Asymptotic behaviour of solutions of the diffusive Lotka-Volterra equations

A spatially discrete version of the diffusive Lotka-Volterra equations is considered. Asymptotical spatial homogeneity of solutions of the equations with equilibrium, periodic or zero flux boundary conditions is proved without regard to crowding effects. The proof does not require the assumption of equal diffusion coefficients and the restrictions on the dimension of space and on the initial data, which are necessary in the spatially continuous model.     

Impairment of the TSH signal transduction system in human thyroid carcinoma cells

In order to further evaluate the role of TSH in the proliferation and the differentiation of human thyroid carcinoma cells, we have analyzed the function of the TSH receptor in the established thyroid carcinoma cell lines NPA and WRO. The TSH signal transduction system in the carcinoma cells was also compared with that in normal thyroid cells. Although unresponsiveness to bovine and human TSH was demonstrated by measurement of cAMP production and [3H]thymidine incorporation after treatment of TSH, cAMP production was induced after stimulation of these cells by forskolin, cholera toxin, and isoproterenol. Specific binding to 125I-TSH was demonstrated in both NPA and WRO cells in addition to the existence of a TSH receptor mRNA and thyroglobulin mRNA species, although thyroid-specific gene expression in these cells was not regulated by TSH. These findings suggest that the unresponsiveness to TSH in these cells may be due to an abnormality of TSH receptor-G protein coupling rather than to a decreased level of TSH-receptor expression or a Gs protein abnormality.     

The transforming potential of the c-erbB-2 protein is regulated by its autophosphorylation at the carboxyl-terminal domain.

The mutant c-erbB-2 protein with Glu instead of Val-659 exhibited transforming activity in NIH 3T3 cells. This protein showed enhanced tyrosine kinase activity in vitro and enhanced autophosphorylation at Tyr-1248 located proximal to the carboxyl terminus. Enhanced tyrosine phosphorylation of several cellular proteins was detected in cells expressing the Glu-659 c-erbB-2 protein. Introduction of an additional mutation at the ATP-binding site (Lys-753 to Met) of this protein resulted in abolition of its transforming ability. These data indicate that the transforming potential of c-erbB-2 is closely correlated with elevated tyrosine kinase activity of the gene product. To investigate the role of autophosphorylation in cell transformation, we introduced an additional mutation at the autophosphorylation site of the Glu-659 c-erbB-2 protein (Tyr-1248 to Phe). This mutant protein exhibited lower tyrosine kinase activity and lower transforming activity. On the other hand, when the carboxyl-terminal 230 amino acid residues were deleted from the c-erbB-2 protein, the tyrosine kinase activity and cell-transforming activity of the protein were enhanced. Thus, the carboxyl-terminal domain, which contains the major autophosphorylation site, Tyr-1248, may regulate cellular transformation negatively and autophosphorylation may eliminate this negative regulation.     

Expression of the gene encoding the coat protein of cucumber mosaic virus (CMV) strain WL appears to provide protection to tobacco plants against infection by several different CMV strains.

The gene (cp) encoding the coat protein (CP) of cucumber mosaic virus (CMV) strain WL (CMV-WL, which belongs to CMV subgroup II) was custom polymerase chain reaction (CPCR)-engineered for expression as described by Slightom [Gene 100 (1991) 251-255]. CPCR amplification was used to add 5'- and 3'-flanking NcoI sites to the CMV-WL cp gene, and cp was cloned into the expression vector, pUC18cpexp. This CMV-WL cp expression cassette was transferred into the genome of tobacco (Nicotiana tabacum cv. Havana 423) via the Agrobacterium T-DNA transfer mechanism. R0 plants that express the CMV-WL cp gene were subcloned, propagated, and challenge-inoculated with CMV-WL. Several R0 plant lines showed excellent protection against CMV-WL infection; however, plants found to accumulate the highest CP levels did not show the highest degree of protection. Thus in our case, CP levels appear not to be a useful predictor of the degree of protection. Plants from the best protected CMV-WL cp gene-expressing R0 tobacco lines were also inoculated with CMV strains belonging to the other major CMV subgroup (subgroup I), CMV-C and CMV-Chi, and compared in a parallel experiment with a transgenic tobacco plant line that expresses the CMV-C cp gene. Plants expressing the CMV-WL cp gene appeared to show a broader spectrum of protection against infection by the various CMV strains than plants expressing the CMV-C cp gene.     

Synthesis of sterols and 5-lipoxygenase products are required for the G1-S phase transition of interleukin-2-dependent lymphocyte proliferation

A murine killer T cell line, G-CTLL 1, whose proliferation depends on the presence of interleukin 2 (IL-2), was used to analyze the mechanism of IL-2 action with respect to sterol synthesis and arachidonate metabolism. De novo sterol synthesis was substantially enhanced much earlier than DNA synthesis, and the rate reached a maximum at 13 hr after the addition of IL-2. Compactin, which is a potent competitive inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG CoA reductase, the enzyme in the rate-limiting step of the sterol synthesis), inhibited the IL-2-induced DNA synthesis. The addition of mevalonate, the product of HMG CoA reductase, prevented the inhibition of DNA synthesis by compactin, suggesting that the supply of a sufficient amount of sterol is an essential prerequisite for IL-2 action. The IL-2-induced DNA synthesis was also inhibited by AA861, a specific inhibitor of arachidonate 5-lipoxygenase, and by other lipoxygenase inhibitors such as nordihydroguaiaretic acid and esculetin. In contrast, indomethacin, an inhibitor of arachidonate cyclooxygenase, had no effect. These findings suggest that synthesis of 5-lipoxygenase products is also a prerequisite. The inhibition of DNA synthesis was effectively inhibited only when compactin or lipoxygenase inhibitors were added early enough to block the synthesis of sterols or 5-lipoxygenase products; addition of the reagents after 3 hr decreased the inhibition with time. Therefore, about 3 hr after the addition of IL-2, several drastic intracellular changes are assumed to begin and to lead to DNA synthesis.     

2-Mercaptoethanol acts as a potentiating factor of interleukin-2-dependent lymphocyte proliferation

An interleukin-2 (IL-2) dependent cell line which could be grown continuously with crude concanavalin A-stimulated rat or mouse spleen cell culture supernatant could not survive for over 48 hr in the culture medium supplemented with partially purified or recombinant IL-2. The cell growth was restored by adding another factor obtained from the same crude culture supernatant. This potentiating activity which was physicochemically inseparable from serum albumin was also obtained from the culture medium containing 2-mercaptoethanol (2-ME) and incubated at 37 C for 24 hr without the spleen cells. By further experiments, it was demonstrated that 2-ME itself had the potentiating activity on the IL-2-dependent proliferation of this cell line and cysteine mediated the activity of 2-ME. The cells could not enter S-phase in the absence of 2-ME even in the presence of IL-2.     

Terminal regions of flagellin are disordered in solution

Limited proteolysis of flagellin from Salmonella typhimurium SJW1103 by subtilisin, trypsin and thermolysin results in homologous degradation patterns. The terminal regions of flagellin are very sensitive to proteolysis. These parts are degraded into small oligopeptides at the very early stage of a mild digestion that yields a relatively stable fragment with a molecular weight of 40,000. Further proteolytic degradation results in a stable 27,000 Mr fragment. The 40,000 Mr tryptic fragment has been identified as residues 67 to 446 of the flagellin sequence, while the 27,000 Mr fragment involves the 179 to 418 segment. The NH2-terminal sequence positions for the corresponding fragments produced by subtilisin are 60 and 174 for the 40,000 Mr and 27,000 Mr fragments, respectively. The fragments lost their polymerizing ability. Structural properties of flagellin and its 40,000 Mr tryptic fragment were compared by circular dichroism spectroscopy and differential scanning calorimetry. Analysis of the calorimetric melting profiles suggests that terminal parts of flagellin have no significant internal stability and they are in extensive contact with water. However, these regions contain some secondary structure, probably alpha-helices, as revealed by comparison of the circular dichroic spectra in the far-ultraviolet region. Our results indicate that, although the terminal regions of flagellin may contain some alpha-helical secondary structure of marginal stability, they have no compact ordered tertiary structure in solution. On the contrary, the central region of the molecule involves at least two compact structural units.     

Chaihu-Shugan-San Administration Ameliorates Perimenopausal Anxiety and Depression in Rats

Chaihu-Shugan-San (CSS) is a traditional Chinese herbal formula that is widely used for treating perimenopausal symptoms in China; however, its mechanisms remain unknown. The present study was designed to investigate potential CSS mechanisms in rats with unpredicted chronic mild stress (UCMS) and normally aging rats (52 weeks of age). We performed the sucrose consumption test along with the forced swimming test to confirm depression-like behavior and the open field test (OFT) to confirm anxiety-like behavior in the animals. In addition, we used an enzyme-linked immunosorbent assay to measure serum and hippocampal estradiol (E₂) levels and a quantitative real-time polymerase chain reaction to assess hippocampal mRNA levels of estrogen receptors (ERs) α and β as well as G protein-coupled receptor 30 (GPR30). We found that CSS administration resulted in a significant increase in the ratio of hippocampal ERα and ERβ mRNA (ERα/ERβ ratio) in UCMS rats (p<0.001). However, no significant changes were observed in E₂ levels, ERα mRNA expression, and GPR30 mRNA expression. In contrast, changes in ERα/ERβ mRNA ratio were sensitively associated with changes in mood states in the animal models. These findings suggest that enhancement of ERα/ERβ ratio may play a role in the pharmacological mechanisms of CSS. Furthermore, this ratio can be employed as a potential index for evaluating mood states in animal models and can be considered as a therapeutic target for perimenopausal anxiety and depression in the future.