Frameshift mutation in codon 176 of the p53 gene in rat esophageal epithelial cells transformed by benzo[a]pyrene dihydrodiol

The detective, prognostic, and predictive value of DNA methylation in human esophageal squamous cell carcinoma

Esophageal cancer is one of the most common malignancies in the world. Squamous cell carcinoma accounts for approximately 90 % of esophageal cancer cases. Genetic and epigenetic changes have been found to accumulate during the development of various cancers, including esophageal squamous carcinoma (ESCC). Tobacco smoking and alcohol consumption are two major risk factors for ESCC, and both tobacco and alcohol were found to induce methylation changes in ESCC. Growing evidence demonstrates that aberrant epigenetic changes play important roles in the multiple-step processes of carcinogenesis and tumor progression. DNA methylation may occur in the key components of cancer-related signaling pathways. Aberrant DNA methylation affects genes involved in cell cycle, DNA damage repair, Wnt, TGF-β, and NF-κB signaling pathways, including P16, MGMT, SFRP2, DACH1, and ZNF382. Certain genes methylated in precursor lesions of the esophagus demonstrate that DNA methylation may serve as esophageal cancer early detection marker, such as methylation of HIN1, TFPI-2, DACH1, and SOX17. CHFR methylation is a late stage event in ESCC and is a sensitive marker for taxanes in human ESCC. FHIT methylation is associated with poor prognosis in ESCC. Aberrant DNA methylation changes may serve as diagnostic, prognostic, and chemo-sensitive markers. Characterization of the DNA methylome in ESCC will help to better understand its mechanisms and develop improved therapies.

Black raspberry components inhibit proliferation, induce apoptosis, and modulate gene expression in rat esophageal epithelial cells

We have shown that a diet containing freeze-dried black raspberries (BRB) inhibits the development of chemically induced cancer in the rat esophagus. To provide insights into possible mechanisms by which BRB inhibit esophageal carcinogenesis, we evaluated an ethanol (EtOH) extract of BRB, and two component anthocyanins (cyanidin-3-O-glucoside and cyanidin-3-O-rutinoside) in BRB, for their effects on growth, apoptosis, and gene expression in rat esophageal epithelial cell lines. The EtOH extract and both anthocyanins selectively caused significant growth inhibition and induction of apoptosis in a highly tumorigenic cell line (RE-149 DHD) but not in a weakly tumorigenic line (RE-149). The uptake of anthocyanins from the EtOH extract into RE-149 DHD cells far exceeded their uptake into RE-149 cells, which may have accounted for the selective effects of the extract on growth and apoptosis of RE-149 DHD cells. The growth inhibitory and proapoptotic effects were enhanced by the daily addition of the EtOH extract and the anthocyanins to the medium. Interestingly, the EtOH extract did not alter cyclooxygenase-2 (COX-2) and nitric oxide synthase (i-NOS) expression in RE-149 DHD cells, whereas both anthocyanins downregulated the expressions of these genes. This differential effect may have been related to the relative amounts of anthocyanins in the extract vs. when they were added individually to the medium. We conclude that the selective effects of the EtOH extract on growth and apoptosis of highly tumorigenic rat esophageal epithelial cells in vitro may be due to preferential uptake and retention of its component anthocyanins, and this may also be responsible for the greater inhibitory effects of freeze-dried whole berries on tumor cells in vivo.

Benzo[a]pyrene diol epoxide suppresses retinoic acid receptor-beta2 expression by recruiting DNA (cytosine-5-)-methyltransferase 3A

Tobacco smoke is an important risk factor for various human cancers, including esophageal cancer. How benzo [a]pyrene diol epoxide (BPDE), a carcinogen present in tobacco smoke as well as in environmental pollution, induces esophageal carcinogenesis has yet to be defined. In this study, we investigated the molecular mechanism responsible for BPDE-suppressed expression of retinoic acid receptor-beta2 (RAR-beta2) in esophageal cancer cells. We treated esophageal cancer cells with BPDE before performing methylation-specific polymerase chain reaction (MSP) to find that BPDE induced methylation of the RAR-beta2 gene promoter. We then performed chromatin immunoprecipitation (ChIP) assays to find that BPDE recruited genes of the methylation machinery into the RAR-beta2 gene promoter. We found that BPDE recruited DNA (cytosine-5-)-methyltransferase 3 alpha (DNMT3A), but not beta (DNMT3B), in a time-dependent manner to methylate the RAR-beta2 gene promoter, which we confirmed by reverse transcription-polymerase chain reaction (RT-PCR) analysis of the reduced RAR-beta2 expression in these BPDE-treated esophageal cancer cell lines. However, BPDE did not significantly change DNMT3A expression, but it slightly reduced DNMT3B expression. DNA methylase inhibitor 5-aza-2'-deoxycytidine (5-Aza) and DNMT3A small hairpin RNA (shRNA) vector antagonized the effects of BPDE on RAR-beta2 expressions. Transient transfection of the DNMT3A shRNA vector also antagonized BPDE's effects on expression of RAR-beta2, c-Jun, phosphorylated extracellular signal-regulated protein kinases 1/2 (ERK1/2), and cyclooxygenase-2 (COX-2), suggesting a possible therapeutic effect. The results of this study form the link between the esophageal cancer risk factor BPDE and the reduced RAR-beta2 expression.

Comparison of phenethyl and 6-phenylhexyl isothiocyanate-induced toxicity in rat esophageal cell lines with and without glutathione depletion

Phenethyl isothiocyanate (PEITC) and its synthetic homolog, 6-phenylhexyl isothiocyanate (PHITC), are both potent inhibitors of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK)-induced lung mice tumorigenesis. However, unlike PEITC, PHITC enhanced N-nitrosomethylbenzylamine (NMBA)-induced rat esophageal tumorigenesis. These findings imply that due to its unique chemical properties, PHITC's effects on esophageal cells are procarcinogenic rather than chemopreventive. Relative to PEITC, PHITC is more lipophilic and less reactive, which could result in higher PHITC intracellular levels. Due to ITCs' inherently high level of thiol reactivity, increased intracellular levels of PHITC have the potential to deplete intracellular glutathione (GSH) reserves. Since GSH is a primary intracellular antioxidant and cytoprotective enzyme cofactor, preservation of intracellular GSH status is crucial for cytoprotection. Despite the recognized importance of isothiocyanate structure with the potential for toxicity, no studies have yet investigated the association between the primary intracellular free thiol, GSH, and isothiocyanate-induced toxicity in this target cell population. The present study investigated whether PEITC and PHITC display unique cytotoxic profiles in cultured rat esophageal cells, and also monitored the effects of ITC challenge on cellular GSH status. A final series of experiments investigated the converse i.e., affects of modulation of intracellular GSH status on ITC-mediated toxicity. Dose-response curves revealed that PEITC was significantly more toxic in tumorigenic and non-tumorigenic cells relative to PHITC. The ITC-GSH interaction studies demonstrated comparable GSH levels following either PEITC or PHITC challenge, and also showed that GSH depletion did not augment ITC-mediated cellular toxicity. While our data demonstrate structure related differences in ITC-mediated cytotoxicities, these differences do not appear to be directly attributable to cellular GSH pools.

Comparative study on Tp53 gene mutations in lung tumors from rats exposed to 239Pu, 237Np and 222Rn

The tumor suppressor gene Tp53 was analyzed by polymerase chain reaction-amplification of genomic DNA extracted from paraffin-embedded tissue sections of rat lung tumors to compare mutations that occurred after inhalation exposures to plutonium dioxide, neptunium dioxide, or radon and radon progenies. Exons 5 to 8 of the gene were amplified in 16 plutonium-, 23 neptunium- and 15 radon-induced lung tumors, and their polymerase chain reaction products were examined for mutations by single strand conformational polymorphism analysis and direct sequencing method. Two point mutations were detected in the plutonium-induced tumors, i.e., a guanine to adenine transition at codon 219 of exon 6 and a cytosine to thymine transition at codon 266 of exon 8. Although only one point mutation was found at codon 175 of exon 5 (cytosine to thymine transition) from neptunium-induced tumors, no mutations were detectable from radon-induced tumors. These results indicate that the abnormalities of the Tp53 gene might not be so critical for the pulmonary carcinogenesis after the inhalation of different alpha emitters, even though the presence and frequencies of the Tp53 gene mutations were different.

Methylglyoxal, an endogenous aldehyde, crosslinks DNA polymerase and the substrate DNA

Methylglyoxal, a known endogenous and environmental mutagen, is a reactive alpha-ketoaldehyde that can modify both DNA and proteins. To investigate the possibility that methylglyoxal induces a crosslink between DNA and DNA polymerase, we treated a 'primed template' DNA and the exonuclease-deficient Klenow fragment (KF(exo-)) of DNA polymerase I with methylglyoxal in vitro. When the reaction mixtures were analyzed by SDS-PAGE, we found that methylglyoxal induced a DNA-KF(exo-) crosslink. The specific binding complex of KF(exo-) and 'primed template' DNA was necessary for formation of the DNA-KF(exo-) crosslink. Methylglyoxal reacted with guanine residues in the single-stranded portion of the template DNA. When 2'-deoxyguanosine was incubated with Nalpha-acetyllysine or N-acetylcysteine in the presence of methylglyoxal, a crosslinked product was formed. No other amino acid derivatives tested could generate a crosslinked product. These results suggest that methylglyoxal crosslinks a guanine residue of the substrate DNA and lysine and cysteine residues near the binding site of the DNA polymerase during DNA synthesis and that DNA replication is severely inhibited by the methylglyoxal-induced DNA-DNA polymerase crosslink.

Establishment and characterization of a SV40T-transformed human bronchial epithelial cell line

The majority of human lung cancers originate from the carcinogenesis of bronchial epithelial cells. To study the malignant progression of human bronchial epithelial cells, we established a SV40T-transformed human bronchial epithelial cell line, and observed some biological and genetic changes of the cell line at different passages. In a 2-year culture, this cell line was approaching malignancy without obvious senescence. Cells in a later passage proliferated faster and required less growth factors than those of an early passage. After continued passaging, these cells were resistant to the terminal squamous differentiation effects of serum, and many of the cells grew anchorage independently. However, no tumor formed after cells were injected into nude mice. Some genetic alterations were found accompanying those morphological changes, such as 3p- and activation of c-myc, c-erbB-2 and bcl2, suggesting that those genetic alterations may contribute to the carcinogenesis of human bronchial epithelial cells at an early stage. This cell line should be particularly useful for studying the progression of human lung cancers.

Chronic stress down-regulates growth hormone gene expression in peripheral blood mononuclear cells of older adults

"Pituitary" peptides are produced in both endocrine and immune cells. Acute and chronic stress can alter pituitary peptide secretion and might also influence neuroendocrine gene expression in human immune cells. We reasoned that, in Alzheimer caregivers, the chronic stress of caregiving would impact on the sympathetic-adrenal-medullary and hypothalamicpituitary-adrenal axis possibly leading to alterations in GH mRNA in their peripheral blood mononuclear cells (PBMCs). Therefore, we evaluated 10 caregivers and 10 controls subjects using a math and speech stress protocol to determine their neuroendocrine profile and to evaluate any relationship with mononuclear cell GH mRNA levels simultaneously acquired and then evaluated by a quantitative competitive RT-PCR technique. We found a significant (p<.0001) decrease 50% in GH mRNA levels in cells from caregivers. Plasma ACTH and norepinephrine levels were negatively correlated with GH mRNA levels, suggesting their possible role in the down-regulation of mononuclear cell GH gene expression. These observations support the hypothesis that experiences associated with caregiving alter the brain's autonomic nervous system and neuroendocrine control of the hypothalamic-pituitary axis. These and perhaps other influences may then produce altered GH gene expression in mononuclear cells of chronically stressed individuals. It is tempting to speculate that the decreased GH mRNA that we found in these chronically stressed caregivers was partially responsible for their poor response to influenza vaccine and their delayed wound healing.