Astrocytes, a major glial cell type in the brain, play a critical role in supporting the progression of medulloblastoma (MB), the most common malignant pediatric brain tumor. Through lineage tracing analyses and single-cell RNA sequencing, we demonstrate that astrocytes are predominantly derived from the transdifferentiation of tumor cells in relapsed MB (but not in primary MB), although MB cells are generally believed to be neuronal-lineage committed. Such transdifferentiation of MB cells relies on Sox9, a transcription factor critical for gliogenesis. Our studies further reveal that bone morphogenetic proteins (BMPs) stimulate the transdifferentiation of MB cells by inducing the phosphorylation of Sox9. Pharmacological inhibition of BMP signaling represses MB cell transdifferentiation into astrocytes and suppresses tumor relapse. Our studies establish the distinct cellular sources of astrocytes in primary and relapsed MB and provide an avenue to prevent and treat MB relapse by targeting tumor cell transdifferentiation.

Background: Medulloblastoma (MB) is the most common malignant brain tumor in children. Approximately one-third of MB patients remain incurable. Understanding the molecular mechanism of MB tumorigenesis is, therefore, critical for developing specific and effective treatment strategies. Our previous work demonstrated that astrocytes constitute the tumor microenvironment (TME) of MB and play an indispensable role in MB progression. However, the underlying mechanisms by which astrocytes are regulated and activated to promote MB remain elusive.Methods: By taking advantage ofMath1-Cre/Ptch1^loxp/loxpmice, which spontaneously develop MB, primary MB cells and astrocytes were isolated and then subjected to administration and coculture in vitro. Immunohistochemistry was utilized to determine the presence of C3a in MB sections. MB cell proliferation was evaluated by immunofluorescent staining. GFAP and cytokine expression levels in C3a-stimulated astrocytes were assessed by immunofluorescent staining, western blotting, q-PCR and ELISA. C3a receptor and TNF-α receptor expression was determined by PCR and immunofluorescent staining. p38 MAPK pathway activation was detected by western blotting. Transplanted MB mice were treated with a C3a receptor antagonist or TNF-α receptor antagonist to investigate their role in MB progression in vivo.Results: We found that complement C3a, a fragment released from intact complement C3 following complement activation, was enriched in both human and murine MB tumor tissue, and its receptor was highly expressed on tumor-associated astrocytes (TAAs). We demonstrated that C3a activated astrocytes and promoted MB cell proliferation via the p38 MAPK pathway. Moreover, we discovered that C3a upregulated the production of proinflammatory cytokines, such as IL-6 and TNF-α in astrocytes. Application of the conditioned medium of C3a-stimulated astrocytes promoted MB cell proliferation, which was abolished by preincubation with a TNF-α receptor antagonist, indicating a TNF-α-dependent event. Indeed, we further demonstrated that administration of a selective C3a receptor or TNF-α receptor antagonist to mice subcutaneously transplanted with MB suppressed tumor progression in vivo.Conclusions: C3a was released during MB development. C3a triggered astrocyte activation and TNF-α production via the p38 pathway, which promoted MB cell proliferation. Our findings revealed the novel role of C3a-mediated TNF-α production by astrocytes in MB progression. These findings imply that targeting C3a and TNF-α may represent a potential novel therapeutic approach for human MB.

Nestin, a class IV intermediate filament protein, is generally considered as a putative marker of neural stem and progenitor cells in the central nervous system. Glioma is a common type of adult brain tumors, and glioblastoma (GBM) represents the most aggressive form of glioma. Here, we report that Nestin expression is significantly upregulated in human GBM, compared with other types of glioma. Nestin knockdown or deletion in U251 cells and tumor cells from GBM patients derived xenografts resulted in G2–M arrest, finally leading to apoptosis in tumor cells. Using proximity-dependent biotin identification method, we identified βII-tubulin as an interacting protein of Nestin in U251 cells. Nestin stabilized βII-tubulin in U251 cells through physical interaction. Knockdown of Nestin or βII-tubulin disrupted spindle morphology in tumor cells. Our studies further revealed that Nestin deficiency in U251 cells and GBM PDX cells repressed tumor growth upon transplantation. Finally, we found that Nestin deficiency sensitized GBM cells to microtubule-destabilizing drugs such as vinblastine and vincristine. Our studies demonstrate the essential functions and underlying mechanisms of Nestin in the growth and drug response of GBM cells.Implications: Through interaction with βII-tubulin, Nestin facilitates cell-cycle progression and spindle assembly of tumor cells in glioblastoma.

Background: Patients with brain tumors, especially pediatric brain tumors such as cerebellar medulloblastoma, always suffer from the severe side effects of radiotherapy. Regeneration of neural cells in irradiation‐induced cerebellar injury has been reported, but the underlying mechanism remains elusive.Methods: We established an irradiation‐induced developing cerebellum injury model in neonatal mice. Microarray, KEGG analysis and semi in vivo slice culture were performed for mechanistic study.Results: Nestin‐expressing progenitors (NEPs) but not granule neuron precursors (GNPs) were resistant to irradiation and able to regenerate after irradiation. NEPs underwent less apoptosis but similar DNA damage following irradiation compared with GNPs. Subsequently, they started to proliferate and contributed to granule neurons regeneration dependent on the sonic hedgehog (Shh) pathway. In addition, irradiation increased Shh ligand provided by Purkinje cells. And microglia accumulated in the irradiated cerebellum producing more IFN‐γ, which augmented Shh ligand production to promote NEP proliferation.Conclusions: NEP was radioresistant and regenerative. IFN‐γ was increased post irradiation to upregulate Shh ligand, contributing to NEP regeneration. Our study provides insight into the mechanisms of neural cell regeneration in irradiation injury of the developing cerebellum and will help to develop new therapeutic targets for minimizing the side effects of radiotherapy for brain tumors.

Background: To detect the mutations of KRAS gene in colorectal cancer patients and other cancer patients, it is of value to develop non‐invasive, sensitive, specific, easy, and low‐cost assays. Methods: Templates harboring hotspot mutations of the KRAS gene were constructed, and primers were designed for evaluation of the specificity, and sensitivity of detection system consisted of exonuclease polymerase‐mediated on/off switch; then, gel electrophoresis and real‐time PCR were performed for verification. The assay was verified by testing the DNA pool of normal controls and circulating DNA (ctDNA) samples from 14 tumor patients, as compared to Sanger sequencing. Results: A specific and sensitive assay consisted of exonuclease polymerase‐mediated on/off switch, and multiplex real‐time PCR method has been established. This assay could detect <100 copies of KRAS mutation in more than 10 million copies of wild‐type KRAS gene fragments. This assay was applied to test KRAS gene mutations in three cases of fourteen ctDNA samples, and the results were consistent with Sanger sequencing. However, this PCR‐based assay was more sensitive and easier to be interpreted. Conclusion: This assay can detect the presence of KRAS hotspot mutations in clinical circulating tumor DNA samples. The assay has a potential to be used in early diagnosis of colorectal cancer as well as other types of cancer.

Lung cancer represents the leading cause of cancer-related mortality worldwide, with up to 50% of cases developing brain metastasis during disease progression. Current therapeutic options for brain metastasis remain limited, resulting in poor clinical outcomes. Previous studies have demonstrated that tumor cell invasion into the brain involves localized activation of astrocytes, with these tumor-associated astrocytes (TAAs) exhibiting either pro-tumor or anti-tumor effects. However, the role of astrocytes during postcolonization stages remains unclear. In this study, employing both a murine model of lung cancer brain metastasis and an in vitro coculture system, we identified the presence of astrocytes within the tumor microenvironment of both clinical specimens and experimental models. Our in vitro experiments revealed that astrocytes significantly enhanced tumor cell survival without affecting proliferation, primarily through inhibition of apoptosis. Mechanistic investigations demonstrated that astrocyte-derived TNF-α mediates this anti-apoptotic effect via activation of the NF-κB signaling pathway in tumor cells. Genetic knockdown of TNF receptor 2 (TNFR2) in tumor cells or pharmacological inhibition of the NF-κB pathway effectively abolished this protective effect. Importantly, TNFR2 knockdown increased intracranial tumor cell apoptosis and prolonged survival in the brain metastasis mouse model. These findings collectively demonstrate that TAAs in lung cancer brain metastasis promote tumor cell survival through a TNFR2–NF-κB-dependent mechanism mediated by TNF-α secretion.