Abstract
AbstractRelapse-specific mutations do not account for all chemotherapy failures in patients with B-cell acute lymphoblastic leukemia (B-ALL). By mining RNA-seq datasets of paired diagnostic/relapse pediatric B-ALL samples, we discovered pervasive aberrant splicing (AS) patterns linked with relapse. They affected drivers of resistance to glucocorticoids, anti-folates, and thiopurines. Most splicing variations represent exon skipping, “poison” exon inclusion, and intron retention, phenocopying well-documented loss-of-function mutations. In addition, relapse-associated AS ofNT5C2mRNA yields an isoform with a cryptic 24-nt in-frame exon 6a. Inclusion of the extra 8 amino acids into this enzyme results in elevated nucleosidase activity, a known consequence of gain-of-function mutations in NT5C2 and a common determinant of 6-mercaptopurine resistance. Furthermore, in B-ALL cells NT5C2ex6a and the R238W hotspot variant confers comparable levels of resistance to 6-mercaptopurinein vitroandin vivo. These results support a role for alternative splicing as a prevalent mechanism driving chemotherapy resistance in relapsed B-ALL.Statement of significanceMutations in chemoresistance genes are found in relapsed/refractory acute lymphoblastic leukemia. However, in this low-mutational-burden disease, up to 30% of cases have no known relapse-specific genetic alterations. Our identification of aberrant splicing as an alternative mechanism of acquired drug resistance fills this gap and suggests new opportunities for therapeutic interventions.
Publisher
Cold Spring Harbor Laboratory