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Expression and stability of wild-type and mutant RUNX1 protein isoforms in T-cell acute lymphoblastic leukemia Olena, Shevchuk Olehivna


Acute lymphoblastic leukemia (ALL) is the most common type of cancer diagnosed in children, and while many patients treated with standard chemotherapy achieve cure, the disease returns in many cases. Current treatments are highly toxic and can cause learning deficits, growth problems, and several other side effects that can persist long after treatment is completed. There is therefore a great need to generate targeted therapies that exploit the molecular linchpins of this disease if clinical improvements are to be made. In seeking out pathways amenable to therapeutic targeting, we have focused recently on the Runt-related (RUNX) gene family members which are known to play important roles in gene regulation generally, are well known to be recurrently mutated in myeloid malignancies, and have recently been discovered to be mutated frequently in T-ALL. The human RUNX1 gene is composed of 12 exons and transcripts are initiated from two different promoters, leading to production of multiple protein isoforms. Of the 3 major isoforms, RUNX1A encodes essentially just the N-terminal, DNA-binding Runt domain and may act in a dominant negative fashion as compared to RUNX1B and RUNX1C, both of which encode substantial C-terminal domains that are thought to mediate protein-protein interactions. Interestingly, a subset of recurrent RUNX1 mutations identified recently in TALL introduce premature stop codons that theoretically encode truncated, RUNX1A-like proteins. In order to understand the role of RUNX1 in T-ALL, we felt it was critical first to determine which of the 3 RUNX1 isoforms are actually expressed at the protein level. To this end, we designed a mass spectrometry based approach to determine the expression and absolute abundance of RUNX1 isoforms in T-ALL cell lines. Further, we sought to determine whether RUNX1 mutations that are predicted to produce dominant-negative polypeptides actually lead to stably expressed truncated peptides, and whether these mutations may alter the expression of the wild-type isoforms. The results from our studies will aid in understanding the functional role of alternatively spliced RUNX1 isoforms and mutations in leukemia and help to determine if targeting of RUNX1 and/or its downstream targets is a viable therapeutic option.

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