Mutations of Chromatin and its Modifying Machineries in Malignancies

Our studies have focused on the characterization of the molecular functions and biochemical properties of the Set1/MLL family of proteins and how their chimeras and mutations are associated with childhood leukemia and other forms of cancer. We have also focused on the role of chromatin and transcriptional elongation machinery in the regulation of developmental gene expression and how the misregulation of their activities is associated with malignancies. Our hope is that our molecular studies will advance our understanding of the molecular mechanisms of rearrangement-based and mutation-based cancer through the epigenetic regulators. Our biochemical and molecular studies demonstrated that Set1 in yeast exists in the Set1/COMPASS complex capable of methylating lysine 4 of histone H3 (H3K4). We demonstrated thatDrosophila cells possess three Set1-related proteins and mammalian cells have six Set1-related proteins all found within COMPASS-like compositions capable of methylating histone H3K4.Furthermore, given that there is almost no sequence homology between many of the MLL translocation partners, for many years, it was unclear why MLL translocations into so many unrelated genes result in the pathogenesis of leukemia. Our biochemical studies on the purification of the MLL-chimeras demonstrated that many of the MLL translocation partners are part of the same macromolecular complex we named the Super Elongation Complex (SEC). We demonstrated that the translocations of MLL within any of the subunits of SEC result in the misrecruitment of SEC to the MLL target genes and in the perturbation of the transcriptional checkpoint control of these genes, triggering leukemic growth. Additionally, the recent cataloging of somatic mutations in cancer have identified a large number of mutations in the components of the MLL1-4 and Set1A/B complexes in both hematological malignancies and solid tumors. However, we know very little why the COMPASS family is mutated in different ca