caused by Egr-1 KO BCR-ABL BM…

Molecular Biology and Genetics

High level DNA methylation of promoter CpG islands (CGIs) represses gene expression. However, low-level CGI methylation is currently not distinguished from complete absence of methylation in the literature. Here we show that very low levels of methylation or methylation seeds (1-20%) on promoter CGIs is present in 5-20% of human genes and negatively correlates with gene expression in all tissues examined. In vitro, seeding directly represses reporter gene expression, an effect mediated by methyl-CpG-binding proteins as transient knockdown of MBD4 reverses this repression. In vivo, seeded genes are enriched for polycomb occupancy but seeding can also occur in H3K4me3 occupied promoters, where it also correlates with gene repression independently of Polycomb repressive complex binding. Seeded CGIs in normal WBCs are 19 fold and 65 fold more likely to gain hypermethylation in Acute Myelogenous Leukemia and Myelodysplastic Syndrome patients respectively, compared to unmethylated CGIs (i.e. those with <1% methylation). This study reveals a novel epigenetic mechanism of tissue specific methylation seeds that have strong effects on gene expression in healthy tissues, possess unique histone status, and predispose to gain of methylation in leukemias more so than previously known factors. In the second part, we analyzed the role of chromodomain protein CHD7 in CpG island methylator phenotype (CIMP) Colorectal Cancers (CRCs). Analysis of CHD7 target genes identified that frequently methylated genes in CIMP-positive CRCs have significantly higher enrichment of CHD7 occupancy in mouse neural stem cells and are among genes regulated by CHD7 in mouse embryonic stem cells. This study provides evidence for a causal link between CHD7 mutations in CRCs and the CIMP phenotype.

Temple University – Theses

Molecular Biology and Genetics

The mammalian cell cycle is divided into four distinct phases: G1, S, G2, and M. The transition from G1 to S and G2 to M is tightly controlled by a set of protein complexes containing cyclin-dependent kinases (Cdks) and cyclins. In G1-phase, Cdk4/6 and Cdk2 bind to and form complexes with D-type and E-type cyclins, respectively. The active Cdk-cyclin complexes phosphorylate retinoblastoma proteins (pRb), enabling transcription of E2F-reponsive genes necessary for S-phase transition. Dysregulation of the cyclin-Cdk-pRb-E2F pathway is frequently found in a variety of human tumors. Previously, our laboratory generated a mouse strain harboring, an activated allele of Cdk4, Cdk4-R24C. The Cdk4-R24C mutation was initially identified in familial melanomas. Mice homozygous for the Cdk4-R24C allele develop spontaneous tumors and die earlier than their wild-type counterparts. The incidence of spontaneous melanoma in Cdk4R24C/R24C mice is very low, at approximately 2%. We sought to determine if cooperation with other oncogenic mutations may be required for development of melanomas in mice. We demonstrate here that mice carrying a melanocytic expression of oncogenic HRAS (G12V) on Cdk4R24C background develop spontaneous cutaneous melanomas with an increased incidence (approximately 30%). Furthermore, Tyr-HRas:Cdk4R24C/R24C mice, upon treatment with carcinogens DMBA/TPA, display an increase in the formation of nevi and develop melanomas with a shorter latency than the Tyr-HRas:Cdk4+/+ mice. Therefore, we demonstrate that the activated CDK4 protein cooperates with oncogenic HRAS (G12V) in the development of melanoma. Previously, our laboratory also generated a mouse strain, lacking expression of Cdk4 gene. This mouse strain, Cdk4Neo/Neo, contained disrupted Cdk4 alleles due to an insertion neomycin gene in the Cdk4 locus. The loss of Cdk4 affects the development of various organs such as ovary, testis and pancreas. Additionally, these mice develop a disease phenotype closely resembling insulin-deficient diabetes in humans. Furthermore, it has previously been shown that in human T-cells, the loss of Cdk4 results in cytokine unresponsiveness. Based on these observations, we sought to determine the role of Cdk4 in thymocytes development by utilizing the Cdk4Neo/Neo mice. We observed a decreased cellularity in the thymus of the Cdk4Neo/Neo mice when compared to that of wildtype mice. Furthermore, we observed a significant decrease in the proliferation of Cdk4Neo/Neo thymocytes to anti-CD3 antibody stimulation. This defect in proliferation may be a result of a decreased level of pRb phosphorylation at Cdk4 consensus site. Interestingly, we observed a significantly higher expression of CD25 receptors on double positive thymocytes of Cdk4Neo/Neo mice. Taken together, these findings suggest that Cdk4 plays an important role in thymocyte proliferation and development in mice.

Temple University – Theses

Molecular Biology and Genetics

The GADD45 family of proteins consists of three small nuclear proteins, GADD45A, GADD45B, and GADD45G, which are implicated in modulating the cellular response to various types of genotoxic/physiological stress. This family of proteins has been shown to interact with and modulate the function of cell-cycle control proteins, such as p21 and cdc2/cyclin B1, the DNA repair protein, PCNA, key stress response MAP kinases, including MEKK4 (an upstream regulator of JNK kinase), and p38 kinase. Despite similarities in amino acid sequence, structure and function, each gadd45 gene is induced differentially, depending on the type of stress stimuli. For example, the alkylating agent, methylmethane sulfonate (MMS), rapidly induces all three genes, whereas hydrogen peroxide and sorbitol preferentially induce gadd45a and gadd45b, respectively. Studies of the mechanisms of the stress-mediated induction of the gadd45 genes have predominantly focused on gadd45a, with knowledge of gadd45b and gadd45g regulation lacking. Thus, in order to generate a more complete understanding of the collective regulation of the gadd45 genes, a comprehensive analysis of the stress-mediated induction of gadd45b has been carried out. Towards this end, a gadd45b promoter-reporter construct was generated, consisting of 3897bp sequence upstream of the transcription start site of gadd45b, fused to a luciferase reporter. In a human colorectal carcinoma cell line (RKO), in which gadd45b mRNA levels profoundly increase by various stress stimuli, we observe similar, high levels of induction of the gadd45b-luciferase construct with MMS or UVC treatments, but surprisingly not with sorbitol or anisomycin. Linker-scanning mutagenesis of the gadd45b promoter reveals several important MMS and UVC cis-acting responsive elements contained within the proximal promoter, including a GC-rich region and the CCAAT box. Furthermore, we have identified three constitutively bound transcription factors, Sp1, MZF1, and NFY, and one inducible factor, Egr1, which bind to these regions and which contribute to MMS-responsiveness. In contrast, a post-transcriptional mechanism appears to regulate gadd45b induction upon sorbitol treatment, as this treatment increases the gadd45b mRNA half-life, compared to MMS treatment. Interestingly, with the exception of a common cis-element, the stress-mediated induction of gadd45b appears to be mechanistically distinct from gadd45a. In conclusion, this study provides novel evidence that gadd45b induction by distinct stress agents, MMS and sorbitol, is regulated differentially at the level of mRNA transcription or mRNA stability, respectively.

Temple University – Theses

Molecular Biology and Genetics

Opioid receptor modulation of pro-inflammatory cytokine production is vital for host defense and the inflammatory response. Previous results have shown the mu-opioid receptor (MOR) selective agonist, DAMGO, has the capacity to increase the expression of the pro-inflammatory chemokines, CCL2/MCP-1, CCL5/RANTES and CXCL10/IP-10 in peripheral blood mononuclear cells (PBMCs). We have shown that MOR activation is able to induce the expression of TGF-β, and TGF-β appears to be required for induction of CCL5 following MOR activation. This work suggests a novel role for TGF-β in the inflammatory response. NF-κB is a transcription factor that plays a pivotal role in inflammation and the immune response. We have found that NF-kB inhibitors can prevent the MOR-induced activation of CCL2 and CCL5, and that the NF-kB subunit, p65, is phosphorylated at serine residues 311 and 536 in response to μ-opioid receptor activation. In vivo, DAMGO administration can induce binding of p. 65 to the enhancer region of the CCL2 promoter. Furthermore, we demonstrate that PKCζ is phosphorylated following DAMGO-induced MOR activation and, is essential for NF-kB activity as well as CCL2 expression and transcriptional activity. In conclusion, these data suggest a pro-inflammatory role for MOR which involves NF-κB activation and PKCζ as well as a novel role for TGF-β as a regulator of pro-inflammatory chemokines.

Temple University – Theses

Molecular Biology and Genetics

Opioid receptor-mediated regulation of chemokine receptors is vital for the host immune response, development, and neurological function. Previous studies have demonstrated that the kappa opioid receptor (KOR) activation results in decreased infectivity of human immunodeficiency virus 1 (HIV-1) in human peripheral blood mononuclear cells (PBMCs). We have found this effect is due to down-regulation of the major HIV-1 co-receptors, CCR5 and CXCR4. Using molecular techniques, CCR5 and CXCR4 mRNA levels drop dramatically following KOR activation. To dissect the mechanism involved, we used transcription factor binding arrays and compared control cell extracts to KOR activated cell extracts. We determined that the interferon regulatory factors (IRFs) and signal transducers and activators of transcription (STATs) could be involved in the KOR-mediated repression of CCR5 and CXCR4 transcription and protein expression. Using chemical inhibitors and small interfering RNA (siRNA) molecules, we determined that JAK2, STAT3, and IRF2 are critical members of this signal transduction pathway. The understanding of these particular mechanisms should prove to be beneficial for the development of potential pharmacological agents targeted at HIV-1 binding and infection since virus infection requires expression of the co-receptors CXCR4 and CCR5. Understanding the molecular basis for KOR-induced inhibition of co-receptor expression may provide a basis for the development of KOR agonist-based therapeutics to treat individuals infected with HIV.

Temple University – Theses

Biochemistry

Antigen presentation to T cells results in their activation through T Cell Receptor (TCR) stimulation, resulting in sustained elevation of cytosolic Ca2+ concentration critical for T cell activation. Sustained Ca2+ signals are important for the activation of Nuclear Factor of Activated T cells (NFAT), which is a key regulator of T cell activation through its transcriptional control of genes in multiple process including cytokine production, proliferation and differentiation(Rao, Luo, & Hogan, 1997). Recently it was shown that Stromal Interaction Molecule 1 (STIM1) inhibits plasma membrane Ca2+/ATPase 4 (PMCA4) function during T cell activation resulting in sustained elevation of Ca2+ signals(Ritchie, Samakai, & Soboloff, 2012). This interaction requires upregulation of both STIM1 and PMCA4. In this thesis, I hypothesize that changes in Ca2+ signals arising from transcriptional changes of STIM1 and PMCA are important for the efficient activation of T cells. In the first part of this thesis, I assess the transcriptional regulation of STIM1 and PMCA4. My in vitro studies show that expression of both proteins is regulated by the EGR family members, EGR1 and EGR4. Additionally, transcriptional regulation of PMCA inhibition by EGR1 and EGR4 is required for efficient activation of T cells. Interestingly, whereas significant roles for EGR1, EGR2 and EGR3 in T cell development and function have been established, a role for EGR4 has not, hitherto been elucidated. In the second half of this thesis, using qPCR, I reveal that EGR4 expression is stimulated by TCR engagement in primary double positive, CD4 and CD8 positive murine T cells. Further, EGR4-null mice exhibit shifts in early thymic development, although this does not affect the relative number of double or single positive T cells in the thymus. Interestingly, EGR4-null primary T cells exhibit normal Ca2+ entry, but fail to exhibit activation-induced inhibition of Ca2+ clearance. Although not all subsets of EGR1 and EGR4 null primary T cells exhibited decreased STIM1 expression, significant defects in proliferation, migration and/or cytokine production were observed upon stimulation in all populations, albeit to different extents. These findings reveal a two-faceted role in which EGRs regulate T cell development and function through both Ca2+-dependent and independent methods. I believe that these findings have important implications towards the general understanding of transcriptional control of Ca2+ signaling, as well as having a possible impact in the quest to advance therapies targeting immunological disorders.

Temple University – Theses

Biomedical Sciences

PARP inhibitors (PARPi) have been used to induce synthetic lethality in BRCA-deficient tumors in clinical trials with limited success due to the development of resistance to PARPi. BRCA-deficient cells are unable to repair DNA double strand breaks by the accurate homologous recombination repair (HR), and therefore rely on alternative DNA repair pathways for survival. We hypothesized that RAD52-mediated DNA repair mechanisms remain active and are thus protecting some PARPi-treated BRCA-deficient tumor cells from apoptosis, and that targeting RAD52 should enhance the synthetic lethal effect of PARPi. We show here that RAD52 inhibitors (RAD52i) attenuated single-strand annealing (SSA) and residual HR activity in BRCA-deficient cells. Simultaneous targeting of PARP1 and RAD52 with small molecule inhibitors or via expression of dominant-negative mutants induced an accumulation of DSBs and selective eradication of BRCA-deficient solid tumor and leukemia cells, while BRCA-proficient cells were unaffected. Parp1-/-Rad52-/- transgenic mice are healthy and indistinguishable from wild-type mice due to the presence of the BRCA-pathway, and Parp1-/-Rad52-/- mice with inducible BRCA1-deficient leukemia displayed significantly prolonged survival when compared to Parp1-/- and Rad52-/- counterparts. Finally, PARPi + RAD52i selectively targeted BRCA1-deficient solid tumors in immunodeficient mice with minimal toxicity to normal cells and tissues which are protected by the BRCA-pathway, indicating minimal side effects. In conclusion, our data indicate that combination treatment of RAD52i and PARPi will significantly improve therapeutic outcome of BRCA-deficient malignancies compared to treatment with PARPi monotherapy, while leaving healthy cells and tissues unharmed.

Temple University – Theses