PRPS2 mutations drive acute lymphoblastic leukemia relapse through influencing PRPS1/2 hexamer stability

Tumor relapse is the major cause of treatment failure in childhood acute lymphoblastic leukemia(ALL),yet the underlying mechanisms are still elusive.Here,we demonstrate that phosphoribosyl pyrophosphate synthetase 2(PRPS2)mutations drive ALL relapse through influencing PRPS1/2 hexamer stability.Ultra-deep sequencing was performed to identify PRPS2 mutations in ALL samples.The effects of PRPS2 mutations on cell survival,cell apoptosis,and drug resistance were evaluated.In vitro PRPS2 enzyme activity and ADP/GDP feedback inhibition of PRPS enzyme activity were assessed.Purine metabolites were analyzed by ultra-performance liquid-chromatography tandem mass spectrometry(UPLC–MS/MS).Integrating sequencing data with clinical information,we identified PRPS2 mutations only in relapsed childhood ALL with thiopurine therapy.Functional PRPS2 mutations mediated purine metabolism specifically on thiopurine treatment by influencing PRPS1/2 hexamer stability,leading to reduced nucleotide feedback inhibition of PRPS activity and enhanced thiopurine resistance.The 3-amino acid V103-G104-E105,the key difference between PRPS1 and PRPS2,insertion in PRPS2 caused severe steric clash to the interface of PRPS hexamer,leading to its low enzyme activity.In addition,we demonstrated that PRPS2 P173R increased thiopurine resistance in xenograft models.Our work describes a novel mechanism by which PRPS2 mutants drive childhood ALL relapse and highlights PRPS2 mutations as biomarkers for relapsed childhood ALL.

PUMA facilitates EMI 1-promoted cytoplasmic Rad51 ubiquitination and inhibits DNA repair in stem and progenitor cells

Maintenance of genetic stability via proper DNA repair in stem and progenitor cells is essential for the tissue repair and regeneration,while preventing cell transformation after damage.Loss of PUMA dramatically increases the survival of mice after exposure to a lethal dose of ionizing radiation(IR),while without promoting tumorigenesis in the long-term survivors.This finding suggests that PUMA(p53 upregulated modulator of apoptosis)may have a function other than regulates apoptosis.Here,we identify a novel role of PUMA in regulation of DNA repair in embryonic or induced pluripotent stem cells(PSCs)and immortalized hematopoietic progenitor cells(HPCs)after IR.We found that PUMA-deficient PSCs and HPCs exhibited a significant higher doublestrand break(DSB)DNA repair activity via Rad51-mediated homologous recombination(HR).This is because PUMA can be associated with early mitotic Inhibitor 1(EMI1)and Rad51 in the cytoplasm to facilitate EMI1-mediated cytoplasmic Rad51 ubiquitination and degradation,thereby inhibiting Rad51 nuclear translocation and HR DNA repair.Our data demonstrate that PUMA acts as a repressor for DSB DNA repair and thus offers a new rationale for therapeutic targeting of PUMA in regenerative cells in the context of DNA damage.