Association of phorbol ester-induced hyperphosphorylation and reversible regulation of transferrin membrane receptors in HL60 cells

Phorbol diesters are tumor-promoting agents that cause differentiation of HL60 human leukemic cells and concomitantly alter surface transferrin-receptor expression [Rovera, G., Ferreo, D., Pagliardi, G. L., Vartikar, J., Pessano, S., Bottero, L., Abraham, S. & Lebman, D. (1982) Ann. N.Y. Acad. Sci. 397, 211-220]. Transferrin-receptor regulation is shown here to result from a rapid and reversible internalization process that is temporally associated with reversible increased phosphorylation (hyperphosphorylation) of the transferrin receptor. Such a reversible mechanism involving regulation of these surface proteins could result in the rapid generation of an early signal for HL60 cellular differentiation.

Specific growth response of ras-transformed embryo fibroblasts to tumour promoters

Chemical carcinogenesis is a process involving multiple steps, as shown in several in vivo experimental systems. Two early steps have been well characterized: initiation, achieved by a single, subthreshold dose of a carcinogen, and promotion, induced by repetitive treatments with a non-carcinogenic tumour promoter. At the cellular level, establishment of the transformed phenotype is also a multi-step process and activation of several, independent genes appears to be required. Here we show that, like initiated cells, primary rat embryo fibroblasts (REFs) containing a ras but not a myc oncogene, are strongly and specifically stimulated to grow by tumour promoters. In the presence of these promoters, ras-containing REFs acquire the ability to overgrow normal cells in the monolayer and to form foci with 100% efficiency. Similar to the in vivo situation, promoter effects can be blocked by the concomitant application of retinoic acid.

Onion and garlic oils inhibit tumor promotion

The tumor yield and incidence of phorbol-myristate-acetate promotion were inhibited in a dose-dependent manner over the range of 10-10 000 micrograms onion oil, applied three times per week. Garlic oil was also inhibitory but was less effective.

Mechanism of action of the phorbol ester tumor promoters: specific receptors for lipophilic ligands

Cells and tissue preparations specifically bind the phorbol ester tumor promoters. The agreement in structure-activity relationships between binding and biological response strongly argues that these binding sites function as phorbol ester receptors. Upon subcellular fractionation, the phorbol ester binding activity is particulate. In addition, a phorbol ester apo-receptor can be detected in cytosol which requires phospholipids for reconstitution. This apo-receptor appears to correspond to protein kinase C. Diacylglycerols, the probable natural activators of protein kinase C, competitively inhibit phorbol ester binding, consistent with their being the postulated endogenous phorbol ester analogs. In certain systems, heterogeneity of phorbol ester binding is found. An outstanding issue therefore is whether protein kinase C is the phorbol ester receptor or whether it is only the most abundant class of receptor. Although this question remains unresolved, we can demonstrate heterogeneity of phorbol ester binding by reconstitution of apo-receptor into a heterogeneous lipid environment.

Stimulation of human polymorphonuclear leukocyte superoxide anion radical production by tumor promoters

Comparison was made of the ability of the potent tumor promoter phorbol myristate acetate (PMA), as well as less active PMA analogs and non-phorbol ester tumor promoters, to stimulate superoxide anion radical (O-.2) production by human polymorphonuclear leukocytes (PMN). The rate of O-.2 production was found to correlate with the tumor-promoting activity of the phorbol esters as opposed to their inflammatory activity. Mezerein and telocidin B were slightly better stimulators of O-.2 production than PMA. Acetic acid was inactive. These data are discussed in terms of a possible role for O-.2 and other reactive oxygen species in tumor promotion.

Activation of protein kinase C by tumor promoting phorbol esters, teleocidin and aplysiatoxin in the absence of added calcium

We have found that maximum stimulation (greater than 10-fold) of kinase activity of a bovine brain preparation of calcium- and phospholipid-dependent protein kinase (PKC) by 12-O-tetradecanoylphorbol-13-acetate (TPA) occurs in the presence of phospholipid, but in the absence of added Ca2+. In effect, nM concentrations of TPA substitute for mM concentrations of added Ca2+, and the two agents are not synergistic. Biologically active analogs of TPA such as phorbol-12,13-dibutyrate (PDBu), 12-O-hexadecanoyl-16-hydroxyphorbol-13-acetate (HHPA) or mezerein were also effective activators of PKC, as were the chemically unrelated tumor promoters teleocidin and aplysiatoxin, when tested at nM concentrations in the absence of added Ca2+. On the other hand, the biologically inactive compounds phorbol, 4-alpha-phorbol-12,13-didecanoate (4-alpha-PDD), HHPA-13,20-diacetate and 1,2-dihydro-20-deoxy-HHPA did not affect PKC activity in the absence or presence of Ca2+. Our results are consistent with a stereochemical model in which the hydrophilic domains of certain diterpenes, teleocidin and aplysiatoxin interact specifically with PKC apoenzyme, while their hydrophobic domains interact with phospholipid, thus forming an enzymatically active ternary complex.

Epidermal cell proliferation and promoting ability of phorbol esters

Dose-response relationships on the abilities of several phorbol ester tumor promoters to promote skin tumors after 7,12-dimethylbenz[a]anthracene initiation and to bring about edema, inflammation, and epidermal hyperplasia were determined in female Charles River CD-1 mice. The promoting ability of the potent synthetic promoter, phorbol-12,13-dioctanoate (PdiC8), was determined over a dose range of 0.1-10 mug/application. Administration of PdiC8 two times weekly at dosages of 4, 6, 8, and 10 mug gave little variation in tumor response. A dose-dependent tumor response occurred at doses of 1-4 mug PdiC8. Only 1 papilloma was observed when PdiC8 was given twice weekly at a dose of 0.1 or 0.5 mug. A similar dose-response relation was observed for the ability of PdiC8 to stimulate epidermal hyperplasia. Investigations of other phorbol esters revealed an excellent correlation between their promoting ability and their ability to induce epidermal hyperplasia; however, that was not the case for compounds outside the phorbol ester series (i.e., acetic acid, cantharidin, and ethylphenylpropiolate).

Dehydroepiandrosterone (DHEA) and 3 beta-methylandrost-5-en-17-one: inhibitors of 7,12-dimethylbenz[a]anthracene (DMBA)-initiated and 12-O-tetradecanoylphorbol-13-acetate (TPA)-promoted skin papilloma formation in mice

Long-term oral administration of the adrenal steroid, dehydroepiandrosterone (DHEA), has previously been shown to inhibit the development of spontaneous breast cancer and chemically induced lung and colon tumors in various mouse strains. In the two-stage skin papilloma system in the mouse, topical application of DHEA inhibits both 7,12-dimethylbenz[a]anthracene initiation and 12-O-tetradecanoylphorbol-13-acetate promotion of these tumors. The synthetic steroid, 3 beta-methylandrost-5-en-17-one, which, unlike DHEA, is not demonstrably estrogenic in the rat, also inhibits papilloma development.

An assay procedure for the comparative irritancy testing of esters in the tigliane and daphnane series

A method is described for testing of diterpene esters for irritancy. The technique involves the application of acetone solutions of the toxins to the inside ears of female LACA mice. The number of mice responding per group and the log10 dose data were evaluated using probit analysis with the assistance of a computer program. This evaluation has the advantage that approximations inherent with an arithmetical evaluation were eliminated, and limits may be placed upon the standard deviation of the irritant dose 50% (ID50). In addition, the use of a chi2 test automatically eliminated results which were not attributed to random biological variation. Observations of the time to onset and the persistence of the inflammation have led to the suggestion that daphnane orthoester diterpenes may elicit their effect by means of a direct action at a receptor site in skin, whereas the tigliane O-acyl esters may in part act by causing more general tissue damage.

Normal and transformed human prokeratinocytes express divergent effects of a tumor promoter on cell cycle-mediated control of proliferation and differentiation

The tumor promoter, 12-O-tetradecanoylphorbol-13-acetate (TPA), is shown to be a potent inhibitor of growth of normal human prokeratinocytes (HPK) cultured in serum-free medium. More specifically TPA inhibits the clonal growth of low density HPK cultures in a dose-dependent manner and the anti-proliferative effect of TPA is selective in that the inactive phorbol diester, 4-alpha-12,13-phorbol didecanoate, does not exert a similar effect. One-hour pulse exposure of HPK to TPA also has an effect comparable with continuous exposure to TPA; both treatments induce rapid growth arrest. Flow cytofluorometric analysis of DNA content shows that in TPA-treated HPK growth arrest is associated with accumulation of cells in both the G1 and G2/M phases of the cell cycle. Most interestingly, the data establish that the growth arrest of HPK induced by TPA is irreversible in that treated cells lose their colony-forming potential and that such cells are committed to differentiate without further cell cycle progression when placed in differentiation-promoting medium. In contrast, a human squamous carcinoma cell line, designated SCC-25, is insensitive to the anti-proliferative effect of TPA regardless of whether these cells are cultured in either serum-containing or serum-free medium. These data are interpreted to suggest that transformed human epithelial cells SCC-25 are defective in their ability to regulate their proliferation and differentiation by TPA-sensitive cell cycle-dependent mechanisms.

Dehydroepiandrosterone and 16 alpha-Br-epiandrosterone inhibit 12-O-tetradecanoylphorbol-13-acetate stimulation of superoxide radical production by human polymorphonuclear leukocytes

Both dehydroepiandrosterone (DHEA) and the synthetic steroid 16 alpha-Br-epiandrosterone (Br-Epi), a more potent inhibitor of glucose-6-phosphate dehydrogenase (G6PDH) than DHEA, inhibit the 12-O-tetradecanoylphorbol-13-acetate (TPA) stimulation of superoxide anion (O2-) formation by human neutrophils. DHEA has previously been shown to inhibit the development of spontaneous breast cancer and chemically induced tumors of the lung and colon as well as TPA promoted skin tumors in the mouse. The inhibition of TPA stimulated O2- formation by DHEA may contribute to the cancer preventive activity of this steroid.

Tumor promoter phorbol-12-myristate-13-acetate induces poly(ADP)-ribosylation in fibroblasts

The tumor promoter phorbol-12-myristate-13-acetate (PMA) causes an increase in pol(ADP)-ribosylation in mouse and human fibroblasts via the intermediate formation of active oxygen. In contrast to poly(ADP)-ribosylation induced by the methylating agent N-methyl-N'-nitro-N-nitrosoguanidine, de novo RNA and protein synthesis are required and the accumulation of the polymer occurs in the absence of detectable DNA strand breakage. Our results suggest a mechanism for PMA-induced modulation of chromatin structure and gene expression.

Phorbol esters potentiate tyrosine phosphorylation of epidermal growth factor receptors in A431 membranes by a calcium-independent mechanism

Incubation of membranes prepared from A431 cells with either epidermal growth factor (EGF) or phorbol 12-myristate 13-acetate (PMA) stimulates the transfer of 32phosphate from [gamma-32P]ATP into 8-10 membrane proteins. The major phosphorylated protein migrates on NaDodSO4/polyacrylamide gels with an apparent Mr of 180,000, corresponding to the previously identified EGF receptor. Stimulation of EGF receptor phosphorylation by PMA does not require Ca2+, suggesting that prior activation of protein kinase C is not a prerequisite for phosphate transfer. PMA-enhanced phosphorylation proceeds at 4 degrees C and requires Mn2+, both properties of tyrosine-specific protein kinases. Phospho amino acid analysis of the Mr 180,000 receptor band shows that only tyrosine residues are phosphorylated when A431 membranes are treated with either EGF or PMA. Moreover, proteolysis reveals that these residues are located in the same peptides of the receptor. These results demonstrate that a potent tumor-promoting phorbol ester can mimic a critical early response usually elicited by EGF.

Induction of differentiation of human promyelocytic leukemia (HL-60) cells by teleocidin and phorbol-12-myristate-13-acetate

Human promyelocytic leukemia cells (HL-60) were induced to differentiate into macrophage-like cells in a dose-dependent manner by the tumor promoters phorbol-12-myristate-13-acetate and teleocidin, a non-phorbol ester promoter. An HL-60 cell variant, designated as R-59, which is resistant to differentiation induction by phorbol-12-myristate-13-acetate was also resistant to differentiation induction by teleocidin. Differentiation was determined by increases in the percent of morphologically mature cells and in lysozyme and nonspecific esterase activities. Both compounds inhibited the growth of HL-60 cells by blocking them from entering the synthesis phase of the cell cycle with an accumulation of cells after 48 h in G1 phase. No such effects were observed in the R-59 cells. They were, however, as susceptible as the parent HL-60 cells, to inducers which are not considered to be tumor promoters such as dimethylsulfoxide and retinoic acid. However, these inducers cause the HL-60 and R-59 cells to differentiate into granulocyte-like cells. These results indicate that teleocidin produces in both the HL-60 and R-59 cells effects which are similar to those cause by phorbol-12-myristate-13-acetate. The possibility that agents producing such effects in these two cell types may represent potential tumor promoters is discussed.

Mitogenic hormones and tumor promoters greatly increase the incidence of colony-forming cells bearing amplified dihydrofolate reductase genes

Previous work has shown that the presence of a phorbol ester tumor promoter, phorbol 12-myristate 13-acetate (PMA), during a single-step selection for methotrexate (MTX)-resistant mouse 3T6 cells results in an up to 100-fold increase in the incidence of MTX-resistant, colony-forming cells. MTX resistance of most of these cells is due to amplification of the gene for dihydrofolate reductase (DHFR), the target enzyme for MTX. We show here that other active, noncytotoxic phorbol ester tumor promoters, such as phorbol 12, 13-didecanoate and 20-phorbol 12,13-butyrate, at their optimal concentrations (approximately equal to 0.1 microM) are approximately equal to PMA in increasing the incidence of MTX-resistant 3T6 colonies. Mezerein, a potent second-stage tumor promoter, but a weak complete promoter, increases the incidence of MTX resistance up to 350-fold, the strongest effect for any of the agents so far tested. PMA analogs that are inactive as tumor promoters, such as phorbol or phorbol 12,13,20-triacetate, have no effect on the incidence of MTX-resistant 3T6 colonies. Anthralin, a nonphorbol tumor promoter, is approximately equal to 40% as active as PMA in the MTX selection assay. Remarkably, the hormones insulin, arginine vasopressin, and epidermal growth factor, all of which are mitogenic for 3T6 cells, also exert a strong PMA-like effect on the incidence of MTX-resistant 3T6 colonies under conditions of MTX selection. The effect of insulin at its optimal concentration (approximately equal to 1 microgram/ml) is approximately equal to 70% that of PMA. Although the effect of PMA on the incidence of MTX-resistant 3T6 colonies does not significantly depend on the initial density of seeded cells or volume of the medium added, the analogous effect of insulin is strongly influenced by these parameters. Mevalonic acid, arachidonic acid, thymidine, caffeine, and nicotine, all of which are known to influence patterns of DNA synthesis in mammalian cells, were tested at their highest noncytotoxic concentrations and failed to produce any significant effect on the incidence of MTX-resistant 3T6 colonies. We discuss possible mechanisms of hormone- and tumor promoter-facilitated gene amplification in mammalian cells, relationship of mitogenic hormones to tumor promoters, and also implications of our findings for the problem of drug resistance in cancer chemotherapy.

Acute effects of 12-O-tetradecanoylphorbol-13-acetate, teleocidin B, or 2,3,7,8-tetrachlorodibenzo-p-dioxin on cultured normal human bronchial epithelial cells

Effects of teleocidin B, 12-O-tetradecanoylphorbol-13-acetate (TPA), phorbol, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and 2,7-dichlorodibenzo-p-dioxin (DCDD) on normal human bronchial epithelial cell cultures were assessed by quantitation of cellular morphology, clonal growth (population doublings per day), cross-linked envelope (CLE) formation and the enzymatic activities of aryl hydrocarbon hydroxylase (AHH), ornithine decarboxylase (ODC) and plasminogen activator (PA). Toxicity was assessed by clonal growth assays. Teleocidin B and TPA had similar effects on growth, morphology and enzyme activities. When the cells were incubated with TPA or teleocidin B at concentrations of 1-100 nM for 6 h, RNA synthesis was unaffected, but DNA synthesis decreased and squamous differentiation, marked by an increase in cell surface area and cross-linked envelope formation, was increased. TPA and teleocidin B also increased ODC activity in LHC-0 medium (a maintenance medium without epidermal growth factor) but caused a decrease of ODC activity in LHC-4 (a growth medium containing epidermal growth factor). Finally, TPA and teleocidin B each caused an increase of PA and a decrease of AHH activities in both media. Phorbol, a non-promoting analogue of TPA, had no effect on growth, morphology or biochemical assays. TCDD (100 nM) caused a 15% decrease in cell growth when cells were incubated in LHC-4, and this was accompanied by an increase in cell surface area, PA activity, and CLE formation. TCDD caused an increase in AHH and ODC activities when the cells were incubated in either LHC-0 or LHC-4 medium. DCDD did not alter cell growth, and its morphological and biochemical effects were similar to those of TCDD although less marked. In conclusion, results reported here are consistent with the hypothesis that an important property of some tumor promoters is their ability to induce terminal differentiation in normal, non-initiated epithelial cells.

Antipromotional activity of dietary N-(4-hydroxyphenyl)retinamide in two-stage skin tumorigenesis in CD-1 and SENCAR mice

The activity of the synthetic retinoid, N-(4-hydroxyphenyl)retinamide (4-HPR), as a promoter and as an inhibitor of tumor promotion in mouse skin was investigated using CD-1 and SENCAR mice. Dietary administration of 4-HPR inhibited skin tumor promotion by 12-O-tetradecanoylphorbol-13-acetate (TPA) in both mouse strains, although protective activity was observed only at high TPA doses. Dietary 4-HPR had no promoting activity in mice receiving initiation and no TPA promotion. These data suggest that retinoid promotion of skin tumorigenesis may be specific to retinoic acid, and is not necessarily characteristic of the entire chemical class.

Inhibition of 12-O-tetradecanoylphorbol-13-acetate-induced increase in vascular permeability in mouse skin by lipoxygenase inhibitors

The painting of mouse dorsal skin with 12-O-tetradecanoylphorbol-13-acetate (TPA) (0.2-2.5 nmol/mouse) induced a dose-related increase in vascular permeability, which was determined by pontamine sky blue exudation into the skin 5 hr after the TPA treatment. Marked infiltration of neutrophils in the dermal interstitium was also observed 5 hr after TPA treatment. Treatment of mice with nordihydroguaiaretic acid (NDGA) (10 mumol/mouse). 2,3,5-trimethyl-6-(12-hydroxy-5,10-dodecadiynyl)-1,4-benzoquinone (AA861) (10 mumol/mouse) and quercetin (3 mumol/mouse) significantly inhibited the TPA-induced dye exudation. However, indomethacin (250-1000 nmol/mouse) tended to inhibit the TPA-induced dye exudation, but the inhibition was not statistically significant. Treatment with AA861 (10 mumol/mouse) also caused a marked inhibition of TPA-induced neutrophil infiltration. Quercetin, NDGA and AA861 inhibited epidermal lipoxygenase activity, but indomethacin failed to inhibit it. On the other hand, indomethacin inhibited epidermal cyclooxygenase, but quercetin, NDGA and AA861 failed to inhibit it. The present study suggests involvement of a lipoxygenase product(s) in the mechanism of the TPA-induced increase in vascular permeability in the dorsal skin of mice.

Indirect induction of a clastogenic effect in epidermal cells by a tumor promoter

The mechanisms by which tumor promoters exert their effects on target tissues are not clearly understood. Recent studies have demonstrated that phorbol ester tumor promoters induce an oxidative burst in phagocytes and DNA single-strand breaks (SSB) in leukocytes. The purpose of the research presented here was to investigate the clastogenic effects of tumor promoters in the target cell population, primary mouse epidermal cells co-incubated with leukocytes. Using the alkaline elution assay to detect DNA SSB, it was demonstrated that tumor promoters induce DNA SSB in primary mouse epidermal cells incubated in the presence of leukocytes. By increasing the ratio of leukocytes to epidermal cells from 1:2 to 10:1, in the presence of 1.6 X 10(-6) M 12-O-tetradecanoylphorbol-13-acetate (TPA), a ratio dependent increase in DNA SSB was observed (from 9 X 10(-2) to 121 DNA SSB per 10(6) nucleotides). A dose response in DNA SSB was seen with TPA over a concentration range of 4 X 10(-9)-1.6 X 10(-6) M. Mezerein, a second stage tumor promoter, induced similar levels of DNA SSB to that of TPA. 4-O-Methyl TPA, a first stage tumor promoter, induced significantly fewer DNA SSB than either TAP or mezerein at similar concentrations. The induction of DNA SSB in epidermal cells treated with TPA and co-incubated with leukocytes was inhibited by catalase but not superoxide dismutase. These data indicate that tumor promoters can act indirectly on target epidermal cells by stimulating the release of a clastogenic factor from leukocytes through a mechanism involving H2O2.

Effect of phorbol esters on guniea pig skin in vivo

When topically applied to guniea pig ear skin the tumor promoting phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) induced inflammation and epidermal hyperproliferation which could be inhibited by indomethacin. This inhibition could be reversed both by prostaglandins E and F. Five minutes after TPA treatment an increase in the level of prostaglandin E but not of prostaglandin F was observed in the epidermis. The non-promoting phorbol ester 4-O-methyl-TPA also stimulated epidermal cell proliferation but this stimulation was not inhibited by indomethacin. The above results are in agreement with those already reported in the mouse system with these two compounds. Ornithine decarboxylase (ODC) activity has been evaluated in the epidermis of guniea pig ear after topical application of 20 nmol of TPA. No increase was noted. This is in contrast with the well documented activation of ODC in mouse skin treated with TPA. Since TPA acts as a promoter in the mouse whereas both croton oil and TPA have no promoting action in the guinea pig, the above result supports the view that ODC activationis related to promotion, and provides a possible explanation for the resistance of this animal species to promotion. This resistance is further documented by the fact that no "dark cells" were found in guinea pig ear skin.

Role of circulating granulocytes in sheep lung injury produced by phorbol myristate acetate

Phorbol myristate acetate (PMA) and endotoxin cause pulmonary granulocyte sequestration and alteration in lung fluid and solute exchange in awake sheep that are felt to be analogous to the adult respiratory distress syndrome in humans. The basic hypothesis that PMA causes lung injury by activating circulating granulocytes has never been tested. The effects of infused PMA on lung mechanics and the cellular constituents of lung lymph have also not been reported. We therefore characterized the effects of intravenous PMA, 5 micrograms/kg, on lung mechanics, pulmonary hemodynamics, lung fluid and solute exchange, pulmonary gas exchange, blood and lymph leukocyte counts, and plasma and lymph cyclooxygenase products of arachidonate metabolism in 10 awake sheep with normal granulocyte counts and after granulocyte depletion with hydroxyurea. PMA significantly altered lung mechanics from base line in both nongranulocyte depleted and granulocyte-depleted sheep. Dynamic compliance decreased by over 50% and resistance to airflow across the lungs increased over threefold acutely following PMA infusion in both sets of experiments. Changes in lung mechanics, pulmonary hemodynamics, lung fluid and solute exchange, pulmonary gas exchange, and plasma and lymph arachidonate metabolites were not significantly affected by greater than 99% depletion of circulating granulocytes. We conclude that the lung injury caused by PMA in chronically instrumented awake sheep probably is not a result of activation of circulating granulocytes.

Cell culture tumor promotion experiments with saccharin, phorbol myristate acetate and several common food materials

The BALB/c-3T3 cell neoplastic transformation system was modified to examine the tumor promoting activity of a set of substances. Following initiation of the target cells with 3-methylcholanthrene, treatment of the cultures with phorbol myristate acetate (0.01 microgram/ml; 1.5 X 10(-8) M) during the remainder of the 4-week assay interval resulted in a marked increase in both spontaneous and initiated Type III transformed foci. In contrast, a similar treatment with saccharin at 20, 100 or 500 microgram/ml (0.08, 0.4 or 2.1 X 10(-3) M) did not influence the occurrence of Type III transformed foci and did not result in a promoting response. Sodium ascorbate (2.53 X 10(-3) M) and L-tryptophan (2.45 X 10(-3) M) almost completely inhibited both spontaneous and initiated Type III transformed foci. Calcium pantothenate (2.10 X 10(-3) M) exhibited a marginal promoting effect. Under the conditions of this study in which the classical tumor promoter phorbol myristate acetate was highly active in promoting Type III transformed foci, saccharin was not active as either a direct transforming or promoting agent at doses up to 5 orders of magnitude higher.