The goal of this project is to understand the mechanism of disease pathogenesis induced by U2AF1 mutations in myelodysplastic syndromes (MDS). The incidence of MDS in the United States is at least 20,000 cases per year (and could be as high as 45,000 by one recent estimate), making it the most common bone marrow failure syndrome in adults. Although there are three US Food and Drug Administration-approved therapies and multiple other agents in clinical trials, the available therapies have so far yielded only modest results. Stem cell transplantation has curative potential, but is available for only a minority of patients with MDS because of advanced age and comorbidities. Low blood counts, iron accumulation, and development of acute myeloid leukemia (AML) contribute to illness and death in MDS and lead to estimated annual expenditures in excess of $120,000 per patient according to current treatment guidelines. Better treatment strategies are urgently needed. Understanding what mutated genes contribute to MDS development and progression may allow us to meet this need.

While our discovery of mutated genes in MDS has rapidly expanded in the past several years, we do not know which of these genes are most important for the development of MDS and progression to leukemia. Four independent groups, including ours, have recently reported mutations in up to eight genes involved in pre-mRNA splicing (spliceosome genes); these mutations occur in up to 57% of MDS patients, making this family of genes the most common known to be mutated in MDS. Cells in our bodies depend on the correct processing of RNA, which involves cutting and pasting RNA molecules together, termed splicing, to make proteins that are essential for normal cell functioning. We discovered mutations in a gene (U2AF1) important for carrying out normal splicing of RNA in 13/150 (8.7%) patients with MDS. We also observed that U2AF1 mutations were present in patient's bone marrow cells at the time of diagnosis, suggesting the mutations may be important for MDS initiation. Patients with U2AF1 mutations were also more likely to develop AML, which is typically resistant to standard chemotherapies and carries a poor prognosis.

The discovery of U2AF1 mutations in MDS creates a new paradigm for how MDS might develop. Mutations in spliceosome genes have now been found in chronic lymphocytic leukemia and a variety of solid tumors, suggesting that studies outlined here will have broad implications for cancer. Understanding how mutations in U2AF1 lead to MDS has not yet been explored and is the major focus of this proposal.

Studying blood cell development requires a model organism to recapitulate the complex bone marrow environment in humans. Therefore, we engineered mice to carry the same U2AF1 mutation in their bone marrow cells that occurs in MDS patients. Preliminary analysis of these mice demonstrates that they develop low blood counts and have an abnormal bone marrow, both characteristics observed in MDS patients. We will use these mice to study how the U2AF1 mutation affects blood cell development and determine whether the mutation can cause MDS. We have evidence from mutant cells grown in culture that U2AF1 mutations change the way RNA is spliced together. We will test whether changes in RNA splicing occur in the bone marrow cells harvested from mutant mice and compare these changes to those observed in MDS patient samples with U2AF1 mutations. Ultimately, if we can identify how U2AF1 mutations change blood cell development, we may be able to develop novel treatments that could improve the health and lives of patients with MDS.