M. Fola Babatunde

MLF1, A CANDIDATE GENE FOR CHEMOTHERAPY INDUCED LEUKEMIA. M. Fola Babatunde¹, Timothy A. Graubert². Biology Department, Washington University in St. Louis, MO¹; Department of Internal Medicine, Washington University Medical School, St. Louis, MO².

Patients treated for both malignant and nonmalignant conditions are at risk for developing alkylator-induced leukemia, which arises as a secondary malignancy from chemotherapy treatment. Our lab is interested in the correlation between germline genetic variability and susceptibility to chemotherapy-induced leukemia. Better understanding of the genetic components of the disease could lead to clinical treatment tailored to the genetic background of patients. Mouse models were used to investigate genetic factors associated with susceptibility. Twenty inbred strains were exposed to N-nitroso-N-ethylurea (ENU), an alkylating agent. Six of the twenty strains were found to be susceptible with incidences ranging from 80% to 18%, SWR/J being the most susceptible. Haplotype association mapping, a computational linkage analysis identified two significant peaks on chromosomes 14 and 3 that were associated with incidence rates. Chromosome 3 contained a 1 Mb region that included six genes, one of which was Myeloid Leukemia Factor 1 (Mlf1), a gene previously implicated in acute myeloid leukemia. Mlf1, therefore, is a strong candidate susceptibility factor for alkylator-induced leukemia. We first sought to determine whether the genetic basis of differences between susceptible and resistant strains existed at the nucleotide level. Therefore, we sequenced all exons, flanking regions of the introns, and 500 bp of the Mlf1 promoter in our 20 strains of interest. Sequencing data reinforced Mlf1 linkage to leukemia susceptibility. The strains were divided into three haplotypes: a reference, a wild derived, and a susceptible. A polymorphism frequency of .08% was found in the nonsuscpetible strains and a frequency of .20% in susceptible strains. Most SNPs were located within introns outside of splicing sites and those in exons were synonymous changes. Further investigations will explore potential correlation between Mlf1 expression differences at the mRNA or protein level with susceptibility and the role of Mlf1 in hematopoiesis. Preliminary results from mRNA quantification through real time PCR indicate low expression of Mlf1 in whole bone marrow. As a result, purification of cell populations will be required to compare expression levels across the twenty strains. To identify the role of Mlf1 in hematopoiesis, Mlf1 deficient mice were obtained (provided by S Morris, St. Judes). We will carefully characterize hematopoiesis under baseline conditions and after ENU exposure. We predict that Mlf1 null mice will have increased susceptibility to alkylator-induced leukemia. Elucidation of the role of Mlf1 in hematopoiesis could improve treatment and decrease the prevalence of this incurable disease.