Biomedical subjects

Zigang Dong

Publications and source records attributed to Zigang Dong.

66 records · Page 4Linked to original sources

PubMed2002

Harvesting cells under anchorage-independent cell transformation conditions for biochemical analyses.

Most molecular biology and biochemical analyses use cultured cells grown in anchorage-dependent monolayer conditions. The standard oncogenic transformation assay for cell lines is usually performed in soft agar rather than in monolayers because of the higher transformation efficiency of cells in soft agar. However, cells suspended in soft agar cannot be readily recovered for studying inducible biochemical and molecular events. We developed an over-agar assay that enables us to study tumor promoter-induced cell transformation and the associated biochemical or molecular events under anchorage-independent conditions.

Agar↗

PubMed2002

Differential gene expression profiles of Jnk1- and Jnk2-deficient murine fibroblast cells.

c-Jun NH(2)-terminal kinase (JNK) 1 and JNK2 have been assumed to complement each other and mediate the same or similar biological functions. However, our recent reports indicated that 7,12-dimethylbenz(a)anthracene/12-O-tetradecanoylphorbol-13-acetate-induced tumor development is suppressed in Jnk2 knockout mice but enhanced in Jnk1 knockout mice. In the present work, primary embryo cells were isolated from wild-type, Jnk1(-/-) and Jnk2(-/-) mice and used for cDNA microarray analysis. The patterns of gene expression in Jnk1(-/-), Jnk2(-/-), and wild-type cells are different. After 12-O-tetradecanoylphorbol-13-acetate treatment, the changes in the gene expression profiles in three different kinds of cells appear to agree with the differences in susceptibility to tumorigenesis of each respective animal model. These results suggest that JNK1 and JNK2 proteins have different roles in modulating cell function.

Animals↗

PubMed2002

Deficiency of c-Jun-NH(2)-terminal kinase-1 in mice enhances skin tumor development by 12-O-tetradecanoylphorbol-13-acetate.

The c-Jun NH(2)-terminal kinase (JNK) has been implicated in regulating cell survival, apoptosis, and transformation. However, the distinct role of JNK isoforms in regulating tumor development is not yet clear. We have found previously that skin tumor formation induced by the tumor promoter, 12-O-tetradecanoylphorbol-13-acetate (TPA), is suppressed in JNK2-deficient (Jnk2(-/-)) mice. Here, we show that JNK1-deficient (Jnk1(-/-)) mice are more susceptible to TPA-induced skin tumor development than wild-type mice. The rate of tumor development in Jnk1(-/-) mice was significantly more rapid than that observed in wild-type mice (P < 0.0001). At the end of 33 weeks of TPA promotion, the number of skin tumors and tumors >1.5 mm in diameter per mouse in Jnk1(-/-) mice was significantly increased by 71% (P < 0.03) and 82% (P < 0.03), respectively, relative to the wild-type mice. Furthermore, the carcinoma incidence and the number of carcinomas per mouse were also higher in Jnk1(-/-) mice. Strikingly, Jnk1(-/-) mouse skin was more sensitive to TPA-induced AP-1 DNA binding activity and phosphorylation of extracellular signal-regulated kinases and Akt, which are two important survival signaling components. These results suggest that JNK1 is a crucial suppressor of skin tumor development.

Animals↗

PubMed2002

Role of MAP kinases in UVB-induced phosphorylation of p53 at serine 20.

Phosphorylation of the p53 tumor suppressor protein is one of the key regulatory steps in its activation process. Serine 20 phosphorylation of p53 has been shown to be required for the activation of p53 following UV radiation, but the signaling pathway mediating UV-induced phosphorylation is unknown. Here, we determined the role of MAP kinases in UVB-induced phosphorylation and found that JNKs are directly involved in the phosphorylation of p53 at serine 20. In a mouse JB6 epidermal cell line, dominant negative JNK1 abrogated UVB-induced phosphorylation of p53 at serine 20, whereas dominant negative p38 kinase or its inhibitor, SB202190, partially attenuated the phosphorylation. In contrast, dominant negative ERK2 or the MEK1 inhibitor, PD98059, had no effect on p53 phosphorylation at serine 20. Importantly, UVB-activated or active recombinant JNK1/2, or the p38 kinase downstream target, MAPKAPK-2, but not ERKs or p38 kinase, phosphorylated p53 at serine 20 in vitro. Furthermore, phosphorylation of p53 at serine 20 by UVB-activated JNKs and UVB-induced p53-dependent transcriptional activity were suppressed in Jnk1 or Jnk2 knockout (Jnk1(-/-) or Jnk2(-/-)) cells. Additionally, Jnk1(-/-), Jnk2(-/-), and p53-deficient (p53(-/-)) cells, as well as re-introduction of a p53 mutant with substitution of serine 20 to alanine into p53(-/-) cells, were defective for UVB-induced apoptosis. These findings strongly suggest that JNKs are the major direct signaling mediators of UVB-induced p53 phosphorylation at serine 20.

Animals↗

PubMed2002

Phosphorylation of 4E-BP1 is mediated by the p38/MSK1 pathway in response to UVB irradiation.

In resting cells, eIF4E-binding protein 1 (4E-BP1) binds to the eukaryotic initiation factor-4E (eIF-4E), preventing formation of a functional eIF-4F complex essential for cap-dependent initiation of translation. Phosphorylation of 4E-BP1 dissociates it from eIF-4E, relieving the translation block. Studies suggested that insulin- or growth factor-induced 4E-BP1 phosphorylation is mediated by phosphatidylinositol 3-kinase (PI3-kinase) and its downstream protein kinase, Akt. In the present study we demonstrated that UVB induced 4E-BP1 phosphorylation at multiple sites, Thr-36, Thr-45, Ser-64, and Thr-69, leading to dissociation of 4E-BP1 from eIF-4E. UVB-induced phosphorylation of 4E-BP1 was blocked by p38 kinase inhibitors, PD169316 and SB202190, and MSK1 inhibitor, H89, but not by mitogen-activated protein kinase kinase inhibitors, PD98059 or U0126. The PI3-kinase inhibitor, wortmannin, did not block UVB-induced 4E-BP1 phosphorylation, but blocked both UVB- and insulin-induced activation of PI3-kinase and phosphorylation of Akt. 4E-BP1 phosphorylation was blocked in JB6 Cl 41 cells expressing a dominant negative p38 kinase or dominant negative MSK1, but not in cells expressing dominant negative ERK2, JNK1, or PI3-kinase p85 subunit. Our results suggest that UVB induces phosphorylation of 4E-BP1, leading to the functional dissociation of 4E-BP1 from eIF-4E. The p38/MSK1 pathway, but not PI3-kinase or Akt, is required for mediating the UVB-induced 4E-BP1 phosphorylation.

Androstadienes↗

PubMed2002

Involvement of c-jun NH(2)-terminal kinases in resveratrol-induced activation of p53 and apoptosis.

Resveratrol, a constituent of grapes and other foods, is one of the most promising agents for cancer prevention. In a previous study, we showed that the antitumor activity of resveratrol occurs through extracellular signal-regulated protein kinases (ERKs) and p38 kinase-mediated p53 activation. In this study, we also determined that c-jun NH(2)-terminal kinases (JNKs) are involved in resveratrol-induced p53 activation and induction of apoptosis. In the JB6 mouse epidermal cell line, resveratrol activated JNKs dose-dependently within a dose range of 10-40 microM, the same dosage responsible for the inhibition of tumor promoter-induced cell transformation. Stable expression of a dominant negative mutant of JNK1 or disruption of the Jnk1 or Jnk2 gene markedly inhibited resveratrol-induced p53-dependent transcription activity and induction of apoptosis. Furthermore, resveratrol-activated JNKs were shown to phosphorylate p53 in vitro, but this activity was repressed in the cells expressing a dominant negative mutant of JNK1 or in Jnk1 or Jnk2 knockout (Jnk1(-/-) or Jnk2(-/-)) cells. These data suggested that JNKs act as mediators of resveratrol-induced activation of p53 and apoptosis, which may occur partially through p53 phosphorylation.

Angiogenesis Inhibitors↗

PubMed2002

The paradox of arsenic: molecular mechanisms of cell transformation and chemotherapeutic effects.

Arsenic is a well-documented carcinogen that also appears to be a valuable therapeutic tool in cancer treatment. This creates a paradox for which no unified hypothesis has been reached regarding the molecular mechanisms that determine whether arsenic will act as a carcinogen or as an effectual chemotherapeutic agent. Much of our knowledge with respect to the actions of arsenic has been drawn from epidemiological or clinical studies. The actions of arsenic are likely to be related to cell type, arsenic species, and length and dose of exposure. Arsenic unquestionably induces apoptosis and may specifically target certain tumor cells. Research data strongly suggest that arsenic influences distinct signaling pathways involved in mediating proliferation or apoptosis, including mitogen-activated protein kinases, p53, activator protein-1 or nuclear factor kappa B. The primary purpose of this review is to examine recent findings, from this laboratory and others, that focus on the molecular mechanisms of arsenic's actions in cell transformation and as a therapeutic agent.

Animals↗

PubMed2002

The molecular mechanisms of arsenic-induced cell transformation and apoptosis.

Arsenic is a well-documented human carcinogen associated with cancers of the skin, lung, liver, and bladder. Interestingly, arsenic has also been used as an effective chemotherapeutic agent in the treatment of certain human cancers. However, the mechanisms by which arsenic induces proliferation of cancer cells or cancer cell death are not well understood. We found that exposure of JB6 P+ cells to low concentrations of arsenic induces cell transformation, whereas higher concentrations of arsenic induce cell apoptosis. Arsenite induces phosphorylation of extracellular signal-regulated protein kinases (Erks) and c-Jun NH(2)-terminal kinases (JNKs). Arsenite-induced Erk activation was markedly inhibited by introduction of dominant-negative Erk2 into cells, whereas expression of dominant-negative Erk2 did not inhibit JNKs or mitogen-activated protein kinase Erk kinase 1/2. Furthermore, arsenite-induced cell transformation was blocked in cells expressing dominant-negative Erk2. In contrast, overexpression of dominant-negative JNK1 increased cell transformation even though it inhibited arsenite-induced JNK activation. Arsenic also induced AP-1 and nuclear factor kappa B (NF-kappaB) activation. Blocking NF-kappaB activation by dominant-negative inhibitory kappa Balpha inhibited arsenic-induced apoptosis and enhanced arsenic-induced cell transformation. Arsenic induced activation of JNKs at a similar dose range that was effective for induction of apoptosis in JB6 cells. In addition, we found that arsenic did not induce p53-dependent transactivation. Similarly, apoptosis induction was not different between p53 wild-type (p53(+/+)) or p53-deficient (p53(-/-)) cells. In contrast, arsenic-induced apoptosis was almost totally blocked by expression of a dominant-negative mutant of JNK. Taken together with previous findings that p53 mutations are involved in approximately 50% of all human cancers and nearly all chemotherapeutic agents kill cancer cells mainly by apoptotic induction, we suggest that arsenic may be a useful agent for the treatment of cancers with p53 mutations. These results suggest that the activation of Erks is required for arsenic-induced cell transformation, whereas the activation of JNKs and NF-kappaB is involved in arsenic-induced apoptosis of JB6 cells.

Animals↗

PubMed2002

Inhibitory effects of sodium salicylate and acetylsalicylic acid on UVB-induced mouse skin carcinogenesis.

We conducted an in vivo carcinogenesis experiment to determine the efficacy of topical aspirin and sodium salicylate (NAS) in preventing UVB-induced nonmelanoma skin cancer. Hairless SKH-1 mice were randomly divided into eight treatment groups. They were treated topically with either 40 or 10 micromol aspirin or NAS three times weekly before 9 kJ/m(2) UVB irradiation. The experiment was carried out over 25 weeks. Both dose levels of NAS significantly inhibited (P < 0.05) the rate of tumor formation when compared with vehicle control. The 40 micromol dose of aspirin significantly inhibited the rate of tumor formation (P < 0.05), whereas the 10 micromol dose had no inhibitory effect when compared with the vehicle control. To investigate the mechanism of this inhibition, we studied UVB-induced thymine dimer formation in the epidermis of the mouse skin. We found that NAS inhibited UVB-induced thymine dimer formation (P = 0.0001), whereas aspirin did not. Therefore, we conclude that NAS prevents UVB-induced tumor growth and formation through a sunscreen effect; whereas, the moderate inhibition of aspirin may be because of a molecular event, such as the inhibition of various UVB signaling pathways.

Administration, Topical↗

PubMed2001

Requirement of ATM in UVA-induced signaling and apoptosis.

Solar UVA, but not UVC, reaches the earth's surface and therefore is an important etiological factor for the induction of human skin cancer. ATM kinase is an important regulator of cell survival and cell cycle checkpoints. Here, we observe that UVA, unlike UVC, triggers ATM kinase activity, and the activation may occur through reactive oxygen species produced after irradiation of cells with UVA. We also show that ATM activation is involved in the apoptotic response to UVA but not UVC. Furthermore, we provide evidence that ATM-dependent p53 and c-Jun N-terminal kinase (JNK) pathways are linked to UVA-induced apoptosis. On the other hand, UVC-induced apoptosis occurs through ATR-dependent p53 phosphorylation as well as the JNK pathway. Therefore, these results suggest that ATM, like p53, is involved in the UVA-induced apoptosis to suppress carcinogenesis.

Animals↗

PubMed2000

Apoptosis induction by arsenic: mechanisms of action and possible clinical applications for treating therapy-resistant cancers.

Arsenic, a known carcinogen, may be useful in cancer treatment. Arsenic may be effective in counteracting drug resistance because it appears to induce apoptosis in tumor cells independently of p53 activation, thereby allowing it to be directed against p53-defective cancers. The role of MAP kinases in arsenic-induced apoptosis in tumor cells is important and may be influenced by reactive oxygen species or glutathione. This review focuses on recent findings from this and other laboratories regarding the mechanism(s) of arsenic-induced apoptosis in tumor cells and considers their relevance in the clinical treatment of therapy-resistant cancers. Copyright 2000 Harcourt Publishers Ltd.

Journal Article↗

PubMedDate not supplied

Molecular mechanism of the chemopreventive effect of resveratrol.

Chemoprevention is a promising approach to control human cancer. Resveratrol has been shown to have a potent chemopreventive effect in multiple carcinogenesis models. However, the precise mechanism explaining its anti-carcinogenic effect is not clear. This review summarizes recent studies from our laboratory on the mechanisms of resveratrol's effects. In JB6 cells, resveratrol was found to induce apoptosis and inhibit tumor promoter-induced cell transformation. We also found that resveratrol-induced activation of p53 and resveratrol-induced apoptosis occurred through a p53-dependent pathway. The MAP kinases, ERKs, JNKs, or p38 kinases, are involved in resveratrol-induced activation of p53 and apoptosis.

Animals↗