Tumor promoters and the mechanism of tumor promotion

Tigliane and daphnane diterpenoids from Thymelaeaceae family: chemistry, biological activity, and potential in drug discovery

Tigliane and daphnane diterpenoids are characteristically distributed in plants of the Thymelaeaceae family as well as the Euphorbiaceae family and are structurally diverse due to the presence of polyoxygenated functionalities in the polycyclic skeleton. These diterpenoids are known as toxic components, while they have been shown to exhibit a wide variety of biological activities, such as anti-cancer, anti-HIV, and analgesic activity, and are attracting attention in the field of natural product drug discovery. This review focuses on naturally occurring tigliane and daphnane diterpenoids from plants of the Thymelaeaceae family and provides an overview of their chemical structure, distribution, isolation, structure determination, chemical synthesis, and biological activities, with a prime focus on the recent findings.

Human cell transformation by combined lineage conversion and oncogene expression

Cancer is the most complex genetic disease known, with mutations implicated in more than 250 genes. However, it is still elusive which specific mutations found in human patients lead to tumorigenesis. Here we show that a combination of oncogenes that is characteristic of liver cancer (CTNNB1, TERT, MYC) induces senescence in human fibroblasts and primary hepatocytes. However, reprogramming fibroblasts to a liver progenitor fate, induced hepatocytes (iHeps), makes them sensitive to transformation by the same oncogenes. The transformed iHeps are highly proliferative, tumorigenic in nude mice, and bear gene expression signatures of liver cancer. These results show that tumorigenesis is triggered by a combination of three elements: the set of driver mutations, the cellular lineage, and the state of differentiation of the cells along the lineage. Our results provide direct support for the role of cell identity as a key determinant in transformation and establish a paradigm for studying the dynamic role of oncogenic drivers in human tumorigenesis.

Ultrastructural Analysis of Epidermal Hyperplasia Induced by Multiple 12-0-Tetradecanoyl-Phorbol-13-Acetate (TPA) Treatment of Mouse Skin

Stationary epidermal hyperplasia induced by exposure of mouse skin to 1-6 TPA applications was analyzed by electron microscopy and found to be of two types. Intermingled orderly and irregularly stratified hyperplastic regions observed prominently after a single TPA application gave way, on multiple treatment, to epidermal hyperplasia populated by either cuboidal cells with expanded cytoplasm or by highly polar, narrow, tall and pleomorphic cells. Both cell types were poorly differentiated and displayed a paucity of intact desmosomal junctions, resulting in an incohesive tissue structure in which a number of phenotypic variants were expressed. The variants were markedly less mature than the adjacent cells and showed basal cell phenotype, acquisition of secretory activity or a disturbed mitotic process, resulting in the formation of binucleated cells. The observations suggest that the disturbed mitotic process, poor cellular differentiation and induction of metaplasia could be the mode by which an initiated cell may express its tumor phenotype and escape differentiation during the early stage of TPA promotion.

Thresholds in Chemical Carcinogenesis

This review deals with the controversial subject of thresholds in chemical carcinogenesis. It is essential to consider this subject in relation to a number of other matters which have a direct bearing on it. These include the use of the maximum tolerated dose (MTD) in animal bioassays. These are at times excessive and not consistent with the definition of the MTD. Many bioassays are carried out at only one or two doses so that reliable dose-response curves and hence a threshold cannot be established. In addition, laboratory animal bioassays even at the lowest doses used are frequently above those encountered in the environment by several orders of magnitude. The various biochemical and biologic events which a xenobiotic is subjected to in vivo are described in more detail in relation to threshold. Also, dose-dependent alterations in metabolic pathways are reviewed for vinyl chloride and 1, 4-dioxane. The value of examining the muta-genidty and cardnogenidty of activated carcinogenic intermediates is examined using a series of chloroalkene epoxides as intermediates. The interdisciplinary approaches that need to be used in risk assessment, which is required by federal regulatory agencies, are pointed out. It is concluded that thresholds do exist for some chemical carcinogens.

3: Final Report on the Safety Assessment of Oleic Acid, Lauric Acid, Palmitic Acid, Myristic Acid, and Stearic Acid

Oleic, Lauric, Palmitic, Myristic, and Stearic Acids are fatty acids with hydrocarbon chains ranging in length from 12 to 18 carbons with a terminal carboxyl group. These fatty acids are absorbed, digested, and transported in animals and humans. Little acute toxicity was observed when Ofeic, Lauric, Palmitic, Myristic, or Stearic Acid or cosmetic formulations containing these fatty acids were given to rats orally at doses of 15-19 g/kg body weight. Feeding of 15% dietary Oleic Acid to rats in a chronic study resulted in normal growth and health, but reproductive capacity of female rats was impaired. Results from topical application of Oleic, Palmitic, and Stearic Acid to the skin of mice, rabbits, and guinea pigs produced little or no apparent toxicity. Studies using product formulations containing Oleic and Stearic acids indicate that neither is a sensitizer or photosensitizing agent. Animal studies also indicate that these fatty acids are not eye irritants. Lauric, Stearic, and Oleic Acids were noncarcinogenic in separate animal tests. In primary and cumulative irritation clinical studies, Oleic, Myristic, and Stearic Acids at high concentrations were nonirritating. Cosmetic product formulations containing Oleic, Lauric, Palmitic, and Stearic Acids at concentrations ranging up to 13% were not primary or cumulative irritants, nor sensitizers. On the basis of available data from studies using animals and humans, it is concluded that Oleic, Lauric, Palmitic, Myristic, and Stearic Acids are safe in present practices of use and concentration in cosmetics.

Treatment of acromegaly in the era of personalized and predictive medicine

Acromegaly is a chronic disorder usually diagnosed late in the disease evolution. Such delayed diagnosis, together with the inability to achieve the treatment goals of normalizing biochemical disease markers and controlling tumour mass may result in substantial morbidity and mortality. Somatostatin analogues (SSA) are accepted as first-line medical therapy or as second-line therapy in patients undergoing unsuccessful surgery and are considered a cornerstone in the treatment of acromegaly. However, because a high percentage of patients experience SSA medical treatment failure, the identification of biomarkers associated with a successful or unsuccessful response to all classes of medical therapy would help in the choice of treatment and potentially allow for a quicker normalization of biochemical parameters. The current treatment algorithms for acromegaly are based upon a "trial-and-error" approach with additional treatment options provided when disease is not controlled. In many other diseases, therapeutic algorithms have been evolving towards personalized treatment with the medication that best matches individual disease characteristics, using biomarkers that identify therapeutic response. Additionally, a personalized approach to complementary treatment of comorbidities present in the acromegalic patient is also required. This review will discuss the development of a potential treatment algorithm for acromegaly addressing the biochemical control of the disease as well of its associated comorbidities, under a personalized approach based upon markers of prognostic and predictive significance, such as tumour size, MRI adenoma signal, GH value after acute octreotide test, granular adenoma pattern, Ki-67, somatostatin receptor phenotype, aryl hydrocarbon-interacting protein expression, gsp mutations, RAF kinase activity, E-cadherin and beta-arrestin-1.

Effects of diterpene esters of tigliane, daphnane, ingenane, and lathyrane types on pink bollworm,Pectinophora gossypiella saunders (Lepidoptera: Gelechiidae)

Twenty esters, representing the biogenetically related tigliane, daphnane, ingenane, and lathyrane series of diterpenes, were screened for growth-inhibitory and insecticidal effects on newly hatched larvae of the North American cotton pest,Pectinophora gossypiella (pink bollworm). Among the tigliane derivatives tested, only 12-O-tetradecanoylphorbol-13-acetate and 12-O-(2-methyl)butyrylphorbol-13-decanoate, of seven phorbol diesters isolated from croton oil by a new procedure involving droplet countercurrent chromatography, were active againstP.gossypiella as both growth inhibitors and insecticides. The effects of the former compound were not significantly diminished by acetylation of its C-20 primary hydroxy group. Three other croton oil phorbol diester constituents, as well as daphnetoxin and daphnetoxin-5,20-diacetate, exhibited activity as growth inhibitors, but not as insecticidal agents, at the doses used. None of the ingenane or lathyrane derivatives investigated was active in either respect. 12-0-Tetradecanoylphorbol-13-acetate was found to cause 100% mortality on second-stadium larvae ofCulex pipiens at 0.6 ppm, but exhibited less significant effects onOncopeltus fasciatus (second-stadium nymphs) andTribolium confusion (adults) when applied at higher doses.

Expression of embryonic characters by malignant cells

While the expression of fetal characters by malignant cells is now well-documented, the mechanism involved and the nature of the cells that are the target of malignant transformation remain controversial. It has often been assumed that carcinogenesis results in 'dedifferentiation' of specialized cells. The alternative hypothesis is that neoplasia results from a disorder of some normal stem cells. This view is discussed in relation to several examples, in particular teratocarcinomas.

Benzo[a]pyrene diol-epoxide (B[a]PDE) upregulates COX-2 expression through MAPKs/AP-1 and IKKbeta/NF-kappaB in mouse epidermal Cl41 cells

Benzo[alpha]pyrene-7,8-diol-9,10-epoxide (B[a]PDE), the major metabolite of benzo[a]pyrene (B[a]P), shows an ultimate complete carcinogen in various animals and is a causative agent for human cancers. However, its effects on the activation of signal pathways and the expression of genes involved in its carcinogenic effect remain largely unknown. In this study, the effects of B[a]PDE on induction of cyclooxygenase (COX)-2 and the signal pathways leading to the induction were investigated. Treatment of mouse epidermal Cl41 cells with B[a]PDE caused an increase in the expression of COX-2 at both transcription and protein levels, while its parental compound B[a]P did not show significant inductive effect. The COX-2 induction by B[a]PDE was dependent on the activation of mitogen-activated protein kinases (MAPK)s/activation protein (AP)-1 pathway, because inhibition of AP-1 by either overexpression of TAM67 (dominant negative mutant of c-jun), or pretreatment of cells with PD98059 (MEK1/2-ERKs pathway inhibitor) or SB202190 (p38K inhibitor), markedly inhibited B[a]PDE-induced COX-2 expression. In addition, impairment of NF-kappaB pathway by either NEMO-BDBP (an NF-kappaB specific inhibitor) or IkappaB kinase (IKK)beta-KM (dominant negative mutant of IKKbeta) also caused marked reduction of COX-2 induction by B[a]PDE. In contrast, inhibition of nuclear factor of activated T cells (NFAT) with FK506, did not show any effect on B[a]PDE-induced COX-2 expression. Collectively, these data indicate that exposure of Cl41 cells to B[a]PDE can induce COX-2 expression by increasing its transcription, which requires the activation of MAPKs/AP-1 and IKKbeta/NF-kappaB pathways, but not NFAT pathway. In view of the importance of COX-2 in carcinogenesis, we anticipate that the induction of COX-2 by B[a]PDE may coordinate its mutagenic effects to facilitate the development of skin cancer.

Neurotrophic factors for the investigation and treatment of movement disorders

Neurotrophic factors (NFs) are proteins that enhance neuronal survival, differentiation, neurotransmitter function and resistance to neurotoxins and lesions. For these reasons the NFs are considered as a new potential therapeutic tool for the treatment of neurodegenerative disorders, a group of diseases that produce the most important cause for disability in the Western world. Some NFs prevent or even reverse the behavioral, biochemical, pharmacological and histological abnormalities observed in several in vitro and in vivo models of neurodegenerative disorders, namely Parkinson's disease. Several NFs have been investigated in primate models of neurological disorders and some of them have been used for patients with these diseases. The results so far obtained in humans have been disappointing for several reasons, including technical problems for delivery, unbearable side effects or lack of efficacy. Future approaches for the use of NFs in humans should include the following: (1) Investigation of the putative compounds in animal models more related to the pathophysiology of each disease, such as in genetic models of neurodegenerative diseases; (2) New methods of delivery including genetic engineering by viral vectors and administration through implantable devices; (3) More precise methods of continuous response evaluation, including the novel neuroimaging techniques; (4) Investigation of the effects of behavioral stimulation and conventional pharmacotherapy on the metabolism of NFs.

Increased tight junction permeability can result from protein kinase C activation/translocation and act as a tumor promotional event in epithelial cancers

Exposure of LLC-PK1 epithelial cell cultures to phorbol ester tumor promoters causes immediate translocation of protein kinase C-alpha (PKC-alpha) from cytosolic to membrane-associated compartments. With a very similar time course, a dramatic and sustained increase in tight junctional (paracellular) permeability occurs. This increased permeability extends not only to salts and sugars but macromolecules as well. Fortyfold increases of transepithelial fluxes of biologically active EGF and insulin occur. Recovery of tight junction barrier function coincides with proteasomal downregulation of PKC-alpha. The failure to downregulate activated membrane-associated PKC-alpha has correlated with the appearance of multilayered cell growth and persistent leakiness of tight junctions. Accelerated downregulation of PKC-alpha results in only a partial and transient increase in tight junction permeability. Transfection of a dominant/negative PKC-alpha results in a slower increase in tight junction permeability in response to phorbol esters. In a separate study using rat colon, dimethylhydrazine (DMH)-induced colon carcinogenesis has been preceded by linear increases in both the number of aberrant crypts and transepithelial permeability, as a function of weeks of DMH treatment. Adenocarcinomas of both rat and human colon have been found to have uniformly leaky tight junctions. Whereas most human colon hyperplastic and adenomatous polyps contain nonleaky tight junctions, adenomatous polyps with dysplastic changes did possess leaky tight junctions. Our overall hypothesis is that tight junctional leakiness is a late event in epithelial carcinogenesis but will allow for growth factors in luminal fluid compartments to enter the intercellular and interstitial fluid spaces for the first time, binding to receptors that are located on only the basal-lateral cell surface, and causing changes in epithelial cell kinetics. Tight junctional leakiness is therefore a promotional event that would be unique to epithelial cancers.

The transient increase of tight junction permeability induced by bryostatin 1 correlates with rapid downregulation of protein kinase C-alpha

The role of PKC-alpha in altered epithelial barrier permeability following the activation of PKC by TPA (12-O-tetradecanoyl phorbol 13-acetate) and bryostatin 1 in LLC-PK1 cells was investigated in this study. Like TPA, bryostatin 1 binds to and activates PKC but unlike TPA, it is not a tumor promoter. TPA at 10(-7) M induced a sustained 95% decrease in transepithelial electrical resistance (R(t)) across LLC-PK1 epithelial cell sheets, while 10(-7) M bryostatin 1 caused only a 30% decrease in R(t), which spontaneously reversed after 5 h. Simultaneous exposure of cell sheets to 10(-7) M TPA and 10(-7) M bryostatin 1 blunted the increase in epithelial permeability observed with 10(-7) M TPA alone. Co-incubation of cell sheets with bryostatin 1 and MG-132, a proteasomal inhibitor, caused a further decrease in R(t) at the 6-h time point and inhibited the recovery in R(t) seen with bryostatin 1 alone at this time point. TPA caused a rapid translocation of PKC-alpha from the cytosol to the membrane of the cell where it remained elevated. Bryostatin 1 treatment resulted in a slower translocation of PKC-alpha from the cytosol to the membrane and a much more rapid downregulation of PKC-alpha, with disappearance from this compartment after only 6 h. The classical PKC inhibitor Go6976 prevented the decrease in R(t) seen with TPA. Treatment of cells with TPA and bryostatin 1 resulted in a PKC-alpha translocation and downregulation profile which more closely resembled that seen with bryostatin 1 alone. Co-incubation of cells with MG-132 and bryostatin 1 caused a slower downregulation of PKC-alpha from the membrane fraction. Bryostatin 1 treatment of cells expressing a dominant/negative form of PKC-alpha resulted in a slower and less extensive decrease in R(t) compared to the corresponding control cells. For both TPA and bryostatin 1, the level of PKC-alpha in the membrane-associated fraction of the treated cells correlated closely with increased transepithelial permeability. Due to its transient effect on tight junction permeability, bryostatin 1 offers a novel pharmacological tool to investigate junctional physiology.

alpha5 integrin distribution and TGFbeta1 gene expression in supraglottic carcinoma: their role in neoplastic local invasion and metastasis

BACKGROUND

Head and neck carcinomas are characterized by tumor-infiltrating lymphocytes (TIL) producing cytokines. Adhesion molecules, extracellular matrix proteins (ECMPs), and cytokines regulate cell-cell and cell-ECMPs interactions. We investigated the distribution of these proteins to contribute to better understanding of their role in local tumor invasion and metastasis.

METHODS

Distribution of integrins, laminin, type IV collagen, tenascin, and fibronectin was immunohistochemically evaluated in 13 supraglottis carcinomas. Cytokines gene expression was assessed by reverse-transcriptase-polymerase chain reaction (RT-PCR).

RESULTS

Neoplastic cells were alpha2beta1, alpha3beta1, alpha4beta1, alpha5beta1 and alpha6beta1 positive. Normal and metaplastic epithelium was alpha5beta1 negative; the stroma of primary and metastatic tumors was tenascin and fibronectin positive. TGFbeta1 and IFNgamma gene expression was observed in the majority of tumors.

CONCLUSIONS

Because TGFbeta1 is known to down-modulate immune processes and to increase alpha2beta1, alpha5beta1, and tenascin distribution, we propose that their expression in neoplastic cells of supraglottis carcinoma might represent an immune-related process able to help tumor growth and progression.

The in vitro effect of the tumor promoter 12-O-tetradecanoylphorbol-13-acetate on Sertoli cell morphology

The objective of the present study was to examine the effects of the well-known tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) on the morphology of cultured Sertoli cells from immature rats. The cells were cultured for 5 days and the TPA was added at the end of the culture period for 8 h at a concentration of 10-7 M. Viability tests showed that controls as well as TPA-treated cells remained viable during the culture period and no deleterious effects were observed as a result. Application of computerized morphometry at both light and electron microscopic levels revealed that TPA caused important changes in cell morphology in vitro. Statistical analysis of the results indicated that compared to the controls, Sertoli cells treated with TPA exhibited fewer astrocytic-type cytoplasmic extensions and a smaller size. Our results support the conclusion that the tumor promoter TPA, when applied to immature Sertoli cells in vitro, causes significant morphological alterations.

Effects of resveratrol on 12-O-tetradecanoylphorbol-13-acetate-induced oxidative events and gene expression in mouse skin

Resveratrol (3,5,4'-trihydroxy-trans-stilbene) is a natural product shown to inhibit carcinogen-induced pre-neoplastic lesions in mouse mammary organ culture and 12-O-tetradecanoylphorbol-13-acetate (TPA)-promoted mouse skin tumors. Application of TPA to mouse skin induces oxidative stress, as evidenced by numerous biochemical responses, including significant generation of H2O2 and enhanced levels of myeloperoxidase and oxidized glutathione reductase activities and decreases in glutathione levels and superoxide dismutase activity. TPA treatment also elevates the expression of cyclooxygenase-1 (COX-1), cyclooxygenase-2 (COX-2), c-myc, c-fos, c-jun, transforming growth factor-beta1 (TGF-beta1) and tumor necrosis factor-alpha (TNF-alpha). As currently reported, pre-treatment of mouse skin with resveratrol negated several of these TPA-induced effects in a dose-dependent manner. H2O2 and glutathione levels were restored to control levels, as were myeloperoxidase, oxidized glutathione reductase and superoxide dismutase activities. As judged by reverse transcriptase-polymerase chain reaction (RT-PCR), TPA-induced increases in the expression of c-fos and TGF-beta1 were selectively inhibited. These data suggest that resveratrol inhibits tumorigenesis in mouse skin through interference with pathways of reactive oxidants and possibly by modulating the expression of c-fos and TGF-beta1.

Overexpression of protein kinase C-delta increases tight junction permeability in LLC-PK1 epithelia

The Ca2+-independent delta-isoform of protein kinase C (PKC-delta) was overexpressed in LLC-PK1 epithelia and placed under control of a tetracycline-responsive expression system. In the absence of tetracycline, the exogenous PKC-delta is expressed. Western immunoblots show that the overexpressed PKC-delta is found in the cytosolic, membrane-associated, and Triton-insoluble fractions. Overexpression of PKC-delta produced subconfluent and confluent epithelial morphologies similar to that observed on exposure of wild-type cells to the phorbol ester 12-O-tetradecanoylphorbol-13-acetate. Transepithelial electrical resistance (RT) in cell sheets overexpressing PKC-delta was only 20% of that in cell sheets incubated in the presence of tetracycline, in which the amount of PKC-delta and RT were similar to those in LLC-PK1 parental cell sheets. Overexpression of PKC-delta also elicited a significant increase in transepithelial flux of D-[14C]mannitol and a radiolabeled 2 x 10(6)-molecular-weight dextran, suggesting with the RT decrease that overexpression increased paracellular, tight junctional permeability. Electron microscopy showed that PKC-delta overexpression results in a multilayered cell sheet, the tight junctions of which are almost uniformly permeable to ruthenium red. Freeze-fracture electron microscopy indicates that overexpression of PKC-delta results in a more disorganized arrangement of tight junctional strands. As with LLC-PK1 cell sheets treated with 12-O-tetradecanoylphorbol-13-acetate, the reduced RT, increased D-mannitol flux, and tight junctional leakiness to ruthenium red that are seen with PKC-delta overexpression suggest the involvement of PKC-delta in regulation of tight junctional permeability.

Potentiation of insulin-induced phosphatidylinositol-3 kinase activity by phorbol ester is mediated by protein kinase C epsilon

Our previous results have demonstrated that phorbol 12-myristate 13-acetate (TPA) and insulin synergistically stimulate the activity of phosphatidylinositol-3 kinase (PI-3 kinase) and PI-3 kinase plays an important role in both of TPA-induced AP-1 activation and cell transformation in tumour promotion sensitive (P+) JB6 cells. In the present study, we investigated the role of PKC and its isozymes in the synergistic induction of PI-3 kinase by TPA and insulin. Bisindolylmaleimide inhibits TPA- and TPA+ insulin-induced PI-3 kinase activity. Pretreatment of cells for 24 h with TPA has significant inhibitory effects on TPA-induced PI-3 kinase activity and abolishes the synergistic effect of TPA and insulin-stimulated PI-3 kinase activity. Furthermore, overexpression of a dominant negative PKC epsilon, but not dominant negative PKC alpha, blocks the synergistic effect of TPA and insulin-induced PI-3 kinase activity. These results indicate that the potentiation effect of TPA on insulin-induced PI-3 kinase activity is specific through PKC epsilon in JB6 cells.

12-O-tetradecanoylphorbol-13-acetate inhibits aminophospholipid translocase activity and modifies the lateral motions of fluorescent phospholipid analogs in the plasma membrane of bovine aortic endothelial cells

The tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) is a potent mitogenic factor which can replace the growth promoting activity of basic fibroblast growth factor (bFGF) on bovine aortic endothelial cells. However, TPA-treated cells lose their strict contact inhibition at confluence, which is a characteristic of cells grown in the presence of bFGF. We have examined whether these changes could be related to modifications of the transbilayer and lateral motions of fluorescent lipids, namely 1-acyl-2-[6-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]caproyl]-p hosphatidylcholine (C6-NBD-PC), -phosphatidylserine (C6-NBD-PS), and -phosphatidylethanolamine (C6-NBD-PE) inserted in the outer leaflet of the cell plasma membrane. In TPA-treated cells, the three fluorescent phospholipids remained located in the outer leaflet for at least 1 h at 20 degrees C after their insertion, indicating a blockade of the aminophospholipid translocase activity which is normally present in the plasma membrane of bFGF-treated cells. TPA also induced a large increase in the percentage of C6-NBD-PC and C6-NBD-PE probes which were free to diffuse laterally. The mobile fractions M reached values of approximately 100% for the two lipids, while for bFGF-treated cells they were found around 85 and 75%, respectively. For the C6-NBD-PS probe, M remained unchanged in bFGF and TPA-treated cells, at around 85%. TPA treatment also induced a twofold increase in the lateral diffusion coefficients of C6-NBD-PC and C6-NBD-PE, while that of C6-NBD-PS remained nearly unchanged. These effects of TPA may be related to the observed loss of differentiated properties of vascular endothelial cells and not to its mitogenic properties.

Phosphatidylinositol-3 kinase is necessary for 12-O-tetradecanoylphorbol-13-acetate-induced cell transformation and activated protein 1 activation

Phorbol esters, which activate isoforms of protein kinase C, are general activators of the transcription factor activated protein 1 (AP-1). The pathway involved in this signal transduction is not very clear. Currently, little is known about whether phosphatidylinositol-3 (PI-3) kinase plays any role in phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced signal transduction. We demonstrate here that TPA not only has markedly synergistic effects on insulin-induced PI-3 kinase activity, but it also can induce PI-3 kinase activity and the PI-3 phosphates by itself. We also found that insulin, a PI-3 kinase activator, enhanced TPA-induced AP-1 trans-activation and transformation in JB6 promotion-sensitive cells. Furthermore, wortmannin and LY294002, two PI-3 kinase inhibitors, markedly decreased AP-1 activity induced by insulin, TPA, or TPA and insulin and inhibited JB6 promotion-sensitive cell transformation induced by TPA or TPA and insulin. Most importantly, constitutive overexpression of the dominant negative PI-3 kinase P85 mutants completely blocked insulin- or TPA-induced AP-1 trans-activation and TPA-induced cell transformation. All evidence from present studies suggests that PI-3 kinase acts as a mediator in TPA-induced AP-1 activation and transformation in JB6 cells.

Novel diterpenoid diacylglycerols from marine molluscs: potent morphogens and protein kinase C activators

Five novel 1,2-sn-diacylglycerols with diterpenoid acyl moieties in the sn-1 position were isolated and characterized, together with the corresponding 1,3-sn-diacylglycerols, from three species of dorid nudibranchs molluscs. Their potent activity as morphogens in vivo in the Hydra tentacle regeneration assay and their parallel activity as activators of rat brain protein kinase C (PKC) in vitro are reported here. Our findings promote the use of these compounds as useful molecular probes for both in vivo and in vitro studies on the participation of PKC in cell development.

Okadaic acid Co-induces vimentin expression and cell cycle arrest in MPC-11 mouse plasmacytoma cells

The effect of the tumor promoter okadaic acid on cell cycle progression and on vimentin expression in MPC-11 mouse plasmacytoma cells was compared with that of the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA). Cell cycle progression of asynchronously grown MPC-11 cells was inhibited by both agents, but, in contrast to the G1 phase arrest caused by TPA, okadaic acid gave rise to G2/M phase and S phase arrest. This effect of okadaic acid was delayed significantly compared to the TPA-caused arrest. Furthermore, okadaic acid was able to induce vimentin expression to an extent comparable to the TPA response. However, vimentin expression was markedly delayed in okadaic acid-treated relative to TPA-treated cells. Another protein phosphatase inhibitor, calyculin A, also induced cell cycle changes and vimentin expression at concentrations at or above 1 x 10(-9) M. Based on these observations, we suggest an involvement of protein phosphatase 1 (possibly also phosphatase 2A and/or other phosphatases) in both the G2/M cell cycle block and the induction of vimentin expression in MPC-11 cells by okadaic acid.

Changes in Ca2+ concentration in phorbol ester and thapsigargin treated glioma C6 cells. The role of protein kinase C in regulation of Ca2+ entry

Glioma C6 cells treated with 12-0-tetradecanoyl-phorbol-13-acetate, TPA (10 nM and 100 nM) manifested slow increase in intracellular calcium concentration ([Ca2+]i), dependent upon both Ca2+ release from intracellular stores and Ca2+ entry, and ranging from 50 to 500 nM in different cells. The effect of TPA was abolished by the down-regulation procedure and by protein kinase C inhibitors, such as staurosporine (100 nM), suramin (100 microM), and sphingosine (100 microM), pointing to a role of protein kinase C (PKC) in this process. On the other hand, thapsigargin (100 nM), a selective inhibitor of the endoplasmic reticulum Ca(2+)-ATPase, produced a rapid increase in [Ca2+]i (up to 800 nM). This increase consisted of a transient initial phase followed by sustained elevation in [Ca2+]i, typical of Ca2+ release from intracellular stores and of Ca2+ entry, respectively. However, when the cells were exposed to TPA (100 nM) prior to thapsigargin (100 nM), then thapsigargin produced only a transient rise in [Ca2+]i. We suggest that TPA, a PKC activator, affects thapsigargin-induced Ca2+ entry, probably by PKC-mediated changes in cytoskeleton structures.

Nutritional factors and colon cancer

During the last 2 decades, substantial progress has been made in understanding the relationship between dietary constituents and the development of colon cancer in man. Unlike studies of cancer among smokers and nonsmokers, nutritional epidemiologic studies are confronted with the inherent difficulty of assessing reasonably precise exposures. The lack of consistency between international correlation studies and case-control studies does not necessarily negate a dietary etiology of colon cancer because these inconsistencies may have arisen, at least in part, from methodological limitations. Some of these deficiencies in epidemiological studies of diet and cancer have been corrected; recent case-control studies demonstrated that high dietary fat is a risk factor for colon cancer development and that an overall increase in intake of foods high in fiber might decrease the risk for colon cancer. The results of epidemiologic studies may be assumed to present conservative estimates of the true risk for cancer associated with diet. The populations with high incidences of colon cancer are characterized by high consumption of dietary fat, which may be a risk factor in the absence of factors that are protective, such as whole-grain cereals and of other high fiber. Laboratory-animal model studies have shown that certain dietary lipids and fibers influence tumorigenesis in the colon. The data of metabolic epidemiological and laboratory-animal model studies are sufficiently convincing with respect to the enhancement of colon cancer by type of fat and protection by certain dietary fibers.

Epidermal growth factor, phorbol esters, and aurintricarboxylic acid are survival factors for MDA-231 cells exposed to adriamycin

The ability of epidermal growth factor (EGF), insulin-like growth factor-1 (IGF-1), insulin, 12-O-tetradecanoylphorbol-13-acetate (TPA), and aurintricarboxylic acid (ATA) to protect the human breast cancer cell line MDA-231 from death induced by the anticancer drug adriamycin was investigated. Cell death was induced in the MDA-231 cells either by a short-time exposure to a high dose of adriamycin (2 micrograms.ml-1.1h-1) and further culturing in the absence of the drug, or by continuous exposure to a low dose of adriamycin (0.3 micrograms/ml). Cell death was evaluated after 48 h of incubation by several techniques (trypan blue dye exclusion, lactic dehydrogenase activity, cellular ATP content, transmission electron microscopy, and DNA fragmentation). EGF, TPA, and ATA, each at an optimal concentration of 20 ng/ml, 5 ng/ml, and 100 micrograms/ml respectively, substantially enhanced survival of cells exposed either to a high or low dose of adriamycin. Neither IGF-1 nor insulin, each at concentrations of 20 ng/ml, had an effect on cell survival. The three survival factors enhanced protein synthesis in the untreated cells and attenuated the continuous decrease in protein synthesis in the adriamycin-treated cells. Moreover, the three survival factors protected the MDA-231 cells from death in the absence of protein synthesis (cycloheximide 30 micrograms/ml). These results suggest that EGF, TPA, and ATA promote survival of adriamycin pretreated cells by at least two mechanisms: enhancement of protein synthesis and by a protein synthesis independent process, probably a posttranslational modification effect.

Chemoprevention of colon cancer by dietary fatty acids

During the last two decades, substantial progress has been made in the understanding of the relationship between the dietary constituents and development of colon cancer in man. Unlike studies of cancer among smokers and nonsmokers, nutritional epidemiologic studies are confronted with the inherent difficulty of assessing reasonably precise exposures. The lack of consistency between international correlation studies and case-control studies does not necessarily negate a dietary etiology of colon cancer because these inconsistencies may have arisen, at least in part, from methodological limitations. Some of these deficiencies in epidemiological studies of diet and cancer have been corrected; recent case-control studies demonstrated that high dietary fat is a risk factor for colon cancer development and that an overall increase in intake of foods high in fiber might decrease the risk for colon cancer. The results of epidemiologic studies may be assumed to present conservative estimates of the true risk for cancer associated with diet. The populations with high incidence of colon cancer are characterized by high consumption of dietary fat, which may be a risk factor in the absence of factors that are protective, such as whole-grain cereals and of other high-fiber. Laboratory animal model studies have shown that certain dietary lipids and fibers influence tumorigenesis in the colon. The data of metabolic epidemiological and laboratory animal model studies are sufficiently convincing with respect to enhancement of colon cancer by type of fat and protection by certain dietary fibers.

Inhibition of proliferation and induction of monocytic differentiation on HL60 human promyelocytic leukemia cells treated with bile acids in vitro

We have tested the effect of several bile acids on the proliferation and differentiation of the HL60 human promyelocytic leukemia cell line in vitro. Deoxycholate, chenodeoxycholate and lithocholic acid caused dose-dependent inhibition of cell proliferation and induction of differentiation along the monocyte/macrophage pathway as determined by morphology, NBT test, non-specific esterase, and staining by monoclonal antibodies against specific cell-surface antigens. Optimal effects were obtained at 100, 75, and 60 microM of the 3 bile acids respectively. Cell-cycle flow-cytometric analysis showed that a substantial fraction of HL60 cells accumulated at the G0/G1 transition. Protein-kinase-C inhibitors such as sphinganine and H-7 inhibited the differentiation-inducing effect of bile acids, suggesting a possible role for PKC in this regulation. When bile acids were combined with non-effective concentrations of all-trans retinoic acid, enhancement of the monocytic differentiation of THP-1 human leukemia cells was observed. Our findings demonstrate induction of tumor-cell differentiation by bile acids, compounds that present minimal undesirable effects in humans.

Cell culture assays for chemicals with tumor-promoting or tumor-inhibiting activity based on the modulation of intercellular communication

The ability of chemicals with tumor-promoting or tumor-inhibiting activity to modulate gap junctional intercellular communication is reviewed. The two most extensively used types of assays for screening tests are (1) metabolic cooperation assays involving exchange between cells of precursors of nucleic acid synthesis and (2) dye-transfer assays that measure exchange of fluorescent dye from loaded cells to adjacent cells. About 300 substances of different biological activities have been studied using various assays. For tumor promoters/epigenetic carcinogens, metabolic cooperation assays have a sensitivity of 62% and dye-transfer assays 60%. Thirty percent of DNA-reactive carcinogens also possess the ability to uncouple cells. The complete estimation of the predictive power of these assays could not be made because the majority of the substances studied for intercellular communication effects in vitro have not yet been studied for promoting activity in vivo. Both metabolic cooperation assays and dye transfer assays respond well to the following classes of substances: phorbol esters, organochlorine pesticides, polybrominated biphenyls, promoters for urinary bladder, some biological toxins, peroxisome proliferators, and some complex mixtures. Results of in vitro assays for such tumor promoters/nongenotoxic carcinogens, such as some bile acids, some peroxides, alkanes, some hormones, mineral dusts, ascorbic acid, okadaic acid, and benz(e)pyrene, do not correlate with the data of in vivo two-stage or complete carcinogenesis. Enhancement of intercellular communication was found for 18 chemicals. Among these, cAMP, retinoids, and carotenoids have demonstrated inhibition of carcinogenesis. We examine a number of factors that are important for routine screening, including the requirement for biotransformation for some agents to exert effects on gap junctions. We also discuss the mechanisms of tumor promoter and tumor inhibitor effects on gap junctional permeability, including influences of protein kinase activation, changes in proton and Ca2+ intracellular concentrations, and effects of oxy radical production.

Phorbol ester-induced neuritic alterations in the rat neocortex. Structural and immunocytochemical studies

In order to explore the effect of aberrant sprouting in the CNS, phorbol 12-myristate 13-acetate (PMA) was administered into the neocortex of adult rats. PMA is a growth-promoting agent that activates and eventually downregulates protein kinase C (PKC), and induces in the rat the expression of several genes, including amyloid precursor protein (APP). We found that multiple injections of 100 nM PMA into the rat neocortex promote, in the first week postinjection, a widespread vacuolization of the neuropil with a subsequent disruption of the synapses in the injection site, followed, at d 15, by the formation of abnormally distended clusters of neurites that resembled aberrant, sprouting axons. At d 30, fewer aberrant sprouts were observed, and many degenerating neurites were found. At the ultrastructural level, the PMA-induced abnormal neurites at d 7-15 resembled growth cones, whereas the dystrophic neurites at d 30 contained abundant dense and laminated bodies. Immunohistochemical analysis indicated that the abnormal neurites in the areas of denervation and PMA administration were positive with antisynaptophysin and antigrowth-associated protein 43 (GAP-43), with an increased APP immunoreactivity surrounding them. APP immunoreactivity around the injection site was mostly associated with pyramidal neurons and glial cells. Control experiments, where saline alone or 4 alpha-phorbol 12, 13-didecanoate (PDD, an inactive phorbol derivative) was injected, failed to show aberrant sprouting neurites. Further immunohistochemical analysis showed that the PMA-treated animals presented increased amyloid beta immunoreactivity in the pyramidal cells at the site of injection, when compared with control injections. These findings suggest that aberrant sprouting induced by overstimulation could be followed by neurodegeneration. Alternatively, PKC downregulation could directly induce the neurodegeneration, with a secondary sprouting response.

Effect of glucocorticoids on TPA-induced inhibition of gap-junctional communication and morphological transformation in Syrian hamster embryo cells

The effect of glucocorticoids on 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced inhibition of gap-junctional intercellular communication (GJIC) and morphological transformation in Syrian hamster embryo (SHE) cells was examined. Fluocinolone acetonide (FA) and dexamethasone (DEX) almost completely suppressed the effect of TPA on induction of transformed morphology. On the other hand, up to 1000 times higher FA and DEX concentrations did not influence the inhibitory effect of TPA on GJIC. Neither treatment with these glucocorticoids for 4, 24 or 48 h before TPA exposure nor 24 h co-exposure with TPA altered the effect of TPA on GJIC. Thus the potent effect of glucocorticoids as inhibitors of the promotional effect of TPA on morphological transformation in SHE cells does not result in alterations of TPA-induced inhibition of GJIC.

Rapid phosphorylation of 28-kDa heat-shock protein by treatment with okadaic acid and phorbol ester of BALB/MK-2 mouse keratinocytes

Protein phosphorylation by okadaic acid and 12-O-tetradecanoylphorbol-13-acetate (TPA) was examined using quiescent cultures of BALB/MK-2, a cell line derived from mouse epidermal keratinocytes. Treatment with okadaic acid caused rapid phosphorylation of five proteins with molecular masses of 65, 55, 50, 28 and 15 kDa (p65, p55, p50, p28, p15, respectively) while TPA caused rapid phosphorylation of five proteins with molecular masses of 80, 70, 40, 34 and 28 kDa (p80, p70, p40, p34, p28, respectively). In the present study, we examined p28, a common target protein of okadaic acid and TPA. The phosphorylation of p28 increased depending on time of exposure and doses of okadaic acid and TPA. Combined treatment with okadaic acid and TPA resulted in an additive effect. Its position on two-dimensional gel electrophoresis suggested that p28 is the 28-kDa heat-shock protein (HSP28). This possibility was confirmed by migration of p28 with HSP28 and comparative peptide mapping of the two proteins. The phosphoamino-acid residue of phosphorylated HSP28 was serine. In two-dimensional tryptic peptide maps, the same peptides were phosphorylated after treatment with both okadaic acid and TPA.

Protein kinase C beta expression in melanoma cells and melanocytes: differential expression correlates with biological responses to 12-O-tetradecanoylphorbol 13-acetate

Normal human melanocytes require 12-O-tetradecanoylphorbol 13-acetate (TPA) for prolonged growth in vitro. In contrast, the growth of human malignant melanoma cells is often inhibited by TPA. In this study, we have confirmed and extended these observations. Since protein kinase C (PKC) is an important mediator of the effects of TPA, we have investigated the nature of this differential growth response by examining PKC expression and activity in primary cultures of human neonatal melanocytes and metastatic melanoma cell strains. PKC, when measured by immunoreactivity or a functional assay, was found to be more abundant in melanoma cells than in melanocytes. When specific isotypes were examined by Northern analysis, PKC-alpha and -epsilon were expressed in both melanocytes and melanoma. PKC-beta was expressed in melanocytes, but was undetectable by Northern analysis in 10 out of 11 melanoma cell strains. Southern analysis revealed that no gross deletions or rearrangements of the PKC-beta gene had occurred. These data suggest that down-regulation of the PKC-beta gene occurs frequently during the process of transformation of melanocytes. Furthermore, differential expression of PKC isotypes may explain the different effects of TPA on melanocyte and melanoma cell growth.

Expression of CD45 isoforms in chronic B-cell leukaemias

CD45 isoform expression was studied in 204 cases of B-cell lymphoproliferative disease, including 162 chronic lymphocytic leukaemia (CLL). In almost half the samples tested, CD45R0 was co-expressed with CD45RA, unlike normal B-cells, which express only CD45RA, except at terminal stages of differentiation. In a small number of cases CD45R0 was the dominant isoform expressed. No correlation could be discerned either with Binet or RAI staging in CLL or with disease type CLL, prolymphocytic leukaemia (PLL) or hairy cell leukaemia (HCL). Comparison of CD45 isoform expression with other markers showed no correlation with apparent maturational status of the cells involved.

A comparison of newborn versus old skin fibroblasts, their potential for tissue repair

An assessment was made of the ability of human skin fibroblasts from newborn and old subjects to produce intracellular urokinase inhibitor and urokinase-plasminogen activator when exposed to phorbol myristate acetate. Urokinase inhibitor produced by human skin fibroblasts may be essential for cell growth regulation. The expression of urokinase inhibitor and/or urokinase-plasminogen activator may possibly be age-related. The principal observation that newborn skin fibroblasts show a low level and poorly sustained production of intracellular inhibitors of urokinase could help to explain the flexibility of the wound healing process in the foetus.

Differential effects of bryostatin 1 on human non-Hodgkin's B-lymphoma cell lines

Bryostatin 1 (Bryo1), a macrocyclic lactone and a protein kinase C activator, is extracted and purified from the marine bryozoan Bugula neritina. In this study we describe its effect on morphology, surface immunophenotype, acid phosphatase (AcP), tartrate-resistant acid phosphatase (TRAP), proliferation and cell cycle of non-Hodgkin's B-lymphoma cell lines representing four differentiation stages. Except for the WSU-BL, a high-grade SCNCL, all other cell lines showed obvious changes in their morphology when treated with 200 nM Bryo1. Phenotypically, a dramatic decrease of CD10 and induction of CD11c and BL7 on some cell lines consistent with further B-cell differentiation was seen. The lines in control cultures showed variable expression of AcP and TRAP. Following treatment with Bryo1, there was a general increase in AcP expression except in WSU-BL line. WSU-FSCCL and WSU-DLCL were TRAP-negative but became TRAP-positive when treated with Bryo1. Cell growth and cycle analysis during treatment of different cell lines revealed evidence of strong, moderate, or no growth inhibition by Bryo1 compared with control cultures. Our results indicate that Bryo1 shows differentiation effects on low-grade FSCCL, intermediate-grade FLCL and high-grade DLCL, and stimulatory or no effect on high-grade SCNCL. Since Bryo1 does not have tumor-promoting activity, it has a potential therapeutic role as a B-cell differentiating agent.

Cholera toxin potentiates TPA-induced mitogenesis and c-fos expression in BALB/c-3T3-derived proadipocytes

Treatment of quiescent density-arrested A31T6 proadipocytes with medium supplemented with either 12-O-tetradecanoylphorbol-13-acetate (TPA), insulin, or cholera toxin alone did not stimulate G0/G1 traverse and initiation of DNA synthesis. Combinations of either TPA and cholera toxin or insulin and cholera toxin caused a small stimulation of proliferation. Addition of medium supplemented with TPA and insulin caused a marked stimulation of cell cycle traverse which was significantly potentiated by the coaddition of cholera toxin. The actions of cholera toxin were mimicked by forskolin. Expression of c-fos was regulated in a manner that reflected the results of the mitogenic experiments. TPA caused a marked induction of expression, while only a small increase in transcript levels was seen after treatment with cholera toxin. Addition of a combination of cholera toxin and TPA caused a synergistic induction of c-fos expression. The model system described in this paper allows a detailed analysis of the regulation, by independent second messenger systems, of the transcription of a gene in a mitogenically relevant manner.

Effects of acute vs. chronic phorbol ester exposure on transepithelial permeability and epithelial morphology

In previous experiments we have shown that acute (30 minutes) exposure to phorbol esters or other protein kinase C activators causes increased transepithelial permeability, specifically by the increased paracellular permeability through tight junctions. However, the role of protein kinase C activators in carcinogenesis is predicted upon a chronic exposure of an effective dose at frequent intervals for a prolonged period of time. We therefore sought to determine the effect of chronic phorbol ester exposure on transepithelial permeability by exposing cells of the polar renal epithelial cell line, LLC-PK1, to phorbol esters for time periods as long as 16 weeks. The following changes ensued: (1) after the initial drop in transepithelial resistance due to phorbol ester exposure, i.e., an increase in transepithelial permeability (in the acute phase of exposure), an adaptive response occurs as transepithelial resistances in chronically exposed cultures recover to approximately 50% of control values, (2) the cell sheets in chronically exposed cultures lose their acute responsiveness of transepithelial permeability to phorbol ester exposure, (3) cell sheet architecture changes as cells occasionally multilayer and actual polyp-like cell masses appear at high frequency, and (4) cytosolic protein kinase C activity decreases to 50% of control level with acute exposure and then is further decreased to less than 1% of control level in chronically treated cells; membrane-associated PKC activity is not as sharply decreased. The possible role of transepithelial permeability in carcinogenesis and the value of chronically treated epithelial cell cultures as a model for two-stage carcinogenesis are discussed.

A phorbol diester resistant monocytic leukemia cell line is PKC deficient

MIA C51 is a rat monocytic leukemia cell line which exhibits undifferentiated monocytic phenotype in culture. The proliferation of MIA C51 cells was not inhibited by the addition of 12-O-tetradecanoyl-phorbol-13-acetate (TPA, 1 microgram/ml) or phorbol 12, 13 dibutyrate (PDBu, 10 micrograms/ml). Comparison of MIA C51 cells to a phorbol diester-sensitive human monoblastoid U-937 cell line demonstrated that MIA C51 cells contained significantly lower number of PDBu receptors, protein kinase C (PKC) activity, and PKC protein level. Further experiments demonstrated that addition of TPA to MIA C51 cells did not induce the expression of c-fos proto-oncogene; whereas incubation of MIA C51 cells with N6, O2-dibutyryl cyclic adenosine 3',5' monophosphate (Bt2cAMP) resulted in a rapid increase of c-fos mRNA level. Thus, this cell line provides a new system for studying the signal transduction mechanisms in induced monocytic differentiation.

Physiological and clinical aspects of vitamin A and its metabolites

Retinoids, including retinol and retinoic acid (RA), are a group of naturally occurring and synthetic compounds that exhibit vitamin A-like biological activity. They achieve their effects by binding to intracellular proteins. Important sites of action are the nuclear retinoic acid receptors (RAR). These receptors, namely, RAR alpha, RAR beta, and RAR gamma, function as transcription factors by binding to RA-responsive elements (RARE) of multiple genes. Retinoids play a role in vision, embryogenesis, immune modulation, growth and differentiation of normal, premalignant and malignant tissues, the suppression of carcinogenesis, and the inhibition of tumor growth in experimental systems and humans. Reports of the significant antitumor effect of all-trans-RA in acute promyelocytic leukemia and the synthesis of new, less toxic, and more potent retinoids has generated renewed interest in these compounds. Retinoids may have an important role to play in the chemoprevention and therapy of cancer.