Ionizing radiation: how fungi cope, adapt, and exploit with the help of melanin

Life on Earth has always existed in the flux of ionizing radiation. However, fungi seem to interact with the ionizing radiation differently from other inhabitants of the Earth. Recent data show that melanized fungal species like those from Chernobyl's reactor respond to ionizing radiation with enhanced growth. Fungi colonize space stations and adapt morphologically to extreme conditions. Radiation exposure causes upregulation of many key genes, and an inducible microhomology-mediated recombination pathway could be a potential mechanism of adaptive evolution in eukaryotes. The discovery of melanized organisms in high radiation environments, the space stations, Antarctic mountains, and in the reactor cooling water combined with phenomenon of 'radiotropism' raises the tantalizing possibility that melanins have functions analogous to other energy harvesting pigments such as chlorophylls.     

Salt-induced changes in lipid composition and membrane fluidity of halophilic yeast-like melanized fungi

The halophilic melanized yeast-like fungi Hortaea werneckii, Phaeotheca triangularis, and the halotolerant Aureobasidium pullulans, isolated from salterns as their natural environment, were grown at different NaCl concentrations and their membrane lipid composition and fluidity were examined. Among sterols, besides ergosterol, which was the predominant one, 23 additional sterols were identified. Their total content did not change consistently or significantly in response to raised NaCl concentrations in studied melanized fungi. The major phospholipid classes were phosphatidylcholine and phosphatidylethanolamine, followed by anionic phospholipids. The most abundant fatty acids in phospholipids contained C₁₆ and C₁₈ chain lengths with a high percentage of C18:2^9,12. Salt stress caused an increase in the fatty acid unsaturation in the halophilic H. werneckii and halotolerant A. pullulans but a slight decrease in halophilic P. triangularis. All the halophilic fungi maintained their sterol-to-phospholipid ratio at a significantly lower level than did the salt-sensitive Saccharomyces cerevisiae and halotolerant A. pullulans. Electron paramagnetic resonance (EPR) spectroscopy measurements showed that the membranes of all halophilic fungi were more fluid than those of the halotolerant A. pullulans and salt-sensitive S. cerevisiae, which is in good agreement with the lipid composition observed in this study.Communicated by W.D. Grant     

Morphological changes in melanized and non-melanized Cryptococcus neoformans cells post exposure to sparsely and densely ionizing radiation demonstrate protective effect of melanin

There is a need for novel and effective prophylactic treatments and radioprotective materials to protect civilians and military personnel from ionizing radiation in contaminated environments. Melanin, a naturally occurring, ubiquitous pigment, has been shown to confer radioresistance, acting as a potential radioprotective agent. We have demonstrated that melanized Cryptococcus neoformans (CN) cells had improved survival post ionizing irradiation than non-melanized ones. The goal of this study was to identify morphological changes in melanized and non-melanized CN cells following irradiation with densely-ionizing deuterons and alpha particles relative to sparsely-ionizing gamma radiation. We observed significant differences between the melanized and non-melanized CN cellular ultrastructure following irradiation. Melanized CN cells were relatively resistant to mid and max-dose levels of alpha particles and deuterons irradiation. Following irradiation the capsule was stripped, but the cell wall was intact and structural integrity was maintained. At the maximum dose, cytoplasmic vacuolization, and mitochondrial swelling started to occur. In contrast, the non-melanized CN strain was sensitive to the mid-dose radiation. Non-melanized cells presented two morphologies: small condensed, and swollen, lacking structural integrity. This morphological investigation provides the first direct evidence of the radioprotective properties of melanin in CN cells subjected to high RBE and high LET ionizing radiation.     

Ionizing radiation enhances IL-6 and IL-8 production by human endothelial cells

Irradiation exposure is known to induce an inflammatory reaction. Endothelial cells play a crucial role both in the inflammatory process and in radiation damage. Therefore, supernatants and cell lysates of (60)Co-irradiated human umbilical vein endothelial cells (HUVEC) have been assessed for the presence of pro-inflammatory cytokines. After gamma irradiation, interleukin (IL)-1alpha, IL-1beta and tumor necrosis factor (TNF)-alpha remained undetectable in both cell supernatants and cell lysates. However, a dose-dependent increase in the production of IL-6 and IL-8 has been demonstrated up to 6 days after exposure. These data indicate that the pro-inflammatory cytokines IL-6 and IL-8 may be involved in the inflammatory response of vascular endothelium induced by exposure to ionizing radiation.     

Ionizing radiation enhances matrix metalloproteinase-2 production in human lung epithelial cells

Radiation pneumonitis is a major complication of radiation therapy. However, the detailed cellular mechanisms have not been clearly defined. Based on the recognition that basement membrane disruption occurs in acute lung injury and that matrix metalloproteinase (MMP)-2 can degrade type IV collagen, one of the major components of the basement membrane, we hypothesized that ionizing radiation would modulate MMP-2 production in human lung epithelial cells. To evaluate this, the modulation of MMP-2 with irradiation was investigated in normal human bronchial epithelial cells as well as in A549 cells. We measured the activity of MMP-2 in the conditioned medium with zymography and the MMP-2 mRNA level with RT-PCR. Both of these cells constitutively expressed 72-kDa gelatinolytic activity, corresponding to MMP-2, and exposure to radiation increased this activity. Consistent with the data of zymography, ionizing radiation increased the level of MMP-2 mRNA. This radiation-induced increase in MMP-2 expression was mediated via p53 because the p53 antisense oligonucleotide abolished the increase in MMP-2 activity as well as the accumulation of p53 after irradiation in A549 cells. These results indicate that MMP-2 expression by human lung epithelial cells is involved in radiation-induced lung injury.     

Isolation and characterization of melanized fungi from limestone formations in Mallorca

Melanized fungi were isolated from limestone surfaces in upland and coastal environments in the Mediterranean island of Mallorca. One hundred seventeen isolates were recovered from two topographically distinct sites. Due to the difficulty in distinguishing among isolates based on morphological criteria, microsatellite-primed PCR techniques were used to group isolates into genotypes that were assumed to represent species. Seventeen genotypes were characterized from one site and twenty six from the other, with four genotypes common to both. Classical and molecular methods were used to identify representative strains. Morphological methods rarely provided a reliable identification; only three isolates, Hortaea werneckii, Trimmatostroma abietis and Aureobasidium pullulans were identified with certainty, and the identification was confirmed by molecular data. Morphological characters that were widespread among the isolates included scarce micronematous conidial states or non-sporulating sterile mycelia, mature mycelia with dark olive green or black hyphae, mycelia with torulous hyphae, whose cells developed one or more transverse septa. In many of these fungi, the cells of mature hyphae disarticulated, suggesting asexual reproduction by a thallic micronematous conidiogenesis or by simple propagative fragmentation. Sequencing of the internal transcribed spacers (ITS1, ITS2) and 5.8S ribosomal gene, as well as the 18S rDNA ribosomal gene were employed to investigate the isolates’ phylogenetic affinities. The majority of the isolates could be grouped in two main classes of Ascomycetes, Dothideomycetes and Chaetothyriomycetes, although many others did not correspond with any sequence deposited in public databases, suggesting they could be of unknown genera that did not correspond with any well-defined Ascomycete order.     

Solar UV-B radiation inhibits the growth of Antarctic terrestrial fungi

We tested the effects of solar radiation, and UV-B in particular, on the growth of Antarctic terrestrial fungi. The growth responses to solar radiation of five fungi, Geomyces pannorum, Phoma herbarum, Pythium sp., Verticillium sp., and Mortierella parvispora, each isolated from Antarctic terrestrial habitats, were examined on an agar medium in the natural Antarctic environment. A 3-h exposure to solar radiation of >287 nm reduced the hyphal extension rates of all species relative to controls kept in the dark. Pythium sp. cultures exposed to solar radiation for 1.5 h on five consecutive days were most sensitive to radiation of >287 nm, but radiation of >313 nm also inhibited growth to a lesser extent. Radiation of >400 nm had no effect on hyphal growth relative to controls kept in the dark. Short-wave solar UV-B radiation of between 287 and 305 nm inhibited the growth of Pythium sp. hyphae on and below the surface of the agar medium after 24 h, but radiation of > or =345 nm only reduced the growth of surface hyphae. Similar detrimental effects of UV-B on surface and, to a lesser extent, submerged hyphae of all five fungi were shown in the laboratory by using artificial UV-B from fluorescent lamps. A comparison of growth responses to solar radiation and temperature showed that the species that were most resistant to UV radiation grew fastest at higher temperatures. These data suggest that solar UV-B reduces the growth of fungi on the soil surface in the Antarctic terrestrial environment.     

食用菌黑色素代谢的研究进展

黑色素的代谢对食用菌的生长发育具有至关重要的影响,黑色素的代谢异常导致了食用菌白色新品种的出现。对食用菌黑色素代谢的影响因子进行了综述,对黑色素代谢异常与食用菌白化菌株形成的关系进行了阐述,并介绍了食用菌黑色素的形成途径,对黑色素合成过程中的关键酶类及其抑制剂的研究进行了简要概括,主要包括酪氨酸酶、漆酶和聚酮合成酶的研究。并展望了食用菌黑色素代谢今后主要的研究方向,旨在为白色食用菌的进一步开发和利用提供参考。     

Ionizing radiation enhances adenoviral vector expressing mda-7/IL-24-mediated apoptosis in human ovarian cancer

Ovarian cancer is the fifth most common cause of cancer-related death in women. Current interventional approaches, including debulking surgery, chemotherapy, and/or radiation have proven minimally effective in preventing the recurrence and/or mortality associated with this malignancy. Subtraction hybridization applied to terminally differentiating human melanoma cells identified melanoma differentiation associated gene-7/interleukin-24 (mda-7/IL-24), whose unique properties include the ability to selectively induce growth suppression, apoptosis, and radiosensitization in diverse cancer cells, without causing any harmful effects in normal cells. Previously, it has been shown that adenovirus-mediated mda-7/IL-24 therapy (Ad.mda-7) induces apoptosis in ovarian cancer cells, however, the apoptosis induction was relatively low. We now document that apoptosis can be enhanced by treating ovarian cancer cells with ionizing radiation (IR) in combination with Ad.mda-7. Additionally, we demonstrate that mda-7/IL-24 gene delivery, under the control of a minimal promoter region of progression elevated gene-3 (PEG-3), which functions selectively in diverse cancer cells with minimal activity in normal cells, displays a selective radiosensitization effect in ovarian cancer cells. The present studies support the use of IR in combination with mda-7/IL-24 as a means of augmenting the therapeutic benefit of this gene in ovarian cancer, particularly in the context of tumors displaying resistance to radiation therapy.     

Ionizing radiation and hematopoietic malignancies: Altering the adaptive landscape

Somatic evolution, which underlies tumor progression, is driven by two essential components: 1) diversification of phenotypes through heritable mutations and epigenetic changes and 2) selection for mutant clones which possess maximal fitness. Exposure to ionizing radiation (IR) is strongly associated with increased risk of carcinogenesis. This link is traditionally attributed to causation of oncogenic mutations through the mutagenic effects of irradiation. On the other hand, potential effects of irradiation on altering fitness and increasing selection for mutant clones are frequently ignored. Recent studies bring the effects of irradiation on fitness and selection into focus, demonstrating that IR exposure results in stable reductions in the fitness of hematopoietic stem and progenitor cell populations. These reductions of fitness are associated with alteration of the adaptive landscape, increasing the selective advantages conferred by certain oncogenic mutations. Therefore, the link between irradiation and carcinogenesis might be more complex than traditionally appreciated: while mutagenic effects of irradiation should increase the probability of occurrence of oncogenic mutations, IR can also work as a tumor promoter, increasing the selective expansion of clones bearing mutations which become advantageous in the irradiation-altered environment, such as activated mutations in Notch1 or disrupting mutations in p53.     

Ionizing radiation and hematopoietic malignancies: Altering the adaptive landscape

Somatic evolution, which underlies tumor progression, is driven by two essential components: (1) diversification of phenotypes through heritable mutations and epigenetic changes and (2) selection for mutant clones which possess higher fitness. Exposure to ionizing radiation (IR) is highly associated with increased risk of carcinogenesis. This link is traditionally attributed to causation of oncogenic mutations through the mutagenic effects of irradiation. On the other hand, potential effects of irradiation on altering fitness and increasing selection for mutant clones are frequently ignored. Recent studies bring the effects of irradiation on fitness and selection into focus, demonstrating that IR exposure results in stable reductions in the fitness of hematopoietic stem and progenitor cell populations. These reductions of fitness are associated with alteration of the adaptive landscape, increasing the selective advantages conferred by certain oncogenic mutations. Therefore, the link between irradiation and carcinogenesis might be more complex than traditionally appreciated: while mutagenic effects of irradiation should increase the probability of occurrence of oncogenic mutations, IR can also work as a tumor promoter, increasing the selective expansion of clones bearing mutations which become advantageous in the irradiation-altered environment, such as activated mutations in Notch1 or disrupting mutations in p53.Key words: Notch, p53, fitness, irradiation, hematopoietic, evolution     

Ionizing radiation sensitivity of DNA polymerase lambda-deficient cells

Ionizing radiation induces a diverse spectrum of DNA lesions, including strand breaks and oxidized bases. In mammalian cells, ionizing radiation-induced lesions are targets of non-homologous end joining, homologous recombination, and base excision repair. In vitro assays show a potential involvement of DNA polymerase lambda in non-homologous end joining and base excision repair. In this study, we investigated whether DNA polymerase lambda played a significant role in determining ionizing radiation sensitivity. Despite increased sensitivity to hydrogen peroxide, lambda-deficient mouse embryonic fibroblasts displayed equal survival after exposure to ionizing radiation compared to their wild-type counterparts. In addition, we found increased sensitivity to the topoisomerase inhibitors camptothecin and etoposide in the absence of polymerase lambda. These results do not reveal a major role for DNA polymerase lambda in determining radiosensitivity in vivo.     

Ionizing and non-ionizing radiation (comparative risk estimations)

The population has widely used mobile communication for already more than 15 years. It is important to note that the use of mobile communication has sharply changed the conditions of daily exposure of the population to EME We expose our brain daily for the first time in the entire civilization. The mobile phone is an open and uncontrollable source of electromagnetic radiation. The comparative risk estimation for the population of ionizing and non-ionizing radiation was carried out taking into account the real conditions of influence. Comparison of risks for the population of ionizing and non-ionizing radiation leads us to a conclusion that EMF RF exposure in conditions of wide use of mobile communication is potentially more harmful than ionizing radiation influence.