The Tumor Suppressor Function of Dnmt3a in Chronic Lymphocytic Leukemia



 DESCRIPTION (provided by applicant): Chronic lymphocytic leukemia (CLL) is a heterogeneous B-cell malignancy with no association with carcinogens, viruses, radiation or underlying genetic defect identified to date. The disease is characterized by an accumulation of mature B-cells in hematopoietic tissues and it is incurable at present. Cytosine methylation of mammalian genomic DNA is critical for normal physiological processes due to its contribution to transcriptional regulation of large sets of genes. Recent genome-wide analysis of human CLL samples revealed a global hypomethylation of the coding portion of the genome, suggesting involvement of DNA methyltransferases (Dnmts) in the pathogenesis of the disease. To induce hypomethylation, we conditionally inactivated Dnmt3a and Dnmt3b in hematopoietic lineages in mice. Loss of Dnmt3a but not Dnmt3b in hematopoietic cells induces cellular transformation of B-cells and CLL, suggesting a tumor suppressor function for Dnmt3a in CLL development. The cellular and molecular basis of this function remains unclear. We hypothesize that the tumor suppressor function of Dnmt3a depends on DNA methylase activity, whose loss results in promoter hypomethylation and up-regulation of genes functioning as epigenetic drivers of CLL. Three Specific Aims will address this: In Aim 1 we will identify and characterize cancer-initiating cells in CLL induced by Dnmt3a deficiency and analyze their biological and molecular properties. In Aim 2 we will determine whether Dnmt3a methyltransferases activity or rather methylation -independent repressor activity is responsible for its tumor suppressor function. In Aim 3 we will test the ability of selected Dnmt3a target genes to induce CLL in vivo and evaluate their roles in maintenance of the tumor phenotype in human CLL cell lines in vitro. A careful analysis of the tumor suppressor function of Dnmt3a will provide useful insight into biological and molecular events governing the development of mouse and human CLL.