UZH-Logo

Maintenance Infos

Identification and Functional Analysis of Epigenetic Alterations in Diffuse Large B cell Lymphoma


Schmid, Corina A. Identification and Functional Analysis of Epigenetic Alterations in Diffuse Large B cell Lymphoma. 2015, University of Zurich, Faculty of Science.

Abstract

Diffuse large B cell lymphoma (DLBCL) is the most common type of non- Hodgkin lymphoma accounting for around 30% of newly diagnosed cases per year. It is a very heterogeneous and aggressive disease, which arises from mature B-cells at different stages of differentiation and is characterized by a diffuse growth of neoplastic large B lymphocytes. Over the past years, enormous progress has been made in identifying key alterations associated with DLBCL, which have largely improved our understanding of the underlying molecular pathogenesis. Having said this, the majority of work has focused on genetic mechanisms and mutational events leading to malignant transformation, the contribution of epigenetic processes such as deregulated microRNA expression or aberrant DNA methylation to lymphomagenesis remains poorly understood. My doctoral studies have therefore been dedicated to elucidate the functional contribution of epigenetic alterations to the pathogenesis of DLBCL.
Previous work in our group has focused on the analysis of aberrantly regulated microRNAs in DLBCL. In the scope of these studies one important tumor suppressor microRNA, miR-34a, was identified and characterized in vitro. In order to investigate the translational potential of the knowledge gained from these in vitro experiments, pre-clinical DLBCL xenograft studies were conducted. Strikingly, growth of subcutaneous tumor grafts was significantly reduced in mice treated locally or systemically with miR-34a mimetics in comparison to control treated mice. These findings suggest that miR-34a replacement therapy constitutes a valid therapeutic approach, especially for treatment of DLBCL patients with low miR-34a expression.
Another major epigenetic event that gained increasing attention in the context of cancer research in recent years is DNA methylation. Aberrant DNA methylation of promoter regions is associated with the silencing of the respective gene and constitutes an important mechanism for cancer cells to silence tumor suppressor genes. The genes targeted by this mechanism in B cell lymphomas and their direct functional contribution to pathogenesis however remain to be elucidated. To address this issue, I set out to identify and functionally characterize hypermethylated genes in DLBCL.
Whole genome DNA methylation analysis of low-grade marginal zone lymphoma of MALT (mucosa-associated lymphoid tissue) type, gastric and nodal DLBCL as well as control tonsil samples revealed a characteristic pattern of aberrant promoter-specific DNA hypermethylation, which is shared between all lymphoma entities analyzed. This suggests that global methylation changes represent an early event in lymphomagenesis and that these alterations are mediated by a shared mechanism operating irrespective of lymphoma localization.
Further integration of this methylation data with data obtained from RNA sequencing after pharmacological demethylation of DLBCL cell lines allowed us to identify candidate tumor suppressor genes, which we subsequently validated in a series of functional screening experiments. One gene that emerged as a particularly interesting tumor suppressor candidate was the dual specificity phosphatase DUSP4, a negative regulator of mitogen-activated protein kinases. We could show that DUSP4 is either epigenetically silenced or deleted in the majority of nodal and extranodal DLBCL cases and that lack of DUSP4 negatively correlates with overall survival probability of DLBCL patients. Furthermore, we could demonstrate that DUSP4 dephosphorylates and thereby inhibits c-JUN N-terminal kinase (JNK) resulting in increased apoptosis in DLBCL cells. Pharmacological inhibition of JNK phenocopies these tumor suppressive effects in vitro and in vivo, reinforcing the importance of active JNK signaling for DLBCL cell survival and providing a mechanistic rationale for targeted JNK therapy as novel treatment approach.
In conclusion, the work performed in the scope of this thesis contributes another valuable puzzle piece to understanding the complex epigenetic and genetic determinants of DLBCL and proposes novel therapeutic approaches for clinical consideration in the future.

Diffuse large B cell lymphoma (DLBCL) is the most common type of non- Hodgkin lymphoma accounting for around 30% of newly diagnosed cases per year. It is a very heterogeneous and aggressive disease, which arises from mature B-cells at different stages of differentiation and is characterized by a diffuse growth of neoplastic large B lymphocytes. Over the past years, enormous progress has been made in identifying key alterations associated with DLBCL, which have largely improved our understanding of the underlying molecular pathogenesis. Having said this, the majority of work has focused on genetic mechanisms and mutational events leading to malignant transformation, the contribution of epigenetic processes such as deregulated microRNA expression or aberrant DNA methylation to lymphomagenesis remains poorly understood. My doctoral studies have therefore been dedicated to elucidate the functional contribution of epigenetic alterations to the pathogenesis of DLBCL.
Previous work in our group has focused on the analysis of aberrantly regulated microRNAs in DLBCL. In the scope of these studies one important tumor suppressor microRNA, miR-34a, was identified and characterized in vitro. In order to investigate the translational potential of the knowledge gained from these in vitro experiments, pre-clinical DLBCL xenograft studies were conducted. Strikingly, growth of subcutaneous tumor grafts was significantly reduced in mice treated locally or systemically with miR-34a mimetics in comparison to control treated mice. These findings suggest that miR-34a replacement therapy constitutes a valid therapeutic approach, especially for treatment of DLBCL patients with low miR-34a expression.
Another major epigenetic event that gained increasing attention in the context of cancer research in recent years is DNA methylation. Aberrant DNA methylation of promoter regions is associated with the silencing of the respective gene and constitutes an important mechanism for cancer cells to silence tumor suppressor genes. The genes targeted by this mechanism in B cell lymphomas and their direct functional contribution to pathogenesis however remain to be elucidated. To address this issue, I set out to identify and functionally characterize hypermethylated genes in DLBCL.
Whole genome DNA methylation analysis of low-grade marginal zone lymphoma of MALT (mucosa-associated lymphoid tissue) type, gastric and nodal DLBCL as well as control tonsil samples revealed a characteristic pattern of aberrant promoter-specific DNA hypermethylation, which is shared between all lymphoma entities analyzed. This suggests that global methylation changes represent an early event in lymphomagenesis and that these alterations are mediated by a shared mechanism operating irrespective of lymphoma localization.
Further integration of this methylation data with data obtained from RNA sequencing after pharmacological demethylation of DLBCL cell lines allowed us to identify candidate tumor suppressor genes, which we subsequently validated in a series of functional screening experiments. One gene that emerged as a particularly interesting tumor suppressor candidate was the dual specificity phosphatase DUSP4, a negative regulator of mitogen-activated protein kinases. We could show that DUSP4 is either epigenetically silenced or deleted in the majority of nodal and extranodal DLBCL cases and that lack of DUSP4 negatively correlates with overall survival probability of DLBCL patients. Furthermore, we could demonstrate that DUSP4 dephosphorylates and thereby inhibits c-JUN N-terminal kinase (JNK) resulting in increased apoptosis in DLBCL cells. Pharmacological inhibition of JNK phenocopies these tumor suppressive effects in vitro and in vivo, reinforcing the importance of active JNK signaling for DLBCL cell survival and providing a mechanistic rationale for targeted JNK therapy as novel treatment approach.
In conclusion, the work performed in the scope of this thesis contributes another valuable puzzle piece to understanding the complex epigenetic and genetic determinants of DLBCL and proposes novel therapeutic approaches for clinical consideration in the future.

Additional indexing

Item Type:Dissertation
Referees:Müller Anne, Krek Wilhelm, Robinson Mark D, Tzankov Alexandar
Communities & Collections:04 Faculty of Medicine > Institute of Molecular Cancer Research
07 Faculty of Science > Institute of Molecular Cancer Research
Dewey Decimal Classification:570 Life sciences; biology
610 Medicine & health
Language:English
Date:2015
Deposited On:28 Jan 2016 11:21
Last Modified:05 Apr 2016 20:01

Download

Full text not available from this repository.

TrendTerms

TrendTerms displays relevant terms of the abstract of this publication and related documents on a map. The terms and their relations were extracted from ZORA using word statistics. Their timelines are taken from ZORA as well. The bubble size of a term is proportional to the number of documents where the term occurs. Red, orange, yellow and green colors are used for terms that occur in the current document; red indicates high interlinkedness of a term with other terms, orange, yellow and green decreasing interlinkedness. Blue is used for terms that have a relation with the terms in this document, but occur in other documents.
You can navigate and zoom the map. Mouse-hovering a term displays its timeline, clicking it yields the associated documents.

Author Collaborations