Effects of 12-O-tetradecanoylphorbol-13-acetate and mezerein on epidermal ornithine decarboxylase activity, isoproterenol-stimulated levels of cyclic adenosine 3':5'-monophosphate, and induction of mouse skin tumors in vivo

The tumor promoter 12-O-tetradecanoylphorbol-13-acetate and the antileukemic agent mezerein are diterpene esters of plant origin with certain structural similarities. Both compounds, when applied topically to mouse skin, were equipotent on a molar basis in inducing hyperplasia, inflammation, and ornithine decarboxylase activity, as well as in reducing cyclic adenosine 3':5'-monophosphate accumulation in response to beta-adrenergic stimulation. In contrast, mezerein was much less effective as a tumor promoter; the phorbol ester at 8.5 nmol/application yielded 78-fold more tumors than did 8.5 nmol mezerein per application to similarly initiated SENCAR mice. The superiority of the phorbol ester was nearly as great in CD-1 mice.

Ultraviolet light induces epidermal ornithine decarboxylase activity

Hairless mice were irradiated with fluorescent sun lamp tubes (peak emission at 313 nm). A singificant increase in epidermal ornithine decarboxylase activity was found after 2 hr. A maximum 80-fold increase was found after 24 hr, decreasing again at 48 hr. Epidermal DNA synthesis was decreased at 6 hr and 24 hr increasing to a maximum 48 hr after irradiation. These results show that polyamine biosynthetic enzyme activity precedes the delayed increase in epidermal DNA synthesis following ultraviolet light exposure.

Effects of retinoic acid and juvenile hormone on the induction of ornithine decarboxylase activity by 12-O-tetradecanoylphorbol-13-acetate

The tumor-promoting agent 12-O-tetradecanoylphorbol-13-acetate (TPA), a highly active comitogen in phytohemagglutinin-treated bovine lymphocytes, induces an 11-fold increase in ornithine decarboxylase activity over cultures treated with the lectin alone. This synergistic action of TPA could be antagonized by the simultaneous addition of the acyclic sesquiterpene, insect juvenile hormone III. Retinoic acid (vitamin A acid), an inhibitor of the tumor-promoting action of TPA in mice, was also an effective antagonist but required administration to lectin-activated lymphocytes 1 hr prior to TPA. These data suggest that metabolic activation of retinoic acid is required in order to exert its antagonistic action. Comparison of the responses in the lymphocytes and mouse skin suggests that the lymphocytes provide an excellent system for studying the molecular processes through which phorbol esters and retinoids influence the growth and differentiation of both normal and premalignant cells.

Formation of alpha-1,2-mannosyl-mannose by an enzyme preparation from rabbit liver

Rabbit liver microsomes catalyzed the formation of 2-O-alpha-D-mannosyl-D-mannose when incubated with GDP-mannose and free D-mannose. Formation of the disaccharide required the addition of divalent metal ions and was inhibited by EDTA and guanosine nucleotides. An enzyme present in the microsomal preparation transferred mannose from GDP-mannose to an endogenous lipid and to exogenous dolichol-P resulting in the formation of a product tentatively identified as dolichol-P-mannose. Formation of the mannosyl-lipid was also metal ion-dependent and was inhibited by EDTA and guanosine nucleotides. A second enzyme in the preparation catalyzed mannosyl transfer from dolichol-P-mannose to free mannose resulting in the formation of 2-O-alpha-D-mannosyl-D-mannose. Transfer from the mannosyl-lipid required the addition of Triton X-100 but was metal ion-independent. The time course of the transfer of mannose from GDP-mannose to the endogenous lipid and to the exogenous saccharide acceptor suggested that the mannosyl-lipid was an intermediate in the formation of the mannobiose. Other evidence, such as similar requirements for divalent metals, inhibition by guanosine nucleotides, and acceptor specificity, also supported the involvement of a mannosyl-lipid as an intermediate in the formation of alpha-1,2-mannosyl-mannose linkages by rabbit liver microsomes.

Accumulation of cyclic adenosine 3',5'-monophosphate in adult and newborn mouse skin: responses to ischemia and isoproterenol

Levels of cyclic adenosine 3',5'-monophosphate in adult mouse skin pieces were rapidly increased on incubation at 37 degrees C, or on exposure to isoproterenol. Accumulation of the cyclic nucleotide under both conditions was greatly decreased in newborn mouse skin, or in adult skin treated with the tumor promotor 12-0-tetradecanoyl-phorbol-13-acetate.

Localization of adenosine o',5'-monophosphate in mouse epidermis by immunofluorescence

Adenosine 3',5'-monophosphate (cyclic AMP) has been localized in mouse epidermal cells using an immunofluorescent technique. Within 10 min following the intraperitoneal injection of isoproterenol or 30 hr following the topical application of croton oil in acetone, staining was clearly visible in the cytoplasm of the basal cells.

Croton oil- and benzo(a)pyrene-induced changes in cyclic adenosine 3':5'-monophosphate and cyclic guanosine 3':5'-monophosphate phosphodiesterase activities in mouse epidermis

The topical application of croton oil, benzo(a)pyrene, acetic acid, and 12-O-tetradecanoyl-phorbol-13-acetate to mouse skin caused an increase in the activity of epidermal low-affinity cyclic adenosine 3':5'-monophosphate (cyclic AMP) phosphodiesterase. The increase was most pronounced with croton oil, began between 4 and 6 hr after application of this material, and was maintained for at least 48 hr. The activity of cyclic guanosine 3':5'-monophosphate phosphodiesterase was also increased by treatment with croton oil or 12-O-tetradecanoyl-phorbol-13-acetate, but detailed time courses were not obtained. Increased activity was observed in both the soluble fractions and the washed particulate fractions of epidermis. Fractionation of soluble extracts from acetone-treated epidermis on DEAE-cellulose columns showed the presence of enzymes with specificity for both cyclic AMP and cyclic guanosine 3':5'-monophosphate, together with a peak catalyzing the hydrolysis of both cyclic AMP and cyclic guanosine 3':5'-monophosphate. The activity of this latter nonspecific activity was selectively increased following treatment with croton oil. The increase in cyclic AMP phosphodiesterase activity was partially abolished by multiple injections of cycloheximide, suggesting that new protein synthesis was involved. Injection of the alpha-receptor antagonist phentolamine abolished a croton oil-induced rise in epidermal cyclic AMP levels and decreased the induction of cyclic AMP phosphodiesterase activity. From these results it was concluded that the increase in enzyme activity was induced by cyclic AMP.

The inhibitory effect of glucose on the differentiation of trophic Hartmannella culbertsoni into viable cysts

During encystation of Hartmannella culbertsoni induced by taurine or epinephrine, 60-70% of the reserve glycogen is degraded. Glycogen phosphorylase is activated and glycogen synthetase is inhibited after 6-8 hr of exposure to the encystation medium. The carbon skeleton of glycogen but not that of protein is utilised in the synthesis of cyst wall cellulose. Exogenously added glucose (225 and 550 mM) blocks encystation, degradation of glycogen and synthesis of cellulose. Cyclic AMP synthesis is also very much reduced in cells exposed to glucose.