p75(NTR) induces apoptosis in medulloblastoma cells.

The classic medulloblastoma (CMB) and the desmoplastic medulloblastoma (DMB) subtypes represent the major medulloblastoma variants. In contrast to CMB, DMB display high levels of the low-affinity nerve growth factor receptor p75(NTR) . Given the reports of a better clinical course of DMB, we hypothesized that p75(NTR) might act as a tumor suppressor in medulloblastomas. In a large set of medulloblastomas, p75(NTR) was screened for mutations, and its mRNA expression and the DNA methylation status of its 5'-region were assessed. p75(NTR) immunostainings were performed in wild-type murine cerebella and medulloblastomas arising in patched heterozygous mice, and murine cerebellar granule cell precursors (GCP) were analyzed in vitro. Medulloblastoma cells engineered to express p75(NTR) were characterized flow cytometrically and morphologically. One CMB displayed a mutation of the p75(NTR) coding sequence. p75(NTR) mRNA levels clearly delineated DMB and CMB; however, CpG island hypermethylation was excluded as the cause of low p75(NTR) expression in CMB. Sonic Hedgehog-treated GCP showed elevated p75(NTR) expression, and strong expression of p75(NTR) was detected in the external granule cell layer of wild-type mice and in murine ptc(±) medulloblastomas. CMB cells overexpressing p75(NTR) displayed a significant increase in apoptosis. In summary, our data link activated Hedgehog signaling in DMB with p75(NTR) expression and characterize p75(NTR) as a biologically relevant inductor of apoptosis in MB.

Phosphatidylinositol-3'-kinase/AKT signaling is essential in synovial sarcoma.

Synovial sarcomas account for 5-10% of all malignant soft tissue tumors. They have been shown to express different membranous growth factor receptors, many of them signaling via intracellular kinase cascades. In our study, the functional role of PI3K/AKT signals in synovial sarcoma is analyzed with regard to tumor biology and therapeutic applicability. Immunohistochemical stainings of (Ser473)-phosphorylated (p)-AKT, its targets p-(Ser9)-GSK-3ß and p-(Ser2448)-mTOR and the cell cycle regulators Cyclin D1 and p27(KIP1) were performed in 36 synovial sarcomas. The PIK3CA gene was screened for mutations. In vitro, four synovial sarcoma cell lines were treated with the PI3K inhibitor LY294002. Phosphorylation of AKT, GSK-3ß and mTOR was assessed, and cellular proliferation and apoptosis were analyzed to functionally characterize the effects of PI3K inhibition. Finally, coincubations of LY294002 with cytotoxic drugs were performed. Most tumors showed significant expression levels of p-AKT, p-GSK-3ß and p-mTOR, indicating activation of the PI3K/AKT signaling cascade in synovial sarcomas; Cyclin D1 and p27(KIP1) were differentially expressed. Mutations in the PIK3CA gene could be excluded. In vitro, PI3K inhibition diminished synovial sarcoma cell growth accompanied by reduced phosphorylation of AKT, GSK-3ß and mTOR. Mechanistically, PI3K pathway inhibition lead to enhanced apoptosis and decreased cellular proliferation linked to reduced Cyclin D1 and increased p27(KIP1) levels. Simultaneous treatment of synovial sarcoma cell lines with LY294002 and cytotoxic drugs resulted in additive effects. In summary, PI3K signaling plays an essential role in growth control of synovial sarcomas and might be successfully targeted in multimodal therapeutic strategies.

MTSS1 is epigenetically regulated in glioma cells and inhibits glioma cell motility.

Epigenetic silencing by DNA methylation in brain tumors has been reported for many genes, however, their function on pathogenesis needs to be evaluated. We investigated the MTSS1 gene, identified as hypermethylated by differential methylation hybridization (DMH). Fifty-nine glioma tissue samples and seven glioma cell lines were examined for hypermethylation of the MTSS1 promotor, MTSS1 expression levels and gene dosage. GBM cell lines were treated with demethylating agents and interrogated for functional consequences of MTSS1 expression after transient transfection. Hypermethylation was significantly associated with IDH1/2 mutation. Comparative SNP analysis indicates higher incidence of loss of heterozygosity of MTSS1 in anaplastic astrocytomas and secondary glioblastomas as well as hypermethylation of the remaining allele. Reversal of promoter hypermethylation results in an increased MTSS1 expression. Cell motility was significantly inhibited by MTSS1 overexpression without influencing cell growth or apoptosis. Immunofluorescence analysis of MTSS1 in human astrocytes indicates co-localization with actin filaments. MTSS1 is down-regulated by DNA methylation in glioblastoma cell lines and is part of the G-CIMP phenotype in primary glioma tissues. Our data on normal astrocytes suggest a function of MTSS1 at focal contact structures with an impact on migratory capacity but no influence on apoptosis or cellular proliferation.

SRC signaling is crucial in the growth of synovial sarcoma cells.

Synovial sarcoma is a soft-tissue malignancy characterized by a reciprocal t(X;18) translocation encoding a chimeric transcriptional modifier. Several receptor tyrosine kinases have been found activated in synovial sarcoma; however, no convincing therapeutic concept has emerged from these findings. On the basis of the results of phosphokinase screening arrays, we here investigate the functional and therapeutic relevance of the SRC kinase in synovial sarcoma. Immunohistochemistry of phosphorylated SRC and its regulators CSK and PTP1B (PTPN1) was conducted in 30 synovial sarcomas. Functional aspects of SRC, including dependence of SRC activation on the SS18/SSX fusion proteins, were analyzed in vitro. Eventually, synovial sarcoma xenografts were treated with the SRC inhibitor dasatinib in vivo. Activated phospho (p)-(Tyr416)-SRC was detected in the majority of tumors; dysregulation of CSK or PTP1B was excluded as the reason for the activation of the kinase. Expression of the SS18/SSX fusion proteins in T-REx-293 cells was associated with increased p-(Tyr416)-SRC levels, linked with an induction of the insulin-like growth factor pathway. Treatment of synovial sarcoma cells with dasatinib led to apoptosis and inhibition of cellular proliferation, associated with reduced phosphorylation of FAK (PTK2), STAT3, IGF-IR, and AKT. Concurrent exposure of cells to dasatinib and chemotherapeutic agents resulted in additive effects. Cellular migration and invasion were dependent on signals transmitted by SRC involving regulation of the Rho GTPases Rac and RhoA. Treatment of nude mice with SYO-1 xenografts with dasatinib significantly inhibited tumor growth in vivo. In summary, SRC is of crucial biologic importance and represents a promising therapeutic target in synovial sarcoma.

Activation of phosphatidylinositol-3'-kinase/AKT signaling is essential in hepatoblastoma survival.

PURPOSE: Hepatoblastoma represents the most frequent malignant liver tumor in childhood. The phosphatidylinositol-3'-kinase (PI3K)/AKT pathway is crucial in downstream signaling of multiple receptor tyrosine kinases of pathogenic importance in hepatoblastoma. Increased PI3K/AKT signaling pathway activity and activating mutations of PIK3CA, encoding a PI3K catalytic subunit, have been reported in different childhood tumors. The current study was done to analyze the role of PI3K/AKT signaling in hepatoblastoma. EXPERIMENTAL DESIGN: Immunohistochemical stainings of (Ser473)-phosphorylated (p)-AKT protein, its targets p-(Ser9)-GSK-3beta and p-(Ser2448)-mTOR, as well as the cell cycle regulators Cyclin D1, p27(KIP1), and p21(CIP1) were done and the PIK3CA gene was screened for mutations. In vitro, two hepatoblastoma cell lines treated with the PI3K inhibitor LY294002 were analyzed for AKT and GSK-3beta phosphorylation, cell proliferation, and apoptosis. Additionally, simultaneous treatments of hepatoblastoma with LY294002 and cytotoxic drugs were carried out. RESULTS: Most tumors strongly expressed p-AKT, p-GSK-3beta, and p-mTOR; subgroups showed significant Cyclin D1, p27(KIP1), and p21(CIP1) expression. One hepatoblastoma carried an E545A mutation in the PIK3CA gene. In vitro, PI3K inhibition diminished hepatoblastoma cell growth being accompanied by reduced AKT and GSK-3beta phosphorylation. Flow cytometry and 4', 6-diamidino-2-phenylindole stainings showed that PI3K pathway inhibition leads to a substantial increase in apoptosis and a decrease in cellular proliferation linked to reduced Cyclin D1 and increased p27(KIP1) levels. Simultaneous treatment of hepatoblastoma cell lines with LY294002 and cytotoxic drugs resulted in positive interactions. CONCLUSIONS: Our findings imply that PI3K signaling plays an essential role in growth control of hepatoblastoma and might be successfully targeted in multimodal therapeutic strategies.