Necroptotic astrocytes contribute to maintaining stemness of disseminated medulloblastoma through CCL2 secretion.

BACKGROUND: Medulloblastoma (MB) with metastases at diagnosis and recurrence correlates with poor prognosis. Unfortunately, the molecular mechanism underlying metastases growth has received less attention than primary therapy-naïve MB. Though astrocytes have been frequently detected in brain tumors, their roles in regulating the stemness properties of MB stem-like cells (MBSCs) in disseminated lesions remain elusive. METHODS: Effects of tumor-associated astrocyte (TAA)-secreted chemokine C-C ligand 2 (CCL2) on MBSC self-renewal was determined by immunostaining analysis. Necroptosis of TAA was examined by measuring necrosome activity. Alterations in Notch signaling were examined after inhibition of CCL2. Progression of MBSC-derived tumors was evaluated after pharmaceutical blockage of necroptosis. RESULTS: TAA, as the essential components of disseminated tumor, produced high levels of CCL2 to shape the inflammation microenvironment, which stimulated the enrichment of MBSCs in disseminated MB. In particular, CCL2 played a pivotal role in maintaining stem-like properties via Janus kinase 2/signal transducer and activator of transcription 3 (JAK2/STAT3)-mediated activation of Notch signaling. Loss of CCL2/C-C chemokine receptor 2 (CCR2) function repressed the JAK2/STAT3-Notch pathway and impaired MBSC proliferation, leading to a dramatic reduction of stemness, tumorigenicity, and metastasizing capability. Furthermore, necroptosis-induced CCL2 release depended on activation of receptor-interacting protein 1 (RIP1)/RIP3/mixed lineage kinase domain-like pseudokinase (MLKL) in TAA, which promoted the oncogenic phenotype. Blockade of necroptosis resulted in CCL2 deprivation and compromised MBSC self-proliferation, indicating MBSCs outsourced CCL2 from necroptotic TAA. Finally, CCL2 was upregulated in high-risk stages of MB, further supporting its value as a prognostic indicator. CONCLUSION: These findings highlighted the critical role of CCL2/CCR2 in Notch signaling activation in MBSCs and revealed a necroptosis-associated glial cytokine microenvironment driving stemness maintenance in disseminations.Key Points1. TAA-derived CCL2 promoted stemness in disseminated MBSCs through Notch signaling activation via the JAK2/STAT3 pathway.2. TAA released CCL2 in a RIP1/RIP3/MLKL-dependent manner leading to necroptosis.

EZH2 Phosphorylation Promotes Self-Renewal of Glioma Stem-Like Cells Through NF-κB Methylation.

Cancer stem-like cells (CSCs) is a cell population in glioma with capacity of self-renewal and is critical in glioma tumorigenesis. Parallels between CSCs and normal stem cells suggest that CSCs give rise to tumors. Oncogenic roles of maternal embryonic leucine-zipper kinase (MELK) and enhancer of zeste homolog 2 (EZH2) have been reported to play a crucial role in glioma tumorigenesis. Herein, we focus on mechanistic contributions of downstream molecules to maintaining stemness of glioma stem-like cells (GSCs). Transcriptional factor, NF-κB, co-locates with MELK/EZH2 complex. Clinically, we observe that the proportion of MELK/EZH2/NF-κB complex is elevated in high-grade gliomas, which is associated with poor prognosis in patients and correlates negatively with survival. We describe the interaction between these three proteins. Specifically, MELK induces EZH2 phosphorylation, which subsequently binds to and methylates NF-κB, leading to tumor proliferation and persistence of stemness. Furthermore, the interaction between MELK/EZH2 complex and NF-κB preferentially occurs in GSCs compared with non-stem-like tumor cells. Conversely, loss of this signaling dramatically suppresses the self-renewal capability of GSCs. In conclusion, our findings suggest that the GSCs depend on EZH2 phosphorylation to maintain the immature status and promote self-proliferation through NF-κB methylation, and represent a novel therapeutic target in this difficult to treat malignancy.

Astrocytes Promote Medulloblastoma Progression through Hedgehog Secretion.

Astrocytes, the most abundant type of glial cells in the brain, play critical roles in supporting neuronal development and brain function. Although astrocytes have been frequently detected in brain tumors, including medulloblastoma (MB), their functions in tumorigenesis are not clear. Here, we demonstrate that astrocytes are essential components of the MB tumor microenvironment. Tumor-associated astrocytes (TAA) secrete the ligand sonic hedgehog (Shh), which is required for maintaining MB cell proliferation despite the absence of its primary receptor Patched-1 (Ptch1). Shh drives expression of Nestin in MB cells through a smoothened-dependent, but Gli1-independent mechanism. Ablation of TAA dramatically suppresses Nestin expression and blocks tumor growth. These findings demonstrate an indispensable role for astrocytes in MB tumorigenesis and reveal a novel Ptch1-independent Shh pathway involved in MB progression. Cancer Res; 77(23); 6692-703. ©2017 AACR.

Novel tools for genetic manipulation of follicle stem cells in the Drosophila ovary reveal an integrin-dependent transition from quiescence to proliferation.

In many tissues, the presence of stem cells is inferred by the capacity of the tissue to maintain homeostasis and undergo repair after injury. Isolation of self-renewing cells with the ability to generate the full array of cells within a given tissue strongly supports this idea, but the identification and genetic manipulation of individual stem cells within their niche remain a challenge. Here we present novel methods for marking and genetically altering epithelial follicle stem cells (FSCs) within the Drosophila ovary. Using these new tools, we define a sequential multistep process that comprises transitioning of FSCs from quiescence to proliferation. We further demonstrate that integrins are cell-autonomously required within FSCs to provide directional signals that are necessary at each step of this process. These methods may be used to define precise roles for specific genes in the sequential events that occur during FSC division after a period of quiescence.

Outcomes of patients who undergo aggressive induction therapy for secondary acute myeloid leukemia.

BACKGROUND: Response and survival in 96 patients with secondary acute myeloid leukemia (sAML) who received aggressive induction chemotherapy was reviewed. METHODS: The median follow-up of survivors was 2.3 years. A total of 70 (73%) patients achieved a morphologic complete remission (CR) confirmed by absence of leukemic blasts by flow cytometry. RESULTS: For all 96 patients, the median event-free survival (EFS) was 8 months, and overall survival (OS) was 13.6 months (range, 1-119 months). Eight patients died shortly after induction therapy because of disease or side effects, and 13 are currently in continuous first remission. The median disease-free survival (DFS) for all 70 patients who achieved a morphologic CR was 9 months (range, 1-51 months), with a 64% chance of surviving 1 year. Patients with AML after previous chemotherapy or radiation therapy had a higher morphologic remission rate compared with those arising from myelodysplastic syndrome or myeloproliferative disease (82% vs 62%; P = .027). However, among the patients from the 2 groups who attained a morphologic remission, there was no difference in terms of CR rate (P = .94), DFS, EFS, or OS (P = .55, .83, and .71, respectively). This is a similar DFS to the group of 7 patients who went directly to ablative allogeneic transplant rather than having induction therapy first. In this population of patients who received aggressive chemotherapy, Charlson comorbidity index or a higher number of factors recognized as high risk in leukemia patients did not affect the chance of OS, DFS, and EFS, although having more recognized leukemia risk factors was related to a lower chance of surviving 1 year. However, it is important to note that those with higher comorbidity indexes were underrepresented in this aggressively treated cohort. CONCLUSIONS: The data from the current study demonstrate that many patients with sAML can tolerate aggressive induction therapy and attain remission, but duration of response and the chance of long-term survival remain poor.