E2A and acute lymphoblastic leukemias (ALL)

A closer look at the E2A gene... Other names: TCF3, ITF1, and Factors E12/E47 Located on chromosome 19 Encodes two proteins: E12 and E47 17 exons

E2A

What are the E2A proteins? Transcription factors Members of the basic helix-loop-helix (bHLH) superfamily Necessary for forming protein dimers and making contact with DNA Bind to consensus E-box sequence sites

Mouse Models... E2A -/- mutants develop to full term without apparent abnormalities High rate of postnatal death Show retarded postnatal growth Contain no B cells while T-cell, macrophage, granulocyte, and erythroid lineages are intact

What about E2A +/- mice? Have half as many B-cells as wild-type embryos Suggests levels of E2A expression in cell translates into levels of B-cells!

Roles of E2A in B-cell Differentiation: Induces expression of other lineage-specific transcription factors (including EBF and RAG proteins) Collaborates with EBF to regulate expression of other B-lineage genes Regulates immunoglobulin gene recombination by facilitating access of RAG recombinase to recombination loci

E2A plays a similar role in T-cell development... E2A-HEB heterodimers contribute to the regulation of CD4 expression Plays important roles in recombination of T-cell receptor Provides survival signal for immature T-cells Proposed to also have many negative affects on T-cell development (not well understood)

E2A’s role in Leukemia formation Chromosomal translocation t(1:19) creates a fusion protein E2A-PBX1 Fusion protein combines the activator domains of E2A with the DNA-binding homeodomain region of PBX1 Fusion protein retains ability to interact with HOX proteins to activate transcription

Two things to consider: The effect of E2A heterozygosity on tumor development( especially considering E2A as a tumor suppressor) The E2A-PBX1 fusion protein: novel biochemical properties and functional activities

E2A as a tumor suppressor...

Displacement of section of PBX1 by the activator domains of E2A could... Increase PBX1 ability to activate transcription E2A-PBX1 localized to the nucleus Affect the ability of inhibitor proteins to bind to PBX1

Downstream Targets EB-1: encodes a phosphotyrosine-binding domain protein, and as such may have a role in the regulation of cell proliferation Wnt16: encodes a member of the WNT/WG family of growth factors; members of this family have been identified as potent activators of growth and differentiation

Acute Lymphoblastic Leukemia (ALL) Most common form of childhood cancer Undifferentiated lymphoid cells accumulate in bone marrow, replace normal blood cells, and spread to other parts of the body ~3,000 children are diagnosed each year Peak incidence from 3-5 years of age 98-99% of children diagnosed early attain initial complete remissions Approximately 80% of patients can be cured

Treatment Options Chemotherapy Hematopoietic Stem Cell Transplant for high-risk cases

Current Research Optimize dosage and scheduling of antileukemic agents based on patient’s leukemic cell genetic features Microarray technology to obtain a profile of gene and protein expression in leukemia cells Safety of stem cell transplant and increase the number of donors

References St. Jude Children’s Research Hospital “Acute Lymphoblastic Leukemia” Atlas of Genetics and Cytogenetics in Oncology and Hematology Cooper, G.M. The Cell: A molecular approach Aspland, S.E. et al The role of E2A-PBX1 in leukemogenesis. Oncogene 20: Zhuang, Yuan et al The helixl-loop-helix gene E2A is required for B cell formation. Cell 79: Greenbaum, Stephen and Yuan Zhuang Regulation of early lymphocyte development by E2A family proteins. Seminars in Immunology 14(6): Schebesta, Michael et al Transcriptional control of B-cell development. Current Opinion in Immunology 14: