Dissecting the Functional Role of PAX5 Mutations in B-cell Acute Lymphoblastic Leukemia

PROJECT SUMMARY B-cell acute lymphoblastic leukemia (B-ALL) is the most common pediatric cancer and remains a leading cause of childhood cancer death. Over 10% of B-ALL cases have point mutations in PAX5, a gene that encodes a key transcription factor for B-cell development. PAX5 mutations are the signature lesions in two recently identified B-ALL subtypes: PAX5alt, characterized by diverse genetic alterations in PAX5, and a subtype defined by PAX5 P80R mutation. While PAX5alt patients, particularly adults, have a significantly worse prognosis compared to PAX5 P80R patients, the underlying mechanisms driving these differences remain poorly understood. Both subtypes frequently acquire additional genetic alterations, such as wild-type PAX5 allele deletion and Ras pathway mutations, which further contribute to disease progression. Despite advances in chemotherapy, many patients experience suboptimal outcomes and poor quality of life, emphasizing the need for improved therapies. Our preliminary studies show that PAX5 P80R leukemic cells have increased sensitivity to Dexamethasone (Dex) treatment, likely due to high dependence on glucose uptake and glycolytic activity. These findings suggest that metabolic alterations contribute to the differential clinical responses observed between the two PAX5-driven subtypes. To systematically dissect these mechanisms, we will use orthogonal experimental models (e.g., B- ALL cell lines, mouse leukemia models, and human B-ALL samples) alongside multi-omics platforms, such as RNA-seq, CUT&Tag, ATAC-seq, END-seq, whole-genome sequencing, and single-cell analyses in this project. We hypothesize that rather than loss of function, PAX5 mutants can exert dominant effects in B-ALL initiation through novel PAX5 binding activities and gene transcription activation, which may block normal B-cell differentiation and give rise to pre-leukemic cells; once additional genetic lesions are acquired, PAX5-mutant clones can progress to overt B-ALL. We aim to (Aim 1) identify the transcriptional and metabolic alterations induced by PAX5 mutants, particularly their different effects on Dex treatment. Additionally, we will (Aim 2) investigate the stepwise acquisition of genetic lesions that drive leukemic transformation, with a focus on the pre-leukemic cells and their transition to overt leukemia using the Pax5 P80R mouse model. Finally, we will (Aim 3) study the role of aMEGF10, a gene significantly overexpressed in PAX5 P80R B-ALL, and assess the therapeutic potential of targeting the novel aMEGF10-SYK signaling pathway. In summary, this project will provide comprehensive insights into the molecular features of PAX5-mutant B-ALL subtypes, reveal novel mechanisms of leukemogenesis and treatment responses, and identify potential therapeutic targets. These findings are expected to improve patient risk-stratification and lead to the development of more effective targeted therapies with lower toxicity for PAX5-mutant B-ALL.