Plasma proteome analysis in HTLV-1-associated myelopathy/tropical spastic paraparesis

Background

A new subgroup of HIV-1, designated Group P, was recently detected in two unrelated patients of Cameroonian origin. HIV-1 Group P phylogenetically clusters with SIVgor suggesting that it is the result of a cross-species transmission from gorillas. Until today, HIV-1 Group P has only been detected in two patients, and its degree of adaptation to the human host is largely unknown. Previous data have shown that pandemic HIV-1 Group M, but not non-pandemic Group O or rare Group N viruses, efficiently antagonize the human orthologue of the restriction factor tetherin (BST-2, HM1.24, CD317) suggesting that primate lentiviruses may have to gain anti-tetherin activity for efficient spread in the human population. Thus far, three SIV/HIV gene products (vpu, nef and env) are known to have the potential to counteract primate tetherin proteins, often in a species-specific manner. Here, we examined how long Group P may have been circulating in humans and determined its capability to antagonize human tetherin as an indicator of adaptation to humans.

Results

Our data suggest that HIV-1 Group P entered the human population between 1845 and 1989. Vpu, Env and Nef proteins from both Group P viruses failed to counteract human or gorilla tetherin to promote efficient release of HIV-1 virions, although both Group P Nef proteins moderately downmodulated gorilla tetherin from the cell surface. Notably, Vpu, Env and Nef alleles from the two HIV-1 P strains were all able to reduce CD4 cell surface expression.

Conclusions

Our analyses of the two reported HIV-1 Group P viruses suggest that zoonosis occurred in the last 170 years and further support that pandemic HIV-1 Group M strains are better adapted to humans than non-pandemic or rare Group O, N and P viruses. The inability to antagonize human tetherin may potentially explain the limited spread of HIV-1 Group P in the human population.     

MDA‐7/IL‐24 regulates proliferation,invasion and tumor cell radiosensitivity: A new cancer therapy?

The novel cytokine MDA-7/IL-24 was identified by subtractive hybridization in the mid-1990s as a cytokine whose expression increased during the induction of terminal differentiation, and that was either not expressed or was present at low levels in tumor cells compared to non-transformed cells. Multiple studies from several laboratories have subsequently demonstrated that expression of IL-24 in tumor cells, but not in non-transformed cells, causes their growth arrest and ultimately cell death. In addition, IL-24 has been noted to be a radiosensitizing cytokine, which in part is due to the generation of reactive oxygen species (ROS) and causing endoplasmic reticulum stress. Recent publications of Phase I trial data have shown that a recombinant adenovirus to express MDA-7/IL-24 (Ad.mda-7 (INGN 241)) was safe and had tumoricidal effects in patients, which argues that IL-24 may have therapeutic value. This review describes what is known about the impact of IL-24 on tumor cell biology in addition to approaches that may enhance the toxicity of this novel cytokine.     

Deoxycholic acid activates the c-Jun N-terminal kinase pathway via FAS receptor activation in primary hepatocytes. Role of acidic sphingomyelinase-mediated ceramide generation in FAS receptor activation

We have shown previously that bile acids can activate the JNK pathway and down-regulate cholesterol 7alpha-hydroxylase (CYP7A1), the rate-limiting enzyme in the neutral pathway of bile acid biosynthesis. In this study, the mechanism(s) by which deoxycholic acid (DCA) activates the JNK pathway were examined. FAS receptor (FAS-R) and acidic sphingomyelinase (ASM)-deficient hepatocytes were resistant to DCA-induced activation of the JNK pathway. Activation of the JNK pathway (2-3-fold) in response to tumor necrosis factor-alpha was similar in both wild-type and FAS-R(-/-) hepatocytes. In wild-type and FAS-R(-/-) hepatocytes, ceramide elevation was detected as early as 2 min and peaked at 10 min after DCA treatment. In contrast, ASM(-/-) hepatocytes were defective in DCA-induced ceramide generation. Treatment with DCA resulted in movement of FAS-R to the cell surface, which was blocked upon treatment with brefeldin A. However, brefeldin A failed to block DCA-mediated JNK activation in wild-type hepatocytes. DCA-induced JNK activation was independent of either the epidermal growth factor receptor activation or free radical generation. Addition of ASM to rat hepatocytes activated JNK and down-regulated CYP7A1 mRNA levels. In conclusion, these results show that DCA activates JNK and represses CYP7A1 mRNA levels in primary hepatocytes via an ASM/FAS-R-dependent mechanism that is independent of either the epidermal growth factor receptor or free radical generation.     

Ceramide plays a prominent role in MDA‐7/IL‐24‐induced cancer‐specific apoptosis

Melanoma differentiation associated gene‐7/interleukin‐24 (mda‐7/IL‐24) uniquely displays broad cancer‐specific apoptosis‐inducing activity through induction of endoplasmic reticulum (ER) stress. We hypothesize that ceramide, a promoter of apoptosis, might contribute to mda‐7/IL‐24 induction of apoptosis. Ad.mda‐7‐infected tumor cells, but not normal cells, showed increased ceramide accumulation. Infection with Ad.mda‐7 induced a marked increase in various ceramides (C16, C24, C24:1) selectively in prostate cancer cells. Inhibiting the enzyme serine palmitoyltransferase (SPT) using the potent SPT inhibitor myriocin (ISP1), impaired mda‐7/IL‐24‐induced apoptosis and ceramide production, suggesting that ceramide formation caused by Ad.mda‐7 occurs through de novo synthesis of ceramide and that ceramide is required for mda‐7/IL‐24‐induced cell death. Fumonisin B1 (FB1) elevated ceramide formation as well as apoptosis induced by Ad.mda‐7, suggesting that ceramide formation may also occur through the salvage pathway. Additionally, Ad.mda‐7 infection enhanced expression of acid sphingomyelinase (ASMase) with a concomitant increase in ASMase activity and decreased sphingomyelin in cancer cells. ASMase silencing by RNA interference inhibited the decreased cell viability and ceramide formation after Ad.mda‐7 infection. Ad.mda‐7 activated protein phosphatase 2A (PP2A) and promoted dephosphorylation of the anti‐apoptotic molecule BCL‐2, a downstream ceramide‐mediated pathway of mda‐7/IL‐24 action. Pretreatment of cells with FB1 or ISP‐1 abolished the induction of ER stress markers (BiP/GRP78, GADD153 and pospho‐eIF2α) triggered by Ad.mda‐7 infection indicating that ceramide mediates ER stress induction by Ad.mda‐7. Additionally, recombinant MDA‐7/IL‐24 protein induced cancer‐specific production of ceramide. These studies define ceramide as a key mediator of an ER stress pathway that may underlie mda‐7/IL‐24 induction of cancer‐specific killing. J. Cell. Physiol. 222: 546–555, 2010. © 2009 Wiley‐Liss, Inc.     

Prenatal malaria immune experience affects acquisition of Plasmodium falciparum merozoite surface protein-1 invasion inhibitory antibodies during infancy

African infants are often born of mothers infected with malaria during pregnancy. This can result in fetal exposure to malaria-infected erythrocytes or their soluble products with subsequent fetal immune priming or tolerance in utero. We performed a cohort study of 30 newborns from a malaria holoendemic area of Kenya to determine whether T cell sensitization to Plasmodium falciparum merozoite surface protein-1 (MSP-1) at birth correlates with infant development of anti-MSP-1 Abs acquired as a consequence of natural malaria infection. Abs to the 42- and 19-kDa C-terminal processed fragments of MSP-1 were determined by serology and by a functional assay that quantifies invasion inhibition Abs against the MSP-1(19) merozoite ligand (MSP-1(19) IIA). Infants had detectable IgG and IgM Abs to MSP-1(42) and MSP-1(19) at 6 mo of age with no significant change by age 24-30 mo. In contrast, MSP-1(19) IIA levels increased from 6 to 24-30 mo of age (16-29%, p < 0.01). Infants with evidence of prenatal exposure to malaria (defined by P. falciparum detection in maternal, placental, and/or cord blood compartments) and T cell sensitization at birth (defined by cord blood lymphocyte cytokine responses to MSP-1) showed the greatest age-related increase in MSP-1(19) IIA compared with infants with prenatal exposure to malaria but who lacked detectable T cell MSP-1 sensitization. These data suggest that fetal sensitization or tolerance to MSP-1, associated with maternal malaria infection during pregnancy, affects the development of functional Ab responses to MSP-1 during infancy.     

Nutrient fluxes via litterfall and leaf litter decomposition vary across a gradient of soil nutrient supply in a lowland tropical rain forest

The extent to which plant communities are determined by resource availability is a central theme in ecosystem science, but patterns of small-scale variation in resource availability are poorly known. Studies of carbon (C) and nutrient cycling provide insights into factors limiting tree growth and forest productivity. To investigate rates of tropical forest litter production and decomposition in relation to nutrient availability and topography in the absence of confounding large-scale variation in climate and altitude we quantified nutrient fluxes via litterfall and leaf litter decomposition within three distinct floristic associations of tropical rain forest growing along a soil fertility gradient at the Sepilok Forest Reserve (SFR), Sabah, Malaysia. The quantity and nutrient content of small litter decreased along a gradient of soil nutrient availability from alluvial forest (most fertile) through sandstone forest to heath forest (least fertile). Temporal variation in litterfall was greatest in the sandstone forest, where the amount of litter was correlated negatively with rainfall in the previous month. Mass loss and N and P release were fastest from alluvial forest litter, and slowest from heath forest litter. All litter types decomposed most rapidly in the alluvial forest. Stand-level N and P use efficiencies (ratios of litter dry mass to nutrient content) were greatest for the heath forest followed by the sandstone ridge, sandstone valley and alluvial forests, respectively. We conclude that nutrient supply limits productivity most in the heath forest and least in the alluvial forest. Nutrient supply limited productivity in sandstone forest, especially on ridge and hill top sites where nutrient limitation may be exacerbated by reduced rates of litter decomposition during dry periods. The fluxes of N and P varied significantly between the different floristic communities at SFR and these differences may contribute to small-scale variation in species composition.     

Defects in the cytochrome b6/f complex prevent light-induced expression of nuclear genes involved in chlorophyll biosynthesis

Mutants with defects in the cytochrome (cyt) b6/f complex were analyzed for their effect on the expression of a subgroup of nuclear genes encoding plastid-localized enzymes participating in chlorophyll biosynthesis. Their defects ranged from complete loss of the cytb6/f complex to point mutations affecting specifically the quinone-binding QO site. In these seven mutants, light induction of the tetrapyrrole biosynthetic genes was either abolished or strongly reduced. In contrast, a normal induction of chlorophyll biosynthesis genes was observed in mutants with defects in photosystem II, photosystem I, or plastocyanin, or in wild-type cells treated with 3-(3'4'-dichlorophenyl)-1,1-dimethylurea or 2,5-dibromo-3-methyl-6-isopropyl benzoquinone. We conclude that the redox state of the plastoquinone pool does not control light induction of these chlorophyll biosynthetic genes. The signal that affects expression of the nuclear genes appears to solely depend on the integrity of the cytb6/f complex QO site. Since light induction of these genes in Chlamydomonas has recently been shown to involve the blue light receptor phototropin, the results suggest that cytb6/f activity regulates a plastid-derived factor required for their expression. This signaling pathway differs from that which regulates state transitions, since mutant stt7, lacking a protein kinase involved in phosphorylation of the light-harvesting complex II, was not altered in the expression of the chlorophyll biosynthetic genes.