Oksana Holian

Resveratrol regulates cellular PKC α and δ to inhibit growth and induce apoptosis in gastric cancer cells

SummaryResveratrol, a dietary phytoalexin, has emerged as a promising chemopreventive agent due to its antiproliferative and pro-apoptotic action toward cancer cells and its ability to inhibit tumor growth in animals. Gastric adenocarcinoma cells respond to resveratrol treatment with suppression of DNA synthesis, activation of nitric oxide synthase, induction of apoptosis and inhibition of total PKC and PKC α activity. Here we demonstrate that treatment of gastric adenocarcinoma SNU-1 cells with resveratrol results in time and concentration dependent accumulation of tumor suppressors p21(cip1/WAF -1) and p53 and is preceded by loss of membrane-associated PKC δ protein and a concomitant increase in cytosolic PKC α. Arrest of the cell cycle at transition of S to G2/M phases correlates with the profile of 3H-thymidine incorporation and accumulation of p21(cip1/WAF -1) and was temporally dependent on increase of p53. SNU-1 cells respond to resveratrol treatment with up-regulation of both Fas and Fas-L proteins, whereas in KATO-III cells, with deleted p53, only Fas-L is increased after resveratrol treatment. Although Fas and Fas-L proteins in SNU-1 cells and Fas-L in KATO-III cells were elevated within 24 h of cell treatment with low concentrations of resveratrol, significant apoptotic response at these concentrations was observed only after 48 h. Altogether, our findings indicate that resveratrol engages PKC α and δ signals in gastric adenocarcinoma SNU-1 cells prior to up-regulation of antiproliferative and pro-apoptotic signals. The specific cell death signals engaged by resveratrol appear to be cell type dependent and suggest that resveratrol has chemopreventive potential even after mutational changes have occurred.

Resveratrol-induced inactivation of human gastric adenocarcinoma cells through a protein kinase C-mediated mechanism

Resveratrol, a polyphenolic phytochemical present in berries, grapes, and wine, has emerged as a promising chemopreventive candidate. Because there is scant information regarding natural agents that prevent, suppress, or reverse gastric carcinogenesis, the aim of the present study was to determine the chemopreventive potential of resveratrol against gastric cancer by investigating cellular and molecular events associated with resveratrol treatment of human gastric adenocarcinoma cells. We determined the action of resveratrol on cellular function and cellular integrity by measuring DNA synthesis, cellular proliferation, cell cycle distribution, cytolysis, apoptosis, and phosphotransferase activities of two key signaling enzymes, protein kinase C (PKC) and mitogen-activated protein kinases (ERK1/ERK2), in human gastric adenocarcinoma KATO-III and RF-1 cells. Resveratrol inhibited [3H]thymidine incorporation into cellular DNA of normally proliferating KATO-III cells and of RF-1 cells whose proliferation was stimulated with carcinogenic nitrosamines. Treatment with resveratrol arrested KATO-III cells in the G(0)/G(1) phase of the cell cycle and eventually induced apoptotic cell death, but had a minimal effect on cell lysis. Resveratrol treatment had no effect on ERK1/ERK2 activity but significantly inhibited PKC activity of KATO-III cells and of human recombinant PKCalpha. Results indicate that resveratrol has potential as a chemopreventive agent against gastric cancer because it exerts an overall deactivating effect on human gastric adenocarcinoma cells. Resveratrol-induced inhibition of PKC activity and of PKCalpha, without any change in ERK1/ERK2 activity, suggests that resveratrol utilizes a PKC-mediated mechanism to deactivate gastric adenocarcinoma cells.

Inhibition of rat brain protein kinase C by lipid soluble psychotropics.

Lipid soluble psychotropics inhibit brain PKC-catalyzed phosphorylation of exogenous and endogenous proteins to varying degrees. These drugs were better inhibitors of Ca2+/PL-dependent phosphorylation of histones (H) than that of Ca2+/PL-independent protamine sulfate (PrSO4): antidepressants/antipsychotics displayed IC50 of 0.1 to 0.16 mM towards H and 0.3 to 4.0 mM towards PrSO4 phosphorylation. Sedatives/anesthetics were less efficient inhibitors with much higher IC50 of 1.3 to 40 mM. Phosphorylation of a Ca2+-dependent but PL-independent p80 protein and of a cluster of Ca2+/PL-dependent proteins, p16-20, in brain was also inhibited by the antidepressants/antipsychotics but not by the sedatives/anesthetics. Phorbol ester binding studies revealed that these inhibitors do not compete for DAG binding site(s) on PKC. However, both drug-PL and drug-PKC interactions seem to be relevant in their mechanism of action. Furthermore, our data suggest that the hydrophobic nature of the propanamine side chain or its N-methylated version as well as the tricyclic nucleus influence drug-PKC interaction. Although many of these drugs have other accepted modes of action, modulation of PKC activity in brain, may be yet another aspect to be considered in their mechanism of action.

Selenomethionine Stimulates MAPK (ERK) Phosphorylation, Protein Oxidation, and DNA Synthesis in Gastric Cancer Cells

Abstract: Selenium is an essential trace element and is required for the synthesis of cellular enzymes that protect against oxidative stress. Epidemiological findings indicate that low selenium intake is associated with increased cancer risk, and, although the majority of studies show that exposure of transformed cells to selenium results in apoptotic cell death, there are reports indicating that cells exposure to low selenium concentrations promotes cellular proliferation. Gastric adenocarcinoma SNU-1 cells responded to selenomethionine with a biphasic proliferative curve: enhanced incorporation of 3H-thymidine into DNA within a very narrow range of selenomethionine concentrations followed by decreased 3H-thymidine uptake at higher levels. Concentrations of selenomethionine that stimulate cellular proliferation also induce cellular oxidation and phosphorylation of MAPK (ERK), a component of cell signaling cascades. MAPK (ERK) phosphorylation is synonymous with MAPK activation and enhanced cell growth. Our findings support previous observations of enhanced proliferation in response to low levels of selenium and suggest that, at certain concentrations, selenomethionine induces mild oxidative stress that, in turn, stimulates DNA synthesis.

Fatty acyl esters potentiate fatty acid induced activation of protein kinase C

Purified rat pancreas protein kinase C (PKC) is activated by unsaturated free fatty acids (oleic and arachidonic). The ethyl esters of these fatty acids are ineffective as enzyme activators. However, when the ethyl esters are added in combination with a free fatty acid, there is significant enhancement of enzyme activation. Nearly optimal PKC activation was obtained when non-activating ethyl oleate or ethyl arachidonate was added to sub-optimally activating concentrations of oleic or arachidonic acids. In addition to the ethyl esters, 1-monooleylglycerol also had a potentiating effect on PKC activation by oleic acid. However, the degree of activation observed in the presence of a free fatty acid and an acyl ester of the fatty acid quantitatively never surpassed that produced by sn-1,2-dioleylglycerol. Our findings indicate that significant PKC activation can be achieved by presenting the enzyme with an environment which we believe approximates the structural characteristics of the endogenous activator, sn-1,2-diacylglycerol.

Apoprotein A-1 is a cofactor independent substrate of protein kinase C

Apoprotein A-1 (apo A-1), the predominant protein constituent of high density lipoproteins (HDL), was phosphorylated by protein kinase C (PKC). Optimal phosphorylation of lipid-free apo A-1 occurs in the absence of calcium, phosphatidyl serine (PS), and diolein (DO). However, HDL-bound apo A-1 was not phosphorylated by PKC. Furthermore, addition of either native or reconstituted HDL particles to lipid-free apo A-1 resulted in a concentration-dependent inhibition of phosphorylation. It appears that the phosphorylatable sites on apo A-1 are involved in hydrophobic interaction with the lipids of HDL. Apo A-1 is a novel substrate of PKC because it does not require calcium and lipid cofactors for optimal phosphorylation.

Response of brain protein kinase C isozymes to ethyl oleate, an alcohol metabolite

Rat brain protein kinase C (PKC) isozymes I, II and III were stimulated by fatty acids in the absence and presence of calcium. Ethyl oleate, which by itself has no effect on PKC activity, had a potentiating effect on fatty acid-induced activation of all 3 isozymes. Potentiation was observed predominantly in the presence of calcium. Interaction of ethyl oleate with a signalling mechanism involving PKC may underlie the cognitive disturbances noted after alcohol consumption.

Action of histamine and 3-isobutyl-1-methylxanthine on cAMP activation of protein kinase in dog gastric mucosa

Dog gastric mucosa was incubated with histamine, IMX and db-cAMP, and the tissue was analyzed for cAMP content and cAMP-dependent protein kinase activity. Results show that in the absence of IMX, histamine does not produce measurable changes in either cAMP content or protein kinase activity ratios. In the presence of 5×10−5 mol/I IMX histamine elicits a dose-dependent accumulation of cAMP, and this accumulation is reflected in elevated protein kinase activity ratios. When IMX concentration is increased to 5×10−4 mol/l, the histamine effect is more pronounced. Incubation of gastric mucosa with 10−6 mol/l db-cAMP results in elevated cAMP tissue levels both in the absence and presence of IMX, but protein kinase activity ratio is significantly elevated only in the presence of 5×10−4 mol/l IMX. It is concluded that histamlen stimulates cAMP formation and protein kinase activation in dog gastric mucosa, but elevations are detectable only when the phosphodiesterase enzyme is inhibited.

Inhibition of Skin Protein Kinase C by Psychotropic Drugs

Lipid-soluble psychotropics are often used to treat skin diseases with psychosomatic indications. Although these drugs are known to exert their effects through the central nervous system, relatively little is known about their mechanism of action in skin. In this communication, several lipid-soluble psychotropic drugs have been examined for their ability to inhibit protein kinase C (PKC)-catalyzed phosphorylation of exogenous substrates and endogenous skin proteins. Phosphorylation of three discrete skin protein substrates at 64, 42 and 28 kDa and a group crowded together at 15-18 kDa was prevented by the antidepressants/antipsychotics. Inhibition was more pronounced in a phospholipid (PL) dependent system, but both drug-PL and drug-PKC interactions seem to be important in the mechanism of action of these drugs. In addition to the tricyclic nucleus, the propanamine side chain or its N-methyl form may influence the interaction of these drugs with PKC and its substrate(s). Chlorpromazine, imipramine, fluoxetine, doxepin, amitriptyline and hydroxyzine used in the practice of dermatology may exert their therapeutic effects by modulating skin PKC activity.

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)