thapsigargin and aplysiatoxin

Rat liver cells (the C-9 cell line) are synergistically stimulated to produce prostaglandin I2 (PGI2) when incubated in the presence of thapsigargin and several recombinant human growth factors or tumor promoters, including basic fibroblast growth factor (bFGF), epidermal growth factor (EGF), interleukin-1 beta (IL-1 beta), tumor necrosis factor-alpha (TNF-alpha), transforming growth factor-alpha (TGF-alpha), 12-O-tetradecanoylphorbol-13-acetate (TPA), teleocidin and aplysiatoxin, but not acidic fibroblast growth factor (aFGF). The production of PGI2 by exogenous arachidonic acid in the presence of thapsigargin is not amplified. The effects of varying levels of bFGF on PGI2 production in the presence of thapsigargin are biphasic: at low levels (0.05 nM) bFGF's effect is synergistic; at high levels (24 nM) it is not.

Topics: Animals; Binding Sites; Cell Line; Epidermal Growth Factor; Epoprostenol; Fibroblast Growth Factor 2; Heparin; Interleukin-1; Liver; Lyngbya Toxins; Rats; Terpenes; Tetradecanoylphorbol Acetate; Thapsigargin; Transforming Growth Factor alpha; Tumor Necrosis Factor-alpha

1. At concentrations above 10 ng ml-1, the tumour promoter thapsigargin stimulates the release of radioactivity from [3H]-arachidonic acid-labelled macrophages harvested from rat peritoneal cavity. 2. The release of radioactivity from prelabelled macrophages was augmented more than additively when the cells were incubated in the medium containing both thapsigargin (10 ng ml-1) and other tumour promoters (10 ng ml-1), such as 12-O-tetradecanoylphorbol-13-acetate (TPA), teleocidin and aplysiatoxin. 3. Thapsigargin required extracellular Ca2+ for the stimulation of arachidonic acid release, while TPA did not. 4. Cytoplasmic free calcium level was increased by thapsigargin treatment but not by TPA treatment. 5. An inhibitor of protein kinases, H-7 inhibited the effect of TPA dose-dependently, whereas H-7 did not inhibit that of thapsigargin. 6. These results suggest that thapsigargin stimulates arachidonic acid release by a mechanism different from that of TPA, viz by acting as a selective Ca2+ mobilizer, but not by activating protein kinase C as TPA does.

Topics: 1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; Animals; Arachidonic Acid; Arachidonic Acids; Calcimycin; Calcium; Carcinogens; Cytoplasm; In Vitro Techniques; Isoquinolines; Lyngbya Toxins; Macrophages; Male; N-Formylmethionine Leucyl-Phenylalanine; Peritoneal Cavity; Piperazines; Plant Extracts; Protein Kinase Inhibitors; Rats; Rats, Inbred Strains; Tetradecanoylphorbol Acetate; Thapsigargin

Ten new tumor promoters which are structurally different from TPA but of similar biological activity were found. Based on their binding to the phorbol ester receptors of cell membranes, these new tumor promoters were classified as TPA-type tumor promoters, teleocidin and aplysiatoxin, which like TPA, activated protein kinase C in vitro, whereas two non-TPA-type tumor promoters, palytoxin and thapsigargin did not induce ODC activity in mouse skin, adhesion of HL-60 cells or activation of protein kinase C, but did show tumor-promoting activity in a two-stage carcinogenesis experiment. Although these two types of tumor promoter exert their tumor-promoting activities through different pathways, production of prostaglandin E2 by rat macrophages was induced by both the TPA-type and non-TPA-type promoters. Therefore, stimulation of arachidonic acid metabolism is suggested to be one of the important biological activities for tumor promotion.

Topics: Acrylamides; Animals; Arachidonic Acid; Arachidonic Acids; Carcinogens; Cnidarian Venoms; Enzyme Activation; Humans; Lyngbya Toxins; Mice; Neoplasms, Experimental; Phorbols; Plant Extracts; Protein Kinase C; Receptors, Cell Surface; Skin Neoplasms; Structure-Activity Relationship; Tetradecanoylphorbol Acetate; Thapsigargin