The Relationship Between XPC Expression And Loss Of Heterozygosity Of Allele Loci On Chromosomes 9 And 17 In Bladder Cancer

Tumors occur and development after a multistage,including oncogene activation,tumor-suppressor gene inactivation,mismatch repair genes deficiency as well as genetic instability at several microsatellite loci. The human genome,like other genomes,encodes information to protect its own integrity.DNA repair enzymes continuously monitor chromosomes to correct damaged nucleotide residues generated by exposure to carcinogens and cytotoxic compounds.The damage is partly a consequence of environmental agents such as ultraviolet(UV)light frome the sun, ironizing radiation (IR), smoking, various chemicals ,and even our own cellular processes including water ,reactive oxygen species,and metabolities that can act as alkylating agents. Genome instability caused by the great variety of DNA-damaging agents would be an overwhelming problem for cells and organisms if it were not for DNA repair. In responding to DNA damage, the cell will react:(1)the damage will be recognized ,and then be repaired;(2)the damage will be recognized ,but the cell can't repair them, but the apoptosis occur .(3)the damage can't be recognized and the mutation will be collected, and all of these lead to the appearance of diseases such as tumors.So,we can conclude that the DNA repair is very important for the integrity of genome.Based on the type of DNA damage,the DNA repair pathway can be categorized into(i)nucleotide excision repair(NER) which removes short segments of nucleotides (calledoligonucleotides) containing damaged bases. NER responds to any alteration that distorts the DNA helix and is the mechanism responsible for repairing bulky base damage caused by carcinogenic chemicals such as benzo [a]pyrene (found in cigarette smoke and automobile exhaust) as well as covalent linkages between adjacent pyrimidine bases resulting from the UV component of sunlight;(ii)base excision repair (BER) which corrects DNA base alterations that do not distort the overall structure of the DNA helix, such as bases damaged by oxidation resulting from normal cellular metabolism; (iii)mismatch repair which mainly removes nucleotides misincorporated by DNA polymerase and thereby improves the overall fidelity of replication. (iv) recombinational repair[both homologousrecombination (HR) and nonhomologous end joining] which mainly repair the breaks in DNA backbone(double-stand breaks DSBs).In all of these DNA repair pathway,the NER pathway is the major DNA repair pathway for repairing bulky DNA damage generated by most environmental factors.Therefore, the presence of a functional NER pathway is essential for maintaining genetic integrity and for preventing the development of many disease conditions from exposure to these DNA- damaging reagents,such as cancer. And the NER pathway can be divided into two classes based on where the repair occurs.NER occurring in DNA that is not undergoing transcription (i.e.,most of the genome) is called global genome repair (GGR),while NER taking place in the transcribed stand of active genes is called transcription-cpupled repair(TCR).The GGR protects against mutations that could ultimately lead to cancer, while TCR ensures that genes are transcribed correctly and efficiently, a function that is now appreciated to be important in protectingagainst aging. Both the two classes can be generally broken down into four steps: damage recognition to initiate repair, helix opening and unwinding, incision of the damage–containing oligonucleotide, and DNA synthesis and ligation. In the four steps the most important one is the recognition of the damage. The NERmachinery responds when DNA suffers damage that distorts its helical structure, and repair is initiated when the helix distortion is recongnized by the XPC(xeroderma pigmentosum gene group C) protein together with its partner hHR23B. The research of XPC and NER is stimulated by the finding that a genetic defect in the NER response causes the human hereditary disease xeroderma pigmentosum(XP),which is fist found by professor Kaposi and characterized by extreme photosensitivity and a 2000-fold increased incidence of sunlight-induced skin cancer.XP individuals also have a higher incidence of internal tumors and tumors and, in some cases, neurological abnormalities, probably reflecting the importance of NER in the repair of endogenous DNA damage. Patients affected by this recessive disorder are classified into seven repair-deficient complementation groups designated XP-A through XP-G.XPC,an about 17kb protein which exist in the cell nucleus, is involved in the damage recognition step in NER. The XPC protein binds tightly with an HR23B to form a stable XPC-HR23B complex. Studies indicate that the XPC-HR23B complex is the first protein component that recognizes and binds to the damaged sites. the study indicate almost cancers are concerned with chromosomal abnormality.chromosomal abnormality include numerical abnormalities and structural abnormalities. chromosomal numerical abnormalities appearance abnormalities diploid cells.structural abnomalities of tumors'chromosomal appearance translocation,deletion,redundancy and so on.Invests of LOH are to tumor's occurrence,development,diagnositic and prognosis with very inportant significance.Urinary bladder caner is the fourth most common neoplasm found in men from western countries, with urothelial cell carcinoma being the most common subtype (about 90 percent).The established risk factors of bladder cancer include cigarette smoking, exposure to industrially related aromatic amines, and the uptake of chemical drugs such as cyclophosphamide. Because of the nature of bladder as an important void organ, the urotherial cells are continuously exposed to many DNA-damaging reagents contained in the urine. Therefore, DNA repair plays an essential role in preventing deleterious DNA damage–induced effects such as mutation accumulation and tumor occurrence. Because the NER pathway is the major DNA repair pathway for repairing bulky DNA damage generated by most environmental factors, such as UV radiation, chemicals, and therapeutic drugs (e.g., cisplatin and mitomycin). Therefore, the presence of a functional NER pathway is essential for maintaining genetic integrity and for preventing the development of many disease conditions from exposure to these DNA-damaging reagents, such as bladder cancer. So, the proficient NER play an important role in preventing the bladder cancer tumorigenesis.Because the XPC gene play an important role in the NER, The aim of this study was to investigate the gene variation and the dependability,at the same time to evaluate possible tumor suppressor genes on chromosome 9 and 17 in the development and progression of TCCB,through detecting the loss of heterozugosity(LOH) in TCCB and its normal tissues,To investigate the relationship between loss of heterozygosity (LOH) of allele loci on chromosomes 9 and 17 and XPC expression in Chinese transitional cell carcinoma ( TCC) of urinary bladder. To gain an insight into the role of ubiquitinated XPC in mediating mammalian cellular response to DNA damage.Methods:1,LOH were studied in the tumor tissues of 41 patients , with their normal tumor-adjacent bladder tissues as control , by means of PCR amplification of 5 polymorphic microsatellite DNA loci D9S283 ,D9S303 ,D9S304,and D9S1751 on chromosome 9 and TP53 on chromosome17. Following 8% denaturing polyacrilamide gel electrophoresis, silver staining was performed.2,Immunohistochemistry was applied to detect the expression of XPC in human bladder cancer tissues.3,The relationship between XPC expression and loss of heterozygosity of allele loci on chromosomes 9 and 17 in Bladder Cancer.All analysis were out using SPSS13.0 software.Results:1,37 (90.2 %) TCCs showed LOH at one or more loci, and 30 TCCs showed LOH at 2 loci or over 2 loci. There was no significant difference between superfacial TCC and invasive TCC at these loci.2,Our results suggested XPC protein expression was lower in tumors of heigh clinical and pathological grade, as XPC protein expressions in invasive (pT 2～4) and heigh grade (G2-3) tumors were significantly lower than those in superficial(pTis～1) or low grade (G1) tumors.3,It is Significant associations that the relationship between XPC expression and loss of heterozygosity of allele loci on chromosomes 9 and 17 in Bladder Cancer.Conclusions:1,LOH on chromosome 9 and P53 might be an significant event of the genesis of TCC of bladder. Racial difference may contribute to different LOH on chromosome 9 and P53 between Chinese people and others.The combination of markers D9S283,D9S303, D9S304, D9S1751 and TP53 enable us to detect 37 out 41 of bladder cancers (90.2%);This panel might be chosen for microsatellite ananlysis in bladder cancer of Chinese.2,The development of bladder cancer closely correlated with abnormality of XPC gene. The level of XPC protein expression and stage may be used as ideal markers for discriminating the generation and prognosis of bladder cancer.3,Our findings suggest that low-regulation of XPC attenuate the coefficient of the NER and involved in the human bladder cancer carcinogenesis. The XPC lower expression or defect in the bladder cancer involved in chromosomal aberration and attenuated expression of XPC is associated with the events in human bladder cancer carcinogenesis and progresis.