Calcium/calmodulin-dependent kinase kinase 2 regulates hematopoietic stem and progenitor cell regeneration

Abstract

Hematopoietic stem and progenitor cells (HSPCs) are predominantly quiescent in adults, but proliferate in response to bone marrow (BM) injury. Here, we show that deletion of Ca2+/calmodulin (CaM)-dependent protein kinase kinase 2 (CaMKK2) promotes HSPC regeneration and hematopoietic recovery following radiation injury. Using Camkk2-enhanced green fluorescent protein (EGFP) reporter mice, we found that Camkk2 expression is developmentally regulated in HSPC. Deletion of Camkk2 in HSPC results in a significant downregulation of genes affiliated with the quiescent signature. Accordingly, HSPC from Camkk2 null mice have a high proliferative capability when stimulated in vitro in the presence of BM-derived endothelial cells. In addition, Camkk2 null mice are more resistant to radiation injury and show accelerated hematopoietic recovery, enhanced HSPC regeneration and ultimately a prolonged survival following sublethal or lethal total body irradiation. Mechanistically, we propose that CaMKK2 regulates the HSPC response to hematopoietic damage by coupling radiation signaling to activation of the anti-proliferative AMP-activated protein kinase. Finally, we demonstrated that systemic administration of the small molecule CaMKK2 inhibitor, STO-609, to irradiated mice enhanced HSPC recovery and improved survival. These findings identify CaMKK2 as an important regulator of HSPC regeneration and demonstrate CaMKK2 inhibition is a novel approach to promoting hematopoietic recovery after BM injury.

Calcium/Calmodulin Dependent Protein Kinase Kinase 2 Regulates the Expansion of Tumor-Induced Myeloid-Derived Suppressor Cells

“…Immunoblots were prepared as published ( 24 ). The following primary antibodies were used in this study: purified mouse anti-CaM kinase kinase (BD Biosciences, CA, USA), anti-phospho-AMPK alpha (T172 40H9) rabbit mAb, anti-AMPK alpha (F6) mouse mAb, anti-phopho-Stat3 (Tyr705 D3A7) rabbit mAb, anti-Stat3 (124H6) mouse mAb, anti-β actin mouse mAb (all from Cell Signaling, CA, USA).…”

“…Outside the brain, CaMKK2 is expressed at detectable levels restricted to a small subset of cell types, including hematopoietic stem and progenitor cells (HSCP) and mature myeloid cell subsets such as circulating monocytes and macrophages ( 22 ). CaMKK2 also regulates granulopoiesis and recently we have demonstrated that this kinase controls HSCP regeneration following bone marrow injury ( 23 , 24 ). Interestingly, CaMKK2 impinges the activation program of macrophages, and consequently, genetic ablation of Camkk2 attenuates the detrimental inflammatory response induced by bacterial endotoxin or obesity ( 25 ).…”

CaMKK2 in myeloid cells is a key regulator of the immune-suppressive microenvironment in breast cancer

“…To date, most studies of CaMKK2 in cancer have focused on its cancer cell intrinsic activities. However, this enzyme is also expressed within hematopoietic stem and progenitor cells, and in more mature myeloid cells, including monocytes and peritoneal macrophages 11,21–23 . Furthermore, genetic ablation of Camkk2 in mice revealed an important role for this enzyme in the development of myeloid cells and in regulating their ability to mount inflammatory responses to various stimuli 22,24 .…”

Differential activation of Ca2+ influx channels modulate stem cell potency, their proliferation/viability and tissue regeneration

“…The C-terminal region of STIM1 gates Orai/TRPC channels and stimulates Ca 2+ entry that could be important for cell fate decisions that are required during stem cells development and function. Ca 2+ entry through SOCC is critical for the activation of calmodulin-dependent protein kinase II (CAMK-II), and CAMK-II is shown to regulate the regeneration of hematopoietic stem and progenitor cells 22 . Similarly, Ca 2+ entry is also critical for switching from quiescence to cell cycle activation and Ca 2+ -dependent pathways are shown to modulate stem cell divisions 23 .…”