Huijun Zhu

Publications (6)25.19 Total impact

• Article: The cooked meat carcinogen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine activates the extracellular signal regulated kinase mitogen-activated protein kinase pathway.

  Stuart K Creton, Huijun Zhu, Nigel J Gooderham
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  ABSTRACT: During the cooking of meat, mutagenic and carcinogenic heterocyclic amines are formed, the most abundant of which, 2-amino-1-methyl-6-phenylimidazo[4-5-b]pyridine (PhIP), induces tumors of the prostate, colon, and mammary gland in rats. Humans consuming cooked meat are exposed to PhIP on a daily basis, yet few studies have assessed the effects of PhIP at dietary relevant concentrations. In addition to its genotoxic properties, recent studies have shown that PhIP can activate estrogen receptor-mediated signaling pathways at doses that are similar to those that may be present in the body following consumption of a cooked meat meal. In the present study, we examined whether such doses of PhIP can affect estrogen receptor-independent signal transduction via the mitogen-activated protein kinase (MAPK) extracellular signal-related kinase (ERK) pathway to influence proliferation and migration in the human mammary epithelial cell line MCF10A and the prostate cancer cell line PC-3. At doses shown to have a proliferative effect on MCF10A cells (10(-11)-10(-7) mol/L), PhIP induced a rapid, transient increase in phosphorylation of both MAPK/ERK kinase 1/2 and ERKs. Inhibition of this pathway significantly reduced the PhIP-induced proliferation of MCF10A cells and the migration of PC-3 cells. The data presented here show that levels of PhIP that approximate to human dietary exposure stimulate cellular signaling pathways and result in increased growth and migration, processes linked to the promotion and progression of neoplastic disease. These findings provide strong evidence that PhIP acts as a tumor initiator and promoter and that dietary exposure to this compound could contribute to carcinogenesis in humans.
  Cancer Research 01/2008; 67(23):11455-62. · 7.86 Impact Factor
• Article: Mechanisms of induction of cell cycle arrest and cell death by cryptolepine in human lung adenocarcinoma a549 cells.

  Huijun Zhu, Nigel J Gooderham
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  ABSTRACT: We investigated p53-dependent and -independent molecular events associated with cell cycle alteration and cell death in human lung adenocarcinoma A549 cells using cryptolepine, a DNA-damaging agent. After a 24-h treatment, cryptolepine caused an accumulation of p53 at concentrations of 1.25-10 microM and induction of p21(Cip1/WAF1) but only at concentrations up to 5muM. p21(Cip1/WAF1) was also strongly induced by cryptolepine (2.5-5 microM) in cells with p53 largely ablated via small interfering RNA-mediated gene silencing. Cryptolepine induced G1-phase block at 1.25-2.5 microM, S-phase and G2/M-phase block at 2.5-5 microM, and cell death at 10 microM. The dead cells displayed condensed and fragmented nuclei, features of apoptosis. Wortmannin, an inhibitor of ataxia telangiectasia-mutated and DNA-dependent protein kinase (DNA-PK), caused cell cycle arrest at G1 phase without inducing p53 and p21(Cip1/WAF1) expression and cell death. The addition of wortmannin partially prevented cryptolepine-induced expression of p53 and p21(Cip1/WAF1) together with the S-phase block and sensitized cells to induction of cell death. NU7026, a DNA-PK-specific inhibitor, showed neither induction of cell cycle arrest and apoptosis nor the expression of p53 and p21(Cip1/WAF1). The presence of NU7026 caused further reduction of cells in G1 phase induced by cryptolepine at 5 microM without affecting the induction of p53 and p21(Cip1/WAF1) and cell death. This study using the A549 cell as a model demonstrated that cryptolepine selects different molecular pathways to cell cycle checkpoint activation in a dose-specific manner and evokes a wortmannin-sensitive antiapoptosis response.
  Toxicological Sciences 06/2006; 91(1):132-9. · 4.65 Impact Factor
• Source

  Available from: PubMed Central

  Article: Responses of genes involved in cell cycle control to diverse DNA damaging chemicals in human lung adenocarcinoma A549 cells.

  Huijun Zhu, Catherine Smith, Charles Ansah, Nigel J Gooderham
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  ABSTRACT: Many anticancer agents and carcinogens are DNA damaging chemicals and exposure to such chemicals results in the deregulation of cell cycle progression. The molecular mechanisms of DNA damage-induced cell cycle alteration are not well understood. We have studied the effects of etoposide (an anticancer agent), cryptolepine (CLP, a cytotoxic alkaloid), benzo [a]pyrene (BaP, a carcinogenic polycyclic aromatic hydrocarbon) and 2-amino-1-methyl-6-phenylimidazo [4,5-b]pyridine (PhIP, a cooked-meat derived carcinogen) on the expression of cell cycle regulatory genes to understand the molecular mechanisms of the cell cycle disturbance. A549 cells were treated with DMSO or chemicals for up to 72 h and periodically sampled for cell cycle analysis, mRNA and protein expression. DMSO treated cells showed a dominant G1 peak in cell cycle at all times examined. Etoposide and CLP both induced G2/M phase arrest yet the former altered the expression of genes functioning at multiple phases, whilst the latter was more effective in inhibiting the expression of genes in G2-M transition. Both etoposide and CLP induced an accumulation of p53 protein and upregulation of p53 transcriptional target genes. Neither BaP nor PhIP had substantial phase-specific cell cycle effect, however, they induced distinctive changes in gene expression. BaP upregulated the expression of CYP1B1 at 6-24 h and downregulated many cell cycle regulatory genes at 48-72 h. By contrast, PhIP increased the expression of many cell cycle regulatory genes. Changes in the expression of key mRNAs were confirmed at protein level. Our experiments show that DNA damaging agents with different mechanisms of action induced distinctive changes in the expression pattern of a panel of cell cycle regulatory genes. We suggest that examining the genomic response to chemical exposure provides an exceptional opportunity to understand the molecular mechanism involved in cellular response to toxicants.
  Cancer Cell International 09/2005; 5:28. · 1.97 Impact Factor
• Article: Responses of genes involved in cell cycle control to diverse DNA damaging chemicals in human lung adenocarcinoma A549 cells

  Huijun Zhu, Catherine Smith, Charles Ansah, Nigel Gooderham
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  ABSTRACT: Abstract Background Many anticancer agents and carcinogens are DNA damaging chemicals and exposure to such chemicals results in the deregulation of cell cycle progression. The molecular mechanisms of DNA damage-induced cell cycle alteration are not well understood. We have studied the effects of etoposide (an anticancer agent), cryptolepine (CLP, a cytotoxic alkaloid), benzo [a]pyrene (BaP, a carcinogenic polycyclic aromatic hydrocarbon) and 2-amino-1-methyl-6-phenylimidazo [4,5-b]pyridine (PhIP, a cooked-meat derived carcinogen) on the expression of cell cycle regulatory genes to understand the molecular mechanisms of the cell cycle disturbance. Results A549 cells were treated with DMSO or chemicals for up to 72 h and periodically sampled for cell cycle analysis, mRNA and protein expression. DMSO treated cells showed a dominant G1 peak in cell cycle at all times examined. Etoposide and CLP both induced G2/M phase arrest yet the former altered the expression of genes functioning at multiple phases, whilst the latter was more effective in inhibiting the expression of genes in G2-M transition. Both etoposide and CLP induced an accumulation of p53 protein and upregulation of p53 transcriptional target genes. Neither BaP nor PhIP had substantial phase-specific cell cycle effect, however, they induced distinctive changes in gene expression. BaP upregulated the expression of CYP1B1 at 6–24 h and downregulated many cell cycle regulatory genes at 48–72 h. By contrast, PhIP increased the expression of many cell cycle regulatory genes. Changes in the expression of key mRNAs were confirmed at protein level. Conclusion Our experiments show that DNA damaging agents with different mechanisms of action induced distinctive changes in the expression pattern of a panel of cell cycle regulatory genes. We suggest that examining the genomic response to chemical exposure provides an exceptional opportunity to understand the molecular mechanism involved in cellular response to toxicants.
  Cancer Cell International. 01/2005;
• Article: Molecular and genetic toxicology of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP).

  Nigel J Gooderham, Huijun Zhu, Sandra Lauber, Antony Boyce, Stuart Creton
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  ABSTRACT: The heterocyclic amine 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), formed when meat containing food is cooked, induces cancer of the colon, prostate and mammary gland of rats, tumours that are strongly associated with a Western diet. After consumption of a meat meal, PhIP is rapidly absorbed, metabolised and bioactivated to DNA damaging species. Thus, PhIP should be considered as a candidate etiological agent for human cancer. Studies in vitro in model mammalian cell culture systems, and in vivo in transgenic animals, have shown that mutation induced by PhIP is dose dependent and describes a mutational "fingerprint" that is characteristic of the chemical. This genetic toxicity is dependent upon CYP1 family metabolic activation and is detectable in these model systems at micro M concentrations. At early time points, PhIP treated cells show subtle signs of toxicity that lead to altered growth and cycling. Using co-culture systems where one cell line bioactivates PhIP with a second cell line as target, we showed in human lymphoblastoid target cells that PhIP induced a dose- and time-dependent S-phase delay of the cell cycle. With time, the cell population became increasingly apoptotic with remaining survivors carrying a mutated gene set. Transcript profiling of treated cells indicated differential expression of genes involved in cell cycle regulation, stress response, receptors and tumour related genes. Prominent was elevation of p21(cip1/waf1) transcript and Western blot analysis confirmed induction of p21(cip1/waf1) and p53 proteins. The dose dependency and temporal aspects of these changes indicate that manipulation of the cell cycle and growth in response to PhIP is a precursor to mutant selection. Reduction of the PhIP dose allows dissection of a different battery of cellular responses that favour cell growth rather than inhibition. This pro-growth stimulus is oestrogen-like and encompasses altered gene expression, proliferation and cell behaviour. In human breast cell lines, these PhIP-mediated pro-oestrogenic responses are inhibited by the anti-oestrogen ICI 182780. This range of molecular and genetic responses induced in cells by PhIP is quite remarkable. Its ability to activate S-phase cell cycle checkpoint, alter gene expression leading to apoptosis and an increased frequency of mutation are probably direct consequences of its genetic toxicity. In contrast, its pro-oestrogenic activity is likely to be a driver of clonal expansion. We suggest that these PhIP-induced genomic and cellular events contrive to manipulate cell cycle and survival. Understanding these molecular processes as well as the genetic toxicology of the chemical will help to define the involvement of PhIP in carcinogenesis and shed light upon its tissue specificity.
  Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis 10/2002; 506-507:91-9. · 2.85 Impact Factor
• Article: Neoplastic transformation of human lung fibroblast MRC-5 SV2 cells induced by benzo[a]pyrene and confluence culture.

  Huijun Zhu, Nigel Gooderham
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  ABSTRACT: Benzo[a]pyrene (BaP) is potent rodent carcinogen and a reputed human carcinogen. Although much is known about its metabolic activation leading to DNA damage, the mechanisms of its actions are not as well understood at a cellular level. In addressing this, we have established an in vitro model that follows the progression toward neoplastic transformation induced by BaP. The model uses immortal nontumorigenic human lung fibroblast MRC-5 SV2 cells as effectors, cocultured with a metabolically competent human lymphoblastoid line h1A1v2 (activator cells). Treatment of the coculture with BaP for 48 h induced a dose-dependent decrease in cloning efficiency of the MRC-5 SV2 cells; nevertheless, cultures continued to progress to confluence. At prolonged confluence culture (day 11), an elevation in the proportion of G2-M phase cells was detected by flow cytometry. By day 15, the G2-M phase peak disappeared, accordant with the appearance of a population with DNA content greater than the cells in G2-M phase. These changes in DNA ploidy were coincident with changes in morphology, specifically the appearance of enlarged and irregular-shaped nuclei. Confluence culture of BaP-treated MRC-5 SV2 cells for more than 2 weeks resulted in cell death; however, a few colonies survived the crisis to reach confluence again after an additional 10-14 days. The number of death-resistant colonies was proportional to the dose of BaP, with the majority of the cells exhibiting abnormal morphology. The degree of morphological change progressively increased with successive rounds of confluence. Cells that survived three rounds of confluence adopted a vastly different morphology, becoming polygonal, spindle, or other irregular-shaped, and acquired the ability to form large dense clumps that grew in an anchorage-independent manner. In parallel experiments, treatment with the vehicle alone (DMSO) resulted in substantially less death resistance and lower numbers of high-density clumps. Our studies demonstrate that a single pulse treatment of human MRC-5 SV2 cells with metabolically activated BaP increased DNA ploidy, induced resistance to confluence-initiated cell death and morphological change, and was accompanied by substantial changes in growth pattern under prolonged confluence culture. The multiple-step nature of this process is characteristic of the development of neoplastic disease, and prolonged confluence seemed to play a pivotal role in selecting for carcinogen-induced transformants.
  Cancer Research 09/2002; 62(16):4605-9. · 7.86 Impact Factor