Inhibition of calcium accumulation by the sarcoplasmic reticulum: a putative mechanism for the cardiotoxicity of adriamycin.

The aim of this study was to examine the effect of adriamycin (ADR) on calcium accumulation by the sarcoplasmic reticulum (SR). Chemical skinning of cultured rat myocardial cells compromised the barrier function of the cell membrane and thus permitted direct exposure of mitochondrial and non-mitochondrial sites to ADR. In the presence of ATP, and sodium azide, mitochondrial calcium accumulation was negligible. Furthermore, it has previously been shown that non-mitochondrial calcium accumulation is mediated mainly by the SR under these conditions. Incubation with 10 microM ADR for 2 hr reduced the level of calcium accumulation by the SR by 50%. A similar effect was obtained after 24 hr incubation with 1 microM ADR. The addition of ferric iron to the culture medium further reduced the level of calcium accumulation. Neither vitamin E nor beta-carotene affected calcium accumulation by the SR. These results suggest that ADR interferes with the calcium accumulation activity of the SR and that ferric iron potentiates this effect.

Escherichia coli FtsH is a membrane-bound, ATP-dependent protease which degrades the heat-shock transcription factor sigma 32.

Escherichia coli FtsH is an essential integral membrane protein that has an AAA-type ATPase domain at its C-terminal cytoplasmic part, which is homologous to at least three ATPase subunits of the eukaryotic 26S proteasome. We report here that FtsH is involved in degradation of the heat-shock transcription factor sigma 32, a key element in the regulation of the E. coli heat-shock response. In the temperature-sensitive ftsH1 mutant, the amount of sigma 32 at a non-permissive temperature was higher than in the wild-type under certain conditions due to a reduced rate of degradation. In an in vitro system with purified components, FtsH catalyzed ATP-dependent degradation of biologically active histidine-tagged sigma 32. FtsH has a zinc-binding motif similar to the active site of zinc-metalloproteases. Protease activity of FtsH for histidine-tagged sigma 32 was stimulated by Zn2+ and strongly inhibited by the heavy metal chelating agent o-phenanthroline. We conclude that FtsH is a novel membrane-bound, ATP-dependent metalloprotease with activity for sigma 32. These findings indicate a new mechanism of gene regulation in E. coli.

Visualisation by electron microscopy of the unique part of the cytoplasmic domain of a desmoglein, a cadherin-like protein of the desmosome type of cell junction.

Part of the cytoplasmic domain of a human desmoglein, Dsg1, a cadherin-like protein found in desmosomes of epithelial cells, has been visualised by electron microscopy. The cloned fragment contains five repeats of a 29 +/- 4 residue sequence unique to desmogleins, followed by a glycine-rich region. In rotary shadowed preparations the molecule consists of a globular head attached to a thin tail, the latter perhaps corresponding to the glycine-rich region. This portion of the molecule is thought to span the width of the inner dense plaque. The structure and dimensions concur well to the configuration deduced from the protein sequence.

Desmosomal glycoprotein DGI, a component of intercellular desmosome junctions, is related to the cadherin family of cell adhesion molecules.

Among the variety of specialized intercellular junctions, those of the adherens type have the most obvious association with cytoskeletal elements. This may be with the actin microfilament system as in the zonula adherens or with intermediate filaments as in the macula adherens, or desmosome. In the former case, it is clear that transmembrane glycoproteins of the cadherin family are important adhesive components of the molecular assembly. We now show for desmosomes that a major glycoprotein component (desmosomal glycoprotein DGI) has extensive homology with the cadherins, defining an extended family, but also has unique features in its cytoplasmic domain that are likely to be relevant to the association with intermediate rather than actin filaments. A novel 282-residue extension contains repeats of approximately 29 amino acid residues predicted to have an antiparallel beta-sheet structure, followed by a glycine-rich sequence. As in the cadherins, the extracellular domain contains possible Ca2(+)-binding sequences and a potential protease processing site. The cell adhesion recognition region (His-Ala-Val) of the cadherins is modified to Arg-Ala-Leu.

Epidermal rupture is the initiating factor for the Koebner response in psoriasis.

The Koebner phenomenon was studied using low pressure suction and/or sellotape stripping. Each of 10 patients with psoriasis had 5 suction blisters induced and sellotape stripping. In each patient the roof of 4 of the 5 blisters was removed. In 6 of the 10 patients, psoriasis developed where the blister roof was removed, but not where the blister was left intact. However, only 3 of these 10 patients were also Koebner-positive at the tape-stripped site. Similarly, in a group of 37 psoriasis patients who were sellotape-stripped alone, only 8 (21.6%) were Koebner-positive at the tape-stripped site. In another experiment, 5 suction blisters were produced in each of 4 patients. The roof of 4 blisters was removed, one of which was occluded. Psoriasis developed in 3 of the 4 patients, but only where the blister roof had been removed and left unoccluded. These findings suggest that rupture of the epidermis can initiate the Koebner response, but that secondary dermal events are necessary for a psoriatic lesion to form.

Sulphamethoxypyridazine for dermatitis herpetiformis, linear IgA disease and cicatricial pemphigoid.

One-hundred and sixty-eight cases of dermatitis herpetiformis were reviewed to compare the clinical response to and incidence of side-effects from dapsone and sulphamethoxypyridazine. Thirty-seven received sulphamethoxypyridazine (0.25-1.5 g/day) as a single agent therapy at some stage during their care and 161 had dapsone only (50-450 mg/day). Thirty of these patients received both drugs, but at different times. Both were highly effective in controlling the skin disease in 97% of patients on dapsone and 89% on sulphamethoxypyridazine. While 36 (22%) of dapsone-treated subjects had intolerable side effects warranting a change in therapy, this occurred in only five (13.5%) of those treated with sulphamethoxypyridazine. Sulphamethoxypyridazine was also effective as a single agent in three patients with linear IgA disease who had suffered adverse effects from dapsone, and in 10 out of 15 patients with oral and cutaneous lesions of cicatricial pemphigoid.

Effect of simulated sunlight on Langerhans' cells in malignant melanoma patients.

The effect of artificial sunlight on the number and HLA class II expression of Langerhans' cells was studied in 10 patients with malignant melanoma and 10 control volunteers. The total number of Langerhans' cell decreased in both groups but at 96 h there was a greater and significant decrease (p less than 0.01) in the number of Langerhans' cells in the melanoma group, compared with controls. This decrease persisted and was still greater in the melanoma group (p less than 0.02) at one week post-irradiation. There was a rise in Langerhans' cell count over the following 3 weeks in both groups. Unexpectedly, during this period in the melanoma group-but not controls-there was a significant median peak rise above pre-irradiation levels (p less than 0.001). Alteration in the response of Langerhans' cells to sunlight may play a part in the aetiology of malignant melanoma.