Normal Cell Counterparts Research Articles

Chronic Lymphocytic Leukemia: Treating an Incurable Disease

Thomas J Kipps speaks to Sophie Breeze, Assistant Commissioning Editor: Thomas Kipps, MD, PhD, is Professor of Medicine, Evelyn and Edwin Tasch Chair in Cancer Research, and Deputy Director of Research Operations at the UC San Diego Moores Cancer Center. Dr Kipps has a national and international reputation for his work in cancer research, immunology and gene therapy. As Deputy Director of Research Operations, Dr Kipps is working to further integrate basic and translational research investigators at the Moores Cancer Center with clinical investigators, epidemiologists and physicians offering state-of-the art therapies for patients with various forms of cancer. A major focus of his laboratory group is the immunobiology and genetics of human B-cell, with emphasis on chronic lymphocytic leukemia (CLL). Discovery of features that distinguish CLL from their normal cell counterparts has helped identify new targets for therapy and/or define surrogate markers associated with more rapid rates of cancer progression or resistance to standard therapy. These studies are integrated with a clinical investigative program that attracts patients seeking improved modalities of treatment for CLL. To further these efforts on a national scale, Dr Kipps has organized and leads the CLL Research Consortium that is comprised of leading CLL investigators at major cancer centers across the country and abroad.

Type III familial hemophagocytic lymphohistiocytosis susceptibility gene UNC13D involves in homologous recombination repair

This study was aimed to explore the pathogenesis of type III familial hemophagocytic lymphohistiocytosis (FHL3) via susceptibility gene UNC13D involving in homologous recombination repair (HRR) of DNA double-strand break (DSB). By means of DNA homologous recombination repair, the change of homologous recombination repair rate of normal control cells and DR-U2OS cells after down-regulation of UNC13D was detected; the UNC13D gene related function was explored. The results showed that DR-U2OS cells displayed a significant reduction in homologous recombination repair of DNA DSB after siRNA knockdown of UNC13D, compared to its normal control cell counterparts (P < 0.05), suggesting that UNC13D was involved in DNA double-stranded breakage repair. It is concluded that UNC13D gene mutation may be involved in the pathogenesis of FHL3 via its dual effects of both the cytotoxic granule exocytosis and decrease of homologous recombination repair rate after the DNA double-strand break, therefore, providing a new theoretical basis to reveal the pathogenesis of FHL3.

Induction of Interferon-Stimulated Genes on the IL-4 Response Axis by Epstein-Barr Virus Infected Human B Cells; Relevance to Cellular Transformation

Epstein-Barr virus (EBV) is an oncogenic virus that is associated with the pathogenesis of several human lymphoid malignancies, including Hodgkin's lymphoma. Infection of normal resting B cells with EBV results in activation to lymphoblasts that are phenotypically similar to those generated by physiological stimulation with CD40L plus IL-4. One important difference is that infection leads to the establishment of permanently growing lymphoblastoid cell lines, whereas CD40L/IL-4 blasts have finite proliferation lifespans. To identify early events which might later determine why EBV infected blasts go on to establish transformed cell lines, we performed global transcriptome analyses on resting B cells and on EBV and CD40L/IL-4 blasts after 7 days culture. As anticipated there was considerable overlap in the transcriptomes of the two types of lymphoblasts when compared to the original resting B cells, reflecting common changes associated with lymphocyte activation and proliferation. Of interest to us was a subset of 255 genes that were differentially expressed between EBV and CD40L/IL-4 blasts. Genes which were more highly expressed in EBV blasts were substantially and significantly enriched for a set of interferon-stimulated genes which on further in silico analyses were found to be repressed by IL-4 in other cell contexts and to be up-regulated in micro-dissected malignant cells from Hodgkin's lymphoma biopsies when compared to their normal germinal center cell counterparts. We hypothesized that EBV and IL-4 were targeting and discordantly regulating a common set of genes. This was supported experimentally in our B cell model where IL-4 stimulation partially reversed transcriptional changes which follow EBV infection and it impaired the efficiency of EBV-induced B cell transformation. Taken together, these data suggest that the discordant regulation of interferon and IL-4 pathway genes by EBV that occurs early following infection of B cells has relevance to the development or maintenance of an EBV-associated malignancy.

A tumor-specific stem cell

Cancer stem cells are thought to share many characteristics with their normal stem cell counterparts, raising concerns about the ability to selectively target them. A new study shows that Dclk1 marks cancer, but not normal, stem cells in the intestine and that targeting this population results in adenoma collapse without affecting normal tissue.

The Role of microRNAs in the Pathogenesis and Treatment of Hematopoietic Malignancies

microRNAs (miRNAs) comprise a recently discovered class of non-coding RNAs with regulatory functions in post-transcriptional gene expression control. Many miRNAs are located in genomic regions that are frequently deleted in cancer, or are subject to epigenetic and transcriptional deregulation in cancer cells. The miRNA transcriptome of cancer cells is very different from that of their normal cell counterparts. miRNAs can exhibit oncogenic or tumor suppressive or even both properties depending on the specific targets and cellular context. It is becoming increasingly clear that miRNAs not only serve as useful tumor biomarkers with implications for diagnosis, prognosis and the prediction of treatment responses, but may also be used for targeted cancer treatment and even as therapeutics. In this review, we provide an overview of recent advances in our understanding of the tumor suppressor miRNAs and oncomiRs involved in the pathogenesis of leukemias and lymphomas, and their target transcripts in cancer signaling networks. In particular, we focus on the role of miRNAs in chronic lymphocytic and acute lymphoblastic leukemia and in B-cell lymphomas. In the second part, we review the various alternative strategies of targeting miRNAs in cancer therapy. Methods of oncomiR antagonization by antagomiRs or locked nucleid acids are contrasted with strategies that harness the tumor suppressive properties of certain miRNAs for cancer treatment. Preclinical progress, also with regard to delivery strategies, possible side effects and other pharmacological aspects, is presented along with results from the first human trials assessing the safety and efficacy of miRNA-targeting therapeutics.

The Role of microRNAs in the Pathogenesis and Treatment of Hematopoietic Malignancies

microRNAs (miRNAs) comprise a recently discovered class of non-coding RNAs with regulatory functions in posttranscriptional gene expression control. Many miRNAs are located in genomic regions that are frequently deleted in cancer, or are subject to epigenetic and transcriptional deregulation in cancer cells. The miRNA transcriptome of cancer cells is very different from that of their normal cell counterparts. miRNAs can exhibit oncogenic or tumor suppressive or even both properties depending on the specific targets and cellular context. It is becoming increasingly clear that miRNAs not only serve as useful tumor biomarkers with implications for diagnosis, prognosis and the prediction of treatment responses, but may also be used for targeted cancer treatment and even as therapeutics. In this review, we provide an overview of recent advances in our understanding of the tumor suppressor miRNAs and oncomiRs involved in the pathogenesis of leukemias and lymphomas, and their target transcripts in cancer signaling networks. In particular, we focus on the role of miRNAs in chronic lymphocytic and acute lymphoblastic leukemia and in B-cell lymphomas. In the second part, we review the various alternative strategies of targeting miRNAs in cancer therapy. Methods of oncomiR antagonization by antagomiRs or locked nucleid acids are contrasted with strategies that harness the tumor suppressive properties of certain miRNAs for cancer treatment. Preclinical progress, also with regard to delivery strategies, possible side effects and other pharmacological aspects, is presented along with results from the first human trials assessing the safety and efficacy of miRNA-targeting therapeutics. Keywords: microRNA, post-transcriptional regulation, leukemia and lymphoma, targeted treatment strategies, microRNA replacement therapy, antagomirs, non-coding RNAs, tumor suppressor miRNAs, cancer therapy, transcriptome

SOX4 enables Oncogenic Survival Signals in Acute Lymphoblastic Leukemia

Abstract 863 Background:The SOX4 (SRY-related HMG-box) transcription factor is expressed in early B- and T- cell development. In the absence of SOX4, B cell development is arrested at the pro-B to pre-B cell transition. In Sox4−/− mice, pro-B cells fail to proliferate in response to IL7 and to expand and differentiate past the pre-B cell receptor checkpoint. Interestingly, SOX4 functions a transcription factor yet closely interacts with membrane-proximal cytokine receptor signaling. The PDZ domain-containing adaptor protein syntenin (SDCBP) recruits the Sox4 protein directly to the cytoplasmic tail of the cytokine receptors. With regard to its receptor-proximal activation, Sox4 resembles the SMAD and STAT transcription factors. A role for Sox4 in acute myeloid leukemia was proposed based on the identification of viral insertions, and Sox4-overexpression causes myeloid leukemia. In this study, we found SOX4 was strongly upregulated upon tyrosine kinase inhibitor (TKI) treatment in Ph+ ALL and high expression of Sox4 correlates with poor clinical outcome of patients with ALL. Results:To elucidate the potential contribution of Sox4 to BCR-ABL1-driven B cell lineage leukemia, we studied a conditional Sox4 knockout mouse model. To this end, we transformed bone marrow B cell precursors from Sox4fl/fl mice with BCR-ABL1 to test its function in a mouse-model for Ph+ ALL. Tamoxifen (4-OHT)-inducible activation of Cre and subsequent deletion of loxP-flanked Sox4 alleles in B cell precursor ALL resulted in reduced mRNA levels of multiple genes that play a known role in survival signaling in Ph+ ALL cells including BCLXL (BCL2l1), Mapk8, Map2k6, PI3K/AKT (Pik3r2, Pik3r3, Rps6ka2, Mtor). Overexpression of Sox4 had the opposite effect and resulted in increased mRNA levels of BCLXL (Bcl2l1), Mapk8, PI3K/AKT (Pik3r2, Pik3r3). Single-locus quantitative ChIP confirmed binding of SOX4 to BCL2l1, PIK3R3 and MAPK8 promoters in human Ph+ ALL cells via its putative DNA binding motif. Transcriptional regulation of components within the PI3K/AKT pathway is indeed functionally relevant since Cre-mediated deletion of Sox4 caused multiple de-phosphorylation events including AKTS473, SRCY416 and RPS6S235/6. In addition, inducible deletion of Sox4 resulted in strong upregulation of both Arf and p53 protein, suggesting that Sox4 mediates survival signaling both by activation of BCLXL (Bcl2l1) and repression of Arf/p53. Consistent with Sox4-mediated negative regulation of Arf/p53, deletion of Sox4 resulted in G0/G1 arrest of BCR-ABL1 ALL cells and loss of self-renewal capacity, failure to form colonies in methylcellulose replating assays and delayed the onset of disease and substantially prolonged overall survival of recipient mice. In agreement with reduced expression of BCLXL (Bcl2l1) and increased levels of Arf/p53, the overall outcome of Sox4 deletion is rapid loss of viability and apoptosis in BCR-ABL1-transformed ALL but not normal pre-B cells. Loss of viability upon Sox4 deletion in the leukemia cells was rescued by transduction with constitutively active (myristoylated; CA) mutants of AKTCA and the p110 catalytic subunit of PI3K (p110αCA) and as well with BCLXL. Clinical relevance:These findings are also relevant to human disease since promoter CpG methylation analysis (HELP assay) revealed lower levels SOX4 promoter methylation in human Ph+ALL cells compared to their normal pre-B cell counterparts. In addition, samples from patients with high risk ALL (n=31) show a trend towards higher SOX4 mRNA levels compared to patients with intermediate risk ALL (n=23, p=0.07; ALL REZ BFM 2002). Analyzing data from a larger study based on 207 patients with ALL (COG P9906) showed a statistically significant association between high mRNA levels of SOX4 and poor clinical outcome (shorter overall survival). Conclusion:Collectively, these findings identify SOX4 as a critical upstream regulator of survival signaling in Ph+ ALL. Pathways affected by SOX4 include PI3K/AKT signaling downstream of BCR-ABL1, activation of BCLXL (BCL2L1) and negative regulation of Arf and p53. Disclosures:No relevant conflicts of interest to declare.

Early-life Disruption of Epigenetic Marks May Contribute to the Origins of Mental Illness

Epigenetic marks, including DNA methyl ation (DNAm), histone modifications and small inhibitory RNAs, are heritable and provide critical layers of gene regulatory control; however, they also are dynamic and can be influenced by environmental exposures [1–3]. Studies primarily focused on cancer and late-onset diseases have revealed that a growing number of human diseases are linked to epigenetic disruptions. For example, DNAm became a hallmark of human cancer, a link that was first recognized in 1983, when tumor cells were found to be aberrantly methylated compared with their normal cell counterparts due to a loss of methylation from repetitive regions of the genome [4]. Together with the finding that healthy monozygotic twins show indistinguishable childhood DNAm [5], epigenetic mechanisms have long been thought to be highly coordinated throughout early development and more susceptible to drift in adulthood. In this article, we will discuss the impact that recent findings, of dramatic DNAm changes throughout childhood, will have on future epigenetic studies conducted in children and adults.

The Blk pathway functions as a tumor suppressor in chronic myeloid leukemia stem cells

A therapeutic strategy for treating cancer is to target and eradicate cancer stem cells (CSCs) without harming their normal stem cell counterparts. The success of this approach relies on identification of molecular pathways that selectively regulate CSC function. Using BCR-ABL-induced chronic myeloid leukemia (CML) as a disease model for CSCs, we show that BCR-ABL down-regulates the B lymphoid kinase (Blk) gene through c-Myc in leukemia stem cells (LSCs) in CML mice and that Blk functions as a tumor suppressor in LSCs but does not affect normal hematopoietic stem cells (HSCs) or hematopoiesis. Blk suppresses LSC function through a pathway involving an upstream regulator, Pax5, and a downstream effector, p27. Inhibition of this Blk pathway accelerates CML development, whereas increased activity of the Blk pathway delays CML development. Blk also suppresses human CML stem cells. Our results demonstrate the feasibility of selectively targeting LSCs, an approach that should be applicable to other cancers.

Quantitative Proteomics Reveals that miR-155 Regulates the PI3K-AKT Pathway in Diffuse Large B-Cell Lymphoma

The aberrant expression of microRNA-155 (miR-155), which has emerged as having a significant impact on the biological characteristics of lymphocytes, plays important roles in B-cell malignancies, such as diffuse large B-cell lymphoma (DLBCL). DLBCL is the most common non-Hodgkin's lymphoma in the adult population, accounting for approximately 40% of newly diagnosed non-Hodgkin's lymphoma cases globally. To determine the specific function of miR-155, a quantitative proteomics approach was applied to examine the inhibitory effects of miR-155 on protein synthesis in DLBCL cells. PIK3R1 (p85α), a negative regulator of the phosphatidylinositol 3-kinase (PI3K)-AKT pathway, was identified as a direct target of miR-155. A luciferase reporter was repressed through the direct interaction of miR-155 and the p85α 3'-untranslated region, and overexpression of miR-155 down-regulated both the transcription and translation of p85α. The PI3K-AKT signaling pathway was highly activated by the sustained overexpression of miR-155 in DHL16 cells, whereas knockdown of miR-155 in OCI-Ly3 cells diminished AKT activity. Taken together, our results reveal a novel target involved in miR-155 biological characteristics and provide a molecular link between the overexpression of miR-155 and the activation of PI3K-AKT in DLBCL.

Abstract 1304: Specific MUC1 isoforms function to regulate gene expression and tumor growth in pancreatic cancer

Abstract Cancer cells, especially adenocarcinomas, express aberrant forms of mucins, as compared to their normal cell counterparts. These aberrant forms arise as a consequence of transformation-related alterations in expression of mucin mRNAs including alternative splice forms, and deregulation of enzymes that post-translationally modify mucin core proteins. Previous work has established that MUC1 is overexpressed and differentially glycosylated in adenocarcinomas and that this overexpression is associated with aggressive forms of pancreatic cancer. Most studies have focused on the full-length MUC1 isoform that contains the VNTR and all seven exons, but alternative splicing of MUC1 yields a minimum of 30 isoforms, of which several have been linked to malignancy in ovarian, cervical, and breast cancer. We evaluated expression of MUC1 alternate splice forms in a series of isogenic clonal pancreatic cancer cell lines that exhibit different properties of morphological differentiation, tumor growth and metastasis. The results revealed significant variation in splice variant expression between these isogenic cell lines and has implicated an association between isoform expression and metastatic potential. The knockdown of specific splice variants and MUC1 isoform families in S2-007 pancreatic cancer cells suggested that individual isoforms show differential capacity for regulating expression of target genes and miRNAs, which in turn led to differences in tumor growth rate and metastatic potential. Specifically, the stable knockdown of all members of the MUC1 X-family significantly altered expression of miRNAs 193b and 320 and reduced tumor growth in a pancreatic cancer animal model. MUC1 X-family also affected expression levels of several genes associated with Gemcitabine resistance and both pro and anti-inflammatory pathways that are predicted to influence disease progression and tumor associated immunosuppression. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1304. doi:1538-7445.AM2012-1304

Small Molecule Antagonists of the Wnt/Beta-Catenin Signaling Pathway Target Breast Tumor-Initiating Cells in a Her2/Neu Mouse Model of Breast Cancer

BackgroundRecent evidence suggests that human breast cancer is sustained by a minor subpopulation of breast tumor-initiating cells (BTIC), which confer resistance to anticancer therapies and consequently must be eradicated to achieve durable breast cancer cure.Methods/FindingsTo identify signaling pathways that might be targeted to eliminate BTIC, while sparing their normal stem and progenitor cell counterparts, we performed global gene expression profiling of BTIC- and mammary epithelial stem/progenitor cell- enriched cultures derived from mouse mammary tumors and mammary glands, respectively. Such analyses suggested a role for the Wnt/Beta-catenin signaling pathway in maintaining the viability and or sustaining the self-renewal of BTICs in vitro. To determine whether the Wnt/Beta-catenin pathway played a role in BTIC processes we employed a chemical genomics approach. We found that pharmacological inhibitors of Wnt/β-catenin signaling inhibited sphere- and colony-formation by primary breast tumor cells and primary mammary epithelial cells, as well as by tumorsphere- and mammosphere-derived cells. Serial assays of self-renewal in vitro revealed that the Wnt/Beta-catenin signaling inhibitor PKF118–310 irreversibly affected BTIC, whereas it functioned reversibly to suspend the self-renewal of mammary epithelial stem/progenitor cells. Incubation of primary tumor cells in vitro with PKF118–310 eliminated their capacity to subsequently seed tumor growth after transplant into syngeneic mice. Administration of PKF118–310 to tumor-bearing mice halted tumor growth in vivo. Moreover, viable tumor cells harvested from PKF118–310 treated mice were unable to seed the growth of secondary tumors after transplant.ConclusionsThese studies demonstrate that inhibitors of Wnt/β-catenin signaling eradicated BTIC in vitro and in vivo and provide a compelling rationale for developing such antagonists for breast cancer therapy.

Changes in LINE-1 methylation level in cancers during metastasis

Background: Significantly lower LINE-1 methylation levels have been observed in several cancers compared to their normal cell counterparts. It is of interest to note that this epigenetic phenomenon is rather common to cancers with multistage oncogenesis. Objective: We compared LINE-1 methylation levels of cancer cells between the primary and matched metastatic sites. Methods: COBRA method was used to determine LINE-1 methylation levels of tumor cells at the primary and matched metastatic sites in five malignancies (10 cases each of head and neck squamous carcinoma, papillary thyroid carcinoma, non-small cell lung cancer, invasive mammary ductal carcinoma, and colorectal adenocarcinoma). LINE-1 methylation levels between the primary and matched metastatic site were compared. Results: Significantly lower LINE-1 methylation levels were observed at metastatic sites (as compared to primary sites) in head and neck squamous cell carcinoma (p = 0.002) and non-small cell lung cancer (p = 0.012). Conclusion: In head, neck, and pulmonary cancers, significantly lower LINE-1 methylation levels were found at metastatic sites, as compared to the matched primary tumor. Further studies are warranted to determine whether this altered methylation is the result or the cause of cancer metastasis. Keywords: LINE-1 methylation, metastasis, multi-step oncogenesis, primary tumor, tumor progression

Changes in LINE-1 methylation level in cancers during metastasis

Background: Significantly lower LINE-1 methylation levels have been observed in several cancers compared to their normal cell counterparts. It is of interest to note that this epigenetic phenomenon is rather common to cancers with multistage oncogenesis. Objective: We compared LINE-1 methylation levels of cancer cells between the primary and matched metastatic sites. Methods: COBRA method was used to determine LINE-1 methylation levels of tumor cells at the primary and matched metastatic sites in five malignancies (10 cases each of head and neck squamous carcinoma, papillary thyroid carcinoma, non-small cell lung cancer, invasive mammary ductal carcinoma, and colorectal adenocarcinoma). LINE-1 methylation levels between the primary and matched metastatic site were compared. Results: Significantly lower LINE-1 methylation levels were observed at metastatic sites (as compared to primary sites) in head and neck squamous cell carcinoma (p = 0.002) and non-small cell lung cancer (p = 0.012). Conclusion: In head, neck, and pulmonary cancers, significantly lower LINE-1 methylation levels were found at metastatic sites, as compared to the matched primary tumor. Further studies are warranted to determine whether this altered methylation is the result or the cause of cancer metastasis. Keywords: LINE-1 methylation, metastasis, multi-step oncogenesis, primary tumor, tumor progression

γ-Synuclein Is a Promising New Marker for Staining Reactive Follicular Dendritic Cells, Follicular Dendritic Cell Sarcoma, Kaposi Sarcoma, and Benign and Malignant Vascular Tumors

Synucleins are small soluble proteins found in normal brain that facilitate rapid release of neurotransmitters. α-synuclein is a major component of the Lewy body of neurodegenerative diseases and γ-synuclein is a marker of aggressive carcinomas. As the role of γ-synuclein has not yet been investigated in the lymphoid system, we immunohistochemically stained normal lymphoid organs, lymph nodes with reactive lymphoid hyperplasia, and malignant lymphomas. The anti-γ-synuclein antibody strongly stained the follicular dendritic cell (FDC) meshworks and vascular and lymphatic endothelial cells in reactive lymphoid tissues, in B-cell lymphomas with a nodular pattern, and in angioimmunoblastic T-cell lymphomas. There were no γ-synuclein-positive FDC meshworks in B-cell or T-cell lymphomas with a diffuse pattern. This is in contrast to CD21, which only stained the arms of the FDCs; γ-synuclein highlighted both the long slender cellular processes and the cell body, thereby clearly demonstrating the number of individual FDCs. In addition, γ-synuclein was strongly expressed by the neoplastic counterpart of reactive FDCs (FDC sarcoma) and by the neoplastic counterparts of normal lymphatic and vascular endothelial cells (Kaposi sarcoma, hemangioma, and angiosarcoma). Only a few spindle cell neoplasms (SSNs) derived from smooth muscle, peripheral nerve, or gastrointestinal stroma expressed γ-synuclein; however, γ-synuclein was not expressed by 11 other types of SSNs tested. These results suggest that γ-synuclein is a promising new adjunct marker for identifying reactive FDCs and for diagnosing FDC sarcoma and benign and malignant vascular tumors.

Regulation of reactive oxygen species in stem cells and cancer stem cells

Stem cells are defined by their ability to self-renew and their multi-potent differentiation capacity. As such, stem cells maintain tissue homeostasis throughout the life of a multicellular organism. Aerobic metabolism, while enabling efficient energy production, also generates reactive oxygen species (ROS), which damage cellular components. Until recently, the focus in stem cell biology has been on the adverse effects of ROS, particularly the damaging effects of ROS accumulation on tissue aging and the development of cancer, and various anti-oxidative and anti-stress mechanisms of stem cells have been characterized. However, it has become increasingly clear that, in some cases, redox status plays an important role in stem cell maintenance, i.e., regulation of the cell cycle. An active area of current research is redox regulation in various cancer stem cells, the malignant counterparts of normal stem cells that are viewed as good targets of cancer therapy. In contrast to cancer cells, in which ROS levels are increased, some cancer stem cells maintain low ROS levels, exhibiting redox patterns that are similar to the corresponding normal stem cell. To fully elucidate the mechanisms involved in stem cell maintenance and to effectively target cancer stem cells, it is essential to understand ROS regulatory mechanisms in these different cell types. Here, the mechanisms of redox regulation in normal stem cells, cancer cells, and cancer stem cells are reviewed.

MicroRNA expression in tumor cells from Waldenstrom's macroglobulinemia reflects both their normal and malignant cell counterparts.

MicroRNAs (miRNAs) are involved in the regulation of many cellular processes including hematopoiesis, with the aberrant expression of differentiation-stage specific miRNA associated with lymphomagenesis. miRNA profiling has been essential for understanding the underlying biology of many hematological malignancies; however the miRNA signature of the diverse tumor clone associated with Waldenstrom's macroglobulinemia (WM), consisting of B lymphocytes, plasmacytes and lymphoplasmacytic cells, has not been characterized. We have investigated the expression of over 13 000 known and candidate miRNAs in both CD19+ and CD138+ WM tumor cells, as well as in their malignant and non-malignant counterparts. Although neither CD19+ nor CD138+ WM cells were defined by a distinct miRNA profile, the combination of all WM cells revealed a unique miRNA transcriptome characterized by the dysregulation of many miRNAs previously identified as crucial for normal B-cell lineage differentiation. Specifically, miRNA-9*/152/182 were underexpressed in WM, whereas the expression of miRNA-21/125b/181a/193b/223/363 were notably increased (analysis of variance; P<0.0001). Future studies focusing on the effects of these dysregulated miRNAs will provide further insight into the mechanisms responsible for the pathogenesis of WM.

505 Role for PP2A Regulatory Subunit B55alpha as a Regulator of AKT and Other Signaling Pathways in AML

Abstract Abstract 1668 Activation of survival kinases such as Protein Kinase B (AKT), Protein Kinase C (PKC), and Extracellular Receptor Activated Kinase (ERK) predict poor clinical outcome for patients with acute myeloid leukemia (AML; Kornblau et al Blood 2006). A better understanding of how the activities of these kinases are regulated by phosphorylation and dephosphorylation will enable the development of targeted therapies directed against this axis. Protein Phosphatase 2A (PP2A) negatively regulates PKC, AKT, and ERK but its role in AML is not clear. In the current study we examined the role of PP2A in regulating AKT in AML. Activation of AKT involves phosphorylation of threonine 308 (T308) and serine 473 (S473). A recent study has indicated that phosphorylation of AKT at T308 but not S473 is a poor prognostic factor for AML patients and that PP2A activity negatively correlated with T308 phosphorylation (Gallay et al Leukemia 2009). PP2A is a family of different isoforms that form hetero-trimers consisting of a catalytic C subunit, a scaffold A subunit, and one of at least 21 different regulatory B subunits. The functionality of each PP2A isoform is determined by the regulatory B subunit. Thus to understand PP2A regulation of AKT in AML, it is essential to study the B subunit that regulates the AKT phosphatase. The PP2A isoform regulating AKT in the AML patients is currently unknown. Evidence suggests that the B55a subunit is responsible for dephosphorylation of AKT at T308. In the current study, we compared B55α gene expression in blast cells derived from AML patients with normal counterpart (i.e. CD34+) cells derived from normal bone marrow donors by real time PCR. Surprisingly, B55α gene expression was higher in the patients. Reverse Phase Protein Analysis (RPPA) is a powerful tool that allows for the analysis of protein expression from patient samples. Protein levels of the PP2A B subunit were analyzed by RPPA in AML blast cells obtained from 511 newly diagnosed AML patients and CD34+ cells obtained from 11 normal bone marrow donors. Levels of B55α protein were significantly lower in the blast cells from the AML patients compared to normal CD34+ cells. While the mechanism for the observed difference in gene versus protein expression in the leukemia cells has yet to be determined, a plausible mechanism is that the B55α protein is being proteolyzed since monomeric PP2A B subunits that are not part of the PP2A hetero-trimer are degraded. Importantly the reduced levels of B55α protein observed would be predicted if AKT were activated in the AML blast cells. We next compared AKT phosphorylation status with B55α protein expression in the AML blast cells using RPPA to answer this question. Analysis of RPPA data revealed that there was no correlation between B55α protein levels and levels of total AKT protein or with levels of AKT phosphorylated at S473 in the AML samples. However, there was a moderate but significant negative correlation between B55α protein levels and levels of AKT phosphorylated at T308. This result suggests that B55α is mediating dephosphorylation of AKT at T308 but not S473 in the AML cells. B55α expression was not associated with FAB classification but was positively correlated with high blast and peripheral blood counts. While the level of expression of the B subunit did not correlate with overall survival, intermediate levels of B55α expression were associated with longer complete remission duration. We predict that higher levels of B55α would reflect low levels of other PP2A B subunits. Consistent with this prediction, B55α expression positively correlated with MYC expression in the AML patients. MYC expression is regulated by a B subunit that competes with B55α (i.e. B56α). These findings suggest that B55α may play an important role in AML as a negative regulator of AKT and perhaps by other as yet unidentified functions. Activation of B55α is a potential therapeutic target for overcoming the AKT activation frequently observed in AML. Disclosures: No relevant conflicts of interest to declare.

II. New perspectives and challenges in the understanding of mantle cell lymphoma

Mantle cell lymphoma (MCL) is a B-cell neoplasia that has been well characterized in recent years. Recognition of the t(11;14)(q13; q32) and cyclin D1 overexpression as the genetic and molecular hallmarks of the tumor have been key elements in recognizing the broad spectrum of clinical, pathological and biological manifestations of the disease [1]. Cyclin D1 expression is now routinely used as one of the most important elements in the diagnosis of this lymphoma. The term mantle cell lymphoma reflects the idea that the normal cell counterpart of this tumor is a lymphocyte whose physiological microenvironment is the mantle zone of the secondary lymphoid follicle.

Is the chemoattractant chemerin a natural tumor-suppressive cytokine?

e13025 Background: Infiltration of specialized immune cells regulates the growth and survival of neoplasia. Chemerin, a recently described chemoattractant, attracts natural killer cells, macrophages, and dendritic cell subsets, immunocytes implicated in tumor responses. Analyses of public gene expression databases revealed that chemerin mRNA is significantly downregulated in malignant melanoma, lung, breast, and prostate adenocarcinomas, and colon adenomas compared to their normal tissue or cell counterparts, suggesting that chemerin might be a tumor suppressive cytokine. Methods: We used mouse xenografts to evaluated the effect of chemerin on tumor growth. In vitro studies were performed to evaluate effect of chemerin on tumor proliferation. In vivo studies evaluated both constitutive secretion from transfected tumor cells and intratumoral injections of chemerin. FACS analysis of tumors were performed on chemerin-treated tumors. Depletion studies were also performed. Results: Consistent with a suppressive role, stable transfection with chemerin inhibited the growth of transplantable mouse melanoma and breast adenocarcinoma cell lines. Growth inhibition was seen in vivo but not in cell culture, suggesting that tumor-expressed chemerin modifies the host response. Chemerin-expressing melanomas and breast adenocarcinomas had enhanced infiltration by leukocytes including natural killer cells, and growth inhibition was abrogated by NK cell depletion. Growth suppression was also lost in mice deficient in the leukocyte chemerin receptor, CMKLR1. Importantly, the inhibitory effect of tumor-expressed chemerin could be recapitulated in un-transfected neoplasia by intratumoral injection of the active chemoattractant protein, suggesting the potential for therapeutic application. Conclusions: In sum, chemerin is an endogenous tumor suppressive chemoattractant cytokine whose downregulation in neoplasia may contribute to immune evasion and enhanced tumor growth.