Phorbol Ester-induced Tumor Promotion Research Articles

Phloretin Inhibits Phorbol Ester–Induced Tumor Promotion and Expression of Cyclooxygenase-2 in Mouse Skin: Extracellular Signal-Regulated Kinase and Nuclear Factor-κB as Potential Targets

The present study investigated the effect of phloretin [2',4',6'-trihydroxy-3-(4-hydroxyphenyl)-propiophenone] on 12-O-tetradecanoylphorbol 13-acetate (TPA)-induced cyclooxygenase-2 (COX-2) expression and tumor promotion in mouse skin and explored the underlying molecular mechanisms. Topical application of phloretin significantly inhibited 7,12-dimethylbenz[a]anthracene-initiated and TPA-promoted mouse skin carcinogenesis. Pretreatment with phloretin on the dorsal skin of mice inhibited TPA-induced COX-2 expression in a dose-dependent manner. To elucidate the molecular mechanism underlying COX-2 inhibition by phloretin, we examined its effect on TPA-induced activation of nuclear factor-κB (NF-κB), a ubiquitous transcription factor responsible for TPA-induced COX-2 expression in mouse skin. Topically applied phloretin decreased the TPA-induced DNA binding of NF-κB. In addition, phloretin inhibited the phosphorylation as well as the catalytic activity of extracellular signal-regulated kinase (ERK), which was previously found to activate NF-κB and induce COX-2 expression in TPA-treated mouse skin. Taken together, the inhibitory effects of phloretin on TPA-induced NF-κB activation and COX-2 expression through the modulation of ERK signaling may partly account for its antitumor-promoting effect on mouse skin carcinogenesis.

Correction: Diallyl Trisulfide Inhibits Phorbol Ester–Induced Tumor Promotion, Activation of AP-1, and Expression of COX-2 in Mouse Skin by Blocking JNK and Akt Signaling

Correction: Diallyl Trisulfide Inhibits Phorbol Ester–Induced Tumor Promotion, Activation of AP-1, and Expression of COX-2 in Mouse Skin by Blocking JNK and Akt Signaling

Diallyl Trisulfide Inhibits Phorbol Ester–Induced Tumor Promotion, Activation of AP-1, and Expression of COX-2 in Mouse Skin by Blocking JNK and Akt Signaling

An inverse relationship exists between the consumption of garlic and the risk of certain cancers. The present study was aimed at investigating the effect of garlic constituent diallyl trisulfide (DATS) on 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced cyclooxygenase-2 (COX-2) expression and tumor promotion in mouse skin and to explore the underlying molecular mechanisms. Pretreatment of mouse skin with different garlic-derived allyl sulfides showed DATS to be the most potent in suppressing TPA-induced COX-2 expression. DATS significantly attenuated the DNA binding of activator protein-1 (AP-1), one of the transcription factors that regulate COX-2 expression, in TPA-stimulated mouse skin. DATS also diminished TPA-induced expression of c-Jun and c-Fos, the principal components of AP-1, and blunted the activation of c-Jun NH(2)-terminal kinase (JNK) and Akt. Pharmacologic inhibition of JNK or Akt by SP600125 or LY294002, respectively, resulted in diminished AP-1 DNA binding, reduced levels of c-Jun and c-Fos, and inhibition of COX-2 expression in TPA-treated mouse skin. The JNK or Akt kinase assay, taking c-Jun fusion protein as a substrate, revealed that TPA induced JNK- or Akt-mediated c-Jun phosphorylation in mouse skin, which was significantly attenuated by DATS or respective pharmacologic inhibitors. Evaluation of antitumor-promoting effect of DATS on 7,12-dimethylbenz(a)anthracene-initiated and TPA-promoted mouse skin carcinogenesis showed that pretreatment with DATS significantly reduced the incidence and multiplicity of papillomas. Taken together, the inhibitory effects of DATS on TPA-induced AP-1 activation and COX-2 expression through modulation of JNK or Akt signaling may partly account for its antitumor-promoting effect on mouse skin carcinogenesis.

Inhibitory effects of oligonol on phorbol ester-induced tumor promotion and COX-2 expression in mouse skin: NF-κB and C/EBP as potential targets

Plant polyphenols possess anti-oxidant and anti-inflammatory activities and are hence potential candidates for preventing cancer. The present study was aimed at evaluating the anti-inflammatory and anti-tumor promoting activity of oligonol, a formulation of catechin-type oligomers, in mouse skin stimulated with a proto-type tumor promoter 12- O-tetradecanoylphorbol-13-acetate (TPA). Pretreatment of mouse skin with oligonol significantly inhibited TPA-induced expression of cyclooxygenase-2 (COX-2). Oligonol diminished nuclear translocation and DNA binding of nuclear factor-kappaB (NF-κB) via blockade of phosphorylation and subsequent degradation of IκBα in TPA-treated mouse skin. Moreover, oligonol suppressed TPA-induced DNA binding of CCAAT/enhancer-binding protein (C/EBP) in mouse skin. Oligonol pretreatment also attenuated the phosphorylation and/or catalytic activities of extracellular signal-regulated protein kinase-1/2 (ERK1/2) and p38 mitogen-activated protein (MAP) kinase. Moreover, p38 MAP kinase inhibitor SB203580, but not the MEK inhibitor U0126, negated TPA-induced DNA binding of C/EBP. In addition, oligonol reduced the incidence and the multiplicity of papillomas and squamous cell carcinomas in 7,12-dimethylbenz[ a]anthracene (DMBA)-initiated and TPA-promoted mouse skin, and prolonged the survival of tumor-bearing mice. Pretreatment with oligonol diminished the levels of proliferating cell nuclear antigen and expression of COX-2 in papillomas and carcinomas, respectively, as compared to DMBA plus TPA treatment alone. Taken together, the above findings suggest that oligonol inhibits TPA-induced COX-2 expression by blocking the activation of NF-κB and C/EBP via modulation of MAP kinases and suppresses chemically induced mouse skin tumorigenesis.

Bran extracts from pigmented rice seeds inhibit tumor promotion in lymphoblastoid B cells by phorbol ester

Using flow cytometry, we quantitatively evaluated anti-tumor-promoting activity of rice bran extracts by measuring inhibition of Epstein-Barr virus early-antigen activation (EBV-EA) induced by the tumor promoter 12- O-tetradecanoylphorbol-13-acetate (TPA). This assay measures anti-tumor-promoting activity and cytotoxicity of target substances using the same batch of cells. Using this short-term procedure, we have determined the anti-tumor-promoting activity of 70% ethanol–water extracts of bran (outer layer) from seeds of five pigmented rice cultivars: Jumlalocal-1, DZ 78, Elwee, LK1-3-6-12-1-1, and LK1A-2-12-1-1. The results show that, compared to an extract from the non-pigmented white cooking rice variety Chuchung, the extracts from the pigmented varieties strongly inhibited phorbol ester-induced tumor promotion in marmoset lymphoblastoid cells B95-8 in vitro. These findings may facilitate development and use of new health-promoting rice varieties.

Antioxidative, Antimutagenic, and Anticarcinogenic Activities of Rice Bran Extracts in Chemical and Cell Assays

Ethanol-water (70:30 v/v) extracts from rice brans removed from seeds of two blackish-purple pigmented (Sanhaehyanghyulla and Suwon 415) and one nonpigmented (Chuchung) brown rice cultivars were evaluated for antioxidative, anti-tumor-promoting, and anticarcinogenic activities in chemical assays and in mammalian cells (human leukemia HL-60, marmoset B lymphoblastoid B95-8, and Chinese hamster V79 lung cells) by the following tests: inhibition of xanthine oxidase activity; chelation of ferrous ions; reduction of potassium ferricyanide; scavenging of superoxide anions, hydroxyl radicals, and intracellular peroxides; inhibition of 4-nitroquinoline N-oxide-induced mutagenesis; and inhibition of phorbol ester-induced tumor promotion. The extracts from the pigmented rice seeds had generally higher activities in all tests than did the extract from the nonpigmented variety. The results suggest that brans from pigmented rice varieties may provide a source of new natural antioxidants and anticarcinogens and that such rice cultivars with high antioxidative potential also provide a genetic resource for the development of new, improved rice cultivars that may make it possible to enhance both the nutritional and medical value of rice-based diets.

Salix caprea inhibits skin carcinogenesis in murine skin: inhibition of oxidative stress, ornithine decarboxylase activity and DNA synthesis

Chemoprevention of free radical-mediated diseases including cancer by natural products is an emerging discipline due to its wider applicability and acceptance. The present study deals with the chemopreventive effect of Salix caprea against phorbol ester-induced oxidative stress and tumor promotion in murine skin. In the present investigation, it was observed that a single application of 12- O-tetradecanoyl-13-phorbol acetate (TPA) (20 nmol/0.2 ml acetone/animal) caused a significant ( P<0.05) depletion of cutaneous antioxidants viz., glutathione, glutathione reductase, glutathione peroxidase, catalase and phase II drug metabolizing enzymes viz., glutathione- S-transferase, quinone reductase. An increase in the hydrogen peroxide generation and protein oxidation (measured in terms of protein carbonyl content) was also observed with a single application of TPA. However, the pretreatment of animals with different doses of Salix caprea (0.5, 1.0 and 1.5 mg/kg/0.2 ml acetone) caused a significant recovery in the TPA-mediated depletion in antioxidant levels. The pretreatment of animals with Salix caprea was observed to inhibit the TPA-mediated depletion in phase II enzymes. It was also observed that Salix caprea reversed the TPA-mediated depletion in the activity of phase II enzymes that is an important characteristic of cancer chemopreventive agents. Phorbol esters are known to induce the tumor promotion by increasing rate of DNA synthesis, ornithine decarboxylase activity (ODC), and xanthine oxidase activity. In the present investigation, it was observed that the pretreatment of animals with Salix caprea caused a significant ( P<0.05) depletion in the TPA-induced DNA synthesis, ODC and xanthine oxidase activity in mice skin. Salix caprea significantly reduced the tumor promotion in mice skin when tested in two-stage chemical carcinogenesis model. It was observed to inhibit significantly ( P<0.05) the 7,12-dimethyl benz[ a] anthracene (DMBA)-initiated phorbol ester promoted skin carcinogenesis. It was concluded from the results that Salix caprea is an effective antioxidant and chemopreventive agent against phorbol ester-induced tumor promotion.

Tephrosia purpurea alleviates phorbol ester-induced tumor promotion response in murine skin

In recent years, considerable emphasis has been placed on identifying new cancer chemopreventive agents, which could be useful for the human population. Tephrosia purpurea has been shown to possess significant activity against hepatotoxicity, pharmacological and physiological disorders. Earlier we showed that Tephrosia purpurea inhibits benzoyl peroxide-mediated cutaneous oxidative stress and toxicity. In the present study, we therefore assessed the effect of Tephrosia purpurea on 12-O-tetradecanoyl phorbal-13-acetate (TPA; a well-known phorbol ester) induced cutaneous oxidative stress and toxicity in murine skin. The pre-treatment of Swiss albino mice with Tephrosia purpurea prior to application of croton oil (phorbol ester) resulted in a dose-dependent inhibition of cutaneous carcinogenesis. Skin tumor initiation was achieved by a single topical application of 7,12-dimethyl benz(a)anthracene (DMBA) (25 μ g per animal per 0.2 ml acetone) to mice. Ten days later tumor promotion was started by twice weekly topical application of croton oil (0.5% per animal per 0.2 ml acetone, v /v). Topical application of Tephrosia purpurea 1 h prior to each application of croton oil (phorbol ester) resulted in a significant protection against cutaneous carcinogenesis in a dose-dependent manner. The animals pre-treated with Tephrosia purpurea showed a decrease in both tumor incidence and tumor yield as compared to the croton oil (phorbol ester)-treated control group. In addition, a significant reduction in TPA-mediated induction in cutaneous ornithine decarboxylase (ODC) activity and [3H]thymidine incorporation was also observed in animals pre-treated with a topical application of Tephrosia purpurea. The effect of topical application of Tephrosia purpurea on TPA-mediated depletion in the level of enzymatic and non-enzymatic molecules in skin was also evaluated and it was observed that topical application of Tephrosia purpurea prior to TPA resulted in the significant recovery of TPA-mediated depletion in the level of these molecules, namely glutathione, glutathione S-transferase, glutathione reductase and catalase. From these data we suggest that Tephrosia purpurea can abrogate the tumor-promoting effect of croton oil (phorbol ester) in murine skin.

Down‐regulation of particulate protein kinase Cε and up‐regulation of nuclear activator protein–1 DNA binding in liver following in vivo exposure of B6C3F1 male mice to heptachlor epoxide

The effects of in vivo administration of the cyclodiene tumor promoter heptachlor epoxide on mouse liver protein kinase C were studied in male B6C3F1 mice by protein kinase C activity assays and Western blotting under conditions known to increase the incidence of hepatocellular carcinoma because protein kinase C is thought to be critical in phorbol ester–induced tumor promotion. Under these test conditions, 20 ppm dietary heptachlor epoxide for 1–20 days increased cytosolic and decreased particulate total protein kinase C activities, while 10 ppm had no effect. Further, total cytosolic and particulate protein kinase C activities were decreased within 1 hour by 10 mg/kg intraperitoneal (i.p.) heptachlor epoxide. Western blotting showed that conventional protein kinase Cα and β isoforms were unaffected by heptachlor epoxide. Particulate novel protein kinase Cϵ, however, was selectively down-regulated by 1, 10, and 20 ppm dietary heptachlor epoxide, whereas the cytosolic isoform was decreased by 1 and 10 ppm heptachlor epoxide for 10 days. The high-dose treatment for 24 hours also decreased particulate novel protein kinase Cϵ but increased the cytosolic titer. These results demonstrate that this isoform is unique in its sensitivity to heptachlor epoxide. Activator protein–1 DNA binding, a critical factor in tumor promotion, was substantially increased at 3 and 6 hours with 3.7 mg/kg (i.p.) heptachlor epoxide and at 3 and 10 days with 20 ppm dietary heptachlor epoxide. The effects of heptachlor epoxide on protein kinase C and activator protein–1 are similar to those caused by phorbol ester treatments and correlate well to heptachlor levels found to induce tumors in mice. However, heptachlor epoxide did not initially activate protein kinase C with in vivo treatments or with in vitro treatments of a plasma membrane fraction aimed at demonstrating direct activation, as has been shown for phorbol esters. The ability of heptachlor epoxide to down-regulate particulate novel protein kinase Cϵ correlates to dosages used in in vivo tumor promotion studies. However, this may represent a negative feedback response rather than a causative effect. © 2001 John Wiley & Sons, Inc. J Biochem Mol Toxicol 15:1–14, 2001

Cheiranthus cheiri Abrogates Phorbol Ester Induced Tumor Promotion Response in Murine Skin

Cancer chemoprevention has become an important area of cancer research for identifying new potentially useful inhibitors of carcinogenesis. Cheiranthus cheiri has been shown to possess significant activity against various physiological disorders. In the present communication, we assessed the effect of Cheiranthus cheiri on 12- O -tetradecanoyl 13-phorbol acetate (TPA)-induced cutaneous oxidative stress and toxicity in murine skin. The pretreatment of Swiss albino mice with Cheiranthus cheiri prior to application of croton oil (phorbol ester) resulted in a dose-dependent inhibition of cutaneous carcinogenesis. Skin tumor initiation was achieved by a single topical application of 7,12-dimethyl benz (a) anthracene (DMBA) (40 µg/animal/0.2 ml acetone) to mice. Ten days later tumor promotion was started by twice weekly topical application of croton oil (1.0%/animal/0.2 ml acetone, v/v). Topical application of Cheiranthus cheiri 1 h prior to each application of croton oil (phorbol ester) resulted in a significant protection against cutaneous carcinogenesis in a dose dependent manner. The animals pretreated with Cheiranthus cheiri showed a significant decrease in both tumor incidence and tumor yield as compared to croton oil (phorbol ester)-treated control group (p < 0.05). In addition a significant reduction in TPA-mediated induction in cutaneous ornithine decarboxylase (ODC) activity and [3 H]-thymidine incorporation was also observed in animals pretreated with topical application of Cheiranthus cheiri (p < 0.05). Prophylactic treatment of mice with Cheiranthus cheiri 1 h before TPA (20 nmol/animal/0.2 ml acetone) treatment resulted in the diminution of TPA-mediated cutaneous oxidative stress. It was observed that topical application of Cheiranthus cheiri prior to TPA resulted in the significant recovery of TPA-mediated depletion in the level and activities of cellular anti-oxidants, viz, glutathione reduced, glutathione S -transferase, glutathione reductase, glutathione peroxidase and catalase (p < 0.05). From these data, we suggest that Cheiranthus cheiri can abrogate the tumor promoting effect of croton oil (phorbol ester) in murine skin.

Down-regulation of particulate protein kinase Cepsilon and up-regulation of nuclear activator protein-1 DNA binding in liver following in vivo exposure of B6C3F1 male mice to heptachlor epoxide.

The effects of in vivo administration of the cyclodiene tumor promoter heptachlor epoxide on mouse liver protein kinase C were studied in male B6C3F1 mice by protein kinase C activity assays and Western blotting under conditions known to increase the incidence of hepatocellular carcinoma because protein kinase C is thought to be critical in phorbol ester-induced tumor promotion. Under these test conditions, 20 ppm dietary heptachlor epoxide for 1-20 days increased cytosolic and decreased particulate total protein kinase C activities, while 10 ppm had no effect. Further, total cytosolic and particulate protein kinase C activities were decreased within 1 hour by 10 mg/kg intraperitoneal (i.p.) heptachlor epoxide. Western blotting showed that conventional protein kinase Calpha and beta isoforms were unaffected by heptachlor epoxide. Particulate novel protein kinase Cepsilon, however, was selectively down-regulated by 1, 10, and 20 ppm dietary heptachlor epoxide, whereas the cytosolic isoform was decreased by 1 and 10 ppm heptachlor epoxide for 10 days. The high-dose treatment for 24 hours also decreased particulate novel protein kinase Cepsilon but increased the cytosolic titer. These results demonstrate that this isoform is unique in its sensitivity to heptachlor epoxide. Activator protein-1 DNA binding, a critical factor in tumor promotion, was substantially increased at 3 and 6 hours with 3.7 mg/kg (i.p.) heptachlor epoxide and at 3 and 10 days with 20 ppm dietary heptachlor epoxide. The effects of heptachlor epoxide on protein kinase C and activator protein-1 are similar to those caused by phorbol ester treatments and correlate well to heptachlor levels found to induce tumors in mice. However, heptachlor epoxide did not initially activate protein kinase C with in vivo treatments or with in vitro treatments of a plasma membrane fraction aimed at demonstrating direct activation, as has been shown for phorbol esters. The ability of heptachlor epoxide to down-regulate particulate novel protein kinase Cepsilon correlates to dosages used in in vivo tumor promotion studies. However, this may represent a negative feedback response rather than a causative effect.

Effect of Dietary Conjugated Linoleic Acid on Phorbol Ester-Induced PGE2 Production and Hyperplasia in Mouse Epidermis

Conjugated linoleic acid (CLA) is a chemoprotective fatty acid that inhibits phorbol ester-induced skin tumor promotion in mice. The goal of the present study was to determine potential chemoprotective mechanisms through which CLA may be acting. Mice were fed diets containing 0.0%, 0.5%, 1.0%, or 1.5% CLA (by wt) for six weeks. The epidermis was evaluated for fatty acid composition, vascular permeability, prostaglandin E2; (PGE2) production, hyperplasia, ornithine decarboxylase activity, and c-myc mRNA accumulation. Fatty acid analysis of mouse epidermis demonstrated a dose-dependent increase of CLA incorporation into phospholipids and neutral lipids. In mice topically treated with the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA), dietary CLA (1.5%) significantly (p < 0.05) reduced PGE2; synthesis (2-fold). Additionally, CLA lowered accumulation of c-myc mRNA, a gene commonly associated with regulating cell cycle components involved in cellular proliferation, although this trend was not significant. Vascular permeability was unaffected by dietary CLA. These data suggest that dietary CLA modulates TPA-induced tumor promotion through a mechanism involving PGE2 production; however, dietary CLA had a moderate effect on c-myc mRNA levels and little effect on TPA-induced hyperplasia and ornithine decarboxylase activity.

Tumor Promotion by Depleting Cells of Protein Kinase Cδ

Tumor-promoting phorbol esters activate, but then deplete cells of, protein kinase C (PKC) with prolonged treatment. It is not known whether phorbol ester-induced tumor promotion is due to activation or depletion of PKC. In rat fibroblasts overexpressing the c-Src proto-oncogene, the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) induced anchorage-independent growth and other transformation-related phenotypes. The appearance of transformed phenotypes induced by TPA in these cells correlated not with activation but rather with depletion of expressed PKC isoforms. Consistent with this observation, PKC inhibitors also induced transformed phenotypes in c-Src-overexpressing cells. Bryostatin 1, which inhibited the TPA-induced down-regulation of the PKCdelta isoform specifically, blocked the tumor-promoting effects of TPA, implicating PKCdelta as the target of the tumor-promoting phorbol esters. Consistent with this hypothesis, expression of a dominant negative PKCdelta mutant in cells expressing c-Src caused transformation of these cells, and rottlerin, a protein kinase inhibitor with specificity for PKCdelta, like TPA, caused transformation of c-Src-overexpressing cells. These data suggest that the tumor-promoting effect of phorbol esters is due to depletion of PKCdelta, which has an apparent tumor suppressor function.

Phorbol ester-induced leukotriene biosynthesis and tumor promotion in mouse epidermis.

In mouse skin in vivo the irritant and hyperplasiogenic tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) strongly increased the epidermal content of the cysteinyl leukotrienes LTC4, LTD4 and LTE4, but not of leukotriene LTB4. This effect was completely suppressed by the selective leukotriene biosynthesis inhibitor MK-886. Intragastric administration of MK-886 prevented phorbol ester-induced ear edema, but not epidermal hyperproliferation and tumor promotion. These data indicate that leukotrienes are involved in the pro-inflammatory effects of the phorbol ester, whereas its hyperproliferative and tumor-promoting activities do not depend on 5-lipoxygenase-catalyzed leukotriene formation. This action differs from several non-selective inhibitors of lipoxygenases that were found to inhibit tumor promotion in initiated mouse skin.

The effect of bryostatin on protein kinase C-regulated functions in human T lymphocytes and epidermal keratinocytes

The bryostatin (Bryo) is a macrocyclic lactone that binds specifically to protein kinase C (PKC) thereby affecting cell growth and differentiation and inhibits phorbol ester-induced tumor promotion. We used human peripheral blood lymphocytes (PBL) and epidermal cells in order to analyze the action mechanism of Bryo and compare it with that of the phorbol ester PMA. Bryo and PMA activated PBL- or T cell-derived PKC in a similar dose-response and induced a similar time kinetic of cytosol-to-membrane translocation of enzymatically active and immunoreactive PKC. In addition, the 2 drugs induced similar patterns of protein phosphorylation and activated the c- fos and c- jun genes that their protein products regulate transcription of TRE-containing genes. In contrast, long-term (20 h) treatment of cells with Bryo resulted in a marked loss of both cytosolic- and membrane-bound PKC while PMA induced only a slight reduction in the amount of cellular PKC. Inhibition of PMA-induced human T-cell proliferation by Bryo correlated with a reduction in the amount of cellular PKC. An opposite effect was observed in human epidurmal cells where Bryo augmented growth and proliferation while PMA induced terminal differentiation and cell death. We propse that at least some of the differences in the biological effects induced by Bryo and PMA are due to distinct regulations of PKC. Thus, although both agents can initially bind to and activate PKC at a later time (∼ 16 h), Bryo, but not PMA, induces rapid PKC degradation and inhibition of PKC-regulated biological responses that are dependent on the continuous presence and/or activation of the enzyme.

Interaction of Phospholipids, Retinoids and PMA with Calcium, Phospholipid-Dependent Protein Kinase-Catalyzed Reaction in Skin

Previous investigations suggested that a mechanism independent of cAMP may be associated with the action of some retinoids. An alternative pathway involving calcium, phospholipid-dependent protein kinase (C-kinase), was therefore studied. In order to demonstrate this, C-kinase was partially purified from skin of hairless, Balb/c normal and Balb/c nude mouse. Interaction and effects of various response modifiers such as phospholipids, retinoids and phorbol ester tumor promoters showed both major and minor differences among these enzymes. In general, retinal, retinoic acid, 13-cis-retinoic acid and etretinate stimulated skin enzyme activity in the absence of the natural stimulants, phosphatidyl serine and diacylglycerol (DAG). However in their presence the C-kinases were inhibited by retinoids. Our data further indicated that the active retinoids may compete with DAG for binding sites on the enzyme. However, the high concentrations of retinoids needed to elicit these effects suggested a pharmacological role for retinoid action as a result of hydrophobic interaction with lipid domains on the enzyme. These investigations also revealed some of the complexity associated with retinoid effects on C-kinase. Tumor promoter, phorbol-12-myristate 13-acetate (PMA) interacted with its receptor (C-kinase) from hairless and normal mouse skin and stimulated enzyme activity. However, PMA-dependent stimulation of nude mouse C-kinase was about half of that noted with the other two C-kinases. Furthermore, unlike its effect on hairless and Balb/c normal C-kinases, PMA was unable to potentiate the retinoid-stimulated activity of nude mouse skin enzyme. This behavior suggested that nude mouse C-kinase may be a variant form of the normal enzyme. The presence of this variant C-kinase may, therefore, be responsible for the lack of phorbol ester-induced tumor promotion observed earlier in nude mouse skin by other investigators. Endogenous substrate phosphorylation catalyzed by C-kinase from hairless and Balb/c normal mice resulted in 32P incorporation into four target polypeptides of molecular weights 75-78, 47-50, 25-29 and 14-18 kilodaltons. However, with the nude mouse enzyme, only the 75- to 78-kilodalton protein served as the target supporting the suggestion that this may be a variant C-kinase. Neither retinoic acid (10(-3) M) nor PMA (10(-6) M) seemed to affect the phosphorylation of any of the four polypeptides.(ABSTRACT TRUNCATED AT 400 WORDS)

The role of calcium in macrophage chemotaxis to the phorbol ester tumor promoter TPA

The significance of the macrophage in the inflammatory response that occurs concurrently with phorbol ester induced tumor promotion has not yet been determined. Biologically active phorbol ester tumor promoters modify several functional responses of macrophages including chemotaxis, cytotoxicity, secretion and prostaglandin synthesis and release. The present study examines calcium metabolism as a possible underlying biochemical mechanism through which 12-0-tetradecanoyl-phorbol-13-acetate (TPA) exerts its effects on macrophage chemotaxis. The chemotaxis of mouse resident peritoneal macrophages was evaluated in the presence of pharmacological agents known to alter cellular calcium metabolism. The calcium ionophore A23187 in uM concentrations enhanced macrophage chemotaxis to TPA by approximately 41%. This enhancement was dependent on the presence of extracellular calcium. TPA-induced chemotaxis was also enhanced by the histological dye ruthenium red (RR), an agent known to modify mitochondrial calcium fluxes and calcium-dependent neuronal transmission. Ruthenium red (0.1 and 1.0 uM) produced a maximal stimulation of macrophage chemotaxis to TPA of approximately 62%. An intracellular calcium antagonist, 8-(N,N-diethylamino) octyl 3,4,5-trimethoxybenzoate hydrochloride (TMB-8) inhibited macrophage chemotaxis to TPA in a dose related fashion (1.0 to 100 uM). Varying extracellular calcium concentrations (0–3.6 mM) had no effect on macrophage chemotaxis in response to TPA. In drug combination studies neither A23187 nor RR was able to overcome the inhibitory effects of TMB-8 on macrophage chemotaxis to TPA. These results indicate that intracellular calcium metabolism may be playing a significant role in modulating TPA's effect on macrophage chemotaxis, while extracellular calcium may be of little import. A possible mode of TPA's effect on the macrophage via mobilization of calcium from cellular storage sites is discussed.

Inhibition of Phorbol Ester-Induced Tumor Promotion in Mice by Vitamin A Analog and Anti-inflammatory Steroid&lt;xref ref-type="fn" rid="FN2"&gt;2&lt;/xref&gt;

The effects of a vitamin A analog, TMMP ethyl retinoate [or ethyl-9-(4-methoxy-2,3,6-trimethylphenyl)-3,7-dimethyl-trans-2,4,6,8-nonatetraenoate] (abbreviated Ro 10-9359), and an anti-inflammatory steroid, fluocinolone acetonide (or 6 alpha, 9 alpha-difluoro-11 beta, 16 alpha, 17,21-tetrahydroxypregna-1,4-diene-3,20-dione cyclic 16,17-acetal) (abbreviated FA), given alone or together were studied in a two-stage carcinogensis system. The phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) was used as the tumor promoter in a 7,12-dimethylbenz[a]anthracene (DMBA)-initiated mouse skin system. Two stocks of female mice, CD-1 and Sencar, which differ in their degrees of sensitivity to skin carcinogenesis, were used. A dose-dependent inhibition of carcinogenic expression, as determined by a decreased number of papillomas per animal, was observed in each mouse stock with the use of both FA and Ro 10-9359 when given alone. When FA and Ro 10-9359 were given together, an enhanced effect on the lowering of tumor incidence was noted. FA effectively inhibited tumor formation in the sensitive mouse stock even when the steroid was given 1 day prior to TPA treatment under conditions of unusually high doses of initiator (DMBA) and/or promoter (TPA). These results suggest that both anti-inflammatory steroids and retinoids inhibit tumor promotion and can be effectively used as a combination regimen for increased chemopreventive response.