Functional analysis of SMYD2 and SMYD3 lysine methyltransferases
Date
2016
Authors
Edwards, Melissa Ashley, author
Brown, Mark, advisor
Tucker, Haley, committee member
Partin, Kathryn, committee member
Hickey, Matthew, committee member
Journal Title
Journal ISSN
Volume Title
Abstract
The proteins SMYD2 and SMYD3 are two of five members of a unique family of lysine methyltransferases defined by a catalytic SET domain that is split into two segments by a MYND protein interaction domain, followed by a cysteine-rich post-SET domain. The SMYD family members have been shown to be essential for cellular development, cell cycle progression, and when dysregulated, tumorigenesis. SMYD1 has been widely studied as a pivotal component of cardiac and skeletal muscle development. Although their three dimensional structures have been solved, less is known about functional consequences of SMYD2 and SMYD3. Aberrant overexpression of SMYDs 2 and 3 have been implicated in numerous malignancies, and both have been studied as potential therapeutic targets. The overriding aim of our research is to obtain a more thorough understanding of SMYD2 and SMYD3 function. In Chapters 1 and 2, we outline essential background regarding the SMYD family and the methods used in our studies. In Chapter 3, we address the consequences of the interaction of SMYD3 with the nuclear chaperone, HSP90. Each have been independently implicated as proto-oncogenes in several human malignancies. Loss of SMYD3-HSP90 interaction leads to SMYD3 mislocalization within the nucleus, thereby severing its association with chromatin. This results in reduction of SMYD3-mediated cell proliferation and, consequentially, impairment of SMYD3’s oncogenic activity. We suggest a novel approach for blocking HSP90-driven malignancy which may have reduced toxicity over current HSP90 inhibitors. In Chapter 4, we turn our attention to SMYD2 and its putative role in hematopoietic carcinogenesis. In order to study the effect of SMYD2 in tumor initiation, we employed transforming oncogenes to study the consequences of SMYD2 loss in three hematopoietic models: B-Acute Lymphocytic Leukemia (B-ALL), Chronic Myeloid Leukemia (CML), and Mixed Lineage Leukemia (MLL). Loss of SMYD2 in CML and MLL, but not in B-ALL, models led to cell cycle block following by widespread apoptosis and cell death. Tumorigenicity, as assessed in vitro by colony formation and in vivo by NOD/SCID transformation, was dependent upon SMYD2. Gene expression analyses indicated that, as previously determined in multiple studies, impairment included reduction in the level of the p53 tumor suppressor. Collectively, these studies establish SMYD2 as a putative proto-oncogene in CML and MLL. In Chapter 5, we report our efforts to extend the above findings to the living organism. SMYD2 was conditionally deleted via cre/Lox methodology from the germline of C57BL.6 mice exclusively in hematopoietic progenitors. SMYD2-deficient mice were born healthy and achieved normal lifespans. However, consistent with our findings of Chapter 4, we observed significant blocks in the progression of fetal and bone marrow hematopoietic stem cells to both B lymphocyte and myeloid lineages. While these blocks led to an overall reduction of mature peripheral B cells, SMYD2-deficient mice maintained a relatively normal immune response. These studies further support a model in which SMYD2 is required for normal hematopoiesis transformation.