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Biomedical subjects

F Marks

Publications and source records attributed to F Marks.

At least 181 records · Page 10Linked to original sources
PubMed1984

Interaction of phorbol derivatives with replicating cells.

The significance of the interaction of phorbol derivatives with replicating cells has been studied in HeLa cells and in tumour promotion experiments. Dose-response relationships for the radiomimetic activity of phorbol derivatives in HeLa cells (Kinzel et al., 1980) were obtained by analysis of the degree of transient blockage in G2 phase of the cell cycle. HeLa cells are shown to be one order of magnitude more sensitive to 12-O-tetradecanoylphorbol-13-acetate (TPA) than to equally mitogenic and irritant but much less promoting derivatives. The susceptibility of HeLa cells reflects the promoting capacity of these compounds. Studies on effects of modifiers on TPA-induced G2 blockage indicate that the influence of TPA, even in a single cell cycle phase, may be the result of a 'multiple site' attack. The significance of the interaction of TPA with replicating mouse epidermal cells in tumour promotion has been demonstrated in animal experiments after initiation with 7-12-dimethylbenz[a]anthracene by using a two-stage protocol which effects promotion with a single dose of TPA followed by repeated treatment with 12-O-retinoylphorbol-13-acetate (Fürstenberger et al., 1981). A single dose of the inhibitor of DNA synthesis, hydroxyurea, given to groups of mice at different times before and after treatment with TPA interferes with tumour formation; almost complete inhibition is observed after 18 h. The interaction of TPA and DNA-synthesizing cells seems to be of crucial importance to the first stage of tumour promotion.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1984

Radiomimetic activity of phorbol esters exerted in HeLa cells in comparison with their tumor-promoting capacity.

The biological activities exerted in mouse skin by three closely related phorbol esters were compared with the effects of these compounds on HeLa cells. The tumor promoter 12-O-tetradecanoylphorbol-13-acetate has been shown previously to influence various cell cycle parameters of these cells, thereby mimicking X-irradiation [Kinzel, V., Richards, J., and Stöhr, M. Science (Wash. D. C.), 210: 429-431, 1980]. Qualitatively similar effects were exerted by the mitogenic and irritant but almost nonpromoting "incomplete" phorbol esters 12-O-tetradeca-2-cis-4-trans-6,8-tetraenoylphorbol-13-acetate and 12-O-retinoylphorbol-13-acetate. Cell cycle parameters were analyzed by measuring thymidine incorporation rates, labeling indices, DNA histograms gained through flow cytometry, and mitotic activity. In every case, 12-O-tetradecanoylphorbol-13-acetate was more effective than 12-O-tetradeca-2-cis-4-trans-6,8-tetraenoylphorbol-13-acetate or 12-O-retinoylphorbol-13-acetate. The analysis of the influence of phorbol esters in G2 phase showed that, in order to reach the effectiveness of 10(-8) M 12-O-tetradecanoylphorbol-13-acetate, approximately 10 times the concentration of either 12-O-tetradeca-2-cis-4-trans-6,8-tetraenoylphorbol-13-acetate or 12-O-retinoylphorbol-13-acetate has to be applied. Therefore, the susceptibility of replicating HeLa cells to these phorbol derivatives reflects the promoting rather than the mitogenic and irritant capacity of these compounds.

Cell Cycle↗
PubMed1983

Inhibition of the calcium- and phospholipid-dependent protein kinase activity from mouse brain cytosol by quercetin.

The flavonoid quercetin is a potent inhibitor of calcium- and phospholipid-dependent protein kinase (Ca, PL-PK) activity from mouse brain. Half-maximal inhibition of the kinase occurs at about 10 microM. If the tumor promoter 12-O-tetradecanoyl-phorbol-13-acetate (TPA) is used instead of calcium as a stimulating factor of the kinase enzyme activity is still inhibited by quercetin. The kinase inhibitor, however, does not interfere with the binding of TPA to its receptor.

Adenosine Triphosphate↗
PubMed1983

Effects of the skin mitogens tumor-promotor 12-O-tetradecanoylphorbol 13-acetate and divalent-cation-ionophore A23187 on ion fluxes and membrane potential in a murine epidermal cell line (HEL30) and in 3T3 fibroblasts.

The transmembrane potential of HEL30 keratinocytes and 3T3 fibroblasts has been determined by measuring the distribution of labelled triphenylmethylphosphonium bromide. The tumor-promotor 12-O-tetradecanoylphorbol 13-acetate (1-5 microM) induces hyperpolarization in 3T3 cells but does not exert any effect on the membrane potential of keratinocytes, whereas the divalent cation ionophore A23187 (0.5 - 1 microM) hyperpolarizes keratinocytes and probably also 3T3 cells. Studies on Na+ and Rb+ fluxes, as well as with different inhibitors, indicate that the hyperpolarizing effect is the consequence of an increased Na+ influx which in turn stimulates the Na+/K+-dependent ATPase. No causal relationship seems to exist between the change of the membrane potential and arachidonic acid release (and subsequent prostaglandin synthesis) which is induced by both drugs in both cell lines. Since the induction of the arachidonic cascade (by both agents) as well as the stimulation of Na+ influx (by A23187) are found to be critically dependent on extracellular Ca2+ and are inhibited by 'Ca2+-blockers', it is concluded that both reactions are triggered by the same event (Ca2+ translocation) but proceed independently of each other. The release of arachidonic acid is already stimulated under conditions where a measurable influx of Ca2+ is not yet observed. This indicates a local mobilization of Ca2+, perhaps across the plasma membrane. It is concluded that monovalent cation fluxes and changes of the membrane potential are not critically involved in the stimulation of the arachidonic acid cascade and cellular proliferation by agents which induce epidermal hyperplasia in vivo.

Animals↗
PubMed1983

Soluble phorbol ester binding sites and phospholipid- and calcium-dependent protein kinase activity in cytosol of chick oviduct.

A large amount of specific high affinity binding sites for tumor promoting phorbol esters as well as of a Ca2+- and phospholipid-dependent protein kinase is present in cytosol of chick oviduct. 12-O-Tetradecanoyl-phorbol-13-acetate (TPA) is able to replace either Ca2+ or the phospholipid phosphatidylserine as activators of the kinase to some extent. The maximum activity of the enzyme in the presence of Ca2+ and phosphatidylserine, however, cannot be increased further by TPA. Various second stage tumor promoters also exhibit the capacity to stimulate the protein kinase, whereas the non-promoting phorbol ester 4-O-methyl-TPA, as well as the non-promoting, but with respect to other responses TPA-like, calcium ionophore A23187, do not affect the kinase.

Animals↗
PubMed1983

Control of endogenous cell regulators by the second-stage tumor promoter phorbol-12-retinoate 13-acetate.

The phorbol esters phorbol 12-retinoate 13-acetate (RPA) and 12-O-tetradecanoyl phorbol 13-acetate (TPA) were used to investigate the role of tumor promoters in the control of hormone response in normal and leukemic myeloid cells. RPA and TPA inhibited the binding of [20-3H]phorbol 12,13-dibutyrate to the leukemic cells in a competitive manner with 50% inhibition values of 5.2 +/- 1.3 and 1.1 +/- 0.6 nM, respectively. RPA, like TPA, enhanced (1) prostaglandin E1-induced cyclic AMP synthesis, (2) the differentiation of leukemic cells induced by the normal myeloid differentiation-inducing protein, and (3) the formation of normal myeloid cells colonies induced by the normal myeloid growth-inducing protein. Both compounds can thus control endogenous cell regulators. Since RPA functions in the second stage of tumor promotion in mouse skin, it is suggested that the control of such endogenous regulators may involve biochemical pathways similar to those that are activated in the second stage of tumor promotion.

Animals↗
PubMed1983

Tumor promotion by phorbol esters in skin: evidence for a memory effect.

By means of a two-stage promotion protocol in mouse epidermis with 12-O-tetradecanoylphorbol-13-acetate as first-stage promoter and 12-O-retinoylphorbol-13-acetate as second-stage promoter, the effects of the former that are critical and obligatory for tumor promotion were shown to be irreversible in nature for at least 8 weeks. The reversibility of tumor promotion was related to the second stage of promotion, reflecting the reversibility of epidermal hyperplasia induced by 12-O-tetradecanoylphorbol-13-acetate.

Animals↗
PubMed1983

Prostaglandins, cyclic nucleotides and the effect of phorbol ester tumor promoters on mouse skin in vivo.

Topical application of prostaglandin E1 or E2 onto the mouse skin results in a 2- to 3-fold increase of the cyclic AMP level in epidermis within 5 min. (15S)-15-methyl-PGE1 is more active in this respect, whereas PGD2 and PGF2 alpha are ineffective. The level of cyclic GMP is not altered by E- or F-prostaglandins. A single PGE2 application desensitizes the cyclic AMP response of mouse epidermis to further treatments in a dose dependent and agonist-specific manner. Delayed and longlasting refractoriness of PGE2-induced cyclic AMP accumulation is also caused by hyperplasiogenic skin irritants such as the phorbol ester tumor promoter TPA or the nonpromoting agents RPA and A23187. The non-irritant skin mitogen 4-O-methyl-TPA does not evoke desensitization. TPA-induced PGE2 refractoriness cannot be prevented by inhibitors of protein synthesis, anti-inflammatory steroids, indomethacin or phentolamine. The development of tachyphylaxis does not seem to be related to endogenous formation of PGE or cyclic AMP. A 2-fold increase of epidermal cyclic AMP observed within 1-2 h of TPA application can be inhibited by indomethacin treatment and correlates with delayed accumulation of PGE2 in TPA-treated epidermis, whilst immediate PGE accumulation (5-10 min after TPA application) which has been shown to be critical for development of TPA-induced epidermal hyperplasia is not accompanied by any change of the intraepidermal cyclic AMP level. It is concluded that mouse epidermis contains two types of PGE-regulated effector systems, one of which is coupled to adenylate cyclase, one of which is not. Only the latter system is involved in the induction of hyperplasia. At least as far as the mitogenic effect is concerned, cyclic AMP does not seem to be involved in TPA action.

Animals↗
PubMed1983

Growth stimulation and tumor promotion in skin.

Stimulation of epidermal growth in adult mouse skin can be induced by chemical agents, such as phorbol esters and other skin mitogens, or by mechanical means, such as skin massage and skin wounding. It leads to different kinds of epidermal hyperproliferation, according to interference with mechanisms of endogenous growth control (G1 chalone) and to mediation by endogenous regulatory factors (prostaglandins). Certain phorbol esters and skin wounding induce epidermal hyperproliferation and, in addition, a metaplastic process. Another property of these metaplasiogenic mitogens is their tumor-promoting efficacy in mouse skin, which has been initiated by a carcinogen in a subthreshold dose. Tailor-made phorbol esters allow the subdivision of the process of tumor promotion into two stages. In the first--probably irreversible--stage, a single application of the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) or wounding brings about the events critical and obligatory for promotion, whereas in the second--probably reversible--stage, repetitive applications of an "incomplete promoter" evoke epidermal hyperplasia necessary to make the tumors visible. Adult guinea pig epidermis in vivo, as well as primary cell cultures derived from adult guinea pig ear epidermis, responds to the proliferative effects of phorbol esters such as TPA along a similar sequence of biochemical events as mouse skin in vivo. The in vitro approach allows the study of the molecular events involved in the mechanism of action of phorbol esters in more detail.

Animals↗
PubMed1983

Multistage tumor promotion in skin.

By introduction of conjugated double bonds into the long-chain fatty acid residue of the phorbol ester tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) the promoting efficacy is abolished, whereas hyperplasiogenic and irritant activities are not impaired. By means of such "disarmed" phorbol esters (with 12-O-retinoylphorbol-13-acetate, RPA, being the most suitable one) the process of skin tumor promotion can be divided into two stages. Stage 1, brought about by short-term (single) treatment with TPA, leads via an induction of cellular proliferation to an apparently irreversible change in skin which is proposed to involve the expression of the neoplastic phenotype. A subsequent long-term (multiple) treatment with RPA (stage 2), results in the appearance of papillomas. There is no positive evidence for a critical role of phorbol ester receptor occupancy and protein kinase C activation or of free radicals such as superoxide anions in stage 1. Retinoic acid inhibits stage 1 only when applied several hours prior to TPA, whereas indomethacin exhibits the strongest inhibitory effect on stage 1 when applied 3 hr after TPA. The indomethacin effect can be specifically overcome by prostaglandin F2 alpha (PGF2 alpha) and correlates with an accumulation of PGF2 alpha in skin 3-4 hr after TPA treatment. After 12-O-retinoylphorbol-13-acetate (RPA) application no prostaglandin accumulation is seen at this time. It is proposed that the expression of the neoplastic phenotype ("conversion" of initiated cells) is accomplished in the course of a PGF2 alpha-mediated metaplastic process which normally plays a physiological role in the wound response.

Animals↗
PubMed1982

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.

Animals↗
PubMed1982

A comparative study on wound-healing in neonatal and adult mouse epidermis in vivo.

A cut made into the back skin of either newborn or adult mice evokes, at both ages, a hyperproliferative response in the epidermis. Differences in the reaction of neonatal as compared with adult epidermis are found in the spatial distribution of proliferative activity as well as in its time course. The response in adult mouse epidermis is inhibited by local application of indomethacin, whereas the response of the newborn epidermis is not.

Animals↗