Rearrangements of the ALL-1/MLL1 gene, resulting in production of ALL-1 fusion proteins, underlie the vast
majority of infant acute leukemias and of a substantial part of a therapy-related leukemia. The way by which
the fusion proteins trigger leukemia is not known. Here we attack this issue in several directions: 1) we have
recently found that expression of ALL-1 fusion proteins in leukemic and transfected cells results in
upregulation of a specific micro RNA. miR-191. We found that the upregulation is due to recruitment of ALL-1
fusion proteins, together with the general processor of microRNAs-Drosha, to the miR-191 locus. Since
Drosha is not recruited with normal ALL-1 to the same locus (nor was it shown to be bound to other rniR
loci), we consider this recruitment as very significant in miR-191 upregulation. Included in the proposal are
experiments concerning potential association between ALL-1 fusion proteins and Drosha, involvement of
Drosha's recruitment in miR-191 overexpression in solid tumors, direct role of miR-191 in onset of acute
leukemia, effect of miR-191 overexpression on differentiation of hematopoietic precursor cells, and
identification of miR-191 target gene(s). 2) We have used a combination of conventional columnes,
immunearflnlty purification, and mass spectrometry analysis to identify a series of proteins associated with
ALL-1/AF4 within a multiprotein complex. The identified proteins will be examined by multiple approaches to
determine whether they constitute integral components of the ALL-1/AF4 complex. A follow-up will focus on
interesting components. 3) Following our success in bringing off a genome-wide location analysis of normal
ALL-1, we will extend it to a global analysis of the gene targets of ALL-1 fusion proteins ALL-1/AF4 and ALLVAF9
in leukemic lymphoid and myeloid cell lines, respectively. |