An Alternatively Spliced Gain-of-Function NT5C2 Isoform Contributes to Chemoresistance in Acute Lymphoblastic...

Area of Science:

• Oncology
• Molecular Biology
• Genetics

Background:

• Relapsed or refractory B-cell acute lymphoblastic leukemia (B-ALL) is a significant cause of pediatric cancer mortality.
• Chemotherapy failures in B-ALL are not fully explained by relapse-specific mutations, indicating other resistance mechanisms.

Purpose of the Study:

• To investigate the role of alternative splicing (AS) in chemotherapy resistance in pediatric B-ALL.
• To identify novel mechanisms of resistance beyond genetic mutations.

Main Methods:

• Analysis of RNA-seq datasets from paired diagnostic/relapse pediatric B-ALL samples.
• Characterization of alternative splicing patterns, including exon skipping, poison exon inclusion, and intron retention.
• Functional assessment of the NT5C2ex6a variant in B-ALL cells in vitro and in vivo.

Main Results:

• Pervasive alternative splicing patterns were discovered in relapsed B-ALL, associated with resistance to glucocorticoids, anti-folates, and thiopurines.
• A novel NT5C2 mRNA isoform (NT5C2ex6a) was identified, conferring resistance to 6-mercaptopurine (6-MP) by increasing nucleosidase activity.
• Both NT5C2ex6a and the R238W variant induced collateral sensitivity to IMPDH inhibitors like mizoribine.

Conclusions:

• Alternative splicing plays a critical role in chemotherapy resistance in relapsed B-ALL.
• IMPDH inhibitors represent a potential therapeutic strategy for thiopurine-resistant leukemias.