Human RPE expression of cell survival factors. Invest Ophthalmol Vis Sci.

PURPOSE. To determine basal and tumor necrosis factor (TNF)-␣-regulated expression of retinal pigment epithelial (RPE) cell survival factors and whether regulation is dependent on nuclear transcription factor (NF)-B. METHODS. Cultured human RPE cells were infected with adenovirus encoding either mutant inhibitory (I)-B or ␤-galactosidase and treated with TNF-␣ for various times. Freshly prepared RPE/choroid and RPE samples were isolated from human donor eyes. Real-time reverse transcription-polymerase chain reaction, Western blot, and immunocytochemistry were used to determine survival factor gene expression, cellular protein levels, and localization, respectively. RESULTS. Multiple survival factor genes, including cellular inhibitor of apoptosis protein (c-IAP1), c-IAP2, TNF receptor-associated factor-1 (TRAF-1), TRAF-2, B-cell leukemia/lymphoma-2 (Bcl-2), Bcl-x, A1, and cellular Fas-associated death domain (FADD)-like interleukin-1␤-converting enzyme-like inhibitory protein (c-FLIP), were expressed in basal conditions in both cultured RPE cells and RPE cells in situ, whereas survivin was expressed only by cultured cells. TNF-␣ upregulated expression of TRAF-1, TRAF-2, c-IAP1, c-IAP2, c-FLIP, and A1. TRAF-1, c-FLIP, and to a lesser extent c-IAP2 protein levels were increased by TNF-␣ in a time-dependent manner, whereas c-IAP1, survivin, Bcl-x L , and TRAF-2 protein levels were not influenced by TNF-␣ treatment at any time point tested. In contrast, Bcl-2 and A1 proteins were not detected under basal conditions or after TNF-␣ treatment. Overexpression of mutant IB blocked TNF-␣-induced TRAF-1, TRAF-2, c-IAP1, c-IAP2, c-FLIP, and A1 gene expression and downregulated TRAF-1 protein levels. TRAF-1 and Bcl-x L proteins were localized diffusely in RPE cytoplasm. CONCLUSIONS. Multiple RPE cell survival factors are expressed by human RPE cells. TNF-␣ regulates expression of some of these factors in an NF-B-dependent manner, whereas others are not influenced by NF-B. RPE cell survival factors may protect RPE cells from apoptosis normally and in diseases such as age-related macular degeneration (AMD) and proliferative vitreoretinopathy (PVR). (Invest Ophthalmol Vis Sci. 2005;46: 1755-176

Plant communities in harsh sites are less invaded: a summary of observations and proposed explanations

Plant communities in abiotically stressful, or ‘harsh’, habitats have been reported to be less invaded by non-native species than those in more moderate habitats. Here, we synthesize descriptive and experimental evidence for low levels of invasion in habitats characterized by a variety of environmental stressors: low nitrogen; low phosphorus; saline, sodic or alkaline soils; serpentine soils; low soil moisture; shallow/rocky soils; temporary inundation; high shade; high elevation; and high latitude. We then discuss major categories of hypotheses to explain this pattern: the propagule limitation mechanism suggests invasion of harsh sites is limited by relatively low arrival rates of propagules compared with more moderate habitats, while invasion resistance mechanisms suggest that harsh habitats are inherently less invasible due to stressful abiotic conditions and/or increased effects of biotic resistance from resident organisms. Both propagule limitation and invasion resistance may simultaneously contribute to low invadedness of harsh sites, but the management implications of these mechanisms differ. If propagule limitation is more important, managers should focus on reducing the likelihood of propagule introductions. If invasion resistance mechanisms are in play, managers should focus on restoring or maintaining harsh conditions at a site to reduce invasibility