The NFKB inducing kinase (NIK) modulates hematopoiesis during stress
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ABSTRACT: The genetic programs that maintain hematopoiesis during steady state in physiologic conditions are different from those activated during stress. Here we show that hematopoietic stem cells (HSCs) with deficiencies in components of the alternative NFkB pathway (the NFkB inducing kinase, NIK, and the downstream molecule NFkB2) had a defect in response to stressors such as supraphysiological doses of cytokines, chemotherapy and hematopoietic transplantation. NIK-deficient mice had peripheral blood and bone marrow leukocyte numbers within normal ranges (except for the already reported defects in B-cell maturation), however, HSCs showed significantly slower expansion capacity in in vitro cultures compared to wild type HSCs. This was due to a delayed cell cycle and increased apoptosis. In vivo experiments showed that NIK-deficient HSCs did not recover at the same pace as controls when challenged with myeloablative chemotherapy. Finally, NIK-deficient HSCs showed a significantly decreased competitive repopulation capacity in vivo. Using HSCs from mice deficient in one of two downstream targets of NIK, i.e., either NFkB2 or c-Rel, only NFkB2 deficiency recapitulated the defects detected with NIK-deficient HSCs. Our results underscore the role of NIK and the alternative NFkB pathway for the recovery of normal levels of hematopoiesis after stress.
Project description:In response to myeloablative stresses, HSCs are rapidly activated to replenish myeloid progenitors, while maintaining full potential of self-renewal to ensure life-long hematopoiesis. However, the key factors that orchestrate HSC activities during physiological stresses remain largely unknown. Here we report that Med23 controls the myeloid potential of activated HSCs. Ablation of Med23 in hematopoietic system leads to lymphocytopenia. Med23- deficient HSCs undergo myeloid-biased differentiation and lose the self-renewal capacity. Interestingly, Med23-deficient HSCs are much easier to be activated in response to physio- logical stresses. Mechanistically, Med23 plays essential roles in maintaining stemness genes expression and suppressing myeloid lineage genes expression. Med23 is downregulated in HSCs and Med23 deletion results in better survival under myeloablative stress. Altogether, our findings identify Med23 as a gatekeeper of myeloid potential of HSCs, thus providing unique insights into the relationship among Med23-mediated transcriptional regulations, the myeloid potential of HSCs and HSC activation upon stresses.
Project description:Mutations involving the NFKB pathway are present in at least 17% of multiple myeloma (MM) tumors and 40% of MM cell lines (MMCL). These mutations, which are thought to be progression events, enable MM tumors to become less dependent on extrinsic bone marrow signals that activate NFKB. Studies on a panel of 50 MMCL provide some clarification of the mechanisms through which these mutations act and the significance of classical vs alternative activation of NFKB. First, only one mutation (NFKB2) selectively activates the alternative pathway, whereas several mutations (CYLD, NFKB1, TACI) selectively activate the classical pathway. However, most mutations affecting NIK level (NIK, TRAF2, TRAF3, cIAP1&2, CD40) activate the alternative but often both pathways. Second, we confirm the critical role of TRAF2 in regulating NIK degradation, whereas TRAF3 enhances but is not essential for cIAP1/2-mediated proteosomal degradation of NIK in MM. Third, using transfection to selectively activate the classical or alternative NFKB pathways, we show virtually identical changes in gene expression in one MMCL, whereas the changes are similar albeit non-identical in a second MMCL. Together, our results suggest that MM tumors can achieve increased autonomy from the bone marrow microenvironment by mutations that activate either NFKB pathway.
Project description:The transcription factor Meis1 is preferentially expressed in hematopoietic stem cells (HSCs) and over-expressed in certain leukemias. However, the functions of Meis1 in hematopoiesis remain largely unknown. Using inducible knock-out mice, we found that Meis1 is required for the maintenance of hematopoiesis under stress and over long term while steady-state hematopoiesis was sustained in the absence of Meis1. Bone marrow cells of Meis1 deficient mice showed reduced colony formation, contained significantly fewer numbers of long- term HSCs and these Meis1-deficient HSCs exhibited loss of quiescence. Further, we found that Meis1 deletion led to the accumulation of reactive oxygen species (ROS) in HSCs and decreased expression of genes implicated in hypoxia response. Finally, ROS scavenging by N-acetyl cysteine or stabilization of hypoxia-signaling by knockdown of the VHL protein led to reversal of the effects of Meis1-deletion. Taken together, these results demonstrate that Meis1 protects and preserves HSCs by restricting oxidative metabolism. Lineage negative cells were harvested from Meis1-flox/CreER or control mice and incubated with 4-OHT for 48 hours. Total RNA was extracted and used for the profiling experiment.
Project description:We demonstrated that the microenvironment-dependent secretion of IL32β was controlled by the CD40L/NFKB2 axis whereas its tumor specificity was the consequence of IL32 promoter hypomethylation in MCL. Through the secretion of IL32β, the tumor was able to corrupt its microenvironment through the polarization of monocytes into specific MCL-associated macrophages, which in turn favor tumor survival. We next highlighted that while IL32β-stimulated macrophages secreted several protumoral factors, they supported tumor survival through a soluble dialog, mostly driven by BAFF. Finally, we demonstrated the efficacy of selective NIK/alternative-NFkB inhibition to counteract both microenvironment-dependent induction of IL32β and BAFF-dependent survival of MCL cells.
Project description:We demonstrated that the microenvironment-dependent secretion of IL32β was controlled by the CD40L/NFKB2 axis whereas its tumor specificity was the consequence of IL32 promoter hypomethylation in MCL. Through the secretion of IL32β, the tumor was able to corrupt its microenvironment through the polarization of monocytes into specific MCL-associated macrophages, which in turn favor tumor survival. We next highlighted that while IL32β-stimulated macrophages secreted several protumoral factors, they supported tumor survival through a soluble dialog, mostly driven by BAFF. Finally, we demonstrated the efficacy of selective NIK/alternative-NFkB inhibition to counteract both microenvironment-dependent induction of IL32β and BAFF-dependent survival of MCL cells.
Project description:To investigate the effects of NFKB signaling, RNA-seq analysis was performed on both Jurkat and MT-2 cells. It was observed that either NFKB1 or NFKB2 knockout could alter the gene expression profile in MT-2 cells compared to Jurkat cells. Gene expression profiles of NFKB1/NFKB2 knockout Jurkat cells were compared to the mock edited Jurkat cells. On the other hand, it was hypothesized that the gene expression profile of MT-2 cells can be more drastically altered by NFKB1 or NFKB2 knockout. NFKB2 knockout MT-2 cells exhibited a unique gene expression profile compared to those of NFKB1 knockout MT-2 cells and mock edited MT-2 cells.
Project description:NF-κB-Inducing Kinase (NIK), which is essential for the activation of the noncanonical NF-κB pathway, regulates diverse processes in immunity, development, and disease. While recent studies have elucidated important functions of NIK in adaptive immune cells and cancer cell metabolism, the role of NIK in metabolic-driven inflammatory responses in innate immune cells remains unclear. Here we demonstrate that NIK-deficient bone marrow-derived macrophages exhibit defects in mitochondrial-dependent metabolism and oxidative phosphorylation (OXPHOS) functions that impair acquisition of a pro-repair, anti-inflammatory phenotype. Subsequently, NIK-deficient mice exhibit skewing of myeloid cells characterized by aberrant eosinophil, monocyte, and macrophage cell populations in the blood, bone marrow, and adipose tissue. Furthermore, NIK-deficient blood monocytes display hyperresponsiveness to bacterial lipopolysaccharide and elevated TNFα production ex vivo, indicative of systemic inflammation. These findings suggest that NIK is required for the metabolic rewiring of mitochondrial respiration that is critical for balancing pro- and anti-inflammatory myeloid immune cell functions. Overall, our work highlights a previously unrecognized role for NIK as a molecular rheostat that fine-tunes immunometabolism in innate immunity and suggests that metabolic dysfunction may be an important driver of inflammatory diseases caused by aberrant NIK expression or activity.
Project description:The transcription factor Meis1 is preferentially expressed in hematopoietic stem cells (HSCs) and over-expressed in certain leukemias. However, the functions of Meis1 in hematopoiesis remain largely unknown. Using inducible knock-out mice, we found that Meis1 is required for the maintenance of hematopoiesis under stress and over long term while steady-state hematopoiesis was sustained in the absence of Meis1. Bone marrow cells of Meis1 deficient mice showed reduced colony formation, contained significantly fewer numbers of long- term HSCs and these Meis1-deficient HSCs exhibited loss of quiescence. Further, we found that Meis1 deletion led to the accumulation of reactive oxygen species (ROS) in HSCs and decreased expression of genes implicated in hypoxia response. Finally, ROS scavenging by N-acetyl cysteine or stabilization of hypoxia-signaling by knockdown of the VHL protein led to reversal of the effects of Meis1-deletion. Taken together, these results demonstrate that Meis1 protects and preserves HSCs by restricting oxidative metabolism.
Project description:The transcription factor hepatic leukemia factor (HLF) is highly expressed in hematopoietic stem cells (HSCs) and has been proposed to influence both HSC self-renewal and leukemogenesis. However, the physiological role of HLF in hematopoiesis and HSC function has remained unknown. Here we report that mice lacking Hlf are viable with essentially normal hematopoietic parameters. By contrast, when challenged through transplantation, Hlf deficient HSCs demonstrate an impaired ability to reconstitute hematopoiesis and gradually exhaust upon serial transplantation. Transcriptional profiling displayed changes associated with cellular activation in Hlf deficient HSCs, and cell cycle analysis showed a significant reduction of dormant HSCs. Accordingly, Hlf deficient mice were hypersensitive to toxic insults targeting dividing cells that completely eradicated the HSC pool. In summary, our findings unravel a novel role for HLF as a critical regulator of HSC quiescence and as an essential factor to maintain the HSC pool during regeneration.