Cancer mortality in health and science technicians

BACKGROUND

Nearly one million U.S. women are employed as health or science technicians with various chemical and biological exposures, but few studies have looked at their health outcomes.

METHODS

Using 1984-1995 mortality data with coded occupation information, we calculated race- and age-adjusted proportionate cancer mortality ratios (PCMRs) and 95% confidence intervals for two age groups for black and white women with occupations of clinical laboratory (CLT), radiologic, and science technician.

RESULTS

For CLTs, the PCMRs for breast cancer were borderline significantly elevated. The PCMRs for leukemia were significantly elevated, particularly for myeloid leukemia. Radiologic technicians had no significantly elevated PCMRs. Science technicians had significantly elevated PCMRs for non-Hodgkin's lymphoma and multiple myeloma in the younger age group.

DISCUSSION

The elevated risks for lymphatic and hematopoietic neoplasms in CLTs and science technicians may be associated with occupational exposures.

Characterisation of the PsbX protein from Photosystem II and light regulation of its gene expression in higher plants

The location and expression of the previously uncharacterised photosystem II subunit PsbX have been analysed in higher plants. We show that this protein is a component of photosystem II (PSII) core particles but absent from light-harvesting complexes or PSII reaction centres. PsbX is, however, localised to the near vicinity of the reaction centre because it can be cross-linked to cytochrome b559, which is known to be associated with the D1/D2 dimer. We also show that the expression of this protein is tightly regulated by light, since neither protein nor mRNA is found in dark-grown plants.

An in vitro study of the use of photodynamic therapy for the treatment of natural oral plaque biofilms formed in vivo

Seven-day oral plaque biofilms have been formed on natural enamel surfaces in vivo using a previously reported in situ device. The devices are then incubated with a cationic Zn(II) phthalocyanine photosensitizer and irradiated with white light. Confocal scanning laser microscopy (CSLM) of the biofilms shows that the photosensitizer is taken up into the biomass of the biofilm and that significant cell death is caused by photodynamic therapy (PDT). In addition, the treated biofilms are much thinner than the control samples and demonstrate a different structure from the control samples, with little evidence of channels and a less dense biomass. Transmission electron microscopy (TEM) of the in vivo-formed plaque biofilms reveals considerable damage to bacteria in the biofilm, vacuolation of the cytoplasm and membrane damage being clearly visible after PDT. These results clearly demonstrate the potential value of PDT in the management of oral biofilms.

Use of a noncontact radiant heat bandage for the treatment of chronic venous stasis ulcers

A noncontact radiant heat bandage was used for the treatment of chronic venous stasis ulcers (mean duration 4.44 years) in inpatients who had failed aggressive inpatient and outpatient conventional therapy. The noncontact radiant heat bandage was placed over the ulcer for 5 hours daily: three 1-hour heating periods separated by two 1-hour nonheating periods during this 2-week trial. Wound size, status, and pain severity were recorded for each patient. A total of 17 patients with 31 total wounds were enrolled. No adverse effects were noted in any patient. There was improvement in 14/17 total patients during the 2-week inpatient trial and 8/17 patients healed completely after discharge. There was 1 recurrence during an 18-month follow-up. Pain scores were improved in most patients after the bandage was applied. The use of a noncontact radiant heat bandage is a safe and efficacious inpatient therapy for the management of chronic venous stasis ulcers in patients who have failed conventional therapy.

Distinct "assisted" and "spontaneous" mechanisms for the insertion of polytopic chlorophyll-binding proteins into the thylakoid membrane

The biogenesis of several bacterial polytopic membrane proteins has been shown to require signal recognition particle (SRP) and protein transport machinery, and one such protein, the major light-harvesting chlorophyll-binding protein (LHCP) exhibits these requirements in chloroplasts. In this report we have used in vitro insertion assays to analyze four additional members of the chlorophyll-a/b-binding protein family. We show that two members, Lhca1 and Lhcb5, display an absolute requirement for stroma, nucleoside triphosphates, and protein transport apparatus, indicating an "assisted" pathway that probably resembles that of LHCP. Two other members, however, namely an early light-inducible protein 2 (Elip2) and photosystem II subunit S (PsbS), can insert efficiently in the complete absence of SRP, SecA activity, nucleoside triphosphates, or a functional Sec system. The data suggest a possibly spontaneous insertion mechanism that, to date, has been characterized only for simple single-span proteins. Of the membrane proteins whose insertion into thylakoids has been analyzed, five have now been shown to insert by a SRP/Sec-independent mechanism, suggesting that this is a mainstream form of targeting pathway. We also show that PsbS and Elip2 molecules are capable of following either "unassisted" or assisted pathways, and we discuss the implications for the mechanism and role of SRP in chloroplasts.

Dual signal peptides mediate the signal recognition particle/Sec-independent insertion of a thylakoid membrane polyprotein, PsbY

The nuclear psbY gene (formerly ycf32) encodes two distinct single-spanning chloroplast thylakoid membrane proteins in Arabidopsis thaliana. After import into the chloroplast, the precursor protein is processed to a polyprotein in which each "mature" protein is preceded by an additional hydrophobic region; we show that these regions function as signal peptides that are cleaved after insertion into the thylakoid membrane. Inhibition of the first or second signal cleavage reaction by enlargement of the -1 residues leads in each case to the accumulation of a thylakoid-integrated intermediate containing three hydrophobic regions after import into chloroplasts; a double mutant is converted to a protein containing all four hydrophobic regions. We propose that the overall insertion process involves (i) insertion as a double-loop structure, (ii) two cleavages by the thylakoidal processing peptidase on the lumenal face of the membrane, and (iii) cleavage by an unknown peptidase on the stromal face on the membrane between the first mature protein and the second signal peptide. We also show that this polyprotein can insert into the thylakoid membrane in the absence of stromal factors, nucleoside triphosphates, or a functional Sec apparatus; this effectively shows for the first time that a multispanning protein can insert posttranslationally without the aid of signal recognition particle, SecA, or the membrane-bound Sec machinery.

Characterisation of an Arabidopsis thaliana cDNA encoding a novel thylakoid lumen protein imported by the delta pH-dependent pathway

An Arabidopsis thaliana (L.) Heynh. cDNA encoding a novel 16-kDa protein (P16) of the chloroplast thylakoid lumen has been characterised. The function of the protein is unknown but it shares some sequence similarity with alpha allophycocyanins. P16 is synthesised with a bipartite, lumen-targeting presequence, and import experiments demonstrated that this protein follows the delta pH-dependent pathway. Analysis of the thylakoid transfer peptide revealed two unusual features. Firstly, the key targeting determinant is predicted to be a twin-arginine followed by a highly hydrophobic residue two residues later, rather than at the third position as in most transfer peptides. Secondly, the C-terminal domain of the transfer peptide contains multiple charged residues which may help to prevent mistargeting by the Sec-type protein translocase.

Protein translocation into and across the bacterial plasma membrane and the plant thylakoid membrane

Over the past decade, some familiar themes have emerged on how proteins are inserted into or translocated across the plant chloroplast thylakoid membrane and bacterial inner membranes. In the SecA and signal recognition particle (SRP) pathways, nucleotides and soluble factors are used to translocate proteins across the membrane bilayer in the unfolded state. However, the delta pH-dependent pathway in thylakoids uses a radically different mechanism: transport of proteins across the membrane is driven by the transmembrane pH gradient, and neither stromal factors nor nucleotide triphosphates are needed. In addition, this pathway, which requires the membrane-bound protein Hcf106, appears to translocate proteins in a tightly folded form. Recently, a similar pathway has been shown to operate in eubacteria, and several of its components have been identified.

The sec-independent twin-arginine translocation system can transport both tightly folded and malfolded proteins across the thylakoid membrane

A subset of lumen proteins is transported across the thylakoid membrane by a Sec-independent translocase that recognizes a twin-arginine motif in the targeting signal. A related system operates in bacteria, apparently for the export of redox cofactor-containing proteins. In this report we describe a key feature of this system, the ability to transport folded proteins. The thylakoidal system is able to transport dihydrofolate reductase (DHFR) when an appropriate signal is attached, and the transport efficiency is almost undiminished by the binding of folate analogs such as methotrexate that cause the protein to fold very tightly. The system is moreover able to transport DHFR into the lumen with methotrexate bound in the active site, demonstrating that the DeltapH-driven transport of large, native structures is possible by this pathway. However, correct folding is not a prerequisite for transport. Truncated, malfolded DHFR can be translocated by this system, as can physiological substrates that are severely malfolded by the incorporation of amino acid analogs.

Beta2-microglobulin can be refolded into a native state from ex vivo amyloid fibrils

Beta2-microglobulin fibrils have been extracted from the femoral head of a patient who has been under chronic haemodialysis for 11 years. The primary structure of the N-terminal portion of the protein and mass determination by electrospray mass spectrometry demonstrate that beta2-microglobulin, extracted as fibrils by the water extraction procedure, was not glycated and that Asn17 was not deamidated. Limited proteolysis was observed in more than 20% of beta2-microglobulin molecules and the main cleavage sites were at the C-terminus of Lys6 and Tyr10. Beta2-microglobulin from fibrils has been purified by gel filtration in 6 M Gdn/HCl and submitted to a refolding procedure. The refolding conditions have been determined through the study of the unfolding pathway of the native protein. Beta2-microglobulin is stable at neutral pH where it displays a lower tendency to self-aggregate than in acidic conditions. Pulse dilution and extensive dialysis in refolding buffer at pH 7.5 yields beta2-microglobulin with a tertiary structure identical to that of the native form. The CD spectrum in the near-ultraviolet region and the spectrum of the intrinsic fluorescence of Trp overlap those of the native protein, but the CD spectrum in the far-ultraviolet region is affected by the contribution of oligomers created by beta2-microglobulin fragments that reduce the positive light polarisation at 205 nm typical of native beta2-microglobulin.

Time trends in human dietary exposure to PCDDs, PCDFs and PCBs in the UK

Total Diet Study samples collected in 1982 and 1992 were analysed. Estimated dietary intakes of PCDDs, PCDFs and PCBs by UK consumers were found to have fallen substantially during this period and are now considerably below the Tolerable Daily Intake (TDI). Composite samples of human milk were also analysed for PCDDs, PCDFs and PCBs. Estimated combined dietary intakes of PCDDs, PCDFs and PCBs by breast fed infants in 1993-94 via breast milk fell from 170 pg TEQ/kg bodyweight/day at 2 months to 39 pg TEQ/kg bodyweight/day at 10 months.

Cell lines of pulmonary and non-pulmonary origin as tools to study the effects of house dust mite proteinases on the regulation of epithelial permeability

BACKGROUND

Allergenic and non-allergenic proteinases from house dust mites (HDM) cause loss of adhesion between airway epithelial cells that may result in a loss of functional cohesion between the cells and thus assist in allergen presentation. Improved cellular assay systems are needed to ascertain the mechanisms involved.

OBJECTIVES

To survey a series of epithelial cell lines (Calu-3, 16HBE14o-, NCI-H292 and A549 from human airways, and MDCK from dog kidney) and establish their utility for studies of the effects of HDM proteinases from D. pteronyssinus on epithelial permeability. To develop an improved method for measuring changes in epithelial permeability induced by HDM proteinases and other provocants.

METHODS

The permeability of epithelial monolayer cultures to mannitol was calculated from measurements of clearance using a technique that permits mathematical estimation and reduction of non-cellular diffusional constraints. Permeability was studied under control conditions and after perturbation of monolayers with HDM proteinases (separated into serine- and cysteine-proteinase classes) or chelation of extracellular Ca2+. Fluorescent antibody staining was used to investigate whether the cells expressed tight junctions (staining of ZO-1), desmosomes (staining of desmoplakin) and zonulae adherentes (staining of E-cadherin).

RESULTS

The Calu-3 line was identified as an airway cell line that expressed functional tight junctions, desmosomes and zonulae adherentes. Calu-3 monolayers exhibited a low clearance and permeability to mannitol, similar to that seen in the extensively characterized MDCK cell line. Clearance and permeability were significantly increased by treatment with either HDM proteinase fraction or by calcium chelation. 16HBE14o- cells also had a low permeability to mannitol under control conditions and expressed a similar repertoire of functional proteins from major intercellular junctions. In contrast, NCI-H292 and A549 cell lines were functionally deficient in tight junctions, although they did express desmosomes and zonulae adherentes to a greater extent. Epithelial permeability was found to be a more appropriate and sensitive index of epithelial perturbation than was tracer clearance.

CONCLUSION

These results suggest that the Calu-3 and 16HBE14o- cell lines are useful tools in studying the mechanism of HDM proteinases on airway epithelial cell function. HDM proteinases of both cysteine and serine mechanistic classes were found to perturb epithelial adhesion and function.

Targeting of thylakoid proteins by the delta pH-driven twin-arginine translocation pathway requires a specific signal in the hydrophobic domain in conjunction with the twin-arginine motif

Superficially similar cleavable targeting signals specify whether lumenal proteins are transported across the thylakoid membrane by a Sec- or delta pH-dependent pathway. A twin-arginine motif is essential but not sufficient to direct delta pH-dependent targeting; here we show that a second determinant is located in the hydrophobic region. A highly hydrophobic amino acid is found either two or three residues C-terminal to the twin-arginine in all known transfer peptides for the delta pH-dependent system, and substitution of this residue in the 23-kDa (23K) peptide markedly inhibits translocation. Further, whereas the insertion of twin-arginine in a Sec-dependent precursor does not permit efficient delta pH-dependent targeting, the simultaneous presence of a leucine at the +3 position (relative to the RR) enables the peptide to function as efficiently as an authentic transfer peptide. RRNVL, RRAAL and RRALA within a Sec targeting signal all support efficient delta pH-dependent targeting, RRNVA is less effective and RRNAA/RRNAG are totally ineffective. We conclude that the core signal for this pathway is a twin-arginine together with an adjacent hydrophobic determinant.

Multiple pathways for the targeting of thylakoid proteins in chloroplasts

The assembly of the photosynthetic apparatus requires the import of numerous cytosolically synthesised proteins and their correct targeting into or across the thylakoid membrane. Biochemical and genetic studies have revealed the operation of several targeting pathways for these proteins, some of which are used for thylakoid lumen proteins whereas others are utilised by membrane proteins. Some pathways can be traced back to the prokaryotic ancestors of chloroplasts but at least one pathway appears to have arisen in response to the transfer of genes from the organelle to the nucleus. In this article we review recent findings in this field that point to the operation of a mechanistically unique protein translocase in both plastids and bacteria, and we discuss emerging data that reconcile the remarkable variety of targeting pathways with the natures of the substrate precursor proteins.

The maternal CCAAT box transcription factor which controls GATA-2 expression is novel and developmentally regulated and contains a double-stranded-RNA-binding subunit

The transcription factor GATA-2 is expressed at high levels in the nonneural ectoderm of the Xenopus embryo at neurula stages, with lower amounts of RNA present in the ventral mesoderm and endoderm. The promoter of the GATA-2 gene contains an inverted CCAAT box conserved among Xenopus laevis, humans, chickens, and mice. We have shown that this sequence is essential for GATA-2 transcription during early development and that the factor binding it is maternal. The DNA-binding activity of this factor is detectable in nuclei and chromatin bound only when zygotic GATA-2 transcription starts. Here we report the characterization of this factor, which we call CBTF (CCAAT box transcription factor). CBTF activity mainly appears late in oogenesis, when it is nuclear, and the complex has multiple subunits. We have identified one subunit of the factor as p122, a Xenopus double-stranded-RNA-binding protein. The p122 protein is perinuclear during early embryonic development but moves from the cytoplasm into the nuclei of embryonic cells at stage 9, prior to the detection of CBTF activity in the nucleus. Thus, the accumulation of CBTF activity in the nucleus is a multistep process. We show that the p122 protein is expressed mainly in the ectoderm. Expression of p122 mRNA is more restricted, mainly to the anterior ectoderm and mesoderm and to the neural tube. Two properties of CBTF, its dual role and its cytoplasm-to-nucleus translocation, are shared with other vertebrate maternal transcription factors and may be general properties of these proteins.

Sec-independent insertion of thylakoid membrane proteins. Analysis of insertion forces and identification of a loop intermediate involving the signal peptide

A group of membrane proteins are synthesized with cleavable signal sequences but inserted into the thylakoid membrane by an unusual Sec/SRP-independent mechanism. In this report we describe a key intermediate in the insertion of one such protein, photosystem II subunit W (PSII-W). A single mutation in the terminal cleavage site partially blocks processing and leads to the formation of an intermediate-size protein in the thylakoid membrane during chloroplast import assays. This protein is in the form of a loop structure: the N and C termini are exposed on the stromal face, whereas the cleavage site has been translocated into the lumen. In this respect the insertion of this protein resembles that of M13 procoat, which also adopts a loop structure during insertion, and we present preliminary evidence that a similar mechanism is used by another thylakoid protein, PSII-X. However, whereas the negatively charged region of procoat is translocated by an apparently electrophoretic mechanism using the DeltamuH+, the corresponding region of PSII-W is equally acidic but insertion is DeltamuH+ independent. We furthermore show that neutralization of this region has no apparent effect on the insertion process. We propose that a central element in this insertion mechanism is a loop structure whose formation is driven by hydrophobic interactions.

Targeting signals for a bacterial Sec-independent export system direct plant thylakoid import by the delta pH pathway

Preproteins targeted to the Sec-independent protein transport systems of plant thylakoids and of bacteria both have unusual transfer peptides bearing a consensus twin-arginine motif. Possible mechanistic similarity between the two Sec-independent transport pathways was investigated by assessing the ability of bacterial twin-arginine transfer peptides to direct thylakoid import. High efficiency import was observed. This process was demonstrated to occur specifically via the Sec-independent deltapH pathway and to depend on an intact twin-arginine motif on the transfer peptide. These results provide strong evidence for the operation of mechanistically related Sec-independent protein transport pathways in chloroplasts and bacteria.

An essential component of a novel bacterial protein export system with homologues in plastids and mitochondria

Proteins are transported across the bacterial plasma membrane and the chloroplast thylakoid membrane by means of protein translocases that recognize N-terminal targeting signals in their cognate substrates. Transport of many of these proteins involves the well defined Sec apparatus that operates in both membranes. We describe here the identification of a novel component of a bacterial Sec-independent translocase. The system probably functions in a similar manner to a Sec-independent translocase in the thylakoid membrane, and substrates for both systems bear a characteristic twin-arginine motif in the targeting peptide. The translocase component is encoded in Escherichia coli by an unassigned reading frame, yigU, disruption of which blocks the export of at least five twin-Arg-containing precursor proteins that are predicted to bind redox cofactors, and hence fold, prior to translocation. The Sec pathway remains unaffected in the deletion strain. The gene has been designated tatC (for twin-arginine translocation), and we show that homologous genes are present in a range of bacteria, plastids, and mitochondria. These findings suggest a central role for TatC-type proteins in the translocation of tightly folded proteins across a spectrum of biological membranes.

Anger of African American women in the south

In this existential-phenomenological investigation middle-class African American women (n = 9) in the Southern United States were interviewed about their experience of anger in daily life. The purpose of the study was to examine what African American women's anger is about, what it means, and how it is experienced. Transcribed interviews were analyzed using a hermeneutic process. The thematic structure of African American women's anger comprises three main elements that stand out as figural: power, control, and respect. These figural elements can be understood only when seen against the ground of a racist Southern culture that produces pervasive mistrust. These findings are of importance to clinicians, who cannot deliver culturally competent interventions to African American female clients without a clear understanding of the complexity and meaning of their anger experience.