Control of lytic function by mitogen-activated protein kinase extracellular regulatory kinase 2 (ERK2) in a human natural killer cell line: Identification of perforin and granzyme B mobilization by functional ERK2

The signal pathways that control effector function in human natural killer (NK) cells are little known. In this study, we have identified the critical role of the mitogen-activated protein kinase (MAPK) pathway in NK lysis of tumor cells, and this pathway may involve the mobilization of granule components in NK cells upon interaction with sensitive tumor target cells. Evidence was provided by biological, biochemical, and gene transfection methods. NK cell binding to tumor cells for 5 min was sufficient to maximally activate MAPK/extracellular signal-regulatory kinase 2 (ERK2), demonstrated by its tyrosine phosphorylation and by its ability to function as an efficient kinase for myelin basic protein. MAPK activation was achieved in NK cells only after contact with NK-sensitive but not NK-resistant target cells. In immunocytochemical studies, cytoplasmic perforin and granzyme B were both maximally redirected towards the tumor contact zone within 5 min of NK cell contact with tumor cells. A specific MAPK pathway inhibitor, PD098059, could block not only MAPK activation but also redistribution of perforin/granzyme B in NK cells, which occur upon target ligation. PD098059 also interfered with NK lysis of tumor cells in a 5-h 51Cr-release assay, but had no ability to block NK cell proliferation. Transient transfection studies with wild-type and dominant-negative MAPK/ERK2 genes confirmed the importance of MAPK in NK cell lysis. These results document a pivotal role of MAPK in NK effector function, possibly by its control of movement of lytic granules, and clearly define MAPK involvement in a functional pathway unlinked to cell growth or differentiation

Soil solarization and sustainable agriculture

Pesticide treatments provide an effective control of soilborne pests in vegetable and fruit crops, but their toxicity to animals and people and residual toxicity in plants and soil, and high cost make their use hazardous and economically expensive. Moreover, actual environmental legislation is imposing severe restrictions on the use or the total withdrawal of most soil-applied pesticides. Therefore, an increasing emphasis has been placed on the use of nonchemical or pesticide-reduced control methods. Soil solarization is a nonpesticidal technique which kills a wide range of soil pathogens, nematodes, and weed seeds and seedlings through the high soil temperatures raised by placing plastic sheets on moist soil during periods of high ambient temperature. Direct thermal inactivation of target organisms was found to be the most important mechanism of solarization biocidal effect, contributed also by a heat-induced release of toxic volatile compounds and a shift of soil microflora to microorganisms antagonist of plant pathogens. Soil temperature and moisture are critical variables in solarization thermal effect, though the role of plastic film is also fundamental for the solarizing process, as it should increase soil temperature by allowing the passage of solar radiation while reducing energetic radiative and convective losses. Best solarizing properties were shown by low-density or vynilacetate- coextruded polyethylene formulations, but a wide range of plastic materials were documented as also suitable to soil solarization. Solar heating was normally reported to improve soil structure and increase soil content of soluble nutrients, particularly dissolved organic matter, inorganic nitrogen forms, and available cations, and shift composition and richness of soil microbial communities, with a marked increase of plant growth beneficial, plant pathogen antagonistic or root quick recolonizer microorganisms. As a consequence of these effects, soil solarization was largely documented to increase plant growth and crop yield and quality along more than two crop cycles. Most important fungal plant pathogenic species were found strongly suppressed by the solarizing treatment, as several studies documented an almost complete eradication of economically relevant pathogens, such as Fusarium spp., Phytophthora spp., Pythium spp., Sclerotium spp., Verticillium spp., and their related diseases in many vegetable and fruit crops and in different experimental conditions. Beneficial effects on fungal pathogens were stated to commonly last for about two growing seasons and also longer. Soil solarization demonstrated to be effective for the control of bacterial diseases caused by Agrobacterium spp., Clavibacter michiganensis and Erwinia amylovora, but failed to reduce incidence of tomato diseases caused by Pseudomonas solanacearum. Solarization was generally found less effective on phytoparasitic nematodes than on other organisms, due to their quicker soil recolonization compared to fungal pathogens and weeds, but field and greenhouse studies documented consistant reductions of root-knot severity and population densities of root-knot nematodes, Meloidogyne spp., as well as a satisfactory control of cyst-nematode species, such as Globodera rostochiensis and Heterodera carotae, and bulb nematode Ditylenchus dipsaci. Weeds were variously affected by solar heating, as annual species were generally found almost completely suppressed and perennial species more difficult to control, due to the occurrence deep propagules not exposed to lethal temperature. Residual effect of solarization on weeds was found much more pronounced than on nematodes and most fungal pathogens. Soil solarization may be perfect fit for all situations in which use of pesticides is restricted or completely banned, such as in organic production, or in farms located next to urban areas, or specialty crops with few labeled pesticides. Advantages of solarization also include economic convenience, as demonstrated by many comparative benefit/cost analyses, ease of use by growers, adaptability to many cropping systems, and a full integration with other control tools, which makes this technique perfectly compatible with principles of integrated pest management required by sustainable agriculture