thapsigargin and helenalin

B lymphocyte-induced maturation protein-1 (BLIMP-1) acts during differentiation of B cells and monocytes, but was originally identified as a repressor of the IFN-beta promoter induced during viral infection. A central regulator of the intracellular response to viral infection is the interferon-inducible double-stranded RNA activated protein kinase (PKR). PKR belongs to a family of kinases that phosphorylate the eukaryotic translation initiation factor 2-alpha (eIF2alpha) and activate common downstream signaling pathways. PERK, the endoplasmic reticulum resident PKR-homologue, is activated during the unfolded protein response (UPR), a stress response involved in both macrophage activation and terminal B-cell differentiation. This suggested that BLIMP-1 might be a target of stress responses involving PERK. We demonstrate that BLIMP-1 is rapidly up-regulated during the UPR in human myeloid and B-cell lines. This response is conserved in murine B-cells and murine macrophages, in which mimics of physiological stress and classical activation stimuli also induce Blimp-1. During the UPR, BLIMP-1 mRNA is induced at the level of transcription. This response is dependent on an intact PERK signaling pathway, independent of new protein synthesis and blocked by an inhibitor of NF-kappaB. Our data provide evidence for a novel pathway linking cellular stress to BLIMP-1, a regulator of differentiation in macrophages and B cells.

Topics: Animals; B-Lymphocytes; Cycloheximide; Dithiothreitol; DNA-Binding Proteins; eIF-2 Kinase; Enzyme Inhibitors; Eukaryotic Initiation Factor-2; HeLa Cells; HL-60 Cells; Humans; Macrophages; Mice; Mice, Inbred C57BL; Nuclear Proteins; Positive Regulatory Domain I-Binding Factor 1; Protein Folding; Protein Synthesis Inhibitors; Regulatory Factor X Transcription Factors; Repressor Proteins; RNA, Messenger; Sesquiterpenes; Sesquiterpenes, Guaiane; Signal Transduction; Thapsigargin; Transcription Factors

The sesquiterpene lactones isolated from Geigeria were found to be incapable of inducing rat peritoneal mast cell degranulation at levels of 0.3-1.6 mM. The sulphydryl reagent, N-ethylmaleimide, too was unable to trigger mast cell secretion. Instead, it was observed that these compounds inhibited the release of histamine induced by Compound 48/80. Pretreatment of the lactones and N-ethylmaleimide with the amino acid, L-cysteine, reduced their inhibition ability of histamine release to a considerable extent, but not completely. Geigerin(V), which lacks an alpha-methylene group and the chemically prepared cysteine-adduct of dihydrogriesenin(I), were also capable of inhibiting mast cell secretion by Compound 48/80, but to a lesser extent.

Topics: Alkylation; Animals; Cysteine; Ethylmaleimide; Histamine Release; Lactones; Male; Mast Cells; p-Methoxy-N-methylphenethylamine; Plant Extracts; Rats; Rats, Inbred Strains; Sesquiterpenes; Sesquiterpenes, Guaiane; Thapsigargin