Consensus guidelines for the use and interpretation of angiogenesis assays.

The formation of new blood vessels, or angiogenesis, is a complex process that plays important roles in growth and development, tissue and organ regeneration, as well as numerous pathological conditions. Angiogenesis undergoes multiple discrete steps that can be individually evaluated and quantified by a large number of bioassays. These independent assessments hold advantages but also have limitations. This article describes in vivo, ex vivo, and in vitro bioassays that are available for the evaluation of angiogenesis and highlights critical aspects that are relevant for their execution and proper interpretation. As such, this collaborative work is the first edition of consensus guidelines on angiogenesis bioassays to serve for current and future reference.

Mouse models of human cancer.

The Helmholtz Alliance Preclinical Comprehensive Cancer Center (PCCC; www.helmholtz-pccc.de) hosted the "1st International Kloster Seeon Meeting on Mouse Models of Human Cancer" in the Seeon monastery (Germany) from March 8 to 11, 2014. The meeting focused on the development and application of novel mouse models in tumor research and high-throughput technologies to overcome one of the most critical bottlenecks in translational bench-to-bedside tumor biology research. Moreover, the participants discussed basic molecular mechanisms underlying tumor initiation, progression, metastasis, and therapy resistance, which are the prerequisite for the development of novel treatment strategies and clinical applications in cancer therapy.

Histone deacetylase 10 promotes autophagy-mediated cell survival.

Tumor cells activate autophagy in response to chemotherapy-induced DNA damage as a survival program to cope with metabolic stress. Here, we provide in vitro and in vivo evidence that histone deacetylase (HDAC)10 promotes autophagy-mediated survival in neuroblastoma cells. We show that both knockdown and inhibition of HDAC10 effectively disrupted autophagy associated with sensitization to cytotoxic drug treatment in a panel of highly malignant V-MYC myelocytomatosis viral-related oncogene, neuroblastoma derived-amplified neuroblastoma cell lines, in contrast to nontransformed cells. HDAC10 depletion in neuroblastoma cells interrupted autophagic flux and induced accumulation of autophagosomes, lysosomes, and a prominent substrate of the autophagic degradation pathway, p62/sequestosome 1. Enforced HDAC10 expression protected neuroblastoma cells against doxorubicin treatment through interaction with heat shock protein 70 family proteins, causing their deacetylation. Conversely, heat shock protein 70/heat shock cognate 70 was acetylated in HDAC10-depleted cells. HDAC10 expression levels in high-risk neuroblastomas correlated with autophagy in gene-set analysis and predicted treatment success in patients with advanced stage 4 neuroblastomas. Our results demonstrate that HDAC10 protects cancer cells from cytotoxic agents by mediating autophagy and identify this HDAC isozyme as a druggable regulator of advanced-stage tumor cell survival. Moreover, these results propose a promising way to considerably improve treatment response in the neuroblastoma patient subgroup with the poorest outcome.

The PEA-15 protein regulates autophagy via activation of JNK.

PEA-15/PED (phosphoprotein enriched in astrocytes 15 kDa/phosphoprotein enriched in diabetes) is a death effector domain-containing protein which is known to modulate apoptotic cell death. The mechanism by which PEA-15 inhibits caspase activation and increases ERK (extracellular-regulated kinase) activity is well characterized. Here, we demonstrate that PEA-15 is not only pivotal in the activation of the ERK pathway but also modulates JNK (c-Jun N-terminal kinase) signaling. Upon overexpression of PEA-15 in malignant glioma cells, JNK is potently activated. The PEA-15-induced JNK activation depends on the phosphorylation of PEA-15 at both phosphorylation sites (serine 104 and serine 116). The activation of JNK is substantially inhibited by siRNA-mediated down-regulation of endogenous PEA-15. Moreover, we demonstrate that glioma cells overexpressing PEA-15 show increased signs of autophagy in response to classical autophagic stimuli such as ionizing irradiation, serum deprivation, or rapamycin treatment. In contrast, the non-phosphorylatable mutants of PEA-15 are not capable of promoting autophagy. The inhibition of JNK abrogates the PEA-15-mediated increase in autophagy. In conclusion, our data show that PEA-15 promotes autophagy in glioma cells in a JNK-dependent manner. This might render glioma cells more resistant to adverse stimuli such as starvation or ionizing irradiation.

Basal caspase activity promotes migration and invasiveness in glioblastoma cells.

Glioblastomas, the most malignant of all brain tumors, are characterized by cellular resistance to apoptosis and a highly invasive growth pattern. These factors contribute to the poor response of glioblastomas to radiochemotherapy and prevent their complete neurosurgical resection. However, the driving force behind the distinct motility of glioma cells is only partly understood. Here, we report that in the absence of cellular stress and proapoptotic stimuli, human glioblastoma cells exhibit a constitutive activation of caspases in vivo and in vitro. The inhibition of caspases by various peptide inhibitors decreases the migration of cells in scrape motility assays and the invasiveness of cells in spheroid assays. Similarly, specific small interfering RNA- or antisense-mediated down-regulation of caspase-3 and caspase-8 results in an inhibition of the migratory potential of glioma cells. The constitutive caspase-dependent motility of glioblastoma cells is independent of CD95 activation and it is not mediated by mitogen-activated protein/extracellular signal-regulated kinase kinase signaling. The basal caspase activity is accompanied by a constant cleavage of the motility-associated gelsolin protein, which may contribute to the caspase-mediated promotion of migration and invasiveness in glioblastoma cells. Our results suggest that the administration of low doses of caspase inhibitors that block glioma cell motility without affecting the execution of apoptotic cell death may be exploited as a novel strategy for the treatment of glioblastomas.

Cdc42 induces activation loop phosphorylation and membrane targeting of mixed lineage kinase 3.

Mixed lineage kinase 3 (MLK3) functions as a mitogen-activated protein kinase kinase kinase to activate multiple mitogen-activated protein kinase pathways. Our current studies demonstrate that lack of MLK3 blocks signaling of activated Cdc42 to c-Jun N-terminal kinase, giving strong support for the idea that Cdc42 is a physiological activator of MLK3. We show herein that Cdc42, in a prenylation-dependent manner, targets MLK3 from a perinuclear region to membranes, including the plasma membrane. Cdc42-induced membrane targeting of MLK3 is independent of MLK3 catalytic activity but depends upon an intact Cdc42/Rac-interactive binding motif, consistent with MLK3 membrane translocation being mediated through direct binding of Cdc42. Phosphorylation of the activation loop of MLK3 requires MLK3 catalytic activity and is induced by Cdc42 in a prenylation-independent manner, arguing that Cdc42 binding is sufficient for activation loop autophosphorylation of MLK3. However, membrane targeting is necessary for full activation of MLK3 and maximal signaling to JNK. We previously reported that MLK3 is autoinhibited through an interaction between its N-terminal SH3 domain and a proline-containing sequence found between the leucine zipper and the CRIB motif of MLK3. Thus we propose a model in which GTP-bound Cdc42/Rac binds MLK3 and disrupts SH3-mediated autoinhibition leading to dimerization and activation loop autophosphorylation. Targeting of this partially active MLK3 to membranes likely results in additional phosphorylation events that fully activate MLK3 and its ability to maximally signal through the JNK pathway.

Mixed lineage kinase 3 inhibits phorbol myristoyl acetate-induced DNA synthesis but not osteopontin expression in rat mesangial cells.

Mixed lineage kinase 3 (MLK 3) (also called SPRK or PTK-1) is a recently described member of the family of the mixed lineage kinase subfamily of Ser/Thr protein kinases that interacts with mitogen-activated protein kinase pathways. In order to test the biological relevance and potential interaction of MLK 3 with protein kinase C-mediated signaling pathways, human MLK 3 was stably expressed in rat glomerular mesangial cells using a retroviral vector (LXSN) and the effects of phorbol myristoyl acetate (PMA) on DNA synthesis and osteopontin mRNA expression were examined. In control (vector-transfected) mesangial cells PMA increased [3H]-thymidine incorporation in a concentration-dependent manner. In mesangial cells stably expressing MLK 3, the PMA-induced increase in [3H]-thymidine incorporation was significantly reduced (> 50%). However, the PMA-induced increase in osteopontin mRNA was not affected by MLK 3 expression. To determine the mechanisms of these effects, activation of ERK2, JNK1 and p38 in response to PMA was examined in both vector and MLK 3 transfected cells. ERK2 activation was increased several fold by PMA in control cells but was attenuated significantly in MLK 3 expressing cells, suggesting that MLK 3 expression in mesangial cells can negatively regulate the ERK pathway. PMA had no significant effect on JNK and P38 activation, in either vector- or MLK 3-expressing cells. PD98059, a MEK inhibitor blocked PMA-induced DNA synthesis without affecting osteopontin expression. These results suggest that while protein kinase C activation increases cellular proliferation and osteopontin mRNA expression, over-expression of MLK 3 affects only the PKC-induced DNA synthesis, probably through inhibition of ERK. These results also indicate a novel mechanism of growth regulation by a member of the mixed-lineage kinase family that might have significant therapeutic implications in proliferative glomerulonephritis.

Mixed lineage kinase 3 inhibits platelet-derived growth factor-stimulated DNA synthesis and matrix mRNA expression in mesangial cells.

Mixed lineage kinase 3 (MLK 3) is a recently described member of the MLK subfamily of Ser/Thr protein kinases that interacts with MAPK pathways. The aim of this study was to test the potential interaction of MLK 3 with signaling pathways stimulated by PDGF in rat mesangial cells. We have established a stable cell line expressing human MLK 3 in rat glomerular mesangial cells. The effects of PDGF on proliferation and matrix mRNA expression were examined. In control (vector-transfected) mesangial cells PDGF increased [(3)H]-thymidine incorporation significantly in a concentration-dependent manner. In mesangial cells expressing MLK 3, PDGF-induced increase in DNA synthesis was significantly reduced. PDGF also induced fibronectin and collagen I mRNA expression in control cells, the effects of which were also significantly blocked in MLK 3-transfected cells. To understand the potential interaction of MLK 3 over expression with the MAPK pathways and to examine the potential mechanism of the effects of MLK 3 over expression on proliferation and matrix expression, activation of ERK2, JNK1 and p38 were examined. ERK2 activation was increased several fold by PDGF in control cells but was attenuated significantly in MLK 3 expressing cells. PDGF did not have any effect on JNK and p38 activation, in either cell types. Using the same stable-transfected cell line, identical results were obtained on proliferation and matrix expression with sarafotoxin-s6b (endothelin receptor agonist) another potent mitogenic and sclerotic agent for mesangial cells. These results indicate an important role for MLK 3 in the regulation of growth and matrix expression in mesangial cells.