Contributions
Abstract: S824
Type: Oral Presentation
Presentation during EHA23: On Saturday, June 16, 2018 from 11:45 - 12:00
Location: Room A6
Background
PAX5, a gene encoding a key transcription factor in B cell differentiation, is altered in one third of B-cell acute lymphoblastic leukemia (B-ALL). Its structural alterations (point mutations and translocations) are considered as primary oncogenic events of B-ALL while its deletion can be considered as an additional hit in leukemia process. Our previous work reported a new chromosomal t(7;9)(q11;p13) translocation in human B-ALL that juxtaposes PAX5 and the sequence of elastin ELN. The resulting protein showed a dominant negative effect on the wild type PAX5 protein in patients cells.
Aims
Despite the well-known role of PAX5 as haploinsufficient tumour suppressor gene in human B-ALL, the function of PAX5 fusion proteins in B-ALL initiation and transformation is less defined. The aim of this work is to study the impact of PAX5-ELN fusion protein in murine B cell development, decipher its molecular role and determine if the PAX5-ELN expression is a princeps event in the B-ALL process.
Methods
We have generated a transgenic mouse model in which PAX5-ELN is expressed from the IgH locus to ensure its early and restricted expression in B cell compartment.
Results
PAX5-ELN transgenic mice efficiently developed B-ALL with an incidence of 80%. Leukemic transformation systematically occurs with a minimal latency of 3 months suggesting requirement of additional oncogenic events. Indeed, exome sequencing revealed that mouse B-ALL induced by PAX5-ELN is associated with recurrent secondary mutations on PTPN11, KRAS, PAX5 and JAK3 genes affecting key signalling pathways required for cell proliferation. At the pre-leukemic stage, PAX5-ELN induces a partial blockade of B-cell differentiation in vivo characterized by an aberrant expansion of the pro-B cell compartment in steady state and in transplantation assay. At the molecular level, we showed that PAX5-ELN downregulates endogenous Pax5 expression and its canonical target genes in pro-B cells, consistent with a dominant-negative effect. At the functional level, PAX5-ELN is not able to restore B-cell differentiation of Pax5-deficient pro-B cells in an ex vivo complementation assay. Together, our functional studies demonstrate that PAX5-ELN perturbs PAX5 activity in pro-B cells to affect B-cell development before malignant transformation.
Conclusion
Our work strongly supports the role of PAX5-ELN as a potent oncoprotein in leukemia development and provides a valuable in vivo model recapitulating the multistep leukemogenesis process of human B-ALL.
Session topic: 1. Acute lymphoblastic leukemia – Biology & Translational Research
Keyword(s): PAX5, Translocation, Acute lymphoblastic leukemia, Mouse model
Abstract: S824
Type: Oral Presentation
Presentation during EHA23: On Saturday, June 16, 2018 from 11:45 - 12:00
Location: Room A6
Background
PAX5, a gene encoding a key transcription factor in B cell differentiation, is altered in one third of B-cell acute lymphoblastic leukemia (B-ALL). Its structural alterations (point mutations and translocations) are considered as primary oncogenic events of B-ALL while its deletion can be considered as an additional hit in leukemia process. Our previous work reported a new chromosomal t(7;9)(q11;p13) translocation in human B-ALL that juxtaposes PAX5 and the sequence of elastin ELN. The resulting protein showed a dominant negative effect on the wild type PAX5 protein in patients cells.
Aims
Despite the well-known role of PAX5 as haploinsufficient tumour suppressor gene in human B-ALL, the function of PAX5 fusion proteins in B-ALL initiation and transformation is less defined. The aim of this work is to study the impact of PAX5-ELN fusion protein in murine B cell development, decipher its molecular role and determine if the PAX5-ELN expression is a princeps event in the B-ALL process.
Methods
We have generated a transgenic mouse model in which PAX5-ELN is expressed from the IgH locus to ensure its early and restricted expression in B cell compartment.
Results
PAX5-ELN transgenic mice efficiently developed B-ALL with an incidence of 80%. Leukemic transformation systematically occurs with a minimal latency of 3 months suggesting requirement of additional oncogenic events. Indeed, exome sequencing revealed that mouse B-ALL induced by PAX5-ELN is associated with recurrent secondary mutations on PTPN11, KRAS, PAX5 and JAK3 genes affecting key signalling pathways required for cell proliferation. At the pre-leukemic stage, PAX5-ELN induces a partial blockade of B-cell differentiation in vivo characterized by an aberrant expansion of the pro-B cell compartment in steady state and in transplantation assay. At the molecular level, we showed that PAX5-ELN downregulates endogenous Pax5 expression and its canonical target genes in pro-B cells, consistent with a dominant-negative effect. At the functional level, PAX5-ELN is not able to restore B-cell differentiation of Pax5-deficient pro-B cells in an ex vivo complementation assay. Together, our functional studies demonstrate that PAX5-ELN perturbs PAX5 activity in pro-B cells to affect B-cell development before malignant transformation.
Conclusion
Our work strongly supports the role of PAX5-ELN as a potent oncoprotein in leukemia development and provides a valuable in vivo model recapitulating the multistep leukemogenesis process of human B-ALL.
Session topic: 1. Acute lymphoblastic leukemia – Biology & Translational Research
Keyword(s): PAX5, Translocation, Acute lymphoblastic leukemia, Mouse model