Evaluation Of Tumor Radiosensitivity And Drug Resistance With Ku80 MRNA Expression In Human Lung Cancer

Ku is a DNA banding protein composed of Ku70 and Ku80 subunits.Ku,asthe regulatory subunit of DNA-dependent protein kinase(DNA-PK),cooperatingwith the catalytic subunit (DNA-PKcs) constitute DNA-dependent proteinkinase.When DNA double-strand break(DBS) caused by radiation or cell toxicantdrug which is analogous radiation,Ku70 and Ku80 rapidly formed a heterodimerthat binds to double-strand DNA breaks(DSBs) and activates the catelytic subunit(DNA-PKcs) to participate in repairing of breaking DNA by Non-homologousend-joining(NHEJ) .As a primary participator,Ku has been implicated to be involved directly ofindirectly in many important cellular metabolic processes,such as DNAdouble-strand break repair,V(D)J recombination of immunoglobulins and T-cellreceptor genes, immnunoglobulin istotype switching,DNA replication,transcription regulation,regulaton of heat shock-induced responses,regulation ofthe precise structure of telomeric termini,and it also plays a novel role in G2 andM phases of the cell cycle.In sometime study,Ku is thought to play a crucial rolein maintance of chromosomal integrity and cell survival.Recent reports suggestthat there is a positive relationship between Ku and the development ofcancer.Specifically,prior studies suggest that a delicate balance exists in Kuexpression as overexpression of Ku proteins promotes oncogenicphenotypes,including hyperproliferation and resistance to apoptosis,whereasdeficient or low expression of Ku leads to genomic instability and tumorigenesis.Currently, the relapse rate of malignant tumor is still high even afterradiotherapy and chemotherapy, a key point may be the different reaction ofbodies or tumor tissue itself to drug and radiation. Now,Gene and protein relatedto anti-radiation and drug resistence in tumor therapy were much more concerned.Previous studies have found mechanisms of the sensitivity of anti-tumor drug andtumor enhanced sensitivity to radiation which related to Ku,and Ku protein isclosely correlation to apoptosis famliy that make Ku become a new target gene oftumor gene therapeutics.it has significant meaning to oncogenesis,diagnosis,treatment, preventionin and prognosis fo tumour on studying role andmechanisms.Previous research on the ku70 and Ku80 using the two subunit for basicresearch units, but now more and more studies show that Ku70 and Ku80 havetheir own unique biological functions.In some study we find the Ku70 deficientcell may become more rediosensitive,and have the DNA ends ligationdeficiency,otherwise,it can not complete V(D)J recombination.So someresearchers tried to transfect the antisense Ku 70 into the human lung cancer cellline,and found that they get a high radiosensitivity,even supersensitivity.The Ku70deficient cell also appears to be hypersensitive to cytotoxin,whose function is tomake DNA double-strand break. Nussenzweig found cellular S phase and G2/Mphase were delayed when Ku80-/-cells and normal cells exposured to gammarays, but normal controlled cells can enter G1 after exposured for eight hours, andKu80-/-cells still stay in G2/M stage even after exposured for 24 hours, the G1phase cells after exposured can not enter s phase over again, indication that theKu80-/-cells will maintain DNA damage in G1 stage or G2/M stage and can notenter the cell cycle. Nussenzweig also observed Ku80-/-mouse, and found theygrow slowly with low survival rate, and gradually lose reproductive capacity, andthe mouse's early stage T and B lymphocyte grow retardarce, the immuneglobulin V (D) J reorganization maintained at a low level, and immunedeficiencies existi.The closely relationship between Ku and apoptosis family make more andmore research concern on molecule mechanism about Ku as apoptosis inhabitor toreverse tumor drug resistance.Ku70 has two known antiapoptoticeffects-facilitating DSBR and sequestering bax to prevent its translocation tomitochondria. The latest study found that the Ku protein bind to Bax in the cellplasma to participate in apoptosis,and level of Ku protein expression decline inapoptosis cell, but in lung cancer tissue,Survivin gene expression increased,indicating Ku protein may play a key role in apoptosis control. the specific waysand molecular mechanisms of ku need further study. Ku also affect telomere DNAand regulate refined structures of telomere terminal,through the control tonuclease and recombinase. Synergies of telomerease inhibitors Pifi and excessiveexpressed Ku can make the cell cycle stop in S phase and DNA damage points inthe form of independent.In Ku80-/-mice synergizes with decreasing of P53 topromote tumorigenesis. The close relevance of Ku and apoptosis family mademore and more attention mass on the molecular mechanism of Ku as the apoptosisinhibitor reversing tumor drug resistant.Foreign scholars have reported ku expression in cervical, colon cancer,transitional cell carcinomas of urinary bladder, but there was no report about therelevance of Ku and lung cancer which is the disease of the highest incidencerate.Our study first examined the different Ku 80mRNA expression in the normallung tissue group, lung cancer group without radiotherapy and chemotherapy, lungcancer group with multiple chemotherapy and/or radiotherapy(N>=2). There issignificant difference between them.Expecially, we found the expression ofKu80 mRNA has a upward trend ,which related to the increased of theradioresistance and chemotherapy resistance after the adding times ofchemotherapy and radiotherapy.Furthermore,it proved that Ku80mRNAexpression may become the new indicators for monitoring the radiotheraphy andchemotherapy sensitivity and can provide prediction and assessment for the effectof pro-and post-chemotheraphy and radiotheraphy. It also suggested that thequantitative expression of Ku may associated with the tumors progress andbecome a useful indicators for early diagnosis and estimated prognosis of thetumors. Particularly in newly study found that the Ku play a new role incontrolling apoptosis/anti-apoptosis, this study will provid preliminary work inthis field. This study has a guiding significance about Ku on studying mechanismof tumor chemotherapy and radiotherapy sensitivity and gene target therapy.Experimental methods: The lung tissue gene level of Ku80 mRNA weremeasured by reverse transcription polymerase chain reation(RT-PCR) in normallung tissue group, lung cancer group without radiotherapy and chemotherapy, lungcancer group with multiple chemotherapy and/or radiotherapy(N>=2). TanonGis-2020 electrophoretic image assays was used to scan the grey scale of theamplified PCR products.the values obtained were divided through the expressionvalue of a housekeepingβ-action and defined as β-action/mRNA ratio.Experimental results:(1)the expression of Ku80 between normal lung tissueand lung cancer tissue is not obvious.it has no statistic significant meaning,p>0.05.(2) Ku80mRNA expression in normal lung tissue compared to lung cancer groupwithout radiotherapy and chemotherapy, lung cancer group with multiplechemotherapy and/or radiotherapy(N>=2) have statistic significantmeaning,respectively p<0.05 and p<0.01. lung cancer group with multiplechemotherapy Ku80mRNA expression is higher than lung cancer group withmultiple chemotherapy and/or radiotherapy(N>=2), p<0.05 .(3) In lung cancergroup without radiotherapy and chemotherapy, clinical stages, pathological typeshave no significant relationship with lung cancer tissue Ku80 mRNA expression.Experimental conclusion: (1)the expression of Ku80 between normal lungtissue and lung cancer tissue is not obvious.it demonstrates that Ku80 express inthe lung tissue of various bionomics,and the ability of DSBs repairing is a basicfunction not only in normal but also in malignant lung tissues. (2)Our study firstexamined the different Ku 80mRNA expression in the normal lung tissue group,lung cancer group without radiotherapy and chemotherapy, lung cancer groupwith multiple chemotherapy and/or radiotherapy(N>=2). There is significantdifference between them.Expecially, we found the expression of Ku80 mRNAhas a upward trend ,related to the inareased of the radioresistance andchemotherapy resistance after the times of chemotherapy and radiotherapy added.Patients who lung tissue expressed a high Ku80mRNA trend to chemotherapyresistance, and may indicate tumors progress, and its related adverse prognosis.(3)In lung cancer group without radiotherapy and chemotherapy, clinical stages,pathological types have no significant relationship with Ku80 mRNA expressionin lung cancer tissue. the study sample of the current experimential is limited ,andit may be the main cause of leading to the findings.which can be expanded in thefurture study. (4) Ku mRNA expression may become a useful indicators for earlydiagnosis ,monitoring tumor radiation and drug sensitivity and estimatedprognosis of the tumors ,and can provide prediction and assessment for the effectof pro-and post-chemotheraphy and radiotheraphy. Particularly in newly studyfound that the Ku play a new role in controlling apoptosis/anti-apoptosis, thisstudy will provid preliminary work in this field.