Host-cell Mediation Of Murine Hepatitis Virus (mhv) Persistence

An in vitro study was undertaken to characterize the mechanisms by which the coronavirus, mouse hepatitis virus (MHV), mediates persistent infection. MHV persists in cultures of mouse fibroblast LM cells (designated LMTK(\u27-)), but produces a lytic infection in L-2 cells. Persistence in LMTK(\u27-) cells was not accompanied by the production of virus mutants nor soluble antiviral factors. Rather, LMTK(\u27-) cells possess two characteristics which allow cultures to support MHV persistence: a reduced level of initial infectability, and a resistance to virus-induced cell fusion. Similar host-cell determinants were found to be operative in persistent MHV infection of another mouse LM cell line, LM-ATCC. A semi-permissive category of host-cells was defined on the basis of reduced infectability by MHV. However, within this category, cell fusion-resistant (LMTK(\u27-) and LM-ATCC) and permissive (mouse neuroblastoma; C-1300) hosts were identified. Evidence is presented that cell fusion by MHV is activated by a cellular chymotrypsin-like enzyme resulting in cleavage of the viral E(,2) glycoprotein (180K MW) to a 90K MW form. Induction of cell fusion by proteolytically-activated E(,2) was not observed in fusion-resistant host cells, due to some inherent property of the plasma membrane. Ammonium chloride, an agent reported to inhibit both virus penetration and cell fusion, was employed in an attempt to convert the acute MHV infection of L-2 cells to a state of persistence. Evidence for an endosomal uncoating mechanism by MHV was found on the basis of uncoating inhibition by ammonium chloride. However, all other parameters of MHV replication, while chronologically displaced due to inhibition of virus uncoating were not otherwise inhibited by ammonium chloride, and the infection followed a lytic, fusogenic course. The expression of cell fusion in permissive L-2 cells was found to be associated with increased cellular permeability to sodium ions. The results of cell-free translation studies indicated that preferential synthesis of MHV proteins occurs in the presence of elevated sodium ion concentration

Epidemiological and nonclinical studies investigating effects of iron in carcinogenesis-A critical review

The efficacy and tolerability of intravenous (i.v.) iron in managing cancer-related anemia and iron deficiency has been clinically evaluated and reviewed recently. However, long-term data in cancer patients are not available; yet, long-term i.v. iron treatment in hemodialysis patients is not associated with increased cancer risk. This review summarizes epidemiological and nonclinical data on the role of iron in carcinogenesis. In humans, epidemiological data suggest correlations between certain cancers and increased iron exposure or iron overload. Nonclinical models that investigated whether iron can enhance carcinogenesis provide only limited evidence relevant for cancer patients since they were typically based on high iron doses as well as injection routes and iron formulations which are not used in the clinical setting. Nevertheless, in the absence of long-term outcome data from prospectively defined trials in i.v. iron-treated cancer patients, iron supplementation should be limited to periods of concomitant anti-tumor treatment

Extracellular Hsp72 concentration relates to a minimum endogenous criteria during acute exercise-heat exposure

Extracellular heat-shock protein 72 (eHsp72) concentration increases during exercise-heat stress when conditions elicit physiological strain. Differences in severity of environmental and exercise stimuli have elicited varied response to stress. The present study aimed to quantify the extent of increased eHsp72 with increased exogenous heat stress, and determine related endogenous markers of strain in an exercise-heat model. Ten males cycled for 90 min at 50% O2peak in three conditions (TEMP, 20°C/63% RH; HOT, 30.2°C/51%RH; VHOT, 40.0°C/37%RH). Plasma was analysed for eHsp72 pre, immediately post and 24-h post each trial utilising a commercially available ELISA. Increased eHsp72 concentration was observed post VHOT trial (+172.4%) (P<0.05), but not TEMP (-1.9%) or HOT (+25.7%) conditions. eHsp72 returned to baseline values within 24hrs in all conditions. Changes were observed in rectal temperature (Trec), rate of Trec increase, area under the curve for Trec of 38.5°C and 39.0°C, duration Trec ≥ 38.5°C and ≥ 39.0°C, and change in muscle temperature, between VHOT, and TEMP and HOT, but not between TEMP and HOT. Each condition also elicited significantly increasing physiological strain, described by sweat rate, heart rate, physiological strain index, rating of perceived exertion and thermal sensation. Stepwise multiple regression reported rate of Trec increase and change in Trec to be predictors of increased eHsp72 concentration. Data suggests eHsp72 concentration increases once systemic temperature and sympathetic activity exceeds a minimum endogenous criteria elicited during VHOT conditions and is likely to be modulated by large, rapid changes in core temperature

Constitutive expression of a groEL-related protein on the surface of human gamma/delta cells

Rabbit antibodies to hsp58 (P1), the human homologue of the Escherichia coli stress protein groEL, react specifically in indirect immunofluorescence and complement-dependent microcytoxicity experiments with a cell surface antigen expressed constitutively by T cell lines bearing gamma/delta receptors. This anti-hsp58-reactive antigen is not demonstrable on T cells that express alpha/beta receptors or on various cells that lack T cell receptors. Certain evidence was obtained to suggest that the target antigen on the surface of gamma/delta T cells is a approximately 77-kD protein distinct from intracellular hsp58 and known members of the hsp70 stress protein family. While the exact nature and significance of this anti-hsp58-reactive protein remain to be determined, these data may help to clarify the roles of groEL- related stress proteins and gamma/delta cells that recognize groEL homologous in immunologic defense against infection and in autoimmune disease

Arabidopsis TAF1 is an MRE11-interacting protein required for resistance to genotoxic stress and viability of the male gametophyte

Repair of DNA double strand breaks (DSBs) by recombination pathways is essential for plant growth and fertility. The recombination endonuclease MRE11 plays important roles in sensing and repair of DNA DSBs. Here we demonstrate protein interaction between Arabidopsis MRE11 and the histone acetyltransferase TAF1, a TATA binding protein Associated Factor (TAF) of the RNA polymerase II transcription initiation factor complex TFIID. Arabidopsis has two TAF1 homologues termed TAF1 and TAF1b and mutant taf1b lines are viable and fertile. In contrast, taf1 null mutations are lethal, demonstrating that TAF1 is an essential gene. Heterozygous taf1+/- plants display abnormal segregation of the mutant allele resulting from defects in pollen tube development, indicating that TAF1 is important for gamete viability. Characterization of an allelic series of taf1 lines revealed that hypomorphic mutants are viable but display developmental defects and reduced plant fertility. Hypersensitivity of taf1 mutants lacking the C-terminal bromodomain to X-rays and mitomycin C, but not to other forms of abiotic stress, established a specific role for TAF1 in plant DNA repair processes. Collectively these studies reveal a function for TAF1 in plant resistance to genotoxic stress, providing further insight into the molecular mechanisms of the DNA damage response in plants

Acetyltransferases and tumour suppression

The acetyltransferase p300 was first identified associated with the adenoviral transforming protein E1A, suggesting a potential role for p300 in the regulation of cell proliferation. Direct evidence demonstrating a role for p300 in human tumours was lacking until the recentl publication by Gayther et al, which strongly supports a role for p300 as a tumour suppressor. The authors identify truncating mutations associated with the loss or mutation of the second allele in both tumour samples and cell lines, suggesting that loss of p300 may play a role in the development of a subset of human cancers

Diminished phosphorylation of a heat shock protein (HSP 27) in infant acute lymphoblastic leukemia

SummaryWe have previously reported lack of expression of a polypeptide designated L3 in infant acute lymphoblastic leukemia (ALL). Expression of L3 occurred predominantly in older children with pre-B ALL. We have recently reported the expression during B cell ontogeny of two other polypeptides, designated L2 and L4 with a similar Mr as L3, which were identified as phosphorylated and non-phosphorylated forms respectively of the low Mr heat shock protein, hsp27. In this study we have characterized L3 and identified it as another phosphorylated form of hsp27. The two phosphorylated forms appear to be differentially expressed in acute leukemia. L3 levels in infants who expressed hsp27 isoforms L2 and L4 were significantly diminished compared to levels in older children with an equivalent amount of hsp27. We conclude that leukemic cells in infant ALL exhibit a unique pattern of phosphorylation of hsp27 expressed at a pre-B cell stage of differentiation.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/29447/1/0000529.pd