MOLECULAR MECHANISMS IN LEUKEMIA
Our lab carries out experimental and correlative research related to hematological cancers. The experimental component of our work is directed at understanding the molecular mechanisms that underlie acute lymphoblastic leukemia, an aggressive and relatively common cancer in children. We are especially interested in an oncogenic transcription factor called E2A-PBX1.1 The figure illustrates how an amino-terminal portion of the E2A gene product E47, a DNA-binding transcription factor that regulates target genes involved in B-lymphoid development, becomes fused to a portion of PBX1, a homeodomain-containing transcription factor, to create oncogenic E2A-PBX1.
E2A-PBX1 disrupts the normal regulation of cellular proliferation and differentiation by mechanisms that involve physical interactions with other proteins and DNA; these ultimately lead to abnormal gene regulation. Essentially, we use a wide range of techniques, including biochemical and cell biology experiments involving mouse models, to identify and elucidate key physical and functional molecular interactions involved in transforming normal hematopoietic cells into leukemic ones. We have shown that oncogenesis mediated by E2A-PBX1 requires binding of its amino-terminal transcriptional activation domain to the KIX domain of the transcriptional co-activator CREB binding protein (CBP).2,3 Exciting experimental avenues for us include biophysical and structural experiments being carried out in collaboration with Dr. Steven Smith, in the Queen's Department of Biomedical and Molecular Sciences. For example, the figure below shows a three-dimensional structure that we solved of a complex that includes an amino-terminal transcriptional activation domain from E2A-PBX1 stably bound to the KIX domain of the transcriptional co-regulator CREB binding protein (CBP).4 The arrow indicates a leucine side chain that is required for both physical binding with CBP and the oncogenic function of E2A-PBX1.
More recently we have used chromatin immunoprecipitation (ChIP) followed by next-generation DNA sequencing (ChIP-seq) to identify hundreds of binding sites for E2A-PBX1 across the genome. These results confirm co-recruitment of CBP to most E2A-PBX1 binding sites and have informed a revised hypothesis as to how E2A-PBX1 is recruited to these sites.
Selected Leukemia Publications
- LeBrun DP: E2A basic helix-loop-helix transcription factors in human leukema. Front Biosci 8:s185,2203.
- Bayly R, Chuen L, Currie RA, Hyndman BD, Casselman R, Blobel GA, LeBrun DP: E2A-PBX1 Interacts directly with the KIX domain of CBP/p300 in the induction of proliferation in primary hematopoietic cells. J Biol Chem 279(53):55362, 2004
- Bayly R, Murase T, Hyndman BD, Savage R, Nurmohamed S, Munro K, Casselman R, Smith SP, LeBrun DP: A critical role for a single leucine residue in leukemia induction by E2A-PBX1. Mol Cell Biol 26(17):6442-52, 2006.
Denis CM, Chitayat S, Plevin MJ, Wang F, Thompson P, Liu S, Spencer HL, Ikura M, LeBrun DP, Smith SP: Structural basis of CBP/p300 recruitment in leukemia induction by E2A-PBX1. Blood 120(19):3968, 2012
TRANSLATIONAL LYMPHOMA RESEARCH
Lymphomas are relatively common solid tumours derived from lymphoid cells. Since they are clinically and biologically diverse, as well as relatively well-characterized from a molecular point of view, lymphomas offer a particular opportunity to exploit new insights in basic cancer biology in order to improve the diagnosis and clinical management of patients. Our work in this area has essentially entailed correlating histological, immunohistological or molecular findings derived from primary lymphoma tumour samples with clinical data. Our correlative lymphoma studies been made possible by the Queen's Laboratory for Molecular Pathology, which provides access to research histology services, including construction of tissue microarrays, routine and fluorescence-based immunohistology, and computer-assisted image analysis services. Selected publications in this area are listed below. As a recent example of this type of work, we used multichannel immunofluorescence coupled with automated image analysis to quantify the Polycomb group (PcG) protein BMI1 in primary follicular lymphoma samples and demonstrated a striking association between BMI1 abundance and reduced overall survival. In the image below, AS refers to "AQUA score", a measure of BMI1 fluorescence intensity; the histogram shows the range of BMI1 abundance observed across our 109 lymphoma samples; and, the survival curves illustrate the association between progressively increasing BMI1 abundance and reduced patient survival.
Selected Lymphoma Publications
- Farmer PL, Bailey DJ, MD, Burns BF, Day A, LeBrun DP: The reliability of lymphoma diagnosis in small tissue samples is heavily influenced by lymphoma subtype. Am J Clin Pathol 128(3):474, 2007.
- LeBrun DP, Baetz T, Foster C, Farmer P, Sidhu R, Guo H, Harrison K, Somogyi R, Greller LD, Feilotter H: Predicting outcome in follicular lymphoma by using interactive gene pairs. Clin Cancer Res 14(2):478, 2008.
- Alhejaily A, Wood B, Foster CJ, Farmer PL, Gilks CB, Brettschneider J, Day AG, Feilotter HE, Baetz T, LeBrun DP: Differential expression of cell cycle regulatory proteins defines distinct classes of follicular lymphoma. Hum Pathol 42:972, 2011
- Wood B, Sikdar S, Choi SJ, Virk S, Alhejaily A, Baetz T, LeBrun DP: Abundant expression of IL-21 receptor in follicular lymphoma cells is associated with more aggressive disease. Leuk Lymphoma 54(6):1212, 2013
- Alhejaily A, Day AG, Feilotter HE, Baetz T, LeBrun DP: Inactivation of the CDKN2A tumour suppressor gene by deletion or methylation is common at diagnosis in follicular lymphoma and associated with poor clinical outcome. Clin Cancer Res, 20(6):1676, 2014
Graham C, LeBrun DP: Tumor suppressors in follicular lymphoma. Leuk Lymphoma 14:1, 2015