A surface-labeled 18 kilodalton antigen in Schistosoma mansoni.

A mild surface-labeling procedure was applied to various developmental stages of Schistosoma mansoni. An 18 kDa protein was preferentially labeled in freshly transformed schistosomula. The labeled protein was equally present on skin-penetrated and mechanically prepared schistosomula and it disappeared upon digestion of intact parasites with proteolytic enzymes. The 18 kDa protein could be specifically precipitated with an antiserum raised against 3-h schistosomula. Six-day lung forms also presented a single major labeled protein component, but the apparent molecular weight of this protein in acrylamide gels was higher than 18 000. Fourteen-day-old and adult schistosomes showed only weak labeling distributed in several bands. The radioactivity pattern of adult worms (but not of schistosomula) could also be obtained by incubating fresh parasites in a medium which had previously been used to label schistosomes and to which a 100 000-fold excess of 127I over 125I had been added. Post-labeling incubation of parasites was found to be essential for the detection of stable surface proteins.

Minimum estimate of the lifetime of histone messenger RNA of HeLa cells.

The lifetime of histone mRNA of HeLa cells has been studied by its kinetic of approach to steady-state labeling. Cells preincubated with low concentrations of actinomycin D to inhibit rRNA synthesis, were incubated with ((3)H)uridine. Linear incorporation of uridine was observed for only two hours under the conditions chosen. Polyribosomes were isolated from cells incubated overnight with trace amounts of ((14)C)uridine and for 30 to 150 min with ((3)H)uridine. RNA was extracted from polyribosomes and fractionated by polyacrylamide gel electrophoresis. Histone mRNA was identified as a peak migrating in a characteristic position, which was absent in gels of RNA obtained from cells treated with the inhibitor of DNA synthesis cytosine arabinoside. The kinetic of labeling of histone mRNA was linear up to 150 min, which represents a minimum estimate of the lifetime of this mRNA.

HLA-DP molecules bind cobalt: a possible explanation for the genetic association with hard metal disease.

Metal dust inhalation induces an interstitial lung disease which may progress to pulmonary fibrosis (hard metal disease, HMD). Cobalt is believed to be the pathogenic agent of HMD. A strong genetic association of HMD with some HLA-DP alleles has been reported although the role of these molecules in the occurrence of the fibrotic disorder remains unclear. A possible explanation of these findings is that HLA-DP but not other HLA class II molecules can bind cobalt. This could have as a consequence an HLA-DP-mediated specific activation of the immune system. To test this hypothesis, we have set up an in vitro binding assay using 57Co and purified HLA-DP and -DR molecules. The results indicate that HLA-DP but not HLA-DR molecules bind cobalt. Moreover, the presence of HLA-DP Glu beta69, which is associated with susceptibility to HMD, determines a higher metal uptake. Molecular modelling of HLA-DP2 molecules places the Glu beta69 residue in a position relevant in determining peptide specificity. The possibility that binding of cobalt by HLA-DP molecules can interfere with their antigen presenting functions is discussed.

Stage-specific expression of a Schistosoma mansoni polypeptide similar to the vertebrate regulatory protein stathmin.

The ubiquitous vertebrate protein stathmin is expressed and phosphorylated in response to a variety of external and internal signals. Stathmin, in turn, controls cell growth and differentiation through its capacity to regulate microtubule assembly dynamics. This is the first report on the molecular cloning and characterization of a stathmin-like protein (SmSLP) in an invertebrate, the human blood fluke Schistosoma mansoni. SmSLP is first synthesized at high levels in the intermediate molluscan host and completely disappears 48 h after penetration into the mammalian host. The protein is preferentially iodinated in intact immature parasites using the Bolton-Hunter reagent, can be quantitatively extracted in high salt buffers, and remains soluble after boiling. Native SmSLP was partially sequenced, and its complete structure was derived from the cloning and sequencing of its cDNA. The sequence is up to 26% identical to vertebrate stathmin sequences and contains two potential phosphorylation sites. Native SmSLP is indeed phosphorylated because phosphatase digestion shifts its mobility in electrofocusing gels. SmSLP associates with tubulin, as suggested by immune co-precipitation results. In vitro experiments demonstrated that SmSLP inhibits tubulin assembly and causes the depolymerization of preassembled microtubules, thus probably fulfilling regulatory roles in critical steps of schistosome development.