Zhuo Yu

The metabolic microenvironment plays important roles in tumorigenesis, but how leukemia-initiating cells (LICs) response to the acidic BM niche remains largely unknown. Here, we show that acid-sensing ion channel 3 (ASIC3) dramatically delays leukemogenesis. Asic3 deletion results in a remarkably enhanced self-renewal, reduced differentiation, and 9-fold greater number of murine acute myeloid LICs. We developed an ultrasensitive, ratiometric, genetically encoded fluorescent pH sensor (pHluorin3) and demonstrated that LICs prefer localizing in the endosteal niche with a neutral pH range of 7.34–7.42, but not in the vascular niche with a lower pH range of 6.89–7.22. Unexpectedly, acid-ASIC3 signaling inhibits both murine and human LIC activities in a noncanonical manner by interacting with the N-terminal of STIM1 to reduce calcium-mediated CAMK1-CREB-MEIS1-LDHA levels, without inducing cation currents. This study reveals a pathway in suppression of leukemogenesis in the acidic BM niche and provides insight into targeting LICs or other cancer stem cells through pH-dependent ASICs.

Purpose Although 60–70% of diffuse large B-cell lymphoma (DLBCL) patients can be cured with the current standard of chemotherapy and immunotherapy, the remaining patients experience treatment resistance and have poor clinical outcomes. More effective strategies are needed for the DLBCL treatment. Methods Databases of clinical patients were analyzed to investigate potential functions of leukocyte immunoglobulin-like receptor B1 (LILRB1) in DLBCL. Short hairpin RNAs were used for validation of in vitro and in vivo function of LILRB1 in DLBCL. RNA-seq was applied to explore potential mechanism, western blot and chromatin immunoprecipitation techniques were used to characterize the underlying signaling of CREB-SORBS3 pathway. Results We found that LILRB1 was highly expressed in DLBCL cells and was adversely correlated with the overall survival of DLBCL patients. Knockdown of LILRB1 effectively inhibited the proliferation of DLBCL cells both in vitro and in vivo. Mechanistically, LILRB1 upregulated CREB/CREB phosphorylation and transactivated SORBS3 expression to maintain DLBCL cell proliferation and tumorigenicity. Conclusion In this work, we revealed that LILRB1 was highly expressed in DLBCL cells and was negatively correlated with patient survival. Furthermore, we found that the LILRB1-CREB-SORBS3 pathway played a role in maintaining the proliferation of DLBCL cells. These data suggest that LILRB1 might be a potential target for the treatment of DLBCL.

Although multiple myeloma (MM) responds well to immunotherapeutic treatment, certain portions of MM are still unresponsive or relapse after immunotherapy. Other immune molecules are needed for the immunotherapy of MM. Here, we revealed that leukocyte immunoglobulin-like receptor B4 (LILRB4) was highly expressed in multiple myeloma cell lines and patient samples and that the expression of LILRB4 was adversely correlated with the overall survival of MM patients. Knockdown of LILRB4 efficiently delayed the growth of MM cells both in vitro and in vivo. Mechanistically, IKZF1 transactivated LILRB4 expression to trigger the downstream of STAT3-PFKFB1 pathways to support MM cell proliferation. Blockade of LILRB4 signaling by blocking antibodies can effectively inhibit MM progression. Our data show that targeting LILRB4 is potentially an additional therapeutic strategy for the immunotherapeutic treatment of MM.

Although multiple myeloma (MM) responds well to immunotherapeutic treatment, certain portions of MM are still unresponsive or relapse after immunotherapy. Other immune molecules are needed for the immunotherapy of MM. Here, we revealed that leukocyte immunoglobulin-like receptor B4 (LILRB4) was highly expressed in multiple myeloma cell lines and patient samples and that the expression of LILRB4 was adversely correlated with the overall survival of MM patients. Knockdown of LILRB4 efficiently delayed the growth of MM cells both in vitro and in vivo. Mechanistically, IKZF1 transactivated LILRB4 expression to trigger the downstream of STAT3-PFKFB1 pathways to support MM cell proliferation. Blockade of LILRB4 signaling by functional antibodies can effectively inhibit MM progression. Our data show that targeting LILRB4 is potentially an additional therapeutic strategy for the immunotherapeutic treatment of MM.

Bone marrow niche cells have been reported to fine-tune hematopoietic stem cell (HSC) stemness via direct interaction or secreted components. Nevertheless, how niche cells control HSC activities remains largely unknown. We previously showed that angiopoietin-like protein 2 (ANGPTL2) can support the ex vivo expansion of HSCs by binding to human leukocyte immunoglobulin-like receptor B2. However, how ANGPTL2 from specific niche cell types regulates HSC activities under physiological conditions is still not clear. Herein, we generated an Angptl2-flox/flox transgenic mouse line and conditionally deleted Angptl2 expression in several niche cells, including Cdh5+ or Tie2+ endothelial cells, Prx1+ mesenchymal stem cells, and Pf4+ megakaryocytes, to evaluate its role in the regulation of HSC fate. Interestingly, we demonstrated that only endothelial cell-derived ANGPTL2 and not ANGPTL2 from other niche cell types plays important roles in supporting repopulation capacity, quiescent status, and niche localization. Mechanistically, ANGPTL2 enhances peroxisome-proliferator-activated receptor D (PPARD) expression to transactivate G0s2 to sustain the perinuclear localization of nucleolin to prevent HSCs from entering the cell cycle. These findings reveal that endothelial cell-derived ANGPTL2 serves as a critical niche component to maintain HSC stemness, which may benefit the understanding of stem cell biology in bone marrow niches and the development of a unique strategy for the ex vivo expansion of HSCs.

How particular bone marrow niche factors contribute to the leukemogenic activities of leukemia-initiating cells (LICs) remains largely unknown. Here, we showed that ATP levels were markedly increased in the bone marrow niches of mice with acute myeloid leukemia (AML), and LICs preferentially localized to the endosteal niche with relatively high ATP levels, as indicated by a sensitive ATP indicator. ATP could efficiently induce the influx of ions into LICs in an MLL-AF9–induced murine AML model via the ligand-gated ion channel P2X7. P2x7 deletion led to notably impaired homing and self-renewal capacities of LICs and contributed to an approximately 5-fold decrease in the number of functional LICs but had no effect on normal hematopoiesis. ATP/P2X7 signaling enhanced the calcium flux–mediated phosphorylation of CREB, which further transactivated phosphoglycerate dehydrogenase (Phgdh) expression to maintain serine metabolism and LIC fates. P2X7 knockdown resulted in a markedly extended survival of recipients transplanted with either human AML cell lines or primary leukemia cells. Blockade of ATP/P2X7 signaling could efficiently inhibit leukemogenesis. Here, we provide a perspective for understanding how ATP/P2X7 signaling sustains LIC activities, which may benefit the development of specific strategies for targeting LICs or other types of cancer stem cells.

Small extracellular vesicles (SEVs) are functional messengers of certain cellular niches that permit noncontact cell communications. Whether niche-specific SEVs fulfill this role in cancer is unclear. Here, we used 7 cell type–specific mouse Cre lines to conditionally knock out Vps33b in Cdh5⁺ or Tie2⁺ endothelial cells (ECs), Lepr⁺ BM perivascular cells, Osx⁺ osteoprogenitor cells, Pf4⁺ megakaryocytes, and Tcf21⁺ spleen stromal cells. We then examined the effects of reduced SEV secretion on progression of MLL-AF9–induced acute myeloid leukemia (AML), as well as normal hematopoiesis. Blocking SEV secretion from ECs, but not perivascular cells, megakaryocytes, or spleen stromal cells, markedly delayed the leukemia progression. Notably, reducing SEV production from ECs had no effect on normal hematopoiesis. Protein analysis showed that EC-derived SEVs contained a high level of ANGPTL2, which accelerated leukemia progression via binding to the LILRB2 receptor. Moreover, ANGPTL2-SEVs released from ECs were governed by VPS33B. Importantly, ANGPTL2-SEVs were also required for primary human AML cell maintenance. These findings demonstrate a role of niche-specific SEVs in cancer development and suggest targeting of ANGPTL2-SEVs from ECs as a potential strategy to interfere with certain types of AML.

Leukemia-initiating cells (LICs) are responsible for the initiation, development, and relapse of leukemia. The identification of novel therapeutic LIC targets is critical to curing leukemia. In this report, we reveal that junctional adhesion molecule 3 (JAM3) is highly enriched in both mouse and human LICs. Leukemogenesis is almost completely abrogated upon Jam3 deletion during serial transplantations in an MLL-AF9–induced murine acute myeloid leukemia model. In contrast, Jam3 deletion does not affect the functions of mouse hematopoietic stem cells. Moreover, knockdown of JAM3 leads to a dramatic decrease in the proliferation of both human leukemia cell lines and primary LICs. JAM3 directly associates with LRP5 to activate the downstream PDK1/AKT pathway, followed by the downregulation of GSK3β and activation of β-catenin/CCND1 signaling, to maintain the self-renewal ability and cell cycle entry of LICs. Thus, JAM3 may serve as a functional LIC marker and play an important role in the maintenance of LIC stemness through unexpected LRP5/PDK1/AKT/GSK3β/β-catenin/CCND1 signaling pathways but not via its canonical role in cell junctions and migration. JAM3 may be an ideal therapeutic target for the eradication of LICs without influencing normal hematopoiesis.

CD274 (programmed death ligand 1, also known as B7H1) is expressed in both solid tumors and hematologic malignancies and is of critical importance for the escape of tumor cells from immune surveillance by inhibiting T cell function via its receptor, programmed death 1 (PD-1). Increasing evidence indicates that functional monoclonal antibodies of CD274 may potently enhance the antitumor effect in many cancers. However, the role of CD274 in leukemia-initiating cells (LICs) remains largely unknown. We established an MLL-AF9-induced acute myeloid leukemia (AML) model with wild-type (WT) and CD274-null mice to elucidate the role of CD274 in the cell fates of LICs, including self-renewal, differentiation, cell cycle, and apoptosis. RNA sequencing was performed to reveal the potential downstream targets, the results of which were further validated both in vitro and in vivo. In silico analysis indicated that CD274 level was inversely correlated with the overall survival of AML patients. In Mac-1+/c-Kit+ mouse LICs, CD274 was expressed at a much higher level than in the normal hematopoietic stem cells (HSCs). The survival of the mice with CD274-null leukemia cells was dramatically extended during the serial transplantation compared with that of their WT counterparts. CD274 deletion led to a significant decrease in LIC frequency and arrest in the G1 phase of the cell cycle. Interestingly, CD274 is not required for the maintenance of HSC pool as shown in our previous study. Mechanistically, we demonstrated that the levels of both phospho-JNK and Cyclin D2 were strikingly downregulated in CD274-null LICs. The overexpression of Cyclin D2 fully rescued the loss of function of CD274. Moreover, CD274 was directly associated with JNK and enhanced the downstream signaling to increase the Cyclin D2 level, promoting leukemia development. The surface immune molecule CD274 plays a critical role in the proliferation of LICs. The CD274/JNK/Cyclin D2 pathway promotes the cell cycle entry of LICs, which may serve as a novel therapeutic target for the treatment of leukemia.