epidermal-growth-factor and debromoaplysiatoxin

Aplysiatoxin and debromoaplysiatoxin, a debrominated form of aplysiatoxin, have both been shown to be potent tumor promoters in a two-stage carcinogenesis experiment on mouse skin. However, debromoaplysiatoxin did not behave like aplysiatoxin in most of the biological assay systems using cultured cells. The discrepancy was supposed to be due to a factor in the bovine serum used for culture, a similar factor not being present in sera of eight other animal species examined. The factor was purified to homogeneity from bovine serum by ammonium sulfate fractionation and chromatographies on DEAE-cellulose, Sephadex G-150, hydroxyapatite, and a reversed-phase HPLC column. The factor was a 40-kDa protein, and partial amino-acid sequencing of its tryptic peptides indicated that the factor is alpha 1-acid glycoprotein. Both the purified factor and the commercially available bovine alpha 1-acid glycoprotein abolished in vitro the activation of protein kinase C by debromoaplysiatoxin but not that by aplysiatoxin. Debromoaplysiatoxin induced differentiation of HL-60 cells into macrophages at a comparable concentration to aplysiatoxin, when serum-free medium was used. These results suggest that alpha 1-acid glycoprotein, which interacts specifically with debromoaplysiatoxin, contained in bovine serum must have masked the in vitro properties of the tumor promoter in the biological assay systems.

Topics: 3T3 Cells; Amino Acid Sequence; Animals; Anticarcinogenic Agents; Carcinogens; Cattle; Drug Interactions; Enzyme Activation; Epidermal Growth Factor; Humans; Kinetics; Lyngbya Toxins; Mice; Mice, Inbred BALB C; Molecular Sequence Data; Orosomucoid; Phorbol 12,13-Dibutyrate; Protein Kinase C; Rabbits; Rats; Sensitivity and Specificity; Sequence Homology, Amino Acid; Tritium

We have compared the activities of aplysiatoxin and debromoaplysiatoxin, two polyacetate marine algae toxins, with teleocidin, a tumor-promoting indole alkaloid from Streptomyces, with respect to inhibition of specific binding of epidermal growth factor, and phorbol-12,13-dibutyrate to their respective receptors and ability to stimulate the release of radioactivity from cells prelabeled with choline or arachidonic acid. Although these compounds have chemical structures that are quite different from the phorbol esters, both aplysiatoxin and teleocidin are essentially equipotent with the potent tumor promoter 12-O-tetradecanoylphorbol-13-acetate in all four assays. The fact that aplysiatoxin and teleocidin inhibit phorbol-12,13-dibutyrate-receptor binding suggests that their biological activities are mediated by binding to the same receptors utilized by the phorbol esters. Debromoaplysiatoxin, a debrominated form of aplysiatoxin, is about 10-fold weaker than aplysiatoxin in inhibiting epidermal growth factor and phorbol-12,13-dibutyrate-receptor binding, but is equipotent with aplysiatoxin in stimulating the release of lipid metabolites from the prelabeled cells. The results are discussed in terms of possible heterogeneity of cellular receptors for this group of compounds.

Topics: Alkaloids; Animals; Caenorhabditis elegans Proteins; Carcinogens; Carrier Proteins; Cell Line; Epidermal Growth Factor; ErbB Receptors; Kinetics; Lactones; Lyngbya Toxins; Marine Toxins; Mice; Mollusk Venoms; Phorbols; Phospholipids; Protein Kinase C; Rats; Receptors, Cell Surface; Receptors, Drug; Tetradecanoylphorbol Acetate

Aplysiatoxin and debromoaplysiatoxin, which are isolated from the seaweed, Lyngbya gracilis, differ in their chemical structure only by the presence or absence of a bromine residue in the hydrophilic region. The function and the structure-activity relation of the hydrophilic region are not known. Aplysiatoxin increased malignant transformation, stimulated DNA synthesis, and inhibited the binding of phorbol-12,13-dibutyrate and epidermal growth factor to cell receptors. Debromoaplysiatoxin inhibited the binding of these two substances as strongly as aplysiatoxin but did not increase malignant transformation or stimulate DNA synthesis. These results indicate that a slight change in the chemical structure of the hydrophilic region of aplysiatoxin affects its abilities to increase cell transformation and stimulate DNA synthesis and that the abilities of the tumor promoters to inhibit the binding of phorbol-12,13-dibutyrate and epidermal growth factor are dissociable from their abilities to increase cell transformation and stimulate DNA synthesis under some circumstances.

Topics: Animals; Caenorhabditis elegans Proteins; Carcinogens; Carrier Proteins; Cell Line; Cell Transformation, Neoplastic; Chemical Phenomena; Chemistry; DNA; Epidermal Growth Factor; ErbB Receptors; Lactones; Lyngbya Toxins; Mice; Phorbol 12,13-Dibutyrate; Phorbol Esters; Protein Kinase C; Receptors, Cell Surface; Receptors, Drug; Structure-Activity Relationship