Live cell kinetic analysis of the LMO2/LDB1 leukemogenic protein complex reveals a hierarchy of turnover with implications for complex assembly

Abstract

Multisubunit protein complexes operate in many cellular functions. The LDB1/LMO2 macromolecular complex has been posited to be critical in hematopoietic stem and progenitor cell specification and in the development of acute leukemia. This complex is comprised of core subunits of LMO2 and LDB1 as well as bHLH and GATA transcription factors. We analyzed the steady state abundance and kinetic stability of LMO2 and its partners via HALO protein tagging in conjunction with variant proteins deficient in binding their respective direct protein partners. We discovered a hierarchy of protein stability, with half lives in descending order: LDB1>SSBP>LMO2>TAL1. Importantly, LDB1 conferred enhanced stability upon each and every subunit component and nucleated the formation of the multisubunit protein complex. Our studies provide significant insights into LDB1/LMO2 macromolecular protein complex assembly and stability, which has implications for understanding its role in blood cell formation and for therapeutically targeting this complex in human leukemias.