Unbalanced activation of ERK1/2 and MEK1/2 in apigenin-induced HeLa cell death

Apigenin, a dietary bioflavonoid with anticarcinogenic properties, was highly cytotoxic for HeLa cells (incubated with 0.5% FBS). This effect was accompanied with a marked increase in ERK1/2 but not MEK1/2 phosphorylation. The cytotoxic effects of apigenin were attenuated by the stimulation of these cells with 10% FBS, which provoked an increase in the phosphorylation levels of MEK1/2 and ERK1/2. The steps in the ERK1/2 pathway relevant to the cytotoxic effects of apigenin, as well as the contribution of other signaling pathways, were investigated. The activation of the pathway by transfection with the constitutively active Ras mutant (RasV12) conferred protection to serum-starved HeLa cells against apigenin, whereas the constitutively active MEK(E) mutant did not. MEK inhibitors (PD098059 or U0126) blocked ERK1/2 phosphorylation induced by apigenin and conferred partial protection against this flavonoid. The effects of apigenin did not involve p38-MAPK or JNK1/2, and were not simply due to inhibition of PI3kinase or protein kinase CK2. These data suggest that the deregulation of the ERK1/2 pathway, due to the potentiation of ERK1/2 phosphorylation without increasing MEK1/2 phosphorylation, is involved in apigenin-induced HeLa cell death.     

The A-superfamily of conotoxins: structural and functional divergence

The generation of functional novelty in proteins encoded by a gene superfamily is seldom well documented. In this report, we define the A-conotoxin superfamily, which is widely expressed in venoms of the predatory cone snails (Conus), and show how gene products that diverge considerably in structure and function have arisen within the same superfamily. A cDNA clone encoding alpha-conotoxin GI, the first conotoxin characterized, provided initial data that identified the A-superfamily. Conotoxin precursors in the A-superfamily were identified from six Conus species: most (11/16) encoded alpha-conotoxins, but some (5/16) belong to a family of excitatory peptides, the kappaA-conotoxins that target voltage-gated ion channels. alpha-Conotoxins are two-disulfide-bridged nicotinic antagonists, 13-19 amino acids in length; kappaA-conotoxins are larger (31-36 amino acids) with three disulfide bridges. Purification and biochemical characterization of one peptide, kappaA-conotoxin MIVA is reported; five of the other predicted conotoxins were previously venom-purified. A comparative analysis of conotoxins purified from venom, and their precursors reveal novel post-translational processing, as well as mutational events leading to polymorphism. Patterns of sequence divergence and Cys codon usage define the major superfamily branches and suggest how these separate branches arose.     

Functional changes of mice Sertoli cells induced by Cr(V)

Transport of macromolecules from the interstitial testis tissue to cells at the adlumenal compartment of the seminiferous epithelium occurs naturally through Sertoli cells. In previous studies we have shown that Cr(V) intoxication disturbed spermatogenesis in mice. To test if Sertoli cells are affected by chromium, a well proved carcinogen, the uptake and the horseradish peroxidase transport ability of isolated seminiferous tubules of mice administered with a chromium(V) compound, have been studied. Male CD-R mice were exposed daily for 5 days to [Cr^V-BT]^2– through subcutaneous injection and comparisons were made with groups of vehicle-treated mice. Using an in vitro assay we demonstrated that the seminiferous tubules were able to uptake and transport the tracer, in a much faster way than controls, mainly via intercellular and transcellular pathways, providing evidence that this functional role of Sertoli cells is affected by the Cr(V) compound. These findings might improve the knowledge on the toxicity mechanisms of chromium.     

Effects of low nitrogen-phosphorus ratios in the phytoplankton community in Laguna de Bay, a shallow eutrophic lake in the Philippines

The effects of low nitrogen-phosphorus ratios on microalgae from a large eutrophic freshwater lake in the Philippines were investigated. Natural microalgal populations from Laguna de Bay, the largest lake in the Philippines, were cultured using three different nitrogen-phosphorus weight ratios (2N:1P; 6N:1P and 12N:1P) at two phosphorus concentrations (0.25 and 0.5 mg l^–1) in each case. The growth and genera composition of the cultures under the different treatments were followed for a 12-week period. Community level responses were assessed based on species richness (s), Shannon-Wiener Index (H), Simpson Index () and Evenness (J). Among the different microalgal groups, only the chlorophytes showed a significantly higher density in response to the 12N:1P treatment at the higher P concentration, indicating that the nutrient ratio had a significant interaction with the nutrient levels used in the experiments. The genera found in the different treatments were generally similar; however, the degree of dominance of some varied with treatment during the experiment. The succession of dominant genera also differed among the N:P treatments. The diatoms like Fragilaria, Aulacoseira (= Melosira) and Nitzschia dominated the lowest N:P. On the other hand, chlorophytes (Kirchneriella and Scenedesmus) dominated the highest N:P treatment, particularly from the second to the seventh week of the experiments with the diatoms becoming co-dominant only towards the eighth week until the end of the experimental. The 6N:1P treatment showed a mixed dominance between the diatoms and the chlorophyte genera. The various indices of diversity indicate significantly lower diversity only in the 12N:1P at 0.5 mg l^–1 P and not in 12N:1P at 0.25 mg l^–1 P.     

Further ultrastructural characterization of the intranuclear ring-shaped bodies of the plant Lacandonia schismatica

Ring-shaped bodies are found in the nucleus of Lacandonia schismatica, a rare plant with the sexual organs inverted. They are 0.5-microm-diameter structures that present an electron-dense external ring surrounding a central core. Ultrastructural studies indicate that these bodies contain RNA. The external ring is labeled with antibodies against small nuclear ribonucleoproteins, suggesting that they may be involved in pre-mRNA metabolism. In the present work we further characterized these intranuclear ring-shaped structures by serial-sectioning analysis. Moreover, we tested the presence of additional molecular elements related to pre-mRNA metabolism, such as SR proteins and poly(A)(+) RNA, using immunoelectron microscopy and ultrastructural in situ hybridization. Our results show that these nuclear bodies are spherical. They contain SR proteins involved in splicing and postsplicing events and little to no poly(A)(+) RNA. We also found similar nuclear bodies in other plant and animal species. Therefore, ring-shaped bodies in L. schismatica are spherical, highly compartmentalized nuclear structures that may be involved in pre-mRNA metabolism.     

Growth, Natural Mortality, Length–weight Relationship, Maximum Length and Length-at-first-maturity of the Coelacanth Latimeria chalumnae

Based on the re-interpretation of published data, the von Bertalanffy growth function parameters of the coelacanth, Latimeria chalumnae, are estimated as L=218cm total length, s.e. 23; K=0.059 (year^–1), s.e. 0.012; t₀=–3.3 (year), s.e. 0.5, corresponding to a life span of 48 years. The length–weight relationship of the form W=a*TLb, with wet weight (W) in g and total length (TL) in cm, is estimated as a=0.0278, b=2.89, r²=0.893, n=87, range=42.5–183cm TL. Using extreme value theory, the maximum length for female coelacanths is estimated as 199cm TL (95% confidence interval=175–223cm TL) and for males as 168cm TL (95% confidence interval 155–180cm TL). Based on data from seven females with embryos or mature eggs, the length-at-first-maturity for females is estimated to be about 150cm TL, corresponding to an age of about 16 years. Based on the value of t₀=–3.3 years and on the presence of three scale rings found in a newborn coelacanth, the period of embryogenesis lasts for about three years, the longest known in vertebrates. The natural mortality rate is estimated at M=0.12. Population food consumption is found to be 1.4 times the existing biomass per year, and gross food conversion efficiency indicates that only 10% of the consumed food is utilized for somatic growth.     

Ellagic acids from Callisthene major

3,3′-Di-O-methyl and 3′-O-methyl-3,4-O,O-methylidene ellagic acids have been isolated from Callisthene major.     

Complementary chromatic and far-red photoacclimations in <Emphasis Type="Italic">Synechococcus</Emphasis> ATCC 29403 (PCC 7335). I: The phycobilisomes,a proteomic approach

Synechococcus ATCC 29403 (PCC 7335) is a unicellular cyanobacterium isolated from Puerto Peñasco, Sonora Mexico. This cyanobacterium performs complementary chromatic acclimation (CCA), far-red light photoacclimation (FaRLiP), and nitrogen fixation. The Synechococcus PCC 7335 genome contains at least 31 genes for proteins of the phycobilisome (PBS). Nine constitutive genes were expressed when cells were grown under white or red lights and the resulting proteins were identified by mass spectrometry in isolated PBS. Five inducible genes were expressed under white light, and phycoerythrin subunits and associated linker proteins were detected. The proteins of five inducible genes expressed under red light were identified, the induced phycocyanin subunits, two rod linkers and the rod-capping linker. The five genes for FaRLiP phycobilisomes were expressed under far-red light together with the apcF gene, and the proteins were identified by mass spectrometry after isoelectric focusing and SDS-PAGE. Based on in silico analysis, Phylogenetic trees, and the observation of a highly conserved amino acid sequence in far-red light absorbing alpha allophycoproteins encoded by FaRLiP gene cluster, we propose a new nomenclature for the genes. Based on a ratio of ApcG2/ApcG3 of six, a model with the arrangement of the allophycocyanin trimers of the core is proposed.