Protein arginine methylation promotes therapeutic resistance in human pancreatic cancer

Pancreatic cancer is a lethal disease with limited treatment options for cure. A high degree of intrinsic and acquired therapeutic resistance may result from cellular alterations in genes and proteins involved in drug transportation and metabolism, or from the influences of cancer microenvironment. Mechanistic basis for therapeutic resistance remains unclear and should profoundly impact our ability to understand pancreatic cancer pathogenesis and its effective clinical management. Recent evidences have indicated the importance of epigenetic changes in pancreatic cancer, including posttranslational modifications of proteins. We will review new knowledge on protein arginine methylation and its consequential contribution to therapeutic resistance of pancreatic cancer, underlying molecular mechanism, and clinical application of potential strategies of its reversal.     

Meiofaunal responses to nutrient additions in a Mediterranean stream

1. The effects of a moderate addition of nutrients (twofold N and threefold P) were examined during a 2‐year period to determine the response to nutrient addition in a meiofaunal community inhabiting sandy patches in a Mediterranean stream. 2. The pattern of meiofaunal assemblages exhibits a high degree of intra‐ and interannual variability. This pattern alternates between periods of hydrological stability and disturbances, such as floods and droughts, which is a characteristic of Mediterranean systems. 3. A before–after–control–impact (BACI) design was used to determine the outcome of the addition by comparing an upstream non‐enriched reach with an enriched downstream reach. Analysis of the study data by means of a nonparametric permutational procedure (permanova ) showed that fertilisation had a significant effect. Density and biomass values increased in the most abundant meiofaunal groups, including microcrustaceans, oligochaetes and chironomids. Microcrustaceans were the dominant group in the permanent meiofauna. 4. We also examined differences in microcrustacean secondary production in both reaches. Ostracods and cyclopoid copepods increased their secondary production in the impacted reach as a result of the nutrient addition. 5. Our study demonstrated that moderate nutrient enrichment can affect the biomass and production of stream meiofauna, but it is still unclear whether this effect was because of autotrophic or heterotrophic pathways.     

Existence of a Novel Hemagglutinin Having No Protease Activity in Vibrio mimicus

The protease elaborated by Vibrio mimicus is known to possess hemagglutinating ability to chicken erythrocytes, the well-known HA/protease. A non-protease hemagglutinin (HA) with strong agglutinating ability towards rabbit erythrocytes was obtained from 32 hr culture supernatant of a pathogenic environmental strain of V. mimicus. This HA (V. mimicus HA: VMHA) appeared stable at relatively higher temperature and agglutinated the erythrocytes from rabbit, guinea pig and mouse but not the erythrocytes from chicken, bovine, horse and sheep. Simple sugars, metal ions and chelating agents failed to inhibit the activity of VMHA. The activity of VMHA was found to be sensitive to digestion by proteolytic enzymes including HA/protease. These results provide evidence for the existence of novel HA other than HA/protease in V. mimicus.     

Pretubulysin: a new option for the treatment of metastatic cancer

Tubulin-binding agents such as taxol, vincristine or vinblastine are well-established drugs in clinical treatment of metastatic cancer. However, because of their highly complex chemical structures, the synthesis and hence the supply issues are still quite challenging. Here we set on stage pretubulysin, a chemically accessible precursor of tubulysin that was identified as a potent microtubule-binding agent produced by myxobacteria. Although much simpler in chemical structure, pretubulysin abrogates proliferation and long-term survival as well as anchorage-independent growth, and also induces anoikis and apoptosis in invasive tumor cells equally potent to tubulysin. Moreover, pretubulysin posseses in vivo efficacy shown in a chicken chorioallantoic membrane (CAM) model with T24 bladder tumor cells, in a mouse xenograft model using MDA-MB-231 mammary cancer cells and finally in a model of lung metastasis induced by 4T1 mouse breast cancer cells. Pretubulysin induces cell death via the intrinsic apoptosis pathway by abrogating the expression of pivotal antiapoptotic proteins, namely Mcl-1 and Bcl-x_L, and shows distinct chemosensitizing properties in combination with TRAIL in two- and three-dimensional cell culture models. Unraveling the underlying signaling pathways provides novel information: pretubulysin induces proteasomal degradation of Mcl-1 by activation of mitogen-activated protein kinase (especially JNK (c-Jun N-terminal kinase)) and phosphorylation of Mcl-1, which is then targeted by the SCF^Fbw7 E3 ubiquitin ligase complex for ubiquitination and degradation. In sum, we designate the microtubule-destabilizing compound pretubulysin as a highly promising novel agent for mono treatment and combinatory treatment of invasive cancer.     

Heterogeneous phenotype of human glioblastoma: In vitro study

Glioblastomas (GBMs) are the most lethal primary brain tumours. Increasing evidence shows that brain tumours contain the population of stem cells, so‐called cancer stem cells (CSCs). Stem cell marker CD133 was reported to identify CSC population in GBM. Further studies have indicated that CD133 negative cells exhibiting similar properties and are able to initiate the tumour, self‐renew and undergo multilineage differentiation. GBM is a highly heterogeneous tumour and may contain different stem cell populations with different functional properties. We characterized five GBM cell lines, established from surgical samples, according to the marker expression, proliferation and differentiation potential. CD133 positive cell lines showed increased proliferation rate in neurosphere condition and marked differentiation potential towards neuronal lineages. Whereas two cell lines low‐expressing CD133 marker showed mesenchymal properties in vitro, that is high proliferation rate in serum condition and differentiation in mesenchymal cell types. Further, we compared therapy resistance capacity of GBM cell lines treated with hydroxyurea. Our results suggest that CSC concept is more complex than it was believed before, and CD133 could not define entire stem cell population within GBM. At least two different subtypes of GBM CSCs exist, which may have different biological characteristics and imply different therapeutic strategies. Copyright © 2013 John Wiley & Sons, Ltd.     

Roles of Subunit NuoK (ND4L) in the Energy-transducing Mechanism of Escherichia coli NDH-1 (NADH:Quinone Oxidoreductase)

The bacterial H⁺-translocating NADH:quinone oxidoreductase (NDH-1) catalyzes electron transfer from NADH to quinone coupled with proton pumping across the cytoplasmic membrane. The NuoK subunit (counterpart of the mitochondrial ND4L subunit) is one of the seven hydrophobic subunits in the membrane domain and bears three transmembrane segments (TM1–3). Two glutamic residues located in the adjacent transmembrane helices of NuoK are important for the energy coupled activity of NDH-1. In particular, mutation of the highly conserved carboxyl residue (_KGlu-36 in TM2) to Ala led to a complete loss of the NDH-1 activities. Mutation of the second conserved carboxyl residue (_KGlu-72 in TM3) moderately reduced the activities. To clarify the contribution of NuoK to the mechanism of proton translocation, we relocated these two conserved residues. When we shifted _KGlu-36 along TM2 to positions 32, 38, 39, and 40, the mutants largely retained energy transducing NDH-1 activities. According to the recent structural information, these positions are located in the vicinity of _KGlu-36, present in the same helix phase, in an immediately before and after helix turn. In an earlier study, a double mutation of two arginine residues located in a short cytoplasmic loop between TM1 and TM2 (loop-1) showed a drastic effect on energy transducing activities. Therefore, the importance of this cytosolic loop of NuoK (_KArg-25, _KArg-26, and _KAsn-27) for the energy transducing activities was extensively studied. The probable roles of subunit NuoK in the energy transducing mechanism of NDH-1 are discussed.     

YAP1 and PRDM14 converge to promote cell survival and tumorigenesis

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