Study On The Repair Of PARP On DNA Damage In Hela Cells Induced By Ionizting Radiation

Radiotherapy is one of the most important treatments for tumors, but itsapplication is currently limited by the side-effects such as theradiation-induced damages in normal tissues nearby the tumor and theradiation-resistanc of certain tumors. To increase the radiosensitivity of tumorsand to decrease the dose of irradiation for radiotherapy has become a new wayto improve the therapeutic effect. In the present study, the inhibiting effect of3-aminobenzamid (3-AB), the poly (ADP-ribose) polymerase (PARP) inhibitor,and the influence of it on radiation-induced cell damage, cell apoptosis andcell cycle progression were observed to discuss the role of PARP in the repairof the radiation-induced cell DNA damage.1 The inhibited effect of PARP inhibitor 3-aminobenzamide (3-AB)The expression of PARP after administration with 3-AB (5 mmol/L) wasstudied with flow cytometer (FCM). The result showed that the expression ofPARP was down-regulated rapidly in Hela cells. At 2 ~ 4 hours after theadministration of 3-AB the inhibiting effect of 3-AB on the expression ofPARP in Hela cells could be significant.2 The influence of 3-AB on survival fraction in Hela cellsThe proliferative activity in Hela cells was detected with thiazolyl blue(MTT) method. The result showed that different dose irradiationdown-regulated the survival rate of Hela cells. However, the survival rate ofHela cells injured with irradiation decreased in varying degree after theadministration with 3-AB as compared with those in irradiation group. Thisindicates that 3-AB can increase the radiosensitivity of Hela cells and enhancethe lethal effect of irradiation.3 Mechanism of radiosensitization effect of 3-AB as a PARP inhibitor3.1 The influence of down-regulation of PARP on radiation-inducedDNA damageAll parameters of Hela cells with single cell gel electrophoresis (SCGE)showed the dose-related increase after irradiation and this indicates that theseparameters could represent the degree of the cell damage. The degree of celldamage deceased gradually after the irradiation with the elapse of time and therecovering degree of the damage of 24 hours after irradiation was to approachthe negative control level. This suggests the repair process ofradiation-induced damage in Hela cells. The radiation-induced damage of Helacells injured with radiation after administrated with 3-AB (5 mmol/L)exceeded the radiation groups. This demonstrated PARP inhibitor canaggravate the irradiation-induced damage. And this may be one of themechanisms that 3-AB could enhance the cell radiosensitivity.3.2 The influence of down-regulation of PARP on apoptosis in Hela cellsThe present study has compared the difference on apoptosis percentagebetween Hela cells with and without 3-AB (5 mmol/L) and there was nostatistical differences was found between the two groups. This result showedthat 3-AB alone can not induce the apoptosis of Hela cells without damgefactors. However, the percentage of apoptosis cells increase after irradiationand 3-AB could enhance this effect and this may be another machnisms of3-AB to increase the radiosensitivity.3.3 The influence of down regulation of PARP on cell cycle progressionThe change of cell cycle progression after administration with 3-AB wasstudied with flow cytometer (FCM) and its was found that 3-AB couldovercome the radiation-induced G2 phage arrest, which was believed to be amechanism to increase the repair of the cell damage, and intensified the celldamage induced by irradiation, enhanced the cell radiosensitivity.This study has great importance in explaining the repair process of celldamage and provides new evidence of PARP in DNA damage repair process. Italso hopes to explore a new way to increase the radiosensitivity of carcinomacells to improve the radiotherapeutics effect.