Distinct and Targetable Role of Calcium-Sensing Receptor in Leukaemia

Haematopoietic stem cells (HSC) reside in the bone marrow microenvironment (BMM), where they respond to extracellular calcium [eCa 2+ ] via the G-protein coupled calcium-sensing receptor (CaSR). Here we show that a calcium gradient exists in this BMM, and that [eCa 2+ ] and response to [eCa 2+ ] differ between leukaemias. CaSR influences the location of MLL-AF9 + acute myeloid leukaemia (AML) cells within this niche and differentially impacts MLL-AF9 + AML versus BCR-ABL1 + leukaemias. Deficiency of CaSR reduces AML leukaemic stem cells (LSC) 6.5-fold. CaSR interacts with filamin A, a crosslinker of actin filaments, affects stemness-associated factors and modulates pERK, β -catenin and c-MYC signaling and intracellular levels of [Ca 2+ ] in MLL-AF9 + AML cells. Combination treatment of cytarabine plus CaSR-inhibition in various models may be superior to cytarabine alone. Our studies suggest CaSR to be a differential and targetable factor in leukaemia progression influencing self-renewal of AML LSC via [eCa 2+ ] cues from the BMM.