Poster abstracts

Poster number 123 submitted by Jarnail Singh

Somatic mutations in spliceosomal factors lead to alternative splicing patterns in myeloid neoplasms

Jarnail Singh (Molecular Genetics, Cleveland Clinic, Cleveland, OH), , Bartlomiej Przychodzen, Andres Jerez, (Translational Hematology and Oncology Research, Cleveland Clinic, Cleveland, OH), Kathryn Guinta, Mikkael A Sekeres (Translational Hematology and Oncology Research, Cleveland Clinic, Cleveland, OH), Richard A Padgett (Molecular Genetics, Cleveland Clinic, Cleveland, OH), Jaroslaw P Maciejewski (Translational Hematology and Oncology Research, Cleveland Clinic, Cleveland, OH), Hideki Makishima (Translational Hematology and Oncology Research, Cleveland Clinic, Cleveland, OH)

Abstract:
Somatic mutations of spliceosomal proteins such as U2AF1, SF3B1, SRSF2 and PRPF8 have been identified in myeloid malignancies. These mutations are usually single heterozygous missense mutations at recurrent sites. While all of these mutations affect proteins in the common splicing pathway, their downstream consequences may be diverse and involve distinct oncogenic pathways. To identify affected genes and gain mechanistic insight into the effects of these mutations, we have analyzed the tumor transcriptomes of multiple AML patients with and without spliceosomal factor mutations. For U2AF1, we analyzed 6 tumors with U2AF1 mutations and 14 tumors that had no known splicing factor mutations. Focusing on cases of alternative exon inclusion, we identified 35 exons in 35 genes whose inclusion was altered using stringent statistical cutoffs. Of these, 8 exons were more included while 27 were more excluded in the U2AF1 mutant tumors. We examined the splice site signals flanking the alternative exons and noted a highly unusual sequence pattern adjacent to the 3’ AG dinucleotide which is the recognition site of U2AF1. The sequence at this position showed a mutually exclusive pattern upon comparing the excluded to the included exons and this pattern also differed from the consensus 3’ splice site sequence. We speculate that the RNA recognition activity of U2AF1 is altered by these mutations. We also found that these splicing changes are not seen in tumors expressing low levels of wild type U2AF1, nor are the patterns the same in similar tumors with mutations in splicing factors SF3B1, SRSF2 or PRPF8.

Keywords: Splicing factors Mutations, alternative splicing, Myeloid leukemia