The DNA damage repair complex MoMMS21-MoSMC5 is required for infection-related development and pathogenicity of Magnaporthe oryzae

The conserved DNA damage repair complex,MMS21-SMC5/6(Methyl methane sulfonate 21-Structural maintenance of chromosomes 5/6),has been extensively studied in yeast,animals,and plants.However,its role in phytopathogenic fungi,particularly in the highly destructive rice blast fungus Magnaporthe oryzae,remains unknown.In this study,we functionally characterized the homologues of this complex,MoMMS21 and MoSMC5,in M.oryzae.We first demonstrated the importance of DNA damage repair in M.oryzae by showing that the DNA damage inducer phleomycin inhibited vegetative growth,infection-related development and pathogenicity in this fungus.Additionally,we discovered that MoMMS21 and MoSMC5 interacted in the nuclei,suggesting that they also function as a complex in M.oryzae.Gene deletion experiments revealed that both MoMMS21 and MoSMC5 are required for infection-related development and pathogenicity in M.oryzae,while only MoMMS21 deletion affected growth and sensitivity to phleomycin,indicating its specific involvement in DNA damage repair.Overall,our results provide insights into the roles of MoMMS21 and MoSMC5 in M.oryzae,highlighting their functions beyond DNA damage repair.

DNA damage response-related immune activation signature predicts the response to immune checkpoint inhibitors: from gastrointestinal cancer analysis to pan-cancer validation

Objective: DNA damage response(DDR) deficiency has emerged as a prominent determinant of tumor immunogenicity. This study aimed to construct a DDR-related immune activation(DRIA) signature and evaluate the predictive accuracy of the DRIA signature for response to immune checkpoint inhibitor(ICI) therapy in gastrointestinal(GI) cancer.Methods: A DRIA signature was established based on two previously reported DNA damage immune response assays. Clinical and gene expression data from two published GI cancer cohorts were used to assess and validate the association between the DRIA score and response to ICI therapy. The predictive accuracy of the DRIA score was validated based on one ICI-treated melanoma and three pan-cancer published cohorts.Results: The DRIA signature includes three genes(CXCL10, IDO1, and IFI44L). In the discovery cancer cohort, DRIA-high patients with gastric cancer achieved a higher response rate to ICI therapy than DRIA-low patients(81.8% vs. 8.8%;P < 0.001), and the predictive accuracy of the DRIA score [area under the receiver operating characteristic curve(AUC) = 0.845] was superior to the predictive accuracy of PD-L1 expression, tumor mutational burden, microsatellite instability, and Epstein–Barr virus status. The validation cohort demonstrated that the DRIA score identified responders with microsatellite-stable colorectal and pancreatic adenocarcinoma who received dual PD-1 and CTLA-4 blockade with radiation therapy. Furthermore, the predictive performance of the DRIA score was shown to be robust through an extended validation in melanoma, urothelial cancer, and pan-cancer.Conclusions: The DRIA signature has superior and robust predictive accuracy for the efficacy of ICI therapy in GI cancer and pancancer, indicating that the DRIA signature may serve as a powerful biomarker for guiding ICI therapy decisions.

LncRNA HOTAIR promotes DNA damage repair and radioresistance by targeting ATR in colorectal cancer

Long non-coding RNAs(lncRNAs)have been implicated in cancer progression and drug resistance development.Moreover,there is evidence that lncRNA HOX transcript antisense intergenic RNA(HOTAIR)is involved in colorectal cancer(CRC)progression.The present study aimed to examine the functional role of lncRNA HOTAIR in conferring radiotherapy resistance in CRC cells,as well as the underlying mechanism.The relative expression levels of HOTAIR were examined in 70 pairs of CRC tumor and para-cancerous tissues,as well as in radiosensitive and radioresistant samples.The correlations between HOTAIR expression levels and clinical features of patients with CRC were assessed using the Chi-square test.Functional assays such as cell proliferation,colony formation and apoptosis assays were conducted to determine the radiosensitivity in CRC cells with HOTAIR silencing after treatment with different doses of radiation.RNA pull-down assay andfluorescence in situ hybridization(FISH)were used to determine the interaction between HOTAIR and DNA damage response mediator ataxia-telangiectasia mutated-and Rad3-related(ATR).HOTAIR was significantly upregulated in CRC tumor tissues,especially in radioresistant tumor samples.The elevated expression of HOTAIR was correlated with more advanced histological grades,distance metastasis and the poor prognosis in patients with CRC.Silencing HOTAIR suppressed the proliferation and promoted apoptosis and radiosensitivity in CRC cells.HOTAIR knockdown also inhibited the tumorigenesis of CRC cells and enhanced the sensitivity to radiotherapy in a mouse xenograft model.Moreover,the data showed that HOTAIR could interact with ATR to regulate the DNA damage repair signaling pathway.Silencing HOTAIR impaired the ATR-ATR interacting protein(ATRIP)complex and signaling in cell cycle progression.Collectively,the present results indicate that lncRNA HOTAIR facilitates the DNA damage response pathway and promotes radioresistance in CRC cells by targeting ATR.

DNA Damage-driven Inflammatory Cytokines:Reprogramming of Tumor Immune Microenvironment and Application of Oncotherapy

DNA damage occurs across tumorigenesis and tumor development.Tumor intrinsic DNA damage can not only increase the risk of mutations responsible for tumor generation but also initiate a cellular stress response to orchestrate the tumor immune microenvironment(TIME)and dominate tumor progression.Accumulating evidence documents that multiple signaling pathways,including cyclic GMP-AMP synthase-stimulator of interferon genes(cGAS-STING)and ataxia telangiectasia-mutated protein/ataxia telangiectasia and Rad3-related protein(ATM/ATR),are activated downstream of DNA damage and they are associated with the secretion of diverse cytokines.These cytokines possess multifaced functions in the anti-tumor immune response.Thus,it is necessary to deeply interpret the complex TIME reshaped by damaged DNA and tumor-derived cytokines,critical for the development of effective tumor therapies.This manuscript comprehensively reviews the relationship between the DNA damage response and related cytokines in tumors and depicts the dual immunoregulatory roles of these cytokines.We also summarize clinical trials targeting signaling pathways and cytokines associated with DNA damage and provide future perspectives on emerging technologies.

TOPK Inhibition Enhances the Sensitivity of Colorectal Cancer Cells to Radiotherapy by Reducing the DNA Damage Response

Objective Abnormal expression of T-lymphokine-activated killer cell-originated protein kinase(TOPK)was reported to be closely related to the resistance of prostate cancer to radiotherapy and to targeted drug resistance in lung cancer.However,the role of TOPK inhibition in enhancing radiosensitivity of colorectal cancer(CRC)cells is unclear.This study aimed to evaluate the radiosensitization of TOPK knockdown in CRC cells.Methods The expression of TOPK was detected in CRC tissues by immunohistochemistry,and the effect of TOPK knockdown was detected in CRC cells by Western blotting.CCK-8 and clonogenic assays were used to detect the growth and clonogenic ability of CRC cells after TOPK knockdown combined with radiotherapy in CRC cells.Furthermore,proteomic analysis showed that the phosphorylation of TOPK downstream proteins changed after radiotherapy.DNA damage was detected by the comet assay.Changes in the DNA damage response signaling pathway were analyzed by Western blotting,and apoptosis was detected by flow cytometry.Results The expression of TOPK was significantly greater in CRC tissues at grades 2–4 than in those at grade 1.After irradiation,CRC cells with genetically silenced TOPK had shorter comet tails and reduced expression levels of DNA damage response-associated proteins,including phospho-cyclin-dependent kinase 1(p-CDK1),phospho-ataxia telangiectasia-mutated(p-ATM),poly ADP-ribose polymerase(PARP),and meiotic recombination 11 homolog 1(MRE11).Conclusions TOPK was overexpressed in patients with moderately to poorly differentiated CRC.Moreover,TOPK knockdown significantly enhanced the radiosensitivity of CRC cells by reducing the DNA damage response.

Blue LED promotes the chemosensitivity of human hepatoma to Sorafenib by inducing DNA damage

Background:Phototherapies based on sunlight,infrared,ultraviolet,visible,and laser-based treatments present advantages like high curative effects,small invasion,and negligible adverse reactions in cancer treatment.We aimed to explore the potential therapeutic effects of blue light emitting diode(LED)in human hepatoma cells and decipher the underlying cellular and molecular mechanisms.Methods:Wound healing and transwell assays were employed to probe the inhibition of the invasion and migration of hepatocellular carcinoma cells in the presence of blue LED.The sphere-forming test was used to evaluate the effect of LED blue light irradiation on cancer stem cell properties.Immunofluorescence and western blotting were used to detect the changes inγ-H2AX.The Cell Counting Kit-8 assay,5-ethynyl-2′-deoxyuridine staining,and colony formation assay were used to detect the combined effect of blue LED and sorafenib on cell proliferation inhibition.Results:We demonstrated that the irradiation of blue LED light in hepatoma cells could lead to cell proliferation reduction along with the increase of cell apoptosis.Simultaneously,blue LED irradiation also markedly suppressed the migration and invasion ability of human hepatoma cells.Sphere formation analysis further revealed the decreased cancer stemness of hepatoma cells upon blue LED irradiation.Mechanistically,blue LED irradiation significantly promoted the expression of the phosphorylation of the core histone protein H2AX(γ-H2AX),a sensitive molecular marker of DNA damage.In addition,we found that the combined treatment of blue LED irradiation and sorafenib increased cancer cell sensitivity to sorafenib.Conclusion:Collectively,we demonstrated that blue LED irradiation exhibited anti-tumor effects on liver cancer cells by inducing DNA damage and could enhance chemosensitivity of cancer cells,which represents a potential approach for human hepatoma treatment.

In Vitro Antioxidant and Radio Protective Activities of Lycopene from Tomato Extract against Radiation—Induced DNA Aberration

Background: The accumulation of free radicals is linked to a number of diseases. Free radicals can be scavenged by antioxidants and reduce their harmful effects. It is therefore essential to look for naturally occurring antioxidants that come from plants, as synthetic antioxidants are toxic, carcinogenic and problematic for the environment. Lycopene is one of the carotenoids, a pigment that dissolves in fat and has antioxidant properties. Materials and Methods: The antioxidant and free radical scavenging activity were assessed using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay. The impact of lycopene on bacteria (E. coli) susceptibility to γ-radiation was examined by radio sensitivity assay. The study also examined the induction of strand breaks in plasmid pUC19 DNA and how lycopene extract protected the DNA from γ-radiation in vitro. Results: At varying concentrations, lycopene demonstrated its ability to scavenge free radicals such as 2, 2-diphenyl-1-picrylhydrazyl (DPPH). IC50 for lycopene was determined at 112 μg/mL which was almost partial to IC50 of standard antioxidant L-ascorbic acid. The D10 value 180 Gy of E. coli was found to be >2-fold higher in the extract-containing lycopene sample than in the extract-free controls. The lycopene extracts inhibited the radiation-induced deterioration of the plasmid pUC19 DNA. At an IC50 concentration, lycopene provided the highest level of protection. Conclusion: Lycopene functions as an efficient free radical scavenger and possible natural antioxidant source. For cancer patients and others who frequently expose themselves to radiation, lycopene may be a useful plant-based pharmaceutical product for treating a variety of diseases caused by free radicals.

Oxidative stress and DNA damages induced by cadmium accumulation

Experimental evidence shows that cadmium （Cd） could induce oxidative stress and then causes DNA damage in animal cells, however, whether such effect exists in plants is still unclear. In the present study, Vicia faba plants was exposed to 5 and 10 mg/L Cd for 4 d to investigate the distribution of Cd in plant, the metal effects on the cell lipids, antioxidative enzymes and DNA damages in leaves. Cd induced an increase in Cd concentrations in plants. An enhanced level of lipid peroxidation in leaves and an enhanced concentration of H2O2 in root tissues suggested that Cd caused oxidative stress in Vicia faba. Compared with control, Cd-induced enhancement in superoxide dismutase activity was significant at 5 mg/L than at 10 mg/kg in leaves, by contrast, catalase and peroxidaseactivities were significantly suppressed by Cd addition. DNA damage was detected by neutral/neutral, alkaline/neutral and alkaline/alkaline Comet assay. Increased levels of DNA damages induced by Cd occurred with reference to oxidative stress in leaves, therefore, oxidative stress induced by Cd accumulation in plants contributed to DNA damages and was possibly an important mechanism of Cd-phytotoxicity in Vicia faba plants.

Apoptosis and DNA damage in human spermatozoa

DNA damage is frequently encountered in spermatozoa of subfertile males and is correlated with a range of adverse clinical outcomes including impaired fertilization, disrupted preimplantation embryonic development, increased rates of miscarriage and an enhanced risk of disease in the progeny. The etiology of DNA fragmentation in human spermatozoa is closely correlated with the appearance of oxidative base adducts and evidence of impaired spermiogenesis. We hypothesize that oxidative stress impedes spermiogenesis, resulting in the generation of spermatozoa with poorly remodelled chromatin. These defective cells have a tendency to default to an apeptotic pathway associated with motility loss, caspase activation, phosphatidylserine exteriorization and the activation of free radical generation by the mitochondria. The latter induces lipid peroxidation and oxidative DNA damage, which then leads to DNA fragmentation and cell death. The physical architecture of spermatozoa prevents any nucleases activated as a result of this apoptotic process from gaining access to the nuclear DNA and inducing its fragmentation. It is for this reason that a majority of the DNA damage encountered in human spermatozoa seems to be oxidative. Given the important role that oxidative stress seems to have in the etiology of DNA damage, there should be an important role for antioxidants in the treatment of this condition. If oxidative DNA damage in spermatozoa is providing a sensitive readout of systemic oxidative stress, the implications of these findings could stretch beyond our immediate goal of trying to minimize DNA damage in spermatozoa as a prelude to assisted conception therapy.

Sperm DNA damage in men from infertile couples

Aim： To investigate the prevalence of high levels of sperm DNA damage among men from infertile couples with both normal and abnormal standard semen parameters. Methods： A total of 350 men from infertile couples were assessed. Standard semen analysis and sperm chromatin structure assay （SCSA） were carried out. Results： Ninety-seven men （28% of the whole study group） had a DNA fragmentation index （DFI） 〉 20%, and 43 men （12%） had a DFI 〉 30%. In the group of men with abnormal semen parameters （n = 224）, 35% had a DFI 〉 20%, and 16% had a DFI 〉 30%, whereas these numbers were 15% and 5%, respectively, in the group of men with normal semen parameters （n = 126）. Men with low sperm motility and abnormal morphology had significantly higher odds ratios （ORs） for having a DFI 〉 20% （4.0 for motility and 1.9 for morphology） and DFI 〉 30% （6.2 for motility and 2.8 for morphology） compared with men with normal sperm motility and morphology. Conclusion： In almost one-third of unselected men from infertile couples, the DFI exceeded the level of 20% above which, according to previous studies, the in vivo fertility is reduced. A significant proportion of men with otherwise normal semen parameters also had high sperm DNA damage levels. Thus, the SCSA test could add to explaining causes of infertility in cases where semen analysis has not shown any deviation from the norm. We also recommend running the SCSA test to choose the appropriate assisted reproductive technique （ART）.

An Investigation of Oxidative DNA Damage in Pharmacy Technicians Exposed to Antineoplastic Drugs in Two Chinese Hospitals Using The Urinary 8-OHdG Assay

Objective To investigate oxidative DNA damage in pharmacy technicians preparing antineoplastic drugs at the PIVAS （Pharmacy Intravenous Admixture Service） in two Chinese hospitals. Methods Urinary 8-OHdG served as a biomarker. 5-Fluorouracil （5-FU） concentrations in air, masks and gloves were determined. The spill exposure of each PIVAS technician to antineoplastic drugs was investigated. Eighty subjects were divided into exposed group t, II, and control group I, II. Results 5-FU concentration ratios for gloves and masks in exposed group I were significantly higher than those in exposed group II （P〈0.05 or P〈0.01）. The average urinary 8-OHdG concentrations in exposed group I, control group I, exposed group II, and control group II were 24.69＋0.93, 20.68＋1.07, 20.57＋0.55, and 12.96_＋0.73 ng/mg Cr, respectively. Urinary 8-OHdG concentration in exposed group I was significantly higher than that in control group I or that in exposed group 11 （P〈0.02）. There was a significant correlation between urinary 8-OHdG concentrations and spill frequencies per technician （P〈0.01）. Conclusion There was detectable oxidative DNA damage in PIVAS technicians exposed to antineoplastic drugs. This oxidative DNA damage may be associated with their spill exposure experience and contamination of their personal protective equipment.

Damage to DNA of effective microorganisms by heavy metals:Impact on wastewater treatment

The research is to test the damage to DNA of effective microorganisms(EMs)by heavy metal ions As3+,Cd2+,Cr3+,Cu2+,Hg2+, Pb2+,and Zn2+,as well as the effects of EM bacteria on wastewater treatment capability when their DNA is damaged.The approach applied in this study is to test with COMET assay the damage of EM DNA in wastewater with different concentrations of heavy metal ions As3+,Cd2+,Cr3+,Cu2+,Hg2+,Pb2+,Zn2+,as well as the effects of EM treated with As3+,Cd2+,Cr3+,Cu2+,Hg2+,Pb2+,and Zn2+ on COD degradin...

Novel association between sperm deformity index and oxidative stress-induced DNA damage in infertile male patients

Aim:To investigate the impact of abnormal sperm morphology using the sperm deformity index (SDI) on reactive oxygen species (ROS) production and its correlation with sperm DNA damage.Methods:Semen samples were collected from men undergoing infertility screening (n=7) and healthy donors (n=6).Mature spermatozoa were isolated and incubated with 5 mmol/L β-nicotinamide adenine dinucleotide phosphate (NADPH) for up to 24 h to induce ROS.Sperm morphology was evaluated using strict Tygerberg's criteria and the SDI.ROS levels and DNA damage were assessed using chemiluminescence and terminal deoxynucleotidyl transferase-mediated fluorescein- dUTP nick end labeling (TUNEL) assays,respectively.Results:SDI values (median [interquartiles]) were higher in patients than donors (2 [1.8,2.1] vs.1.53 [1.52,1.58],P=0.008).Aliquots treated with NADPH showed higher ROS levels (1.22 [0.30,1.87] vs.0.39 [0.10,0.57],P=0.03) and higher incidence of DNA damage than those not treated (10 [4.69,24.85] vs.3.85 [2.58,5.10],P=0.008).Higher DNA damage was also seen following 24 h of incubation in patients compared to donors.SDI correlated with the percentage increase in sperm DNA damage following incubation for 24 h in samples treated with NADPH (r=0.7,P=0.008) and controls (r=0.58,P=0.04). Conclusion:SDI may be a useful tool in identifying potential infertile males with abnormal prevalence of oxidative stress (OS)-induced DNA damage.NADPH plays a role in ROS-mediated sperm DNA damage,which appears to be more evident in infertile patients with semen samples containing a high incidence of morphologically abnormal spermatozoa.

Randomized Terminal Linker-dependent PCR: A Versatile and Sensitive Method for Detection of DNA Damage

Objective To design and develop a novel, sensitive and versatile method for in vivo foot printing and studies of DNA damage, such as DNA adducts and strand breaks. Methods Starting with mammalian genomic DNA, single-stranded products were made by repeated primer extension, these products were ligated to a double-stranded linker having a randomized 3 overhang, and used for PCR. DNA breaks in p53 gene produced by restriction endonuclease AfaI were detected by using this new method followed by Southern hybridization with DIG-labeled probe. Results This randomized terminal linker-dependent PCR (RDPCR) method could generate band signals many-fold stronger than conventional ligation-mediated PCR (LMPCR), and it was more rapid, convenient and accurate than the terminal transferase-dependent PCR (TDPCR). Conclusion DNA strand breakage can be detected sensitively in the gene level by RDPCR. Any lesion that blocks primer extension should be detectable.

Typical Cell Signaling Response to Ionizing Radiation: DNA Damage and Extranuclear Damage

To treat many types of cancer, ionizing radiation （IR） is primarily used as external-beam radiotherapy, brachytherapy, and targeted radionuclide therapy. Exposure of tumor cells to JR can induce DNA damage as well as generation of reactive oxygen species （ROS） and reactive nitrogen species （RNS） which can cause non-DNA lesions or extracellular damage like lipid perioxidation. The initial radiation-induced cell responses to DNA damage and ROS like the proteolytic processing, as well as synthesis and releasing ligands （such as growth factors, cytokines, and hormone） can cause the delayed secondary responses in irradiated and unirradiated bystander cells through paracrine and autocrine pathways.

Sperm DNA damage and its clinical relevance in assessingreproductive outcome

The routine examination of semen, which assesses sperm concentration, percentage motility and morphology, does not identify subtle defects in sperm chromatin architecture. The focus on the genomic integrity of the male gamete has intensified recently due to the growing concern that genetic diseases may be transmitted via assisted reproductive techniques (ART). Accordingly, the intent of this review is to describe the details of the information pertaining to mitochondrial/nuclear sperm DNA damage with an emphasis on its clinical significance and its relation ship with male infertility. Assessment of sperm DNA damage appears to be a potential tool for evaluating semen samples prior to their use in ART. Testing DNA integrity may help select spermatozoa with intact DNA or with the least amount of DNA damage for use in assisted conception. In turn, this may alleviate the financial, social and emotional problems associated with failed ART attempts.

In vitro Study on Role of Hsp70 Expression in DNA Damage of Human Embryonic Lung Cells Exposed to Benzo[a]pyrene

Objective Benzo[a]pyrene (B[a]P), a ubiquitous environmental pollutant, is a potent procarcinogen and mutagen that can elicit tumors, leading to malignancy. Heat shock proteins (Hsp) have been shown to protect cells against damages caused by various stresses including exposure to numerous chemicals. Whether Hsps, or more specifically Hsp70, are involved in repair of B[a]P-induced DNA damage is currently unknown. Methods We assessed the potential role of the inducible form of Hsp70 in B[a]P-induced DNA damage of human embryonic lung (HEL) cells using immunoblot and the comet assay (i.e., the single cell gel electrophoresis assay). Results Exposure to B[a]P induced a dose-dependent decrease in the level of Hsp70, but a dose-dependent +-increase in DNA damage both in untreated (control) HEL cells and in cells preconditioned by a heat treatment. Heat preconditioning prior to B[a]P exposure potentiated the effect of B[a]P at a low dose (10 μmol/L), but appeared to be protective at higher doses. There was a negative correlation between Hsp70 level and DNA damage in the non-preheated as well as in the preconditioned cells. Conclusion These data suggest that exposure of HEL cells to B[a]P may induce a dose-dependent reduction in the levels of the inducible Hsp70. The detailed mechanisms for the reduction of Hsp70 levels by B[a]P and the role of Hsp70 in DNA damage under different concentrations of B[a]P remains to be determined.

Effects of Nitrobenzenes on DNA Damage in Germ Cells of Rats

The single cell gel electrophoresis （SCGE） technique was used to detect DNA damage in germ cells of rats, which was induced by five tested nitroaromatic compounds. Mixed cultures of Sertoli and germ cells were prepared from the rats testis and their responses to rn-dinitrobenzene （ m-DNB）, 2,4-dinitrotoluene （ 2,4-DNT）, 2,6-dinitroto-luene（2,6-DNT）, 4-nitrotoluene（4-NT） and 2,4-dinitroaniline（2,4-DNAn） were studied. The results show that all the five chemicals have a reproductive toxicity. Each dose group and the control group were significantly different （ P 〈 0. 01 ）. All of them can lead to the damage to DNA in the germ cells of Kunming male rats in the definite range of concentration（m-DNB ： 0. 04-25μmol/L; 2,4-DNT, 2,6-DNT and 4-NT： 0. 032-500μmol/L; 2,4-DNAn ：0. 8-20μmol/L）. When the concentration increases, the damage rate will become higher, which shows an evident logarithm dose-effect relationship.

Effects of Cadmium on Hepatocellular DNA Damage,Proto-Oncogene Expression and Apoptosis in Rats

Objective To study the effects of cadmium on hepatocellular DNA damage, expression of proto-oncogenes c-myc, c-fos, and c-jun as well as apoptosis in rats. Methods Cadmium chloride at the doses of 5, 10, and 20 μmol/kg was given to rats by i.p. and there were 5 male SD rats in each group. Hepatocellular DNA damage was measured by single cell gel electrophoresis （or comet assay）, while expression of proto-oncogenes c-myc, c-fos, and c-jun in rat hepatocytes were measured by Northern dot hybridization. C-Myc, c-Fos, and c-Jun were detected with immuno-histochemical method. Hepatocellular apoptosis was determined by TUNEL （TdT-mediated dUTP Nick End Labelling） and flow cytometry. Results At the doses of 5, 10, and 20 μmol/kg, cadmium chloride induced DNA damage in rat hepatocytes and the rates of comet cells were 50.20%, 88.40%, and 93.80%, respectively. Results also showed an obvious dose-response relationship between the rates of comet cells and the dose of cadmium chloride （r=0.9172, P〈0.01）. Cadmium chloride at the doses of 5, 10, and 20 μmol/kg induced expression of proto-oncogenes c-myc, c-fos, and c-jun. The positive brown-yellow signal for c-myc, c-fos, and c-jun was mainly located in the cytoplasm of hepatocytes with immunohistochemical method. TUNEL-positive cells were detected in cadmium-treated rat livers. Apoptotic rates （%） of cadmium-treated liver cells at the doses of 5, 10, and 20 μmol/kg were （17.24 ±2.98）, （20.58± 1.35）, and （24.06±1.77） respectively, being significantly higher than those in the control. The results also displayed an obvious dose-response relationship between apoptotic rates and the dose of cadmium chloride （r=0.8619, P〈0.05）. Conclusion Cadmium at 5-20 μmol/kg can induce hepatocellular DNA damage, expression of proto-oncogenes c-myc, c-fos, and c-jun as well as apoptosis in rats.