Fas-negative osteosarcoma tumor cells are selected during metastasis to the lungs: the role of the Fas pathway in the metastatic process of osteosarcoma

Low expression of Fas by different tumors including osteosarcoma, correlates with poor prognosis. We found that osteosarcoma lung metastases from patients expressed negligible amounts of Fas, but primary tumors often expressed high Fas levels. The reason for this discrepancy is unknown. We hypothesized that because FasL is constitutively expressed in the lungs, Fas-positive (Fas(+)) tumor cells entering the lungs would bind with FasL and die from Fas-induced apoptosis, resulting in the "selection" of Fas-negative (Fas(-)) cells, which would eventually form metastases. To test this hypothesis, we injected K7 osteosarcoma cells, which express functional Fas in vitro, into mice and confirmed that its bone tumors were Fas(+), but lung metastases were Fas(-). Next, to inhibit Fas signaling without affecting Fas expression, we transfected these cells with a FADD-dominant negative (FDN) plasmid and developed K7/FDN cells. Metastases formed by K7/FDN cells contained Fas(+) tumor cells. Moreover, K7/FDN cells were retained in the lungs longer and formed more lung metastases than K7 cells. In addition, the incidence of lung metastases in FasL-deficient mice injected with K7 cells was higher than that in wild-type mice. Metastases from FasL-deficient mice but not from wild-type mice contained Fas(+) tumor cells. Based on that, we conclude that Fas(-) osteosarcoma cells are selected during lung metastases formation and that inhibition of Fas signaling in tumors or lack of FasL in the host environment allows the proliferation of Fas(+) osteosarcoma cells in the lungs and promotes metastases growth. Therefore, Fas may be considered as a new therapeutic target for osteosarcoma treatment.     

Testing the link between species interactions and species co‐occurrence in a trophic network

Species interactions are dynamic processes that vary across environmental and ecological contexts, and operate across scale boundaries, making them difficult to quantify. Nevertheless, ecologists are increasingly interested in inferring species interactions from observational data using statistical analyses of their spatial co‐occurrence patterns. Trophic interactions present a particular challenge, as predators and prey may frequently or rarely co‐occur, depending on the spatial or temporal scale of observation. In this study, we investigate the accuracy of inferred interactions among species that both compete and trophically interact. We utilized a long‐term dataset of pond‐breeding amphibian co‐occurrences from Mt Rainier National Park (Washington, USA) and compiled a new dataset of their empirical interactions from the literature. We compared the accuracy of four statistical methods in inferring these known species interactions from spatial associations. We then used the best performing statistical method, the Markov network, to further investigate the sensitivity of interaction inference to spatial scale‐dependence and the presence of predators. We show that co‐occurrence methods are generally inaccurate when estimating trophic interactions. Further the strength and sign of inferred interactions were dependent upon the spatial scale of observation and predator presence influenced the detectability of competitive interactions among prey species. However, co‐occurrence analysis revealed new patterns of spatial association among pairs of species with known interactions. Overall, our study highlights a limiting frontier in co‐occurrence theory and the disconnect between widely implemented methodologies and their ability to accurately infer interactions in trophically‐structured communities.     

Cholesterol signaling at the endoplasmic reticulum occurs in npc1(-/-) but not in npc1(-/-), LDLR(-/-) mice

It remains controversial whether deficiency of the Niemann-Pick C1 (npc1) protein results in altered cholesterol signaling at the endoplasmic reticulum (ER). In this report, we have measured the processed, nuclear form of sterol regulatory element binding protein (SREBP)-1 in livers of npc1 wild-type, heterozygous, and homozygous deficient mice, alone, and in combination with deficiencies of the low density lipoprotein receptor (LDLR) or the multiple drug resistant (mdr)1a, P-glycoprotein. Cleavage of SREBPs to activated forms normally occurs when the ER is deficient in cholesterol. A large decrease in processed SREBP-1 was evident in fasted npc1(-/-) mice and npc1(-/-), mdr1a(-/-) mice, with no decrease evident in npc1(-/-), LDLR(-/-) mice. These results suggest that the increase in cellular cholesterol which occurs in npc1(-/-) and in npc1(-/-), mdr1a(-/-) mice includes the sites responsible for cholesterol signaling, while the similar increase in cholesterol found in npc1(-/-), LDLR(-/-) mice does not.     

Characterization of the Aspergillus nidulans septin (asp) gene family

Members of the septin gene family are involved in cytokinesis and the organization of new growth in organisms as diverse as yeast, fruit fly, worm, mouse, and human. Five septin genes have been cloned and sequenced from the model filamentous fungus A. nidulans. As expected, the A. nidulans septins contain the highly conserved GTP binding and coiled-coil domains seen in other septins. On the basis of hybridization of clones to a chromosome-specific library and correlation with an A. nidulans physical map, the septins are not clustered but are scattered throughout the genome. In phylogenetic analysis most fungal septins could be grouped with one of the prototypical S. cerevisiae septins, Cdc3, Cdc10, Cdc11, and Cdc12. Intron-exon structure was conserved within septin classes. The results of this study suggest that most fungal septins belong to one of four orthologous classes.     

Site-specific phosphorylation of tau accompanied by activation of mitogen-activated protein kinase (MAPK) in brains of Niemann-Pick type C mice

Niemann-Pick type C (NPC) disease is characterized by an accumulation of cholesterol in most tissues and progressive neurodegeneration with the formation of neurofibrillary tangles. Neurofibrillary tangles are composed of paired helical filaments (PHF), a major component of which is the hyperphosphorylated tau. In this study we used NPC heterozygous and NPC homozygous mouse brains to investigate the molecular mechanism responsible for tauopathy in NPC. Immunoblot analysis using anti-tau antibodies (Tau-1, PHF-1, AT-180, and AT-100) revealed site-specific phosphorylation of tau at Ser-396 and Ser-404 in the brains of NPC homozygous mice. Mitogen-activated protein kinase, a potential serine kinase known to phosphorylate tau, was activated, whereas other serine kinases such as glycogen synthase kinase-3beta and cyclin-dependent kinase 5 were inactive. Morphological examination demonstrated that a number of neurons, the perikarya of which strongly immunostained with PHF-1, exhibited polymorphorous cytoplasmic inclusion bodies and multi-concentric lamellar-like bodies. Importantly, the accumulation of intracellular cholesterol in NPC mouse brains was determined to be a function of age. From these results we conclude that abnormal cholesterol metabolism due to the genetic mutation in NPC1 may be responsible for activation of the mitogen-activated protein kinase-signaling pathway and site-specific phosphorylation of tau in vivo, leading to tauopathy in NPC.     

Regulation of frequency of luteinizing hormone pulses by magnitude of acute change in circulating concentration of progesterone of female cattle

The hypothesis was the greater the magnitude of acute increase in circulating concentration of progesterone of female cattle, the greater the acute inhibitory effect on frequency of pulsatile LH release. From Day 0 to 4 of the treatment period, females without functional corpora lutea were treated with varying doses of progesterone to result in varying concentrations of progesterone within the typical physiological range in blood. From Day 4 to 7, cattle were treated with a single dose of progesterone to achieve a similar circulating concentration of progesterone among all females in the study. Therefore, from Day 0 to 4 relative to Day 4 to 7 of the treatment period, females had a: (1) large (3.1 ng/ml), (2) moderate (2.5 ng/ml), or (3) small (0.5 ng/ml) increase in concentration of progesterone in blood. Frequency of LH pulses was greater (P <0.10) in females with the greatest magnitude of change in concentration of progesterone during the first 24 h following the change in concentration as compared with females with the moderate or small of change in concentration of progesterone suggesting our working hypothesis should be rejected. The greater the magnitude of acute change in concentration of progesterone, however, the longer time required for re-initiation of release of LH pulses of the amplitude of pulses that preceded the change in concentration of progesterone.