ERKs and p38 kinase phosphorylate p53 protein at serine 15 in response to UV radiation

Nutrition and gastric cancer risk: an update

Data from epidemiologic, experimental, and animal studies indicate that diet plays an important role in the etiology of gastric cancer. High intake of fresh fruits and vegetables, lycopene and lycopene-containing food products, and potentially vitamin C and selenium may reduce the risk for gastric cancer. Data also suggest that high intake of nitrosamines, processed meat products, salt and salted foods, and overweight and obesity are associated with increased risk for gastric cancer. However, current data provide little support for an association of beta-carotene, vitamin E, and alcohol consumption with risk for gastric cancer.

Phosphorylation by p38 MAPK as an alternative pathway for GSK3beta inactivation

Glycogen synthase kinase 3beta (GSK3beta) is involved in metabolism, neurodegeneration, and cancer. Inhibition of GSK3beta activity is the primary mechanism that regulates this widely expressed active kinase. Although the protein kinase Akt inhibits GSK3beta by phosphorylation at the N terminus, preventing Akt-mediated phosphorylation does not affect the cell-survival pathway activated through the GSK3beta substrate beta-catenin. Here, we show that p38 mitogen-activated protein kinase (MAPK) also inactivates GSK3beta by direct phosphorylation at its C terminus, and this inactivation can lead to an accumulation of beta-catenin. p38 MAPK-mediated phosphorylation of GSK3beta occurs primarily in the brain and thymocytes. Activation of beta-catenin-mediated signaling through GSK3beta inhibition provides a potential mechanism for p38 MAPK-mediated survival in specific tissues.

Tumor necrosis factor-alpha potentiates genotoxic effects of benzo[a]pyrene in rat liver epithelial cells through upregulation of cytochrome P450 1B1 expression

Benzo[a]pyrene (BaP) is a ubiquitous environmental pollutant, which may contribute to the development of human cancer. The ultimate carcinogenic BaP metabolite produced by cytochrome P450 enzymes (CYP), such as CYP1A1 and CYP1B1, anti-BaP-7,8-diol-9,10-epoxide, binds covalently to DNA and causes mutations. The levels of various CYP isoforms can be significantly modulated under inflammatory conditions. As the chronic inflammation is known to contribute to carcinogenesis, we investigated interactions of a major proinflammatory cytokine, tumor necrosis factor-alpha (TNF-alpha), and BaP in regulation of the expression of CYP1A1/1B1 and induction of DNA damage in rat liver epithelial WB-F344 cells. TNF-alpha enhanced induction of CYP1B1, while it simultaneously suppressed the BaP-induced CYP1A1 expression. The observed deregulation of CYP1 induction was found to be associated with a significantly enhanced formation of DNA adducts. The elevated DNA damage corresponded with increased phosphorylation of p53 tumor suppressor at Ser-15 residue, enhanced accumulation of cells in the S-phase of cell cycle and potentiation of BaP-induced apoptosis. Inhibition of CYP1B1 by fluoranthene significantly decreased both the formation of DNA adducts and the induction of apoptosis in WB-F344 cells treated with BaP and TNF-alpha, thus suggesting that this isoform might be responsible for genotoxic effects of BaP in nonparenchymal liver cells. Our results seem to indicate that inflammatory conditions might enhance genotoxic effects of carcinogenic polycyclic aromatic hydrocarbons through upregulation of CYP1B1 expression.

p53 tumor suppressor gene: a critical molecular target for UV induction and prevention of skin cancer

The relationship between exposure to UV radiation and development of skin cancer has been well established. Several studies have shown that UVB induces unique mutations (C-->T and CC-->TT transitions) in the p53 tumor suppressor gene that are not commonly induced by other carcinogens. Our studies have demonstrated that UV-induced mouse skin cancers contain p53 mutations at a high frequency and that these mutations can be detected in UV-irradiated mouse skin well before the appearance of skin tumors. This observation suggested that it might be possible to use p53 mutations as a biologic endpoint for testing the efficacy of sunscreens in photoprotection studies. Indeed, application of SPF 15 sunscreens to mouse skin before each UVB irradiation resulted in reduction in the number of p53 mutations. Because p53 mutations represent an early essential step in photocarcinogenesis, these results imply that inhibition of this event may protect against skin cancer development. This hypothesis was confirmed by our finding that sunscreens used in p53 mutation inhibition experiments also protected mice against UVB-induced skin cancer.

DNA adducts formation and induction of apoptosis in rat liver epithelial 'stem-like' cells exposed to carcinogenic polycyclic aromatic hydrocarbons

The bipotent liver progenitor cells, so called oval cells, may participate at the early stages of hepatocarcinogenesis induced by chemical carcinogens. Unlike in mature parenchymal cells, little is known about formation of DNA adducts and other genotoxic events in oval cells. In the present study, we employed spontaneously immortalized rat liver WB-F344 cell line, which is an established in vitro model of oval cells, in order to study genotoxic effects of selected carcinogenic polycyclic aromatic hydrocarbons (PAHs). With exception of dibenzo[a,l]pyrene, and partly also benzo[g]chrysene and benz[a]anthracene, all other PAHs under the study induced high levels of CYP1A1 and CYP1B1 mRNA. In contrast, we observed distinct genotoxic and cytotoxic potencies of PAHs. Dibenzo[a,l]pyrene, and to a lesser extent also benzo[a]pyrene, benzo[g]chrysene and dibenzo[a,e]pyrene, formed high levels of DNA adducts. This was accompanied with accumulation of Ser-15 phosphorylated form of p53 protein and induction of apoptosis. Contrary to that, benz[a]anthracene, chrysene, benzo[b]fluoranthene and dibenzo[a,h]anthracene induced only low amounts of DNA adducts formation and minimal apoptosis, without exerting significant effects on p53 phosphorylation. Finally, we studied effects of 2,4,3',5'-tetramethoxystilbene and fluoranthene, inhibitors of CYP1B1 activity, which plays a central role in metabolic activation of dibenzo[a,l]pyrene. In a dose-dependent manner, both compounds inhibited apoptosis induced by dibenzo[a,l]pyrene, suggesting that it interferes with the metabolic activation of the latter one. The present data show that in model cell line sharing phenotypic properties with oval cells, PAHs can be efficiently metabolized to form ultimate genotoxic metabolites. Liver progenitor cells could be thus susceptible to this type of genotoxic insult, which makes WB-F344 cell line a useful tool for studies of genotoxic effects of organic contaminants in liver cells. Our results also suggest that, unlike in mature hepatocytes, CYP1B1 might be a primary enzyme responsible for formation of DNA adducts in liver progenitor cells.

A sensitive flow cytometry-based nucleotide excision repair assay unexpectedly reveals that mitogen-activated protein kinase signaling does not regulate the removal of UV-induced DNA damage in human cells

In response to diverse genotoxic stimuli (e.g. UV and cisplatin), the mitogen-activated protein kinases ERK1/2, JNK1/2, and p38alpha/beta become rapidly phosphorylated and in turn activate multiple downstream effectors that modulate apoptosis and/or growth arrest. Furthermore, previous lines of evidence have strongly suggested that ERK1/2 and JNK1/2 participate in global-genomic nucleotide excision repair, a critical antineoplastic pathway that removes helix-distorting DNA adducts induced by a variety of mutagenic agents, including UV. To rigorously evaluate the potential role of mitogen-activated protein kinases in global-genomic nucleotide excision repair, various human cell strains (primary skin fibroblasts, primary lung fibroblasts, and HCT116 colon carcinoma cells) were treated with highly specific chemical inhibitors, which, following UV exposure, (i) abrogated the capacities of ERK1/2, JNK1/2, or p38alpha/beta to phosphorylate specific downstream effectors and (ii) characteristically modulated cellular proliferation, clonogenic survival, and/or apoptosis. A highly sensitive flow cytometry-based nucleotide excision repair assay recently optimized and validated in our laboratory was then employed to directly demonstrate that the kinetics of UV DNA photoadduct repair are highly similar in mock-treated versus mitogen-activated protein kinase inhibitor-treated cells. These data on primary and tumor cells treated with pharmacological inhibitors were fully corroborated by repair studies using (i) short hairpin RNA-mediated knockdown of ERK1/2 or JNK1/2 in human U2OS osteosarcoma cells and (ii) expression of a dominant negative p38alpha mutant in human primary lung fibroblasts. Our results provide solid evidence for the first time, in disaccord with a burgeoning perception, that mitogen-activated protein kinase signaling does not influence the efficiency of human global-genomic nucleotide excision repair.

Thiothymidine plus low-dose UVA kills hyperproliferative human skin cells independently of their human papilloma virus status

The thymidine analogue 4-thiothymidine (S(4)TdR) is a photosensitizer for UVA radiation. The UV absorbance spectrum of S(4)TdR and its incorporation into DNA suggests that it might act synergistically with nonlethal doses of UVA to selectively kill hyperproliferative or cancerous skin cells. We show here that nontoxic concentrations of S(4)TdR combine with nonlethal doses of UVA to kill proliferating cultured skin cells. Established cell lines with a high fraction of proliferating cells were more sensitive than primary keratinocytes or fibroblasts to apoptosis induction by S(4)TdR/UVA. Although S(4)TdR plus UVA treatment induces stabilization of p53, cell death, as measured by apoptosis or clonal survival, occurs to a similar extent in both p53 wild-type and p53-null backgrounds. Furthermore, different types of human papilloma virus E6 proteins, which protect against UVB-induced apoptosis, have little effect on killing by S(4)TdR/UVA. S(4)TdR/UVA offers a possible therapeutic intervention strategy that seems to be applicable to human papilloma virus-associated skin lesions.

Inhibition of benzopyrene diol epoxide-induced apoptosis by cadmium(II) is AP-1-independent: role of extracelluler signal related kinase

Cadmium, a major metal constituent of tobacco smoke, elicits synergistic enhancement of cell transformation when combined with benzo[a]pyrene (BP) or other PAHs. The mechanism underlying this synergism is not clearly understood. We observed that (+/-)-anti-benzo[a]pyrene-7,8-diol-9,10-epoxide (BPDE), an ultimate carcinogen of BP, induces apoptosis in promotion sensitive mouse epidermal JB6 Cl41 cells at non-cytotoxic concentrations. BPDE also activates AP-1 several folds in AP-1 reporter JB6 cells. Cadmium at non-cytotoxic concentrations inhibits both AP-1 activation and apoptosis in response to BPDE. Since AP-1 is known to be involved in stress-induced apoptosis we investigated whether inhibition of AP-1 by cadmium has any role in the inhibition of BPDE-induced apoptosis. MAP kinases (particularly ERKs, p38 and JNKs) are known to have important role in DNA damage-induced AP-1 activation. We observed that ERK and JNK, but not p38 MAP kinase, are involved in BPDE-induced AP-1 activation. Effect of cadmium on MAP kinases and the effect of inhibition of above three MAP kinases on BPDE-induced AP-1 activation and apoptosis indicate that AP-1 is probably not involved in BPDE-induced apoptosis. Cadmium up-regulates BPDE-activated ERKs and ERK inhibition by U0126 relieves cadmium-mediated inhibition of BPDE-induced apoptosis. We suggest that cadmium inhibits BPDE-induced apoptosis not involving AP-1 but probably through a different mechanism by up-regulating ERK which is known to promote cell survival.

Guggulsterone-induced apoptosis in human prostate cancer cells is caused by reactive oxygen intermediate dependent activation of c-Jun NH2-terminal kinase

Guggulsterone, a constituent of Indian Ayurvedic medicinal plant Commiphora mukul, causes apoptosis in cancer cells but the sequence of events leading to cell death is poorly understood. We now show that guggulsterone-induced cell death in human prostate cancer cells is caused by reactive oxygen intermediate (ROI)-dependent activation of c-Jun NH(2)-terminal kinase (JNK). Exposure of PC-3 and LNCaP cells to apoptosis inducing concentrations of guggulsterone resulted in activation of JNK and p38 mitogen-activated protein kinase (p38 MAPK) in both cell lines and activation of extracellular signal-regulated kinase 1/2 (ERK1/2) in LNCaP cells. The guggulsterone-induced apoptosis in PC-3/LNCaP cells was partially but statistically significantly attenuated by pharmacologic inhibition (SP600125) as well as genetic suppression of JNK activation. On the other hand, pharmacologic inhibition of p38 MAPK activation in PC-3 or LNCaP cells (SB202190) and ERK1/2 activation in LNCaP cells (PD98059) did not protect against guggulsterone-induced cell death. The guggulsterone treatment caused generation of ROI in prostate cancer cells but not in a normal prostate epithelial cell line (PrEC), which was also resistant to guggulsterone-mediated JNK activation. The guggulsterone-induced JNK activation as well as cell death in prostate cancer cells was significantly attenuated by overexpression of catalase and superoxide dismutase. In addition, guggulsterone treatment resulted in a decrease in protein level and promoter activity of androgen receptor in LNCaP cells. In conclusion, the present study reveals that the guggulsterone-induced cell death in human prostate cancer cells is regulated by ROI-dependent activation of JNK and guggulsterone inhibits promoter activity of androgen receptor.

Absence of Smad3 confers radioprotection through modulation of ERK-MAPK in primary dermal fibroblasts

BACKGROUND

Transforming growth factor-beta1 (TGF-beta1), a key biological mediator following ionizing radiation, plays a role in a complex tissue reaction involved in local radiation-induced pathological damage. Knocking out Smad3 (S3KO), a downstream signaling intermediate in the TGF-beta pathway, in mice protects their skin from radiation damage as demonstrated by decreased epithelial acanthosis and dermal fibrosis as compared to Smad3 wild-type (S3WT) mice.

OBJECTIVE

The present study was designed to investigate the molecular mechanisms contributing to increased radioprotection in the absence of Smad3.

METHODS

Primary dermal fibroblasts derived from S3WT and KO mice were exposed to 5Gy ionizing radiation in vitro. Western blot analyses, immunocytochemistry, and reporter transfections were used to dissect the radiation-induced events.

RESULTS

There was increased phosphorylation of ERK-MAPK, p53 and H2A.X in S3KO compared to the S3WT fibroblasts, implicating them in a key signaling cascade in response of these cells to radiation. Pro-fibrotic gene expression was decreased in S3KO fibroblasts post-irradiation.

CONCLUSION

The absence of Smad3 may decrease radio-responsiveness by increasing activation of DNA damage sensing mechanisms and decreasing induction of pro-fibrotic genes.

The pathways to tumor suppression via route p38

Besides its well-known functions in inflammation and other stresses, the p38 mitogen-activated protein kinase pathway also negatively regulates cell proliferation and tumorigenesis. Inactivation of the p38 pathway enhances cellular transformation and renders mice prone to tumor development with concurrent disruption of the induction of senescence. Conversely, persistent activation of p38 inhibits tumorigenesis. Mechanistic insights into this additional p38 function are starting to emerge. For example, p38 has been shown to have a crucial role in oncogene-induced senescence, replicative senescence, DNA-damage responses and contact-inhibition. In addition, the role of the p38 pathway in proliferative control and tumor suppression is mediated by its impact on several cell-cycle regulators. These findings reveal a tumor-suppressing function of the p38 pathway, and indicate that components of the p38 pathway are potential targets for novel cancer therapies.

Oxidative stress enhances phosphorylation of p53 in neonatal rat cardiomyocytes

p53 is an important regulator of cell growth and apoptosis and its activity is regulated by phosphorylation. Accordingly, in neonatal rat cardiomyocytes we examined the involvement of p53 in H(2)O(2)-induced apoptosis. Treatment with 50-100 microM H(2)O(2) markedly induced apoptosis in cardiomyocytes, as assessed by gel electrophoresis of genomic DNA. To examine whether H(2)O(2) increases p53 phosphorylation in cardiomyocytes, we utilized an antibody that specifically recognizes phosphorylated p53 at serine-15. The level of phosphorylated p53 was markedly increased by 100 microM H(2)O(2) at 30 and 60 min. Using specific protein kinase inhibitors we examined the involvement of protein kinases in p53 phosphorylation in response to H(2)O(2) treatment. However, staurosporine, a broad spectrum inhibitor of protein kinases, SB202190, a specific p38 kinase inhibitor, PD98059, a MAP kinase inhibitor, wortmannin, an inhibitor of DNA-PK and PI3 kinase, SP600125, a JNK inhibitor and caffeine,an inhibitor of ATM and ATR, failed to prevent the H(2)O(2)-induced phosphorylation of p53. cDNA microarray revealed that H(2)O(2) markedly increased expression of several p53 upstream modifiers such as the p300 coactivator protein and several downstream effectors such as gadd45, but decreased the expression of MDM2, a negative regulator of p53. Our results suggest that phosphorylation of p53 at serine-15 may be an important signaling event in the H(2)O(2)-mediated apoptotic process.

Catalase, Bax and p53 expression in the visual system of the crab Ucides cordatus following exposure to ultraviolet radiation

In invertebrates, a few studies have suggested apoptosis as the mechanism of choice to protect the retina after exposure to ultraviolet (UV) radiation. We demonstrated previously, by electron microscopy, that the retina and lamina ganglionaris (or lamina) cells of the crab Ucides cordatus displayed subcellular signs of apoptosis after exposure to UVB and UVC. Here, we first ascertained, by the TdT-mediated dUTP-biotin nick end-labeling (TUNEL) technique, that UV irradiation indeed produced the previously reported results. We next tested, in the visual system of U. cordatus, whether the expression (as analyzed by immunohistochemistry and observed with laser scanning microscopy) and levels (as examined by Western blotting) of catalase, Bax, and p53 were affected by the same dose of UV radiation as that used previously. Our data revealed that the intensity of catalase, Bax, and p53 labeling was stronger in irradiated retina and lamina cells than in non-irradiated retina and lamina. However, no significant difference was observed in the concentrations of these proteins isolated from the whole optic lobe. The results thus suggest that UVB and UVC induce apoptosis in the crustacean retina and lamina by increasing catalase expression and activating the Bax- and p53-mediated apoptosis pathways.

A new p38 MAP kinase-regulated transcriptional coactivator that stimulates p53-dependent apoptosis

The p38 mitogen-activated protein kinase (MAPK) signaling pathway plays an important role in stress-induced cell-fate decisions by orchestrating responses that go from cell-cycle arrest to apoptosis. We have identified a new p38 MAPK-regulated protein that we named p18(Hamlet), which becomes stabilized and accumulates in response to certain genotoxic stresses such as UV or cisplatin treatment. Overexpression of p18(Hamlet) is sufficient to induce apoptosis, whereas its downregulation reduces the apoptotic response to these DNA damage-inducing agents. We show that p18(Hamlet) interacts with p53 and stimulates the transcription of several proapoptotic p53 target genes such as PUMA and NOXA. This correlates with enhanced p18(Hamlet)-induced recruitment of p53 to the promoters. In proliferating cells, low steady-state levels of p18(Hamlet) are probably maintained by a p53-dependent negative feedback loop. Therefore, p18(Hamlet) is a new cell-fate regulator that links the p38 MAPK and p53 pathways and contributes to the establishment of p53-regulated stress responses.

p38 MAPK in regulating cellular responses to ultraviolet radiation

Solar ultraviolet (UV) radiation is a major environmental factor that causes DNA damage, inflammation, erythema, sunburn, immunosuppression, photoaging, gene mutations, and skin cancer. p38 mitogen activated protein kinase (MAPK) are strongly activated by UV radiation, and play important roles in regulating cellular responses to UV. In this review, we examine the role played by p38 MAPK in mediating UV-induced cell cycle, apoptosis, inflammation, and skin tanning response. We review the role played by p38 MAPK in transcriptional regulation of key downstream genes that have been implicated in the regulation of cellular responses to UV radiation. Understanding this will undoubtedly help in the prevention and control of UV-induced damage and the development of novel therapeutic strategies.

Dibenzanthracenes and benzochrysenes elicit both genotoxic and nongenotoxic events in rat liver ‘stem-like’ cells

Polycyclic aromatic hydrocarbons (PAHs) with molecular weight 278 are a group of PAHs that are mostly not covered by the current monitoring programs, despite their relative abundance in environmental samples and possible carcinogenicity. Although benzo[g]chrysene (BgChry) and dibenz[a,h]anthracene (DBahA) have been for a long time studied as genotoxic, tumour-initiating compounds, little is known about the potential tumour-promoting effects of this group of PAHs. In the present study, we investigated their impact on activation of the aryl hydrocarbon receptor (AhR), induction of enzymes involved in metabolic activation of PAHs, disruption of cell cycle control in confluent cell population and inhibition of gap junctional intercellular communication (GJIC), using the rat liver epithelial cell line WB-F344 as a model of liver progenitor cells. We found that BgChry was the weakest inducer of the AhR-mediated activity, while relative potencies of benzo[b]chrysene (BbChry) and benzo[c]chrysene (BcChry) were comparable to the previously reported values for dibenzanthracenes. All compounds increased expression of cytochromes P450 1A1 and 1B1, and aldo-keto reductase 1C9. BgChry was found to induce high amounts of DNA adducts, which corresponded with induction of p53 phosphorylation at Ser15, apoptosis and accumulation of cells in S-phase of cell cycle, leading to a decrease in cell numbers. All other compounds were found to stimulate cell proliferation in contact-inhibited WB-F344 cells in a dose-dependent manner. We found that only BgChry, and to a lesser extent also BcChry, inhibited GJIC at high concentrations. Taken together, dibenzanthracenes and benzochrysenes, with exception of BgChry, seem to act primarily through deregulation of cell proliferation in liver epithelial cells, which is related to their relatively high AhR-mediated activity. The disruption of cell cycle control might contribute to their carcinogenic effects, as well as to carcinogenicity of complex environmental mixtures containing high levels of PAHs with molecular weight 278.

Phosphorylation of p53 at serine 15 in A549 pulmonary epithelial cells exposed to vanadate: involvement of ATM pathway

When A549 cells were exposed to sodium metavanadate (NaVO(3)), the pentavalent species of vanadium (vanadate), phosphorylation of p53 protein at Ser15 was found in a time (8-48 h)- and dose (10-200 microM)-dependent manner. After the incubation with 50 or 100 microM NaVO(3) for 48 h, accumulation of p53 protein was accompanied with Ser15 phosphorylation. Among serines in p53 protein immunoprecipitated from A549 cells treated with 100 microM NaVO(3) for 48 h, only Ser15 was markedly phosphorylated. Treatment with other vanadate compounds, sodium orthovanadate (Na(3)VO(4)) and ammonium metavanadate (NH(4)VO(3)), also induced Ser15 phosphorylation and accumulation of p53 protein. While phosphorylation of extracellular signal-regulated protein kinase (ERK) was found in cells treated with NaVO(3), treatment with U0126 did not suppress Ser15 phosphorylation. On the other hand, treatment with wortmannin or caffeine, the inhibitors to phosphatidylinositol 3-kinase related kinases (PIKKs), suppressed both NaVO(3)-induced Ser15 phosphorylation and accumulation of p53 protein. The silencing of ataxia telangiectasia mutated (ATM) expression using short-interference RNA resulted in the marked suppression of Ser15 phosphorylation in A549 cells exposed to NaVO(3). However, treatment with antioxidants such as catalase and N-acetylcysteine did not suppress NaVO(3)-induced Ser15 phosphorylation. Transcriptional activation of p53 and DNA fragmentation in A549 cells treated with NaVO(3) were suppressed only slightly by S15A mutation, suggesting that Ser15 phosphorylation is not essential for these responses. The present results showed that vanadate induces the phosphorylation of p53 at Ser15 depending on ATM, one of the members of PIKK family, in this human pulmonary epithelial cell line.

Taiwanin A induced cell cycle arrest and p53-dependent apoptosis in human hepatocellular carcinoma HepG2 cells

Taiwanin A, a lignan isolated from Taiwania cryptomerioides Hayata, has previously been reported to have cytotoxicity against human tumor cells, but the mechanisms are unclear. In this study, we examined the molecular mechanism of cell death of human hepatocellular carcinoma HepG2 cells induced by Taiwanin A. Taiwanin A has been found to induce cell cycle arrest at G2/M phase as well as caspase-3-dependent apoptosis within 24 h. We performed both in vitro turbidity assay and immunofluorescence staining of tubulin to show that Taiwanin A can inhibit microtubule assembly. Moreover, the tumor suppressor protein p53 in HepG2 cells was activated by Taiwanin A within 12 h. Inhibition of p53 by either pifithrin-alpha or by short hairpin RNA which blocks p53 expression attenuates Taiwanin A cytotoxicity. Our results demonstrate that Taiwanin A can act as a new class of microtubule damaging agent, arresting cell cycle progression at mitotic phase and inducing apoptosis through the activation of p53.

Protection of Human Keratinocytes from UVB-Induced Inflammation Using Root Extract of Lithospermum erythrorhizon

UVB irradiation is an important inducer of biological changes in skin and can activate inflammatory reactions and apoptotic pathways, leading to skin damage. A root extract of Lithospermum erythrorhizon (SK), which has naphthoquinone pigments containing shikonin and shikonin derivatives, is known for its anti-inflammatory, anti-bacterial, and anti-tumor activity, and for its scavenging of reactive oxygen species. However, the effect of SK against UV damage is not clear. The aim of this study was to evaluate the efficacy of SK against UVB induced damage in normal human epidermal keratinocytes (NHEK). UVB-irradiated NHEK showed decreased cell viability, increased production of interleukin (IL)-1alpha, IL-6, IL-8, and tumor necrosis factor-alpha, and induced apoptosis. In an apoptosis pathway assay, UVB-irradiated NHEK showed increased caspase-3 activity, p53 and its phosphorylation at serine 15 compared with non-irradiated cells. All these effects induced by UVB irradiation were clearly inhibited by treatment with SK before and after UVB irradiation for 24 h. It is suggested that SK can protect epidermal cells against harmful effects of UVB irradiation and that SK treatment is probably beneficial for photoprotection of the skin.

PP2Cδ (Ppm1d, WIP1), an endogenous inhibitor of p38 MAPK, is regulated along WithTrp53 andCdkn2a following p38 MAPK inhibition during mouse preimplantation development

Preimplantation embryos utilize mitogen-activated protein kinase signaling (MAPK) pathways to relay signals from the external environment to prepare appropriate responses and adaptations to a changing milieu. It is therefore important to investigate how MAPK pathways are regulated during preimplantation development. This study was conducted to investigate whether PP2Cdelta (Ppm1d, WIP1) is expressed during mouse preimplantation development and to determine the influences of p38 MAPK inhibition on expression of Trp53 (p53), Ppm1d, (WIP1), and Cdkn2a (p16) during mouse preimplantation development. Our results indicate that Trp53, Ppm1d, and Cdkn2a mRNAs and TRP53 and PP2Cdelta proteins are expressed throughout mouse preimplantation development. Treatment of 2-cell embryos with SB220025 (potent inhibitor of p38 MAPK alpha/beta/MAPK 14/11) significantly increased Trp53, Ppm1d and Cdkn2a and Mapk14 mRNA levels at 12 and 24 hr. Treatment of 8-cell embryos with SB220025 for 12 hr increased Trp53, Ppm1d, and Cdkn2a mRNA levels, but not Mapk14 mRNA levels. Treatment of 8-cell embryos for 24 hr increased Trp53, and Ppm1d mRNA levels, but decreased Cdkn2a and Mapk14 mRNA levels. Therefore, blockade of p38 MAPK activity is associated with embryo stage specific influences on Trp53, Ppm1d, Cdkn2a, and Mapk14 expression during mouse preimplantation development. These results define downstream targets of p38 MAPK during preimplantation development and indicate that the p38 MAPK pathway regulates Trp53, Ppm1d, and Cdkn2a expression. This study increases our understanding of the mechanisms controlling preimplantation development and of the interactions between preimplantation embryos and their culture environments.

The protective role of a small GTPase RhoE against UVB-induced DNA damage in keratinocytes

RhoE, a p53 target gene, was identified as a critical factor for the survival of human keratinocytes in response to UVB. The Rho family of GTPases regulates many aspects of cellular behavior through alterations to the actin cytoskeleton, acting as molecular switches cycling between the active, GTP-bound and the inactive, GDP-bound conformations. Unlike typical Rho family proteins, RhoE (also known as Rnd3) is GTPase-deficient and thus expected to be constitutively active. In this study, we investigated the response of cultured human keratinocyte cells to UVB irradiation. RhoE protein levels increase upon exposure to UVB, and ablation of RhoE induction through small interfering RNA resulted in a significant increase in apoptosis and a reduction in the levels of the pro-survival targets p21, Cox-2, and cyclin D1, as well as an increase of reactive oxygen species levels when compared with control cells. These data indicate that RhoE is a pro-survival factor acting upstream of p38, JNK, p21, and cyclin D1. HaCat cells expressing small interfering RNA to p53 indicate that RhoE functions independently of its known associates, p53 and Rho-associated kinase I (ROCK I). Targeted expression of RhoE in epidermis using skin-specific transgenic mouse model resulted in a significant reduction in the number of apoptotic cells following UVB irradiation. Thus, RhoE induction counteracts UVB-induced apoptosis and may serve as a novel target for the prevention of UVB-induced photodamage regardless of p53 status.

Indole-3-carbinol mediated cell cycle arrest of LNCaP human prostate cancer cells requires the induced production of activated p53 tumor suppressor protein

Indole-3-carbinol (I3C), a dietary compound found naturally in cruciferous vegetables of the Brassica genus such as broccoli and brussels sprouts, induces a G1 growth arrest of human reproductive cancer cells. We previously reported that in LNCaP prostate cancer cells, I3C down-regulated cyclin-dependent kinase (CDK) 2 activity. In our current study, Western blotting and quantitative RT-PCR demonstrated that I3C treatment increased both the transcripts and protein levels of the CDK2 inhibitor p21(waf1/cip1) (p21). Transfection of luciferase reporter plasmids containing wild-type and mutated p21 promoter fragments revealed that I3C induced p21 gene transcription through a p53 DNA binding element. Oligonucleotide precipitation showed that I3C increased the level of activated p53 nuclear protein that is competent to bind its DNA target site on the p21 promoter. Ablation of p53 production using short interfering RNA (siRNA) prevented that the I3C induced G1 arrest and up-regulation of p21 expression. Western blots using p53 phospho-specific antibodies revealed that I3C treatment increased the levels of three phosphorylated forms of p53 (Ser15, Ser37, Ser392) that are known to contribute to p53 protein stability and greater transactivation potential. Taken together, our results establish that the I3C induced G1 arrest of human prostate cancer cells requires the induced production of the activated phosphorylated forms of p53, which stimulate transcription of the CDK2 inhibitor p21.

Sulindac-derived reactive oxygen species induce apoptosis of human multiple myeloma cells via p38 mitogen activated protein kinase-induced mitochondrial dysfunction

Non-steroidal anti-inflammatory drugs are well known to induce apoptosis of cancer cells independent of their ability to inhibit cyclooxygenase-2, but the molecular mechanism for this effect has not yet been fully elucidated. The purpose of this study was to elucidate the potential signaling components underlying sulindac-induced apoptosis in human multiple myeloma (MM) cells. We found that sulindac induces apoptosis by promoting ROS generation, accompanied by opening of mitochondrial permeability transition pores, release of cytochrome c and apoptosis inducing factor from mitochondria, followed by caspase activation. Bcl-2 cleavage and down-regulation of the inhibitor of apoptosis proteins (IAPs) family including cIAP-1/2, XIAP, and survivin, occurred downstream of ROS production during sulindac-induced apoptosis. Forced expression of survivin and Bcl-2 blocked sulindac-induced apoptosis. Most importantly, sulindac-derived ROS activated p38 mitogen-activated protein kinase and p53. SB203580, a p38 mitogen-activated protein kinase inhibitor, and RNA inhibition of p53 inhibited the sulindac-induced apoptosis. Furthermore, p53, Bax, and Bak accumulated in mitochondria during sulindac-induced apoptosis. All of these events were significantly suppressed by SB203580. Our results demonstrate a novel mechanism of sulindac-induced apoptosis in human MM cells, namely, accumulation of p53, Bax, and Bak in mitochondria mediated by p38 MAPK activation downstream of ROS production.

ERK1/2 activation attenuates TRAIL-induced apoptosis through the regulation of mitochondria-dependent pathway

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) functions as an extracellular signal, which triggers apoptosis in tumor cells. In order to characterize the molecular events involved in TRAIL cytotoxic signaling, we attempted to determine the role of extracellular signal-regulated kinase 1/2 (ERK1/2), as well as its downstream targets in TRAIL-treated HeLa cells. Here we demonstrate that TRAIL exposure resulted in the activation of ERK1/2, and the elevation of anti-apoptotic Bcl-2 protein levels. ERK1/2 inhibition with PD98059 promoted cell death via the down-regulation of Bcl-2 protein levels, together with increasing mitochondrial damage, including the collapse of mitochondrial membrane potential, the release of cytochrome c from mitochondria to cytoplasm and caspase activity. These results suggest that the ERK1/2 activation is a kind of survival mechanism to struggle against TRAIL-induced stress condition in early stage, via activating cellular defense mechanisms like as the up-regulation of the Bcl-2/Bax ratio, as well as several mitochondrial events.

Modulation of p53 transcriptional activity by PRIMA-1 and Pifithrin-alpha on staurosporine-induced apoptosis of wild-type and mutated p53 epithelial cells

We recently argued for a major role of p53 in staurosporine(ST)-induced apoptosis of immortalized epithelial cells, depending on their p53 status. Here, we studied the effects of PRIMA-1 (p53 reactivation and induction of massive apoptosis) and Pifithrin-alpha (p fifty-three inhibitor) in combination with ST to reinforce our previous results by respectively restoring or inhibiting the p53 transcriptional activity in different cell lines.PRIMA-1 does modify neither expression of apoptosis-related proteins nor the percentage of wild-type p53 HeLa and CaSki cells with [symbol: see text]delta psi m and DNA cleavage, whilst it increases by 45% Bax expression and apoptosis of mutated p53 C33A cells. Pifithrin-alpha, does modify neither Bax expression nor apoptosis level of C33A cells, but readily inhibits both [symbol: see text]delta psi m and DNA fragmentation of p53wt cells with decreasing Bax expression. These data support the evidence that PRIMA-1 could be a good candidate, as an anti-cancer drug targeting mutant p53, in order to increase ST efficiency. Moreover, Pifithrin-alpha could be used in combination with ST and PRIMA-1 to prevent side effects of anti-tumor therapies in cells expressing mutant P53.

Busulfan selectively induces cellular senescence but not apoptosis in WI38 fibroblasts via a p53-independent but extracellular signal-regulated kinase-p38 mitogen-activated protein kinase-dependent mechanism

Busulfan (BU) is a unique alkylating agent that primarily targets slowly proliferating or nonproliferating cells in the body, leading to various normal tissue damage while killing leukemia cells. However, the mechanism(s) of action whereby BU injures normal cells has not been well defined and, therefore, was investigated in the present study by using the normal human diploid WI38 fibroblasts as a model system. We found that WI38 fibroblasts incubated with BU (from 7.5-120 microM) for 24 h underwent senescence but not apoptosis in a dose-independent manner, whereas cells incubated with 80 and 20 microM etoposide (Etop) were committed to apoptosis and senescence, respectively. The induction of WI38 cell senescence by Etop was associated with p53 activation and could be attenuated by down-regulation of p53 using alpha-pifithrin (alpha-PFT) or p53 small interference RNA (siRNA). In contrast, WI38 cell senescence induced by BU was associated with prolonged activation of extracellular signal-regulated kinase (Erk), p38 mitogen-activated protein kinase (p38), and c-Jun NH(2)-terminal kinase (JNK) and could be suppressed by the inhibition of Erk and/or p38 with PD98059 (2'-amino-3'-methoxyflavone) and/or SB203580 [4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)1H-imidazole], respectively. However, inhibition of p53 with alpha-PFT or p53 siRNA or JNK with SP600125 (1,9-pyrazoloanthrone) failed to protect WI38 cells from BU-induced senescence. These findings suggest that BU is a distinctive chemotherapeutic agent that can selectively induce normal human fibroblast senescence through the Erk and p38 pathways.

Protein serine/threonine phosphatase-1 dephosphorylates p53 at Ser-15 and Ser-37 to modulate its transcriptional and apoptotic activities

We have previously demonstrated that the serine/threonine protein phosphatase-1 (PP-1) plays an important role in promoting cell survival. However, the molecular mechanisms by which PP-1 promotes survival remain largely unknown. In the present study, we provide evidence to show that PP-1 can directly dephosphorylate a master regulator of apoptosis, p53, to negatively modulate its transcriptional and apoptotic activities, and thus to promote cell survival. As a transcriptional factor, the function of p53 can be greatly regulated by phosphorylation and dephosphorylation. While the kinases responsible for phosphorylation of the 17 serine/threonine sites have been identified, the dephosphorylation of these sites remains largely unknown. In the present study, we demonstrate that PP-1 can dephosphorylate p53 at Ser-15 and Ser-37 through co-immunoprecipitation, in vitro and in vivo dephosphorylation assays, overexpression and silence of the gene encoding the catalytic subunit for PP-1. We further show that mutations mimicking constitutive dephosphorylation or phosphorylation of p53 at these sites attenuate or enhance its transcriptional activity, respectively. As a result of the changed p53 activity, expression of the downstream apoptosis-related genes such as bcl-2 and bax is accordingly altered and the apoptotic events are either largely abrogated or enhanced. Thus, our results demonstrate that PP-1 directly dephosphorylates p53, and dephosphorylation of p53 has as important impact on its functions as phosphorylation does. In addition, our results reveal that one of the molecular mechanisms by which PP-1 promotes cell survival is to dephosphorylate p53, and thus negatively regulate p53-dependent death pathway.

Multiple actions of pifithrin-alpha on doxorubicin-induced apoptosis in rat myoblastic H9c2 cells

Doxorubicin (Dox) is a chemotherapeutic agent that causes significant cardiotoxicity. We showed previously that Dox activates p53 and induces apoptosis in mouse hearts. This study was designed to elucidate the molecular events that lead to p53 stabilization, to examine the pathways involved in Dox-induced apoptosis, and to evaluate the effectiveness of pifithrin-alpha (PFT-alpha), a p53 inhibitor, in blocking apoptosis of rat H9c2 myoblasts. H9c2 cells that were exposed to 5 muM Dox had elevated levels of p53 and phosphorylated p53 at Ser15. Dox also triggered a transient activation of p38, p42/p44ERK, and p46/p54JNK MAP kinases. Caspase activity assays and Western blot analysis showed that H9c2 cells treated with Dox for 16 h had marked increase in the levels of caspases-2, -3, -8, -9, -12, Fas, and cleaved poly(ADP ribose) polymerase (PARP). There was a concomitant increase in p53 binding activity, cytochrome c release, and apoptosis. These results suggest that Dox can trigger intrinsic, extrinsic, and endoplasmic reticulum-associated apoptotic pathways. Pretreatment of cells with PFT-alpha followed by Dox administration attenuated Dox-induced increases in p53 levels and p53 binding activity and partially blocked the activation of p46/p54JNK and p42/p44ERK. PFT-alpha also led to decreased levels of caspases-2, -3, -8, -9, -12, Fas, PARP, cytochrome c release, and apoptosis. Our results suggest that p53 stabilization is a focal point of Dox-induced apoptosis and that PFT-alpha interferes with multiple steps of Dox-induced apoptosis.

Activation of ERK1/2 and p38 kinases by polycyclic aromatic hydrocarbons in rat liver epithelial cells is associated with induction of apoptosis

Deregulation of various signaling pathways, linked either to induction of cell proliferation or to modulation of cellular differentiation and apoptosis, has been proposed to contribute to carcinogenicity of polycyclic aromatic hydrocarbons (PAHs). In the present study, we investigated effects of the PAHs previously shown to induce cell proliferation and/or apoptosis in contact-inhibited rat liver epithelial WB-F344 cells, with an aim to define the role of mitogen-activated protein kinases in both events. We found that only strong genotoxin dibenzo[a,l]pyrene (DBalP) activated extracellular signal-regulated kinases 1 and 2 (ERK1/2) and p38 kinase, but not c-Jun N-terminal kinases (JNKs), at concentrations inducing both apoptosis and phosphorylation of p53 tumor suppressor at serine 15 residue. In contrast, the PAHs stimulating cell proliferation in WB-F344 cell line had no effect on activation of ERK1/2, p38 or JNKs. Synthetic inhibitors of ERK1/2 activation (U0126) or p38 kinase activity (SB203580) prevented both apoptosis and induction of p53 phosphorylation by DBalP. Pifithrin-alpha, inhibitor of p53 transcriptional activity, prevented induction of apoptosis and activation of ERK1/2 and p38. Taken together, our data suggest that both ERK1/2 and p38 are activated in response to DBalP and that they might be involved in regulation of cellular response to DNA damage induced by DBalP, while neither kinase is involved in the release from contact inhibition induced by PAHs.

Silencing of human phosphatidylethanolamine-binding protein 4 sensitizes breast cancer cells to tumor necrosis factor-alpha-induced apoptosis and cell growth arrest

PURPOSE

The current therapeutic approach is not so effective in breast cancer patients. Alternative treatment protocols aimed at different targets need to be explored. We recently reported a novel phosphatidylethanolamine-binding protein, human phosphatidylethanolamine-binding protein 4 (hPEBP4), as an antiapoptotic molecule. The finding led us to explore a promising approach for breast cancer therapy via silencing the expression of hPEBP4.

EXPERIMENTAL DESIGN

hPEBP4 expression in clinical breast specimens was examined by Tissue Microarrays. RNA interference was used to silence hPEBP4 expression in MCF-7 breast carcinoma cells and the effects on cell proliferation, cell cycle progression, apoptosis, as well as underlying mechanisms, were investigated.

RESULTS

hPEBP4 was found to be expressed in up to 50% of breast cancers but in only <4% of normal breast tissues. Silencing of hPEBP4 potentiated tumor necrosis factor-alpha (TNF-alpha)-induced apoptosis and cell cycle arrest in MCF-7 cells, which was due to the increased mitogen-activated protein kinase activation and the enhanced phosphatidylethanolamine externalization. Further investigation showed that silencing of hPEBP4 in MCF-7 cells promoted TNF-alpha-induced stability of p53, up-regulation of phospho-p53ser15, p21waf/cip, and Bax, and down-regulation of Bcl-2 and Bcl-xL, which were shown to depend on extracellular signal-regulated kinase 1/2 and c-jun NH2-terminal kinase activation by hPEBP4 silencing. Moreover, the increased proportion of cells in the G0-G1 phase of cell cycle was observed in hPEBP4-silenced MCF-7 cells on TNF-alpha treatment and the expression of cyclin A and cyclin E was down-regulated more significantly.

CONCLUSIONS

The antiapoptotic effect and the preferential expression pattern in breast cancer tissues make hPEBP4 a new target for breast cancer therapy. Silencing of hPEBP4 expression may be a promising approach for the treatment of breast carcinoma.

Activation of p38 MAP kinase by DNA double-strand breaks in V(D)J recombination induces a G2/M cell cycle checkpoint

Delay of cell cycle progression in response to double-strand DNA breaks (DSBs) is critical to allow time for DNA repair and prevent cellular transformation. Here, we show that the p38 mitogen-activated protein (MAP) kinase signaling pathway is activated in immature thymocytes along with TcRbeta gene V(D)J recombination. Active p38 MAP kinase promotes a G2/M cell cycle checkpoint through the phosphorylation and activation of p53 in these cells in vivo. Inactivation of p38 MAP kinase and p53 is required for DN3 thymocytes to exit the G2/M checkpoint, progress through mitosis and further differentiate. We propose that p38 MAP kinase is activated by V(D)J-mediated DSBs and induces a p53-mediated G2/M checkpoint to allow DNA repair and prevent cellular transformation.

The Involvement of MAPK Signaling Pathways in Determining the Cellular Response to p53 Activation

The effect of ERK, p38, and JNK signaling on p53-dependent apoptosis and cell cycle arrest was investigated using a Friend murine erythroleukemia virus (FVP)-transformed cell line that expresses a temperature-sensitive p53 allele, DP16.1/p53ts. In response to p53 activation at 32 degrees C, DP16.1/p53ts cells undergo p53-dependent G(1) cell cycle arrest and apoptosis. As a result of viral transformation, these cells express the spleen focus forming env-related glycoprotein gp55, which can bind to the erythropoietin receptor (EPO-R) and mimics many aspects of EPO-induced EPO-R signaling. We demonstrate that ERK, p38 and JNK mitogen-activated protein kinases (MAPKs) are constitutively active in DP16.1/p53ts cells. Constitutive MEK activity contributes to p53-dependent apoptosis and phosphorylation of p53 on serine residue 15. The pro-apoptotic effect of this MAPK kinase signal likely reflects an aberrant Ras proliferative signal arising from FVP-induced viral transformation. Inhibition of MEK alters the p53-dependent cellular response of DP16.1/p53ts from apoptosis to G(1) cell cycle arrest, with a concomitant increase in p21(WAF1), suggesting that the Ras/MEK pathway may influence the cellular response to p53 activation. p38 and JNK activity in DP16.1/p53ts cells is anti-apoptotic and capable of limiting p53-dependent apoptosis at 32 degrees C. Moreover, JNK facilitates p53 protein turnover, which could account for the enhanced apoptotic effects of inhibiting this MAPK pathway in DP16.1/p53ts cells. Overall, these data show that intrinsic MAPK signaling pathways, active in transformed cells, can both positively and negatively influence p53-dependent apoptosis, and illustrate their potential to affect cancer therapies aimed at reconstituting or activating p53 function.

Combined antioxidant (beta-carotene, alpha-tocopherol and ascorbic acid) supplementation increases the levels of lung retinoic acid and inhibits the activation of mitogen-activated protein kinase in the ferret lung cancer model

Interactions among beta-carotene (BC), alpha-tocopherol (AT) and ascorbic acid (AA) led to the hypothesis that using a combination of these antioxidants could be more beneficial than using a single antioxidant alone, particularly against smoke-related lung cancer. In this investigation, we have conducted an animal study to determine whether combined BC, AT and AA supplementation (AOX) protects against 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK)-induced lung carcinogenesis in smoke-exposed (SM) ferrets. Ferrets were treated for 6 months in the following four groups: (i) control, (ii) SM + NNK, (iii) AOX and (iv) SM + NNK + AOX. Results showed that the combined AOX supplementation (i) prevented the SM + NNK-decreased lung concentrations of retinoic acid (RA) and BC; (ii) inhibited the SM + NNK-induced phosphorylation of Jun N-terminal kinase (JNK), extracellular-signal-regulated protein kinase (ERK) and proliferating cellular nuclear antigen proteins in the lungs of ferrets; and (iii) blocked the SM + NNK-induced up-regulation of total p53 and Bax proteins, as well as phosphorylated p53 in the lungs of ferrets. In addition, there were no lesions observed in the lung tissue of ferrets in the control and/or the AOX groups after 6 months of intervention, but combined AOX supplementation resulted in a trend toward lower incidence of both preneoplastic lung lesions and lung tumor formation in SM + NNK + AOX group of ferrets, as compared with the SM + NNK group alone. These data indicate that combined AOX supplementation could be a useful chemopreventive strategy against lung carcinogenesis through maintaining normal tissue levels of RA and inhibiting the activation of mitogen-activated protein kinase pathways, cell proliferation and phosphorylation of p53.

7H-Dibenzo[c,g]carbazole and 5,9-dimethyldibenzo[c,g]carbazole exert multiple toxic events contributing to tumor promotion in rat liver epithelial 'stem-like' cells

Immature liver progenitor cells have been suggested to be an important target of hepatotoxins and hepatocarcinogens. The goal of the present study was to assess the impact of 7H-dibenzo[c,g]carbazole (DBC) and its tissue-specific carcinogenic N-methyl (N-MeDBC) and 5,9-dimethyl (DiMeDBC) derivatives on rat liver epithelial WB-F344 cells, in vitro model of liver progenitor cells. We investigated the cellular events associated with both tumor initiation and promotion, such as activation of aryl hydrocarbon receptor (AhR), changes in expression of enzymes involved in metabolic activation of DBC and its derivatives, effects on cell cycle, cell proliferation/apoptosis and inhibition of gap junctional intercellular communication (GJIC). N-MeDBC, a tissue-specific sarcomagen, was only a weak inhibitor of GJIC or inducer of AhR-mediated activity, and it did not affect either cell proliferation or apoptosis. DBC was efficient GJIC inhibitor, while DiMeDBC manifested the strongest AhR inducing activity. Accordingly, DiMeDBC was also the most potent inducer of cytochrome P450 1A1 (CYP1A1) and CYP1A2 expression among the three compounds tested. Both DBC and DiMeDBC induced expression of CYP1B1 and aldo-keto reductase 1C9 (AKR1C9). N-MeDBC failed to significantly upregulate CYP1A1/2 and it only moderately increased CYP1B1 or AKR1C9. Only the potent liver carcinogens, DBC and DiMeDBC, caused a significant increase of p53 phosphorylation at Ser15, an increased accumulation of cells in S-phase and apoptosis at micromolar concentrations. In addition, DiMeDBC was found to stimulate cell proliferation of contact-inhibited WB-F344 cells at 1 microM concentration, which is a mode of action that might further contribute to its hepatocarcinogenicity. The present data seem to suggest that the AhR activation, induction of enzymes involved in metabolic activation, inhibition of GJIC or stimulation of cell proliferation might all contribute to the hepatocarcinogenic effects of DBC and DiMeDBC.

The activation of ERK1/2 via a tyrosine kinase pathway attenuates trail-induced apoptosis in HeLa cells

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) serves as an extracellular signal that triggers apoptosis in tumor cells. To characterize the molecular events involved in TRAIL-induced apoptotic signaling, we investigated the role of extracellular signal-regulated kinase 1/2 (ERK1/2) in HeLa cell death. Here we show that TRAIL-activated ERK1/2 through a tyrosine kinase-dependent pathway, subsequently elevated anti-apoptotic Bcl-2 protein levels. ERK1/2 inhibition with PD98059 promoted apoptotic cell death through the downregulation of ERK1/2 activity and Bcl-2 protein levels. Moreover, tyrosine kinase inhibition with Genistein in TRAIL-induced apoptosis effectively attenuated ERK1/2 activity and enhanced apoptotic cell death. Taken together, our results indicate that ERK1/2 activation via tyrosine kinase pathway plays a protective role as the cellular defense mechanism through the upregulation of Bcl-2 protein levels in TRAIL-induced apoptosis.

Lycopene supplementation prevents smoke-induced changes in p53, p53 phosphorylation, cell proliferation, and apoptosis in the gastric mucosa of ferrets

Cigarette smoking increases the risk for gastric cancer. Higher intakes or blood levels of lycopene are associated with a decreased risk of gastric cancer. However, the biological mechanisms by which lycopene may protect against gastric carcinogenesis are poorly understood. We evaluated the effects of lycopene supplementation on smoke-induced changes in protein levels of p53, p53 target genes (p21(Waf1/Cip1) and Bax-1), cell proliferation, and apoptosis in the gastric mucosa of ferrets. Ferrets were assigned to cigarette smoke exposure or to no exposure and to no, low-dose, or high-dose lycopene supplementation (2 x 3 factorial design) for 9 wk. Lycopene concentrations were significantly elevated in a dose-dependent manner in the gastric mucosa of ferrets supplemented with lycopene alone, but were markedly reduced in ferrets supplemented with lycopene and exposed to smoke. Although ferrets were given lycopene containing 95% all-trans isomers, cis isomers were the predominant forms in the gastric mucosa. Total p53 and phosphorylated p53 levels were greater in ferrets exposed to smoke alone than in all other groups. Levels were approximately 300 and 500% of the controls, respectively. However, smoke-elevated total p53 and phosphorylated p53 were markedly attenuated by both doses of lycopene. p21(Waf1/Cip1), Bax-1, and cleaved caspase 3 were substantially decreased, whereas cyclin D1 and proliferating cellular nuclear antigen (PCNA) were increased in ferrets exposed to smoke alone. Lycopene prevented smoke-induced changes in p21(Waf1/Cip1), Bax-1, cleaved caspase 3, cyclin D1, and PCNA in a dose-dependent fashion. These data indicate that lycopene may prevent smoke exposure-induced changes in p53, p53 phosphorylation, p53 target genes, cell proliferation, and apoptosis in the gastric mucosa of ferrets.

The Course of Uncarinic Acid E-Induced Apoptosis of HepG2 Cells from Damage to DNA and p53 Activation to Mitochondrial Release of Cytochrome c

Uncarinic acid E, an active component isolated from Gelsemium elegans BENTH, has been reported to exhibit antitumor effects, but little is known about its molecular mechanisms of action. In this study, the growth-inhibitory activity of uncarinic acid E for HepG2 cells is in time- and dose-dependent manner. HepG2 cells treated with uncarinic acid E exhibited several typical characteristics of apoptosis through photomicroscopical observation, DNA agarose gel electrophoresis. The inhibitory effect of uncarinic acid E on HepG2 cells was partially reversed by the inhibitors of pan-caspase, caspase-3 and caspase-6. The protein expression ratio of Bcl-xL/Bax and Bcl-2/Bax was down-regulated and uncarinic acid E-induced apoptosis involves the initial phase mediated by the balance among Bcl-xL, Bcl-2 and Bax proteins, resulting in cytochrome c release from the mitochondria. Uncarinic acid E significantly increased the expression of p53 proteins indicates that p53 plays a pivotal role in the initiation phase of uncarinic acid E-induced HepG2 cell apoptosis. The phoshatidylinositol 3-kinase (PI3-K) family inhibitor wortmanin and the MEK inhibitor (PD98059) rescued the viability loss induced by uncarinic acid E through the expression of p53. Taken together, uncarinic acid E induces apoptosis in HepG2 cells via accumulation of p53, alters the Bax/Bcl-2 ratio, and activates caspases, resulting in cytochrome c release from the mitochondria.

G-protein-coupled OX1 orexin/hcrtr-1 hypocretin receptors induce caspase-dependent and -independent cell death through p38 mitogen-/stress-activated protein kinase

We have investigated the signaling of OX(1) receptors to cell death using Chinese hamster ovary cells as a model system. OX(1) receptor stimulation with orexin-A caused a delayed cell death independently of cytosolic Ca(2+) elevation. The classical mitogen-activated protein kinase (MAPK) pathways, ERK and p38, were strongly activated by orexin-A. p38 was essential for induction of cell death, whereas the ERK pathway appeared protective. A pathway often implicated in the p38-mediated cell death, activation of p53, did not mediate the cell death, as there was no stabilization of p53 or increase in p53-dependent transcriptional activity, and dominant-negative p53 constructs did not inhibit cell demise. Under basal conditions, orexin-A-induced cell death was associated with compact chromatin condensation and it required de novo gene transcription and protein synthesis, the classical hallmarks of programmed (apoptotic) cell death. However, though the pan-caspase inhibitor N-benzyloxycarbonyl-Val-Ala-Asp-(O-methyl)fluoromethyl ketone (Z-VAD-fmk) fully inhibited the caspase activity, it did not rescue the cells from orexin-A-induced death. In the presence of Z-VAD-fmk, orexin-A-induced cell death was still dependent on p38 and de novo protein synthesis, but it no longer required gene transcription. Thus, caspase inhibition causes activation of alternative, gene transcription-independent death pathway. In summary, the present study points out mechanisms for orexin receptor-mediated cell death and adds to our general understanding of the role of G-protein-coupled receptor signaling in cell death by suggesting a pathway from G-protein-coupled receptors to cell death via p38 mitogen-/stress-activated protein kinase independent of p53 and caspase activation.

A Low UVB Dose, with the Potential to Trigger a Protective p53-Dependent Gene Program, Increases the Resilience of Keratinocytes against Future UVB Insults

One protein central in the response of human keratinocytes to ultraviolet B damage is p53. By transactivating genes involved in either cell cycle arrest or DNA repair, p53 has a leading role in the recovery from this damage. Considering this role, we wished to investigate whether the triggering of a p53-dependent gene program by repetitive ultraviolet B (UVB) exposure can induce an adaptive response in human skin cells. In particular, we examined two p53-target genes, p21/WAF1 and p53R2, with a crucial role in p53-induced cell cycle arrest and p53-induced DNA repair respectively. Exposure to a mild UVB dose was able to induce an adaptive response in human keratinocytes, leading to increased survival of cells that maintain their capacity to repair DNA damage upon exposure to apoptotic doses of UVB. Our study indicates that this adaptation response is only achieved if the interval between subsequent UVB insults allows sufficient time for the p53-induced protective gene program to be induced. Our results also demonstrate that small but quickly recurring UVB exposures are as harmful as one intense, continual exposure to UVB irradiation. Future research will be oriented toward investigating alternative ways to induce an adaptive response without pre-exposing the cells to UV.

Attenuation of BPDE-induced p53 accumulation by TPA is associated with a decrease in stability and phosphorylation of p53 and downregulation of NFkappaB activation: role of p38 MAP kinase

DNA damage caused by benzo[a]pyrene (B[a]P) or other polynuclear hydrocarbons (PAHs) induce p53 protein as a protective measure to eliminate the possibility of mutagenic fixation of the DNA damage. 12-O-tetradecanoylphorbol-13-acetate (TPA) inhibits p53 response induced by B[a]P and other DNA-damaging agents and may cause tumor promotion. The molecular mechanism of attenuation of B[a]P-induced p53 response by TPA is not known. We investigated the effect of TPA on p53 response in (+/-)-anti-benzo[a]pyrene-7,8-diol-9,10-epoxide (BPDE)-treated mouse epidermal JB6(P(+)) Cl 41 cells. BPDE treatment induced p53 accumulation which was attenuated significantly by TPA. Cells treated with BPDE and TPA showed increased ratio of Mdm2 to p53 proteins in p53 immunoprecipitate and decreased p53 life span compared to BPDE-treated cells indicating p53 destabilization by TPA. TPA also inhibited BPDE-induced p53 phosphorylation at serine15. Activation of both ERKs and p38 MAPK by BPDE and attenuation of BPDE-induced p53 accumulation by U0126 or SB202190, specific inhibitor of MEK1/2 or p38 MAPK, indicate the role of ERKs and p38 MAPK in p53 accumulation. Interestingly, TPA potentiated BPDE-induced activation of ERKs whereas p38 MAPK activation was significantly inhibited by TPA, suggesting that inhibition of p38 MAPK is involved in p53 attenuation by TPA. Furthermore, SB202190 treatment caused decreased p53 stability and inhibition of phosphorylation of p53 at serine15 in BPDE-treated cells. We also observed that TPA or SB202190 attenuated BPDE-induced nuclear factor kappa B (NFkappaB) activation in JB6 Cl 41 cells harboring NFkappaB reporter plasmid. To our knowledge this is the first report that TPA inhibits chemical carcinogen-induced NFkappaB activation. Interference of TPA with BPDE-induced NFkappaB activation implicates abrogation of p53 function which has been discussed. Overall, our data suggest that abrogation of BPDE-induced p53 response and of NFkappaB activation by TPA is mediated by impairment of the signaling pathway involving p38 MAPK.

Chronically increased oxidative stress in fibroblasts from Alzheimer's disease patients causes early senescence and renders resistance to apoptosis by oxidative stress

It is well established that oxidative stress is involved in several neurodegenerative disorders, including Alzheimer's disease (AD). Study of the induction and consequences of oxidative stress in the peripheral tissues of the familial AD patients can help to elucidate the inherent abnormalities and the mechanism of pathogenesis of this disease. AD fibroblasts have been used as a model to investigate the underlying mechanisms of oxidative stress. In our study, we used AD fibroblasts from six different donors who are either at high risk of developing AD or have already been diagnosed with AD to study the effect of oxidative stress in comparison with the effect on non-AD normal human fibroblast. Oxidative stress was induced by a brief exposure of the cells to 250microM H(2)O(2) followed by incubation in normal conditions. Neuronal loss due to oxidative stress is a characteristic of Alzheimer's patients; however, our results showed that AD fibroblasts were more resistant to oxidative stress compared to non-AD fibroblasts. Measurement of reactive oxygen species (ROS) indicated that AD fibroblasts produced more ROS than did non-AD NHF cells either in basal conditions or after induction of oxidative stress. Furthermore, we found that expression of p21 was significantly higher in AD cells than in non-AD cells and expression of Bax, a pro-apoptotic protein was downregulated/absent in AD cells during normal or under conditions of external oxidative stress. Further experiments revealed that mitochondria in AD cells moved to the peri-nuclear region following induction of oxidative stress. Thus, these results suggest that AD fibroblasts are chronically exposed to oxidative stress that may trigger senescent phenotype, making AD cell resistant to apoptosis by external oxidative stress.

Involvement of the extracellular signal-regulated protein kinase pathway in phosphorylation of p53 protein and exerting cytotoxicity in human neuroblastoma cells (SH-SY5Y) exposed to acrylamide

Using human neuroblastoma SH-SY5Y cells, effects of acrylamide on p53 protein and intracellular signal transducting pathways were examined. Acrylamide increased p53, phosphorylated p53, and p53-associated protein murine double minute 2 (MDM2). The phosphorylation of p53 was specific for the Ser15 site. Among mitogen-activated protein kinases (MAPKs), acrylamide caused phosphorylation of extracellular signal-regulated protein kinase (ERK) and p38 but not c-Jun NH(2)-terminal kinase. Nevertheless, blocking p38 pathway by LL-Z1640-2 did not suppress the phosphorylation of p53 at Ser15. In contrast, a specific inhibitor of ERK kinase (U0126 or PD98059) could abolish the accumulation as well as the phosphorylation of p53 at Ser15. Elevation of MDM2 was also abolished by U0126. An inhibitor of phosphatidylinositol 3-kinase-related kinase (PIKK) pathway (wortmannin) suppressed the increase of p53 and its phosphorylation at Ser15. Hence, acrylamide increases p53 protein and its phosphorylation at Ser15 through ERK and/or PIKK pathways. On the other hand, U0126 and PD98059 suppressed to some extent the cytotoxicity of acrylamide evaluated by trypan blue exclusion and lactate dehydrogenase (LDH) leakage, whereas neither LL-Z1640-2 nor wortmannin was effective in suppressing the toxicity. Thus, ERK pathway seems to play a role both in causing the phosphorylation of p53 at Ser15 and in the cytotoxicity of acrylamide in SH-SY5Y cells.

Protein kinase C delta induces apoptosis of vascular smooth muscle cells through induction of the tumor suppressor p53 by both p38-dependent and p38-independent mechanisms

Apoptotic death of vascular smooth muscle cells (SMCs) is a prominent feature of blood vessel remodeling. In the present study, we examined the novel PKC isoform protein kinase C delta (PKCdelta) and its role in vascular SMC apoptosis. In A10 SMCs, overexpression of PKCdelta was sufficient to induce apoptosis, whereas inhibition of PKCdelta diminished H2O2-induced apoptosis. Moreover, evidence is provided that the tumor suppressor p53 is an essential mediator of PKCdelta-induced apoptosis in SMCs. Activation of PKCdelta led to accumulation as well as phosphorylation of p53 in SMCs; this induction correlated with apoptosis. Furthermore, blocking p53 induction with small interference RNA or targeted gene deletion prevented PKCdelta-induced apoptosis, whereas restoring p53 expression rescued the ability of PKCdelta to induce apoptosis in p53 null SMCs. We also establish that PKCdelta regulates p53 at both transcriptional and post-translational levels. Specifically, the transcriptional regulation required p38 MAPK, whereas the post-translational modification, at least for serine 46, did not involve MAPK. Additionally, PKCdelta, p38 MAPK, and p53 co-associate in cells under conditions favoring apoptosis. Together, our data suggest that SMC apoptosis proceeds through a pathway that involves PKCdelta, the intermediary p38 MAPK, and the downstream target tumor suppressor p53.

The effect of ultraviolet (UV) A1, UVB and solar-simulated radiation on p53 activation and p21

BACKGROUND

High-dose ultraviolet (UV) A1 therapy (doses in the order of 130 J cm(-2)) is effective for atopic dermatitis and scleroderma. UVA1 has been shown to induce a dose-dependent increase in p53 expression in keratinocytes.

OBJECTIVES

To examine the effect of UVA1 on the activation of p53 by phosphorylation, which has not yet been studied.

METHODS

Five adult volunteers were exposed to dose series of UVA1 (10-100 J cm(-2)) and, for comparison, narrowband UVB (TL-01) (25-550 mJ cm(-2)) and solar-simulated radiation (SSR) (5.6-30 J cm(-2)) on photoprotected buttock skin and the minimal erythema dose (MED) for each was determined at 24 h. Separate sites on the buttock were subsequently irradiated with a 3-MED dose of UVA1, TL-01 and SSR. At 24 h, punch biopsies (4 mm) were taken from each irradiated site and from an adjacent unirradiated control site, and immunohistochemical staining for p53 (Do-1), activation of p53 (assessed by phosphorylation at serine 15 and serine 392) and p21 was performed. Cell staining was expressed as the mean number of cells stained per three high-power fields (HPFs) and as a percentage of 1000 cells. Sunburn cells (SBCs) were also counted per HPF.

RESULTS

UVA1 produced negligible numbers of SBCs, relatively little p53 (Do-1) staining (mean +/- SD cell count per HPF 16 +/- 10), no p53 activation and very little evidence of p21 expression (mean +/- SD cell count per HPF 5.3 +/- 7), in contrast to TL-01 (mean +/- SD cell count per HPF of 11.83 +/- 2.1 SBCs, 146.3 +/- 38 for Do-1, 26.6 +/- 15 for serine 15, 14.9 +/- 12 for serine 392 and 77.9 +/- 30 for p21) or SSR irradiation (mean +/- SD cell count per HPF of 3.5 +/- 1.2 SBCs, 147.5 +/- 62 for Do-1, 54 +/- 50 for serine 15, 38.9 +/- 18 for serine 392 and 56.7 +/- 30 for p21).

CONCLUSIONS

These data indicate that there are fundamental differences in the effects of UVA1 on p53 and its activation pathways compared with TL-01 and SSR, and may in part explain the differential effects of these phototherapies.

Influenza virus infection increases p53 activity: role of p53 in cell death and viral replication

The induction of apoptotic cell death is a hallmark of influenza virus infection. Although a variety of cellular and viral proteins have been implicated in this process, to date no conserved cellular pathway has been identified. In this study, we report that the tumor suppressor protein p53 is essential for the induction of cell death in influenza virus-infected cells. In primary human lung cells, influenza virus increased p53 protein levels. This was also noted in the human lung cell line A549, along with the up-regulation of p53-dependent gene transcription. Reduction of p53 activity in A549 cells inhibited influenza virus-induced cell death as measured by trypan blue exclusion and caspase activity. These findings were not cell type specific. Influenza virus-induced cell death was absent in mouse embryo fibroblasts isolated from p53 knockout mice, which was not the case in wild-type mouse embryo fibroblasts, suggesting that p53 is a common cellular pathway leading to influenza virus-induced cell death. Surprisingly, inhibiting p53 activity led to elevated virus replication. Mechanistically, this may be due to the decrease in interferon signaling in p53-deficient cells, suggesting that functional p53 is involved in the interferon response to influenza infection. To our knowledge, these are the first studies demonstrating that p53 is involved in influenza virus-induced cell death and that inhibiting p53 leads to increased viral titers, potentially through modulation of the interferon response.

Ras-ERK MAPK cascade regulates GATA3 stability and Th2 differentiation through ubiquitin-proteasome pathway

Differentiation of naive CD4 T cells into Th2 cells requires protein expression of GATA3. Interleukin-4 induces STAT6 activation and subsequent GATA3 transcription. Little is known, however, on how T cell receptor-mediated signaling regulates GATA3 and Th2 cell differentiation. Here we demonstrated that T cell receptor-mediated activation of the Ras-ERK MAPK cascade stabilizes GATA3 protein in developing Th2 cells through the inhibition of the ubiquitin-proteasome pathway. Mdm2 was associated with GATA3 and induced ubiquitination on GATA3, suggesting its role as a ubiquitin-protein isopeptide ligase for GATA3 ubiquitination. Thus, the Ras-ERK MAPK cascade controls GATA3 protein stability by a post-transcriptional mechanism and facilitates GATA3-mediated chromatin remodeling at Th2 cytokine gene loci leading to successful Th2 cell differentiation.

The PI3K inhibitor LY294002 prevents p53 induction by DNA damage and attenuates chemotherapy-induced apoptosis

The p53 tumor suppressor plays a key role in the natural protection against cancer. Activation of p53 by DNA-damaging agents can contribute to successful elimination of cancer cells via chemotherapy-induced apoptosis. The phosphatidylinositol-3 kinase (PI3K) pathway, triggered in normal cells upon exposure to growth factors, regulates a cascade of proliferation and survival signals. The PI3K pathway is abnormally active in many cancers, thus making it an attractive target for inactivation in an attempt to achieve better cancer therapy. We report here that exposure to LY294002, a potent PI3K inhibitor, aborts the activation of p53 by several drugs commonly used in cancer chemotherapy. Concomitantly, LY294002 attenuates p53-dependent, chemotherapy-induced apoptosis of cancer cells. These findings invoke an unexpected positive role for PI3K in p53 activation by anticancer agents, and suggest that the efficacy of PI3K inhibitors in cancer therapy may be greatly affected by the tumor p53 status.