Interleukin-6 production by activated human monocytic cells is enhanced by MK-571, a specific inhibitor of the multi-drug resistance protein-1

1. The intracellular transport of leukotriene C4 (LTC4) in hematopoietic cells such as human monocytes is controlled by an ATP dependent carrier encoded by the multidrug resistance protein1 (MRPI) gene whose function can be blocked by the compound MK-571. Since LTs play a major role in control of cytokine expression in monocytes, we questioned whether blocking of the MRPI mediated function by MK-571 might affect cytokine production. 2. MK-571 strongly enhanced IL-6 expression at mRNA and protein level in lipopolysaccharide (LPS) and interleukin-1 (IL-1) stimulated human monocytes giving rise to 2.0+/-0.4 (x+/-s.d.) and 5.7+/-3.5 fold induction of IL-6 protein secretion. The increase in IL-6 secretion was accompanied by an enhanced phosphorylation of p38 but not of c-Jun-N terminal kinase. 3. The involvement of the kinase signalling pathways was further analysed by using SB203580 and PD98059, specific inhibitors of the p38 and ERK1/2 signalling route. MK-571 mediated upregulation of IL-6 in the presence of IL-1 was partially attenuated by SB203580 and PD98059. Electrophoretic mobility shift assays demonstrated that MK-571 did not affect the IL-1 induced DNA binding activity of Activator Protein-1 and Nuclear Factor-kappaB but rather enhanced the transactivational activity of an IL-6 promoter construct. Finally it was shown that the MK-571 mediated effects on IL-6 secretion could not be inhibited by the LT synthesis inhibitor SB203347 or by the anti-oxidant pyrrolidine dithiocarbamate (PDTC). 4. These results indicate that the membrane transporter MRP1 is involved in the regulation of IL-6 expression in activated human peripheral blood monocytes.

Interleukin-4 prevents the induction of G-CSF mRNA in human adherent monocytes in response to endotoxin and IL-1 stimulation

Human recombinant interleukin-4 (IL-4) was studied for its effects on the expression of granulocyte-colony stimulating factor (G-CSF) mRNA in human adherent monocytes in the absence and presence of endotoxin and interleukin 1 (IL-1). IL-4 (15 ng/ml) did not induce G-CSF transcripts in monocytes but suppressed the endotoxin-induced G-CSF expression when added simultaneously. Sequential treatment of monocytes with IL-4 followed by endotoxin suppressed G-CSF mRNA induction totally. This effect was independent of the presence of fetal bovine serum but dependent of the IL-4 dose. Comparable results were obtained with IL-1. IL-1 (50 U/ml) induced G-CSF expression in human adherent monocytes which could be counteracted by IL-4 pretreatment. In addition, it was shown that the induction of G-CSF mRNA by the calcium-ionophore A23187 or by c-AMP elevating agents could be blocked by IL-4. These suppressive effects of IL-4 were not related to changes in the half-life of G-CSF mRNA and were independent of protein synthesis. Finally it was demonstrated that IL-4 had comparable effects on the G-CSF secretion of endotoxin and IL-1 stimulated human monocytes by using a murine bone marrow assay. These results indicate that IL-4 down-regulates the expression of G-CSF gene and secretion of proteins in human activated monocytes.

Partial amino acid sequence of a hemocyanin subunit from Palinurus vulgaris

1. Hemocyanin from the spiny lobster Palinurus vulgaris was separated into two fractions, which were designated as subunits a and b. 2. 55% of the amino acid sequence of subunit b has been determined. A comparison with Panulirus interruptus hemocyanins shows 78% sequence identity with subunit a and 56% with subunit c. It has carbohydrate attached to domain one. Two half-cystines have been substituted, indicating that it probably possesses only one disulfide bridge. Heterogeneity has been observed in seven out of 380 positions determined so far. 3. Subunit a is almost identical with subunit b. In contrast to Panulirus interruptus and Panulirus japonicus, Palinurus vulgaris hemocyanin contains no c-type subunit. 4. A position in the tentative evolutionary tree of arthropod hemocyanins based on sequence differences has been assigned to Palinurus vulgaris subunit b.